v4.19.13 snapshot.
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
new file mode 100644
index 0000000..664fa7d
--- /dev/null
+++ b/net/ipv4/tcp_input.c
@@ -0,0 +1,6545 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * INET An implementation of the TCP/IP protocol suite for the LINUX
+ * operating system. INET is implemented using the BSD Socket
+ * interface as the means of communication with the user level.
+ *
+ * Implementation of the Transmission Control Protocol(TCP).
+ *
+ * Authors: Ross Biro
+ * Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
+ * Mark Evans, <evansmp@uhura.aston.ac.uk>
+ * Corey Minyard <wf-rch!minyard@relay.EU.net>
+ * Florian La Roche, <flla@stud.uni-sb.de>
+ * Charles Hedrick, <hedrick@klinzhai.rutgers.edu>
+ * Linus Torvalds, <torvalds@cs.helsinki.fi>
+ * Alan Cox, <gw4pts@gw4pts.ampr.org>
+ * Matthew Dillon, <dillon@apollo.west.oic.com>
+ * Arnt Gulbrandsen, <agulbra@nvg.unit.no>
+ * Jorge Cwik, <jorge@laser.satlink.net>
+ */
+
+/*
+ * Changes:
+ * Pedro Roque : Fast Retransmit/Recovery.
+ * Two receive queues.
+ * Retransmit queue handled by TCP.
+ * Better retransmit timer handling.
+ * New congestion avoidance.
+ * Header prediction.
+ * Variable renaming.
+ *
+ * Eric : Fast Retransmit.
+ * Randy Scott : MSS option defines.
+ * Eric Schenk : Fixes to slow start algorithm.
+ * Eric Schenk : Yet another double ACK bug.
+ * Eric Schenk : Delayed ACK bug fixes.
+ * Eric Schenk : Floyd style fast retrans war avoidance.
+ * David S. Miller : Don't allow zero congestion window.
+ * Eric Schenk : Fix retransmitter so that it sends
+ * next packet on ack of previous packet.
+ * Andi Kleen : Moved open_request checking here
+ * and process RSTs for open_requests.
+ * Andi Kleen : Better prune_queue, and other fixes.
+ * Andrey Savochkin: Fix RTT measurements in the presence of
+ * timestamps.
+ * Andrey Savochkin: Check sequence numbers correctly when
+ * removing SACKs due to in sequence incoming
+ * data segments.
+ * Andi Kleen: Make sure we never ack data there is not
+ * enough room for. Also make this condition
+ * a fatal error if it might still happen.
+ * Andi Kleen: Add tcp_measure_rcv_mss to make
+ * connections with MSS<min(MTU,ann. MSS)
+ * work without delayed acks.
+ * Andi Kleen: Process packets with PSH set in the
+ * fast path.
+ * J Hadi Salim: ECN support
+ * Andrei Gurtov,
+ * Pasi Sarolahti,
+ * Panu Kuhlberg: Experimental audit of TCP (re)transmission
+ * engine. Lots of bugs are found.
+ * Pasi Sarolahti: F-RTO for dealing with spurious RTOs
+ */
+
+#define pr_fmt(fmt) "TCP: " fmt
+
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/sysctl.h>
+#include <linux/kernel.h>
+#include <linux/prefetch.h>
+#include <net/dst.h>
+#include <net/tcp.h>
+#include <net/inet_common.h>
+#include <linux/ipsec.h>
+#include <asm/unaligned.h>
+#include <linux/errqueue.h>
+#include <trace/events/tcp.h>
+#include <linux/static_key.h>
+#include <net/busy_poll.h>
+
+int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
+
+#define FLAG_DATA 0x01 /* Incoming frame contained data. */
+#define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */
+#define FLAG_DATA_ACKED 0x04 /* This ACK acknowledged new data. */
+#define FLAG_RETRANS_DATA_ACKED 0x08 /* "" "" some of which was retransmitted. */
+#define FLAG_SYN_ACKED 0x10 /* This ACK acknowledged SYN. */
+#define FLAG_DATA_SACKED 0x20 /* New SACK. */
+#define FLAG_ECE 0x40 /* ECE in this ACK */
+#define FLAG_LOST_RETRANS 0x80 /* This ACK marks some retransmission lost */
+#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
+#define FLAG_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
+#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
+#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
+#define FLAG_SET_XMIT_TIMER 0x1000 /* Set TLP or RTO timer */
+#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
+#define FLAG_UPDATE_TS_RECENT 0x4000 /* tcp_replace_ts_recent() */
+#define FLAG_NO_CHALLENGE_ACK 0x8000 /* do not call tcp_send_challenge_ack() */
+#define FLAG_ACK_MAYBE_DELAYED 0x10000 /* Likely a delayed ACK */
+
+#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
+#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
+#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE|FLAG_DSACKING_ACK)
+#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
+
+#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
+#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
+
+#define REXMIT_NONE 0 /* no loss recovery to do */
+#define REXMIT_LOST 1 /* retransmit packets marked lost */
+#define REXMIT_NEW 2 /* FRTO-style transmit of unsent/new packets */
+
+#if IS_ENABLED(CONFIG_TLS_DEVICE)
+static DEFINE_STATIC_KEY_FALSE(clean_acked_data_enabled);
+
+void clean_acked_data_enable(struct inet_connection_sock *icsk,
+ void (*cad)(struct sock *sk, u32 ack_seq))
+{
+ icsk->icsk_clean_acked = cad;
+ static_branch_inc(&clean_acked_data_enabled);
+}
+EXPORT_SYMBOL_GPL(clean_acked_data_enable);
+
+void clean_acked_data_disable(struct inet_connection_sock *icsk)
+{
+ static_branch_dec(&clean_acked_data_enabled);
+ icsk->icsk_clean_acked = NULL;
+}
+EXPORT_SYMBOL_GPL(clean_acked_data_disable);
+#endif
+
+static void tcp_gro_dev_warn(struct sock *sk, const struct sk_buff *skb,
+ unsigned int len)
+{
+ static bool __once __read_mostly;
+
+ if (!__once) {
+ struct net_device *dev;
+
+ __once = true;
+
+ rcu_read_lock();
+ dev = dev_get_by_index_rcu(sock_net(sk), skb->skb_iif);
+ if (!dev || len >= dev->mtu)
+ pr_warn("%s: Driver has suspect GRO implementation, TCP performance may be compromised.\n",
+ dev ? dev->name : "Unknown driver");
+ rcu_read_unlock();
+ }
+}
+
+/* Adapt the MSS value used to make delayed ack decision to the
+ * real world.
+ */
+static void tcp_measure_rcv_mss(struct sock *sk, const struct sk_buff *skb)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ const unsigned int lss = icsk->icsk_ack.last_seg_size;
+ unsigned int len;
+
+ icsk->icsk_ack.last_seg_size = 0;
+
+ /* skb->len may jitter because of SACKs, even if peer
+ * sends good full-sized frames.
+ */
+ len = skb_shinfo(skb)->gso_size ? : skb->len;
+ if (len >= icsk->icsk_ack.rcv_mss) {
+ icsk->icsk_ack.rcv_mss = min_t(unsigned int, len,
+ tcp_sk(sk)->advmss);
+ /* Account for possibly-removed options */
+ if (unlikely(len > icsk->icsk_ack.rcv_mss +
+ MAX_TCP_OPTION_SPACE))
+ tcp_gro_dev_warn(sk, skb, len);
+ } else {
+ /* Otherwise, we make more careful check taking into account,
+ * that SACKs block is variable.
+ *
+ * "len" is invariant segment length, including TCP header.
+ */
+ len += skb->data - skb_transport_header(skb);
+ if (len >= TCP_MSS_DEFAULT + sizeof(struct tcphdr) ||
+ /* If PSH is not set, packet should be
+ * full sized, provided peer TCP is not badly broken.
+ * This observation (if it is correct 8)) allows
+ * to handle super-low mtu links fairly.
+ */
+ (len >= TCP_MIN_MSS + sizeof(struct tcphdr) &&
+ !(tcp_flag_word(tcp_hdr(skb)) & TCP_REMNANT))) {
+ /* Subtract also invariant (if peer is RFC compliant),
+ * tcp header plus fixed timestamp option length.
+ * Resulting "len" is MSS free of SACK jitter.
+ */
+ len -= tcp_sk(sk)->tcp_header_len;
+ icsk->icsk_ack.last_seg_size = len;
+ if (len == lss) {
+ icsk->icsk_ack.rcv_mss = len;
+ return;
+ }
+ }
+ if (icsk->icsk_ack.pending & ICSK_ACK_PUSHED)
+ icsk->icsk_ack.pending |= ICSK_ACK_PUSHED2;
+ icsk->icsk_ack.pending |= ICSK_ACK_PUSHED;
+ }
+}
+
+static void tcp_incr_quickack(struct sock *sk, unsigned int max_quickacks)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ unsigned int quickacks = tcp_sk(sk)->rcv_wnd / (2 * icsk->icsk_ack.rcv_mss);
+
+ if (quickacks == 0)
+ quickacks = 2;
+ quickacks = min(quickacks, max_quickacks);
+ if (quickacks > icsk->icsk_ack.quick)
+ icsk->icsk_ack.quick = quickacks;
+}
+
+void tcp_enter_quickack_mode(struct sock *sk, unsigned int max_quickacks)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ tcp_incr_quickack(sk, max_quickacks);
+ icsk->icsk_ack.pingpong = 0;
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+}
+EXPORT_SYMBOL(tcp_enter_quickack_mode);
+
+/* Send ACKs quickly, if "quick" count is not exhausted
+ * and the session is not interactive.
+ */
+
+static bool tcp_in_quickack_mode(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ const struct dst_entry *dst = __sk_dst_get(sk);
+
+ return (dst && dst_metric(dst, RTAX_QUICKACK)) ||
+ (icsk->icsk_ack.quick && !icsk->icsk_ack.pingpong);
+}
+
+static void tcp_ecn_queue_cwr(struct tcp_sock *tp)
+{
+ if (tp->ecn_flags & TCP_ECN_OK)
+ tp->ecn_flags |= TCP_ECN_QUEUE_CWR;
+}
+
+static void tcp_ecn_accept_cwr(struct sock *sk, const struct sk_buff *skb)
+{
+ if (tcp_hdr(skb)->cwr) {
+ tcp_sk(sk)->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+
+ /* If the sender is telling us it has entered CWR, then its
+ * cwnd may be very low (even just 1 packet), so we should ACK
+ * immediately.
+ */
+ inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
+ }
+}
+
+static void tcp_ecn_withdraw_cwr(struct tcp_sock *tp)
+{
+ tp->ecn_flags &= ~TCP_ECN_DEMAND_CWR;
+}
+
+static void __tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ switch (TCP_SKB_CB(skb)->ip_dsfield & INET_ECN_MASK) {
+ case INET_ECN_NOT_ECT:
+ /* Funny extension: if ECT is not set on a segment,
+ * and we already seen ECT on a previous segment,
+ * it is probably a retransmit.
+ */
+ if (tp->ecn_flags & TCP_ECN_SEEN)
+ tcp_enter_quickack_mode(sk, 2);
+ break;
+ case INET_ECN_CE:
+ if (tcp_ca_needs_ecn(sk))
+ tcp_ca_event(sk, CA_EVENT_ECN_IS_CE);
+
+ if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
+ /* Better not delay acks, sender can have a very low cwnd */
+ tcp_enter_quickack_mode(sk, 2);
+ tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
+ }
+ tp->ecn_flags |= TCP_ECN_SEEN;
+ break;
+ default:
+ if (tcp_ca_needs_ecn(sk))
+ tcp_ca_event(sk, CA_EVENT_ECN_NO_CE);
+ tp->ecn_flags |= TCP_ECN_SEEN;
+ break;
+ }
+}
+
+static void tcp_ecn_check_ce(struct sock *sk, const struct sk_buff *skb)
+{
+ if (tcp_sk(sk)->ecn_flags & TCP_ECN_OK)
+ __tcp_ecn_check_ce(sk, skb);
+}
+
+static void tcp_ecn_rcv_synack(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || th->cwr))
+ tp->ecn_flags &= ~TCP_ECN_OK;
+}
+
+static void tcp_ecn_rcv_syn(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if ((tp->ecn_flags & TCP_ECN_OK) && (!th->ece || !th->cwr))
+ tp->ecn_flags &= ~TCP_ECN_OK;
+}
+
+static bool tcp_ecn_rcv_ecn_echo(const struct tcp_sock *tp, const struct tcphdr *th)
+{
+ if (th->ece && !th->syn && (tp->ecn_flags & TCP_ECN_OK))
+ return true;
+ return false;
+}
+
+/* Buffer size and advertised window tuning.
+ *
+ * 1. Tuning sk->sk_sndbuf, when connection enters established state.
+ */
+
+static void tcp_sndbuf_expand(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
+ int sndmem, per_mss;
+ u32 nr_segs;
+
+ /* Worst case is non GSO/TSO : each frame consumes one skb
+ * and skb->head is kmalloced using power of two area of memory
+ */
+ per_mss = max_t(u32, tp->rx_opt.mss_clamp, tp->mss_cache) +
+ MAX_TCP_HEADER +
+ SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
+ per_mss = roundup_pow_of_two(per_mss) +
+ SKB_DATA_ALIGN(sizeof(struct sk_buff));
+
+ nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
+ nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
+
+ /* Fast Recovery (RFC 5681 3.2) :
+ * Cubic needs 1.7 factor, rounded to 2 to include
+ * extra cushion (application might react slowly to EPOLLOUT)
+ */
+ sndmem = ca_ops->sndbuf_expand ? ca_ops->sndbuf_expand(sk) : 2;
+ sndmem *= nr_segs * per_mss;
+
+ if (sk->sk_sndbuf < sndmem)
+ sk->sk_sndbuf = min(sndmem, sock_net(sk)->ipv4.sysctl_tcp_wmem[2]);
+}
+
+/* 2. Tuning advertised window (window_clamp, rcv_ssthresh)
+ *
+ * All tcp_full_space() is split to two parts: "network" buffer, allocated
+ * forward and advertised in receiver window (tp->rcv_wnd) and
+ * "application buffer", required to isolate scheduling/application
+ * latencies from network.
+ * window_clamp is maximal advertised window. It can be less than
+ * tcp_full_space(), in this case tcp_full_space() - window_clamp
+ * is reserved for "application" buffer. The less window_clamp is
+ * the smoother our behaviour from viewpoint of network, but the lower
+ * throughput and the higher sensitivity of the connection to losses. 8)
+ *
+ * rcv_ssthresh is more strict window_clamp used at "slow start"
+ * phase to predict further behaviour of this connection.
+ * It is used for two goals:
+ * - to enforce header prediction at sender, even when application
+ * requires some significant "application buffer". It is check #1.
+ * - to prevent pruning of receive queue because of misprediction
+ * of receiver window. Check #2.
+ *
+ * The scheme does not work when sender sends good segments opening
+ * window and then starts to feed us spaghetti. But it should work
+ * in common situations. Otherwise, we have to rely on queue collapsing.
+ */
+
+/* Slow part of check#2. */
+static int __tcp_grow_window(const struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ /* Optimize this! */
+ int truesize = tcp_win_from_space(sk, skb->truesize) >> 1;
+ int window = tcp_win_from_space(sk, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]) >> 1;
+
+ while (tp->rcv_ssthresh <= window) {
+ if (truesize <= skb->len)
+ return 2 * inet_csk(sk)->icsk_ack.rcv_mss;
+
+ truesize >>= 1;
+ window >>= 1;
+ }
+ return 0;
+}
+
+static void tcp_grow_window(struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Check #1 */
+ if (tp->rcv_ssthresh < tp->window_clamp &&
+ (int)tp->rcv_ssthresh < tcp_space(sk) &&
+ !tcp_under_memory_pressure(sk)) {
+ int incr;
+
+ /* Check #2. Increase window, if skb with such overhead
+ * will fit to rcvbuf in future.
+ */
+ if (tcp_win_from_space(sk, skb->truesize) <= skb->len)
+ incr = 2 * tp->advmss;
+ else
+ incr = __tcp_grow_window(sk, skb);
+
+ if (incr) {
+ incr = max_t(int, incr, 2 * skb->len);
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh + incr,
+ tp->window_clamp);
+ inet_csk(sk)->icsk_ack.quick |= 1;
+ }
+ }
+}
+
+/* 3. Tuning rcvbuf, when connection enters established state. */
+static void tcp_fixup_rcvbuf(struct sock *sk)
+{
+ u32 mss = tcp_sk(sk)->advmss;
+ int rcvmem;
+
+ rcvmem = 2 * SKB_TRUESIZE(mss + MAX_TCP_HEADER) *
+ tcp_default_init_rwnd(mss);
+
+ /* Dynamic Right Sizing (DRS) has 2 to 3 RTT latency
+ * Allow enough cushion so that sender is not limited by our window
+ */
+ if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf)
+ rcvmem <<= 2;
+
+ if (sk->sk_rcvbuf < rcvmem)
+ sk->sk_rcvbuf = min(rcvmem, sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
+}
+
+/* 4. Try to fixup all. It is made immediately after connection enters
+ * established state.
+ */
+void tcp_init_buffer_space(struct sock *sk)
+{
+ int tcp_app_win = sock_net(sk)->ipv4.sysctl_tcp_app_win;
+ struct tcp_sock *tp = tcp_sk(sk);
+ int maxwin;
+
+ if (!(sk->sk_userlocks & SOCK_RCVBUF_LOCK))
+ tcp_fixup_rcvbuf(sk);
+ if (!(sk->sk_userlocks & SOCK_SNDBUF_LOCK))
+ tcp_sndbuf_expand(sk);
+
+ tp->rcvq_space.space = tp->rcv_wnd;
+ tcp_mstamp_refresh(tp);
+ tp->rcvq_space.time = tp->tcp_mstamp;
+ tp->rcvq_space.seq = tp->copied_seq;
+
+ maxwin = tcp_full_space(sk);
+
+ if (tp->window_clamp >= maxwin) {
+ tp->window_clamp = maxwin;
+
+ if (tcp_app_win && maxwin > 4 * tp->advmss)
+ tp->window_clamp = max(maxwin -
+ (maxwin >> tcp_app_win),
+ 4 * tp->advmss);
+ }
+
+ /* Force reservation of one segment. */
+ if (tcp_app_win &&
+ tp->window_clamp > 2 * tp->advmss &&
+ tp->window_clamp + tp->advmss > maxwin)
+ tp->window_clamp = max(2 * tp->advmss, maxwin - tp->advmss);
+
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh, tp->window_clamp);
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+}
+
+/* 5. Recalculate window clamp after socket hit its memory bounds. */
+static void tcp_clamp_window(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct net *net = sock_net(sk);
+
+ icsk->icsk_ack.quick = 0;
+
+ if (sk->sk_rcvbuf < net->ipv4.sysctl_tcp_rmem[2] &&
+ !(sk->sk_userlocks & SOCK_RCVBUF_LOCK) &&
+ !tcp_under_memory_pressure(sk) &&
+ sk_memory_allocated(sk) < sk_prot_mem_limits(sk, 0)) {
+ sk->sk_rcvbuf = min(atomic_read(&sk->sk_rmem_alloc),
+ net->ipv4.sysctl_tcp_rmem[2]);
+ }
+ if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf)
+ tp->rcv_ssthresh = min(tp->window_clamp, 2U * tp->advmss);
+}
+
+/* Initialize RCV_MSS value.
+ * RCV_MSS is an our guess about MSS used by the peer.
+ * We haven't any direct information about the MSS.
+ * It's better to underestimate the RCV_MSS rather than overestimate.
+ * Overestimations make us ACKing less frequently than needed.
+ * Underestimations are more easy to detect and fix by tcp_measure_rcv_mss().
+ */
+void tcp_initialize_rcv_mss(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ unsigned int hint = min_t(unsigned int, tp->advmss, tp->mss_cache);
+
+ hint = min(hint, tp->rcv_wnd / 2);
+ hint = min(hint, TCP_MSS_DEFAULT);
+ hint = max(hint, TCP_MIN_MSS);
+
+ inet_csk(sk)->icsk_ack.rcv_mss = hint;
+}
+EXPORT_SYMBOL(tcp_initialize_rcv_mss);
+
+/* Receiver "autotuning" code.
+ *
+ * The algorithm for RTT estimation w/o timestamps is based on
+ * Dynamic Right-Sizing (DRS) by Wu Feng and Mike Fisk of LANL.
+ * <http://public.lanl.gov/radiant/pubs.html#DRS>
+ *
+ * More detail on this code can be found at
+ * <http://staff.psc.edu/jheffner/>,
+ * though this reference is out of date. A new paper
+ * is pending.
+ */
+static void tcp_rcv_rtt_update(struct tcp_sock *tp, u32 sample, int win_dep)
+{
+ u32 new_sample = tp->rcv_rtt_est.rtt_us;
+ long m = sample;
+
+ if (new_sample != 0) {
+ /* If we sample in larger samples in the non-timestamp
+ * case, we could grossly overestimate the RTT especially
+ * with chatty applications or bulk transfer apps which
+ * are stalled on filesystem I/O.
+ *
+ * Also, since we are only going for a minimum in the
+ * non-timestamp case, we do not smooth things out
+ * else with timestamps disabled convergence takes too
+ * long.
+ */
+ if (!win_dep) {
+ m -= (new_sample >> 3);
+ new_sample += m;
+ } else {
+ m <<= 3;
+ if (m < new_sample)
+ new_sample = m;
+ }
+ } else {
+ /* No previous measure. */
+ new_sample = m << 3;
+ }
+
+ tp->rcv_rtt_est.rtt_us = new_sample;
+}
+
+static inline void tcp_rcv_rtt_measure(struct tcp_sock *tp)
+{
+ u32 delta_us;
+
+ if (tp->rcv_rtt_est.time == 0)
+ goto new_measure;
+ if (before(tp->rcv_nxt, tp->rcv_rtt_est.seq))
+ return;
+ delta_us = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcv_rtt_est.time);
+ if (!delta_us)
+ delta_us = 1;
+ tcp_rcv_rtt_update(tp, delta_us, 1);
+
+new_measure:
+ tp->rcv_rtt_est.seq = tp->rcv_nxt + tp->rcv_wnd;
+ tp->rcv_rtt_est.time = tp->tcp_mstamp;
+}
+
+static inline void tcp_rcv_rtt_measure_ts(struct sock *sk,
+ const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tp->rx_opt.rcv_tsecr == tp->rcv_rtt_last_tsecr)
+ return;
+ tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
+
+ if (TCP_SKB_CB(skb)->end_seq -
+ TCP_SKB_CB(skb)->seq >= inet_csk(sk)->icsk_ack.rcv_mss) {
+ u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
+ u32 delta_us;
+
+ if (!delta)
+ delta = 1;
+ delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
+ tcp_rcv_rtt_update(tp, delta_us, 0);
+ }
+}
+
+/*
+ * This function should be called every time data is copied to user space.
+ * It calculates the appropriate TCP receive buffer space.
+ */
+void tcp_rcv_space_adjust(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 copied;
+ int time;
+
+ trace_tcp_rcv_space_adjust(sk);
+
+ tcp_mstamp_refresh(tp);
+ time = tcp_stamp_us_delta(tp->tcp_mstamp, tp->rcvq_space.time);
+ if (time < (tp->rcv_rtt_est.rtt_us >> 3) || tp->rcv_rtt_est.rtt_us == 0)
+ return;
+
+ /* Number of bytes copied to user in last RTT */
+ copied = tp->copied_seq - tp->rcvq_space.seq;
+ if (copied <= tp->rcvq_space.space)
+ goto new_measure;
+
+ /* A bit of theory :
+ * copied = bytes received in previous RTT, our base window
+ * To cope with packet losses, we need a 2x factor
+ * To cope with slow start, and sender growing its cwin by 100 %
+ * every RTT, we need a 4x factor, because the ACK we are sending
+ * now is for the next RTT, not the current one :
+ * <prev RTT . ><current RTT .. ><next RTT .... >
+ */
+
+ if (sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf &&
+ !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) {
+ int rcvmem, rcvbuf;
+ u64 rcvwin, grow;
+
+ /* minimal window to cope with packet losses, assuming
+ * steady state. Add some cushion because of small variations.
+ */
+ rcvwin = ((u64)copied << 1) + 16 * tp->advmss;
+
+ /* Accommodate for sender rate increase (eg. slow start) */
+ grow = rcvwin * (copied - tp->rcvq_space.space);
+ do_div(grow, tp->rcvq_space.space);
+ rcvwin += (grow << 1);
+
+ rcvmem = SKB_TRUESIZE(tp->advmss + MAX_TCP_HEADER);
+ while (tcp_win_from_space(sk, rcvmem) < tp->advmss)
+ rcvmem += 128;
+
+ do_div(rcvwin, tp->advmss);
+ rcvbuf = min_t(u64, rcvwin * rcvmem,
+ sock_net(sk)->ipv4.sysctl_tcp_rmem[2]);
+ if (rcvbuf > sk->sk_rcvbuf) {
+ sk->sk_rcvbuf = rcvbuf;
+
+ /* Make the window clamp follow along. */
+ tp->window_clamp = tcp_win_from_space(sk, rcvbuf);
+ }
+ }
+ tp->rcvq_space.space = copied;
+
+new_measure:
+ tp->rcvq_space.seq = tp->copied_seq;
+ tp->rcvq_space.time = tp->tcp_mstamp;
+}
+
+/* There is something which you must keep in mind when you analyze the
+ * behavior of the tp->ato delayed ack timeout interval. When a
+ * connection starts up, we want to ack as quickly as possible. The
+ * problem is that "good" TCP's do slow start at the beginning of data
+ * transmission. The means that until we send the first few ACK's the
+ * sender will sit on his end and only queue most of his data, because
+ * he can only send snd_cwnd unacked packets at any given time. For
+ * each ACK we send, he increments snd_cwnd and transmits more of his
+ * queue. -DaveM
+ */
+static void tcp_event_data_recv(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ u32 now;
+
+ inet_csk_schedule_ack(sk);
+
+ tcp_measure_rcv_mss(sk, skb);
+
+ tcp_rcv_rtt_measure(tp);
+
+ now = tcp_jiffies32;
+
+ if (!icsk->icsk_ack.ato) {
+ /* The _first_ data packet received, initialize
+ * delayed ACK engine.
+ */
+ tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
+ icsk->icsk_ack.ato = TCP_ATO_MIN;
+ } else {
+ int m = now - icsk->icsk_ack.lrcvtime;
+
+ if (m <= TCP_ATO_MIN / 2) {
+ /* The fastest case is the first. */
+ icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + TCP_ATO_MIN / 2;
+ } else if (m < icsk->icsk_ack.ato) {
+ icsk->icsk_ack.ato = (icsk->icsk_ack.ato >> 1) + m;
+ if (icsk->icsk_ack.ato > icsk->icsk_rto)
+ icsk->icsk_ack.ato = icsk->icsk_rto;
+ } else if (m > icsk->icsk_rto) {
+ /* Too long gap. Apparently sender failed to
+ * restart window, so that we send ACKs quickly.
+ */
+ tcp_incr_quickack(sk, TCP_MAX_QUICKACKS);
+ sk_mem_reclaim(sk);
+ }
+ }
+ icsk->icsk_ack.lrcvtime = now;
+
+ tcp_ecn_check_ce(sk, skb);
+
+ if (skb->len >= 128)
+ tcp_grow_window(sk, skb);
+}
+
+/* Called to compute a smoothed rtt estimate. The data fed to this
+ * routine either comes from timestamps, or from segments that were
+ * known _not_ to have been retransmitted [see Karn/Partridge
+ * Proceedings SIGCOMM 87]. The algorithm is from the SIGCOMM 88
+ * piece by Van Jacobson.
+ * NOTE: the next three routines used to be one big routine.
+ * To save cycles in the RFC 1323 implementation it was better to break
+ * it up into three procedures. -- erics
+ */
+static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ long m = mrtt_us; /* RTT */
+ u32 srtt = tp->srtt_us;
+
+ /* The following amusing code comes from Jacobson's
+ * article in SIGCOMM '88. Note that rtt and mdev
+ * are scaled versions of rtt and mean deviation.
+ * This is designed to be as fast as possible
+ * m stands for "measurement".
+ *
+ * On a 1990 paper the rto value is changed to:
+ * RTO = rtt + 4 * mdev
+ *
+ * Funny. This algorithm seems to be very broken.
+ * These formulae increase RTO, when it should be decreased, increase
+ * too slowly, when it should be increased quickly, decrease too quickly
+ * etc. I guess in BSD RTO takes ONE value, so that it is absolutely
+ * does not matter how to _calculate_ it. Seems, it was trap
+ * that VJ failed to avoid. 8)
+ */
+ if (srtt != 0) {
+ m -= (srtt >> 3); /* m is now error in rtt est */
+ srtt += m; /* rtt = 7/8 rtt + 1/8 new */
+ if (m < 0) {
+ m = -m; /* m is now abs(error) */
+ m -= (tp->mdev_us >> 2); /* similar update on mdev */
+ /* This is similar to one of Eifel findings.
+ * Eifel blocks mdev updates when rtt decreases.
+ * This solution is a bit different: we use finer gain
+ * for mdev in this case (alpha*beta).
+ * Like Eifel it also prevents growth of rto,
+ * but also it limits too fast rto decreases,
+ * happening in pure Eifel.
+ */
+ if (m > 0)
+ m >>= 3;
+ } else {
+ m -= (tp->mdev_us >> 2); /* similar update on mdev */
+ }
+ tp->mdev_us += m; /* mdev = 3/4 mdev + 1/4 new */
+ if (tp->mdev_us > tp->mdev_max_us) {
+ tp->mdev_max_us = tp->mdev_us;
+ if (tp->mdev_max_us > tp->rttvar_us)
+ tp->rttvar_us = tp->mdev_max_us;
+ }
+ if (after(tp->snd_una, tp->rtt_seq)) {
+ if (tp->mdev_max_us < tp->rttvar_us)
+ tp->rttvar_us -= (tp->rttvar_us - tp->mdev_max_us) >> 2;
+ tp->rtt_seq = tp->snd_nxt;
+ tp->mdev_max_us = tcp_rto_min_us(sk);
+ }
+ } else {
+ /* no previous measure. */
+ srtt = m << 3; /* take the measured time to be rtt */
+ tp->mdev_us = m << 1; /* make sure rto = 3*rtt */
+ tp->rttvar_us = max(tp->mdev_us, tcp_rto_min_us(sk));
+ tp->mdev_max_us = tp->rttvar_us;
+ tp->rtt_seq = tp->snd_nxt;
+ }
+ tp->srtt_us = max(1U, srtt);
+}
+
+static void tcp_update_pacing_rate(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ u64 rate;
+
+ /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
+ rate = (u64)tp->mss_cache * ((USEC_PER_SEC / 100) << 3);
+
+ /* current rate is (cwnd * mss) / srtt
+ * In Slow Start [1], set sk_pacing_rate to 200 % the current rate.
+ * In Congestion Avoidance phase, set it to 120 % the current rate.
+ *
+ * [1] : Normal Slow Start condition is (tp->snd_cwnd < tp->snd_ssthresh)
+ * If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
+ * end of slow start and should slow down.
+ */
+ if (tp->snd_cwnd < tp->snd_ssthresh / 2)
+ rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
+ else
+ rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
+
+ rate *= max(tp->snd_cwnd, tp->packets_out);
+
+ if (likely(tp->srtt_us))
+ do_div(rate, tp->srtt_us);
+
+ /* WRITE_ONCE() is needed because sch_fq fetches sk_pacing_rate
+ * without any lock. We want to make sure compiler wont store
+ * intermediate values in this location.
+ */
+ WRITE_ONCE(sk->sk_pacing_rate, min_t(u64, rate,
+ sk->sk_max_pacing_rate));
+}
+
+/* Calculate rto without backoff. This is the second half of Van Jacobson's
+ * routine referred to above.
+ */
+static void tcp_set_rto(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ /* Old crap is replaced with new one. 8)
+ *
+ * More seriously:
+ * 1. If rtt variance happened to be less 50msec, it is hallucination.
+ * It cannot be less due to utterly erratic ACK generation made
+ * at least by solaris and freebsd. "Erratic ACKs" has _nothing_
+ * to do with delayed acks, because at cwnd>2 true delack timeout
+ * is invisible. Actually, Linux-2.4 also generates erratic
+ * ACKs in some circumstances.
+ */
+ inet_csk(sk)->icsk_rto = __tcp_set_rto(tp);
+
+ /* 2. Fixups made earlier cannot be right.
+ * If we do not estimate RTO correctly without them,
+ * all the algo is pure shit and should be replaced
+ * with correct one. It is exactly, which we pretend to do.
+ */
+
+ /* NOTE: clamping at TCP_RTO_MIN is not required, current algo
+ * guarantees that rto is higher.
+ */
+ tcp_bound_rto(sk);
+}
+
+__u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst)
+{
+ __u32 cwnd = (dst ? dst_metric(dst, RTAX_INITCWND) : 0);
+
+ if (!cwnd)
+ cwnd = TCP_INIT_CWND;
+ return min_t(__u32, cwnd, tp->snd_cwnd_clamp);
+}
+
+/* Take a notice that peer is sending D-SACKs */
+static void tcp_dsack_seen(struct tcp_sock *tp)
+{
+ tp->rx_opt.sack_ok |= TCP_DSACK_SEEN;
+ tp->rack.dsack_seen = 1;
+ tp->dsack_dups++;
+}
+
+/* It's reordering when higher sequence was delivered (i.e. sacked) before
+ * some lower never-retransmitted sequence ("low_seq"). The maximum reordering
+ * distance is approximated in full-mss packet distance ("reordering").
+ */
+static void tcp_check_sack_reordering(struct sock *sk, const u32 low_seq,
+ const int ts)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ const u32 mss = tp->mss_cache;
+ u32 fack, metric;
+
+ fack = tcp_highest_sack_seq(tp);
+ if (!before(low_seq, fack))
+ return;
+
+ metric = fack - low_seq;
+ if ((metric > tp->reordering * mss) && mss) {
+#if FASTRETRANS_DEBUG > 1
+ pr_debug("Disorder%d %d %u f%u s%u rr%d\n",
+ tp->rx_opt.sack_ok, inet_csk(sk)->icsk_ca_state,
+ tp->reordering,
+ 0,
+ tp->sacked_out,
+ tp->undo_marker ? tp->undo_retrans : 0);
+#endif
+ tp->reordering = min_t(u32, (metric + mss - 1) / mss,
+ sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
+ }
+
+ /* This exciting event is worth to be remembered. 8) */
+ tp->reord_seen++;
+ NET_INC_STATS(sock_net(sk),
+ ts ? LINUX_MIB_TCPTSREORDER : LINUX_MIB_TCPSACKREORDER);
+}
+
+/* This must be called before lost_out is incremented */
+static void tcp_verify_retransmit_hint(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ if (!tp->retransmit_skb_hint ||
+ before(TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(tp->retransmit_skb_hint)->seq))
+ tp->retransmit_skb_hint = skb;
+}
+
+/* Sum the number of packets on the wire we have marked as lost.
+ * There are two cases we care about here:
+ * a) Packet hasn't been marked lost (nor retransmitted),
+ * and this is the first loss.
+ * b) Packet has been marked both lost and retransmitted,
+ * and this means we think it was lost again.
+ */
+static void tcp_sum_lost(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ __u8 sacked = TCP_SKB_CB(skb)->sacked;
+
+ if (!(sacked & TCPCB_LOST) ||
+ ((sacked & TCPCB_LOST) && (sacked & TCPCB_SACKED_RETRANS)))
+ tp->lost += tcp_skb_pcount(skb);
+}
+
+static void tcp_skb_mark_lost(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
+ tcp_verify_retransmit_hint(tp, skb);
+
+ tp->lost_out += tcp_skb_pcount(skb);
+ tcp_sum_lost(tp, skb);
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ }
+}
+
+void tcp_skb_mark_lost_uncond_verify(struct tcp_sock *tp, struct sk_buff *skb)
+{
+ tcp_verify_retransmit_hint(tp, skb);
+
+ tcp_sum_lost(tp, skb);
+ if (!(TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_ACKED))) {
+ tp->lost_out += tcp_skb_pcount(skb);
+ TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
+ }
+}
+
+/* This procedure tags the retransmission queue when SACKs arrive.
+ *
+ * We have three tag bits: SACKED(S), RETRANS(R) and LOST(L).
+ * Packets in queue with these bits set are counted in variables
+ * sacked_out, retrans_out and lost_out, correspondingly.
+ *
+ * Valid combinations are:
+ * Tag InFlight Description
+ * 0 1 - orig segment is in flight.
+ * S 0 - nothing flies, orig reached receiver.
+ * L 0 - nothing flies, orig lost by net.
+ * R 2 - both orig and retransmit are in flight.
+ * L|R 1 - orig is lost, retransmit is in flight.
+ * S|R 1 - orig reached receiver, retrans is still in flight.
+ * (L|S|R is logically valid, it could occur when L|R is sacked,
+ * but it is equivalent to plain S and code short-curcuits it to S.
+ * L|S is logically invalid, it would mean -1 packet in flight 8))
+ *
+ * These 6 states form finite state machine, controlled by the following events:
+ * 1. New ACK (+SACK) arrives. (tcp_sacktag_write_queue())
+ * 2. Retransmission. (tcp_retransmit_skb(), tcp_xmit_retransmit_queue())
+ * 3. Loss detection event of two flavors:
+ * A. Scoreboard estimator decided the packet is lost.
+ * A'. Reno "three dupacks" marks head of queue lost.
+ * B. SACK arrives sacking SND.NXT at the moment, when the
+ * segment was retransmitted.
+ * 4. D-SACK added new rule: D-SACK changes any tag to S.
+ *
+ * It is pleasant to note, that state diagram turns out to be commutative,
+ * so that we are allowed not to be bothered by order of our actions,
+ * when multiple events arrive simultaneously. (see the function below).
+ *
+ * Reordering detection.
+ * --------------------
+ * Reordering metric is maximal distance, which a packet can be displaced
+ * in packet stream. With SACKs we can estimate it:
+ *
+ * 1. SACK fills old hole and the corresponding segment was not
+ * ever retransmitted -> reordering. Alas, we cannot use it
+ * when segment was retransmitted.
+ * 2. The last flaw is solved with D-SACK. D-SACK arrives
+ * for retransmitted and already SACKed segment -> reordering..
+ * Both of these heuristics are not used in Loss state, when we cannot
+ * account for retransmits accurately.
+ *
+ * SACK block validation.
+ * ----------------------
+ *
+ * SACK block range validation checks that the received SACK block fits to
+ * the expected sequence limits, i.e., it is between SND.UNA and SND.NXT.
+ * Note that SND.UNA is not included to the range though being valid because
+ * it means that the receiver is rather inconsistent with itself reporting
+ * SACK reneging when it should advance SND.UNA. Such SACK block this is
+ * perfectly valid, however, in light of RFC2018 which explicitly states
+ * that "SACK block MUST reflect the newest segment. Even if the newest
+ * segment is going to be discarded ...", not that it looks very clever
+ * in case of head skb. Due to potentional receiver driven attacks, we
+ * choose to avoid immediate execution of a walk in write queue due to
+ * reneging and defer head skb's loss recovery to standard loss recovery
+ * procedure that will eventually trigger (nothing forbids us doing this).
+ *
+ * Implements also blockage to start_seq wrap-around. Problem lies in the
+ * fact that though start_seq (s) is before end_seq (i.e., not reversed),
+ * there's no guarantee that it will be before snd_nxt (n). The problem
+ * happens when start_seq resides between end_seq wrap (e_w) and snd_nxt
+ * wrap (s_w):
+ *
+ * <- outs wnd -> <- wrapzone ->
+ * u e n u_w e_w s n_w
+ * | | | | | | |
+ * |<------------+------+----- TCP seqno space --------------+---------->|
+ * ...-- <2^31 ->| |<--------...
+ * ...---- >2^31 ------>| |<--------...
+ *
+ * Current code wouldn't be vulnerable but it's better still to discard such
+ * crazy SACK blocks. Doing this check for start_seq alone closes somewhat
+ * similar case (end_seq after snd_nxt wrap) as earlier reversed check in
+ * snd_nxt wrap -> snd_una region will then become "well defined", i.e.,
+ * equal to the ideal case (infinite seqno space without wrap caused issues).
+ *
+ * With D-SACK the lower bound is extended to cover sequence space below
+ * SND.UNA down to undo_marker, which is the last point of interest. Yet
+ * again, D-SACK block must not to go across snd_una (for the same reason as
+ * for the normal SACK blocks, explained above). But there all simplicity
+ * ends, TCP might receive valid D-SACKs below that. As long as they reside
+ * fully below undo_marker they do not affect behavior in anyway and can
+ * therefore be safely ignored. In rare cases (which are more or less
+ * theoretical ones), the D-SACK will nicely cross that boundary due to skb
+ * fragmentation and packet reordering past skb's retransmission. To consider
+ * them correctly, the acceptable range must be extended even more though
+ * the exact amount is rather hard to quantify. However, tp->max_window can
+ * be used as an exaggerated estimate.
+ */
+static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack,
+ u32 start_seq, u32 end_seq)
+{
+ /* Too far in future, or reversed (interpretation is ambiguous) */
+ if (after(end_seq, tp->snd_nxt) || !before(start_seq, end_seq))
+ return false;
+
+ /* Nasty start_seq wrap-around check (see comments above) */
+ if (!before(start_seq, tp->snd_nxt))
+ return false;
+
+ /* In outstanding window? ...This is valid exit for D-SACKs too.
+ * start_seq == snd_una is non-sensical (see comments above)
+ */
+ if (after(start_seq, tp->snd_una))
+ return true;
+
+ if (!is_dsack || !tp->undo_marker)
+ return false;
+
+ /* ...Then it's D-SACK, and must reside below snd_una completely */
+ if (after(end_seq, tp->snd_una))
+ return false;
+
+ if (!before(start_seq, tp->undo_marker))
+ return true;
+
+ /* Too old */
+ if (!after(end_seq, tp->undo_marker))
+ return false;
+
+ /* Undo_marker boundary crossing (overestimates a lot). Known already:
+ * start_seq < undo_marker and end_seq >= undo_marker.
+ */
+ return !before(start_seq, end_seq - tp->max_window);
+}
+
+static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
+ struct tcp_sack_block_wire *sp, int num_sacks,
+ u32 prior_snd_una)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq);
+ u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq);
+ bool dup_sack = false;
+
+ if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) {
+ dup_sack = true;
+ tcp_dsack_seen(tp);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV);
+ } else if (num_sacks > 1) {
+ u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq);
+ u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq);
+
+ if (!after(end_seq_0, end_seq_1) &&
+ !before(start_seq_0, start_seq_1)) {
+ dup_sack = true;
+ tcp_dsack_seen(tp);
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPDSACKOFORECV);
+ }
+ }
+
+ /* D-SACK for already forgotten data... Do dumb counting. */
+ if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 &&
+ !after(end_seq_0, prior_snd_una) &&
+ after(end_seq_0, tp->undo_marker))
+ tp->undo_retrans--;
+
+ return dup_sack;
+}
+
+struct tcp_sacktag_state {
+ u32 reord;
+ /* Timestamps for earliest and latest never-retransmitted segment
+ * that was SACKed. RTO needs the earliest RTT to stay conservative,
+ * but congestion control should still get an accurate delay signal.
+ */
+ u64 first_sackt;
+ u64 last_sackt;
+ struct rate_sample *rate;
+ int flag;
+ unsigned int mss_now;
+};
+
+/* Check if skb is fully within the SACK block. In presence of GSO skbs,
+ * the incoming SACK may not exactly match but we can find smaller MSS
+ * aligned portion of it that matches. Therefore we might need to fragment
+ * which may fail and creates some hassle (caller must handle error case
+ * returns).
+ *
+ * FIXME: this could be merged to shift decision code
+ */
+static int tcp_match_skb_to_sack(struct sock *sk, struct sk_buff *skb,
+ u32 start_seq, u32 end_seq)
+{
+ int err;
+ bool in_sack;
+ unsigned int pkt_len;
+ unsigned int mss;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
+ !before(end_seq, TCP_SKB_CB(skb)->end_seq);
+
+ if (tcp_skb_pcount(skb) > 1 && !in_sack &&
+ after(TCP_SKB_CB(skb)->end_seq, start_seq)) {
+ mss = tcp_skb_mss(skb);
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
+
+ if (!in_sack) {
+ pkt_len = start_seq - TCP_SKB_CB(skb)->seq;
+ if (pkt_len < mss)
+ pkt_len = mss;
+ } else {
+ pkt_len = end_seq - TCP_SKB_CB(skb)->seq;
+ if (pkt_len < mss)
+ return -EINVAL;
+ }
+
+ /* Round if necessary so that SACKs cover only full MSSes
+ * and/or the remaining small portion (if present)
+ */
+ if (pkt_len > mss) {
+ unsigned int new_len = (pkt_len / mss) * mss;
+ if (!in_sack && new_len < pkt_len)
+ new_len += mss;
+ pkt_len = new_len;
+ }
+
+ if (pkt_len >= skb->len && !in_sack)
+ return 0;
+
+ err = tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
+ pkt_len, mss, GFP_ATOMIC);
+ if (err < 0)
+ return err;
+ }
+
+ return in_sack;
+}
+
+/* Mark the given newly-SACKed range as such, adjusting counters and hints. */
+static u8 tcp_sacktag_one(struct sock *sk,
+ struct tcp_sacktag_state *state, u8 sacked,
+ u32 start_seq, u32 end_seq,
+ int dup_sack, int pcount,
+ u64 xmit_time)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Account D-SACK for retransmitted packet. */
+ if (dup_sack && (sacked & TCPCB_RETRANS)) {
+ if (tp->undo_marker && tp->undo_retrans > 0 &&
+ after(end_seq, tp->undo_marker))
+ tp->undo_retrans--;
+ if ((sacked & TCPCB_SACKED_ACKED) &&
+ before(start_seq, state->reord))
+ state->reord = start_seq;
+ }
+
+ /* Nothing to do; acked frame is about to be dropped (was ACKed). */
+ if (!after(end_seq, tp->snd_una))
+ return sacked;
+
+ if (!(sacked & TCPCB_SACKED_ACKED)) {
+ tcp_rack_advance(tp, sacked, end_seq, xmit_time);
+
+ if (sacked & TCPCB_SACKED_RETRANS) {
+ /* If the segment is not tagged as lost,
+ * we do not clear RETRANS, believing
+ * that retransmission is still in flight.
+ */
+ if (sacked & TCPCB_LOST) {
+ sacked &= ~(TCPCB_LOST|TCPCB_SACKED_RETRANS);
+ tp->lost_out -= pcount;
+ tp->retrans_out -= pcount;
+ }
+ } else {
+ if (!(sacked & TCPCB_RETRANS)) {
+ /* New sack for not retransmitted frame,
+ * which was in hole. It is reordering.
+ */
+ if (before(start_seq,
+ tcp_highest_sack_seq(tp)) &&
+ before(start_seq, state->reord))
+ state->reord = start_seq;
+
+ if (!after(end_seq, tp->high_seq))
+ state->flag |= FLAG_ORIG_SACK_ACKED;
+ if (state->first_sackt == 0)
+ state->first_sackt = xmit_time;
+ state->last_sackt = xmit_time;
+ }
+
+ if (sacked & TCPCB_LOST) {
+ sacked &= ~TCPCB_LOST;
+ tp->lost_out -= pcount;
+ }
+ }
+
+ sacked |= TCPCB_SACKED_ACKED;
+ state->flag |= FLAG_DATA_SACKED;
+ tp->sacked_out += pcount;
+ tp->delivered += pcount; /* Out-of-order packets delivered */
+
+ /* Lost marker hint past SACKed? Tweak RFC3517 cnt */
+ if (tp->lost_skb_hint &&
+ before(start_seq, TCP_SKB_CB(tp->lost_skb_hint)->seq))
+ tp->lost_cnt_hint += pcount;
+ }
+
+ /* D-SACK. We can detect redundant retransmission in S|R and plain R
+ * frames and clear it. undo_retrans is decreased above, L|R frames
+ * are accounted above as well.
+ */
+ if (dup_sack && (sacked & TCPCB_SACKED_RETRANS)) {
+ sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= pcount;
+ }
+
+ return sacked;
+}
+
+/* Shift newly-SACKed bytes from this skb to the immediately previous
+ * already-SACKed sk_buff. Mark the newly-SACKed bytes as such.
+ */
+static bool tcp_shifted_skb(struct sock *sk, struct sk_buff *prev,
+ struct sk_buff *skb,
+ struct tcp_sacktag_state *state,
+ unsigned int pcount, int shifted, int mss,
+ bool dup_sack)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 start_seq = TCP_SKB_CB(skb)->seq; /* start of newly-SACKed */
+ u32 end_seq = start_seq + shifted; /* end of newly-SACKed */
+
+ BUG_ON(!pcount);
+
+ /* Adjust counters and hints for the newly sacked sequence
+ * range but discard the return value since prev is already
+ * marked. We must tag the range first because the seq
+ * advancement below implicitly advances
+ * tcp_highest_sack_seq() when skb is highest_sack.
+ */
+ tcp_sacktag_one(sk, state, TCP_SKB_CB(skb)->sacked,
+ start_seq, end_seq, dup_sack, pcount,
+ skb->skb_mstamp);
+ tcp_rate_skb_delivered(sk, skb, state->rate);
+
+ if (skb == tp->lost_skb_hint)
+ tp->lost_cnt_hint += pcount;
+
+ TCP_SKB_CB(prev)->end_seq += shifted;
+ TCP_SKB_CB(skb)->seq += shifted;
+
+ tcp_skb_pcount_add(prev, pcount);
+ BUG_ON(tcp_skb_pcount(skb) < pcount);
+ tcp_skb_pcount_add(skb, -pcount);
+
+ /* When we're adding to gso_segs == 1, gso_size will be zero,
+ * in theory this shouldn't be necessary but as long as DSACK
+ * code can come after this skb later on it's better to keep
+ * setting gso_size to something.
+ */
+ if (!TCP_SKB_CB(prev)->tcp_gso_size)
+ TCP_SKB_CB(prev)->tcp_gso_size = mss;
+
+ /* CHECKME: To clear or not to clear? Mimics normal skb currently */
+ if (tcp_skb_pcount(skb) <= 1)
+ TCP_SKB_CB(skb)->tcp_gso_size = 0;
+
+ /* Difference in this won't matter, both ACKed by the same cumul. ACK */
+ TCP_SKB_CB(prev)->sacked |= (TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS);
+
+ if (skb->len > 0) {
+ BUG_ON(!tcp_skb_pcount(skb));
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTED);
+ return false;
+ }
+
+ /* Whole SKB was eaten :-) */
+
+ if (skb == tp->retransmit_skb_hint)
+ tp->retransmit_skb_hint = prev;
+ if (skb == tp->lost_skb_hint) {
+ tp->lost_skb_hint = prev;
+ tp->lost_cnt_hint -= tcp_skb_pcount(prev);
+ }
+
+ TCP_SKB_CB(prev)->tcp_flags |= TCP_SKB_CB(skb)->tcp_flags;
+ TCP_SKB_CB(prev)->eor = TCP_SKB_CB(skb)->eor;
+ if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
+ TCP_SKB_CB(prev)->end_seq++;
+
+ if (skb == tcp_highest_sack(sk))
+ tcp_advance_highest_sack(sk, skb);
+
+ tcp_skb_collapse_tstamp(prev, skb);
+ if (unlikely(TCP_SKB_CB(prev)->tx.delivered_mstamp))
+ TCP_SKB_CB(prev)->tx.delivered_mstamp = 0;
+
+ tcp_rtx_queue_unlink_and_free(skb, sk);
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKMERGED);
+
+ return true;
+}
+
+/* I wish gso_size would have a bit more sane initialization than
+ * something-or-zero which complicates things
+ */
+static int tcp_skb_seglen(const struct sk_buff *skb)
+{
+ return tcp_skb_pcount(skb) == 1 ? skb->len : tcp_skb_mss(skb);
+}
+
+/* Shifting pages past head area doesn't work */
+static int skb_can_shift(const struct sk_buff *skb)
+{
+ return !skb_headlen(skb) && skb_is_nonlinear(skb);
+}
+
+/* Try collapsing SACK blocks spanning across multiple skbs to a single
+ * skb.
+ */
+static struct sk_buff *tcp_shift_skb_data(struct sock *sk, struct sk_buff *skb,
+ struct tcp_sacktag_state *state,
+ u32 start_seq, u32 end_seq,
+ bool dup_sack)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *prev;
+ int mss;
+ int pcount = 0;
+ int len;
+ int in_sack;
+
+ /* Normally R but no L won't result in plain S */
+ if (!dup_sack &&
+ (TCP_SKB_CB(skb)->sacked & (TCPCB_LOST|TCPCB_SACKED_RETRANS)) == TCPCB_SACKED_RETRANS)
+ goto fallback;
+ if (!skb_can_shift(skb))
+ goto fallback;
+ /* This frame is about to be dropped (was ACKed). */
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una))
+ goto fallback;
+
+ /* Can only happen with delayed DSACK + discard craziness */
+ prev = skb_rb_prev(skb);
+ if (!prev)
+ goto fallback;
+
+ if ((TCP_SKB_CB(prev)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED)
+ goto fallback;
+
+ if (!tcp_skb_can_collapse_to(prev))
+ goto fallback;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq) &&
+ !before(end_seq, TCP_SKB_CB(skb)->end_seq);
+
+ if (in_sack) {
+ len = skb->len;
+ pcount = tcp_skb_pcount(skb);
+ mss = tcp_skb_seglen(skb);
+
+ /* TODO: Fix DSACKs to not fragment already SACKed and we can
+ * drop this restriction as unnecessary
+ */
+ if (mss != tcp_skb_seglen(prev))
+ goto fallback;
+ } else {
+ if (!after(TCP_SKB_CB(skb)->end_seq, start_seq))
+ goto noop;
+ /* CHECKME: This is non-MSS split case only?, this will
+ * cause skipped skbs due to advancing loop btw, original
+ * has that feature too
+ */
+ if (tcp_skb_pcount(skb) <= 1)
+ goto noop;
+
+ in_sack = !after(start_seq, TCP_SKB_CB(skb)->seq);
+ if (!in_sack) {
+ /* TODO: head merge to next could be attempted here
+ * if (!after(TCP_SKB_CB(skb)->end_seq, end_seq)),
+ * though it might not be worth of the additional hassle
+ *
+ * ...we can probably just fallback to what was done
+ * previously. We could try merging non-SACKed ones
+ * as well but it probably isn't going to buy off
+ * because later SACKs might again split them, and
+ * it would make skb timestamp tracking considerably
+ * harder problem.
+ */
+ goto fallback;
+ }
+
+ len = end_seq - TCP_SKB_CB(skb)->seq;
+ BUG_ON(len < 0);
+ BUG_ON(len > skb->len);
+
+ /* MSS boundaries should be honoured or else pcount will
+ * severely break even though it makes things bit trickier.
+ * Optimize common case to avoid most of the divides
+ */
+ mss = tcp_skb_mss(skb);
+
+ /* TODO: Fix DSACKs to not fragment already SACKed and we can
+ * drop this restriction as unnecessary
+ */
+ if (mss != tcp_skb_seglen(prev))
+ goto fallback;
+
+ if (len == mss) {
+ pcount = 1;
+ } else if (len < mss) {
+ goto noop;
+ } else {
+ pcount = len / mss;
+ len = pcount * mss;
+ }
+ }
+
+ /* tcp_sacktag_one() won't SACK-tag ranges below snd_una */
+ if (!after(TCP_SKB_CB(skb)->seq + len, tp->snd_una))
+ goto fallback;
+
+ if (!skb_shift(prev, skb, len))
+ goto fallback;
+ if (!tcp_shifted_skb(sk, prev, skb, state, pcount, len, mss, dup_sack))
+ goto out;
+
+ /* Hole filled allows collapsing with the next as well, this is very
+ * useful when hole on every nth skb pattern happens
+ */
+ skb = skb_rb_next(prev);
+ if (!skb)
+ goto out;
+
+ if (!skb_can_shift(skb) ||
+ ((TCP_SKB_CB(skb)->sacked & TCPCB_TAGBITS) != TCPCB_SACKED_ACKED) ||
+ (mss != tcp_skb_seglen(skb)))
+ goto out;
+
+ len = skb->len;
+ if (skb_shift(prev, skb, len)) {
+ pcount += tcp_skb_pcount(skb);
+ tcp_shifted_skb(sk, prev, skb, state, tcp_skb_pcount(skb),
+ len, mss, 0);
+ }
+
+out:
+ return prev;
+
+noop:
+ return skb;
+
+fallback:
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_SACKSHIFTFALLBACK);
+ return NULL;
+}
+
+static struct sk_buff *tcp_sacktag_walk(struct sk_buff *skb, struct sock *sk,
+ struct tcp_sack_block *next_dup,
+ struct tcp_sacktag_state *state,
+ u32 start_seq, u32 end_seq,
+ bool dup_sack_in)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *tmp;
+
+ skb_rbtree_walk_from(skb) {
+ int in_sack = 0;
+ bool dup_sack = dup_sack_in;
+
+ /* queue is in-order => we can short-circuit the walk early */
+ if (!before(TCP_SKB_CB(skb)->seq, end_seq))
+ break;
+
+ if (next_dup &&
+ before(TCP_SKB_CB(skb)->seq, next_dup->end_seq)) {
+ in_sack = tcp_match_skb_to_sack(sk, skb,
+ next_dup->start_seq,
+ next_dup->end_seq);
+ if (in_sack > 0)
+ dup_sack = true;
+ }
+
+ /* skb reference here is a bit tricky to get right, since
+ * shifting can eat and free both this skb and the next,
+ * so not even _safe variant of the loop is enough.
+ */
+ if (in_sack <= 0) {
+ tmp = tcp_shift_skb_data(sk, skb, state,
+ start_seq, end_seq, dup_sack);
+ if (tmp) {
+ if (tmp != skb) {
+ skb = tmp;
+ continue;
+ }
+
+ in_sack = 0;
+ } else {
+ in_sack = tcp_match_skb_to_sack(sk, skb,
+ start_seq,
+ end_seq);
+ }
+ }
+
+ if (unlikely(in_sack < 0))
+ break;
+
+ if (in_sack) {
+ TCP_SKB_CB(skb)->sacked =
+ tcp_sacktag_one(sk,
+ state,
+ TCP_SKB_CB(skb)->sacked,
+ TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq,
+ dup_sack,
+ tcp_skb_pcount(skb),
+ skb->skb_mstamp);
+ tcp_rate_skb_delivered(sk, skb, state->rate);
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)
+ list_del_init(&skb->tcp_tsorted_anchor);
+
+ if (!before(TCP_SKB_CB(skb)->seq,
+ tcp_highest_sack_seq(tp)))
+ tcp_advance_highest_sack(sk, skb);
+ }
+ }
+ return skb;
+}
+
+static struct sk_buff *tcp_sacktag_bsearch(struct sock *sk,
+ struct tcp_sacktag_state *state,
+ u32 seq)
+{
+ struct rb_node *parent, **p = &sk->tcp_rtx_queue.rb_node;
+ struct sk_buff *skb;
+
+ while (*p) {
+ parent = *p;
+ skb = rb_to_skb(parent);
+ if (before(seq, TCP_SKB_CB(skb)->seq)) {
+ p = &parent->rb_left;
+ continue;
+ }
+ if (!before(seq, TCP_SKB_CB(skb)->end_seq)) {
+ p = &parent->rb_right;
+ continue;
+ }
+ return skb;
+ }
+ return NULL;
+}
+
+static struct sk_buff *tcp_sacktag_skip(struct sk_buff *skb, struct sock *sk,
+ struct tcp_sacktag_state *state,
+ u32 skip_to_seq)
+{
+ if (skb && after(TCP_SKB_CB(skb)->seq, skip_to_seq))
+ return skb;
+
+ return tcp_sacktag_bsearch(sk, state, skip_to_seq);
+}
+
+static struct sk_buff *tcp_maybe_skipping_dsack(struct sk_buff *skb,
+ struct sock *sk,
+ struct tcp_sack_block *next_dup,
+ struct tcp_sacktag_state *state,
+ u32 skip_to_seq)
+{
+ if (!next_dup)
+ return skb;
+
+ if (before(next_dup->start_seq, skip_to_seq)) {
+ skb = tcp_sacktag_skip(skb, sk, state, next_dup->start_seq);
+ skb = tcp_sacktag_walk(skb, sk, NULL, state,
+ next_dup->start_seq, next_dup->end_seq,
+ 1);
+ }
+
+ return skb;
+}
+
+static int tcp_sack_cache_ok(const struct tcp_sock *tp, const struct tcp_sack_block *cache)
+{
+ return cache < tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
+}
+
+static int
+tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
+ u32 prior_snd_una, struct tcp_sacktag_state *state)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ const unsigned char *ptr = (skb_transport_header(ack_skb) +
+ TCP_SKB_CB(ack_skb)->sacked);
+ struct tcp_sack_block_wire *sp_wire = (struct tcp_sack_block_wire *)(ptr+2);
+ struct tcp_sack_block sp[TCP_NUM_SACKS];
+ struct tcp_sack_block *cache;
+ struct sk_buff *skb;
+ int num_sacks = min(TCP_NUM_SACKS, (ptr[1] - TCPOLEN_SACK_BASE) >> 3);
+ int used_sacks;
+ bool found_dup_sack = false;
+ int i, j;
+ int first_sack_index;
+
+ state->flag = 0;
+ state->reord = tp->snd_nxt;
+
+ if (!tp->sacked_out)
+ tcp_highest_sack_reset(sk);
+
+ found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire,
+ num_sacks, prior_snd_una);
+ if (found_dup_sack) {
+ state->flag |= FLAG_DSACKING_ACK;
+ tp->delivered++; /* A spurious retransmission is delivered */
+ }
+
+ /* Eliminate too old ACKs, but take into
+ * account more or less fresh ones, they can
+ * contain valid SACK info.
+ */
+ if (before(TCP_SKB_CB(ack_skb)->ack_seq, prior_snd_una - tp->max_window))
+ return 0;
+
+ if (!tp->packets_out)
+ goto out;
+
+ used_sacks = 0;
+ first_sack_index = 0;
+ for (i = 0; i < num_sacks; i++) {
+ bool dup_sack = !i && found_dup_sack;
+
+ sp[used_sacks].start_seq = get_unaligned_be32(&sp_wire[i].start_seq);
+ sp[used_sacks].end_seq = get_unaligned_be32(&sp_wire[i].end_seq);
+
+ if (!tcp_is_sackblock_valid(tp, dup_sack,
+ sp[used_sacks].start_seq,
+ sp[used_sacks].end_seq)) {
+ int mib_idx;
+
+ if (dup_sack) {
+ if (!tp->undo_marker)
+ mib_idx = LINUX_MIB_TCPDSACKIGNOREDNOUNDO;
+ else
+ mib_idx = LINUX_MIB_TCPDSACKIGNOREDOLD;
+ } else {
+ /* Don't count olds caused by ACK reordering */
+ if ((TCP_SKB_CB(ack_skb)->ack_seq != tp->snd_una) &&
+ !after(sp[used_sacks].end_seq, tp->snd_una))
+ continue;
+ mib_idx = LINUX_MIB_TCPSACKDISCARD;
+ }
+
+ NET_INC_STATS(sock_net(sk), mib_idx);
+ if (i == 0)
+ first_sack_index = -1;
+ continue;
+ }
+
+ /* Ignore very old stuff early */
+ if (!after(sp[used_sacks].end_seq, prior_snd_una))
+ continue;
+
+ used_sacks++;
+ }
+
+ /* order SACK blocks to allow in order walk of the retrans queue */
+ for (i = used_sacks - 1; i > 0; i--) {
+ for (j = 0; j < i; j++) {
+ if (after(sp[j].start_seq, sp[j + 1].start_seq)) {
+ swap(sp[j], sp[j + 1]);
+
+ /* Track where the first SACK block goes to */
+ if (j == first_sack_index)
+ first_sack_index = j + 1;
+ }
+ }
+ }
+
+ state->mss_now = tcp_current_mss(sk);
+ skb = NULL;
+ i = 0;
+
+ if (!tp->sacked_out) {
+ /* It's already past, so skip checking against it */
+ cache = tp->recv_sack_cache + ARRAY_SIZE(tp->recv_sack_cache);
+ } else {
+ cache = tp->recv_sack_cache;
+ /* Skip empty blocks in at head of the cache */
+ while (tcp_sack_cache_ok(tp, cache) && !cache->start_seq &&
+ !cache->end_seq)
+ cache++;
+ }
+
+ while (i < used_sacks) {
+ u32 start_seq = sp[i].start_seq;
+ u32 end_seq = sp[i].end_seq;
+ bool dup_sack = (found_dup_sack && (i == first_sack_index));
+ struct tcp_sack_block *next_dup = NULL;
+
+ if (found_dup_sack && ((i + 1) == first_sack_index))
+ next_dup = &sp[i + 1];
+
+ /* Skip too early cached blocks */
+ while (tcp_sack_cache_ok(tp, cache) &&
+ !before(start_seq, cache->end_seq))
+ cache++;
+
+ /* Can skip some work by looking recv_sack_cache? */
+ if (tcp_sack_cache_ok(tp, cache) && !dup_sack &&
+ after(end_seq, cache->start_seq)) {
+
+ /* Head todo? */
+ if (before(start_seq, cache->start_seq)) {
+ skb = tcp_sacktag_skip(skb, sk, state,
+ start_seq);
+ skb = tcp_sacktag_walk(skb, sk, next_dup,
+ state,
+ start_seq,
+ cache->start_seq,
+ dup_sack);
+ }
+
+ /* Rest of the block already fully processed? */
+ if (!after(end_seq, cache->end_seq))
+ goto advance_sp;
+
+ skb = tcp_maybe_skipping_dsack(skb, sk, next_dup,
+ state,
+ cache->end_seq);
+
+ /* ...tail remains todo... */
+ if (tcp_highest_sack_seq(tp) == cache->end_seq) {
+ /* ...but better entrypoint exists! */
+ skb = tcp_highest_sack(sk);
+ if (!skb)
+ break;
+ cache++;
+ goto walk;
+ }
+
+ skb = tcp_sacktag_skip(skb, sk, state, cache->end_seq);
+ /* Check overlap against next cached too (past this one already) */
+ cache++;
+ continue;
+ }
+
+ if (!before(start_seq, tcp_highest_sack_seq(tp))) {
+ skb = tcp_highest_sack(sk);
+ if (!skb)
+ break;
+ }
+ skb = tcp_sacktag_skip(skb, sk, state, start_seq);
+
+walk:
+ skb = tcp_sacktag_walk(skb, sk, next_dup, state,
+ start_seq, end_seq, dup_sack);
+
+advance_sp:
+ i++;
+ }
+
+ /* Clear the head of the cache sack blocks so we can skip it next time */
+ for (i = 0; i < ARRAY_SIZE(tp->recv_sack_cache) - used_sacks; i++) {
+ tp->recv_sack_cache[i].start_seq = 0;
+ tp->recv_sack_cache[i].end_seq = 0;
+ }
+ for (j = 0; j < used_sacks; j++)
+ tp->recv_sack_cache[i++] = sp[j];
+
+ if (inet_csk(sk)->icsk_ca_state != TCP_CA_Loss || tp->undo_marker)
+ tcp_check_sack_reordering(sk, state->reord, 0);
+
+ tcp_verify_left_out(tp);
+out:
+
+#if FASTRETRANS_DEBUG > 0
+ WARN_ON((int)tp->sacked_out < 0);
+ WARN_ON((int)tp->lost_out < 0);
+ WARN_ON((int)tp->retrans_out < 0);
+ WARN_ON((int)tcp_packets_in_flight(tp) < 0);
+#endif
+ return state->flag;
+}
+
+/* Limits sacked_out so that sum with lost_out isn't ever larger than
+ * packets_out. Returns false if sacked_out adjustement wasn't necessary.
+ */
+static bool tcp_limit_reno_sacked(struct tcp_sock *tp)
+{
+ u32 holes;
+
+ holes = max(tp->lost_out, 1U);
+ holes = min(holes, tp->packets_out);
+
+ if ((tp->sacked_out + holes) > tp->packets_out) {
+ tp->sacked_out = tp->packets_out - holes;
+ return true;
+ }
+ return false;
+}
+
+/* If we receive more dupacks than we expected counting segments
+ * in assumption of absent reordering, interpret this as reordering.
+ * The only another reason could be bug in receiver TCP.
+ */
+static void tcp_check_reno_reordering(struct sock *sk, const int addend)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (!tcp_limit_reno_sacked(tp))
+ return;
+
+ tp->reordering = min_t(u32, tp->packets_out + addend,
+ sock_net(sk)->ipv4.sysctl_tcp_max_reordering);
+ tp->reord_seen++;
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRENOREORDER);
+}
+
+/* Emulate SACKs for SACKless connection: account for a new dupack. */
+
+static void tcp_add_reno_sack(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 prior_sacked = tp->sacked_out;
+
+ tp->sacked_out++;
+ tcp_check_reno_reordering(sk, 0);
+ if (tp->sacked_out > prior_sacked)
+ tp->delivered++; /* Some out-of-order packet is delivered */
+ tcp_verify_left_out(tp);
+}
+
+/* Account for ACK, ACKing some data in Reno Recovery phase. */
+
+static void tcp_remove_reno_sacks(struct sock *sk, int acked)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (acked > 0) {
+ /* One ACK acked hole. The rest eat duplicate ACKs. */
+ tp->delivered += max_t(int, acked - tp->sacked_out, 1);
+ if (acked - 1 >= tp->sacked_out)
+ tp->sacked_out = 0;
+ else
+ tp->sacked_out -= acked - 1;
+ }
+ tcp_check_reno_reordering(sk, acked);
+ tcp_verify_left_out(tp);
+}
+
+static inline void tcp_reset_reno_sack(struct tcp_sock *tp)
+{
+ tp->sacked_out = 0;
+}
+
+void tcp_clear_retrans(struct tcp_sock *tp)
+{
+ tp->retrans_out = 0;
+ tp->lost_out = 0;
+ tp->undo_marker = 0;
+ tp->undo_retrans = -1;
+ tp->sacked_out = 0;
+}
+
+static inline void tcp_init_undo(struct tcp_sock *tp)
+{
+ tp->undo_marker = tp->snd_una;
+ /* Retransmission still in flight may cause DSACKs later. */
+ tp->undo_retrans = tp->retrans_out ? : -1;
+}
+
+static bool tcp_is_rack(const struct sock *sk)
+{
+ return sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION;
+}
+
+/* If we detect SACK reneging, forget all SACK information
+ * and reset tags completely, otherwise preserve SACKs. If receiver
+ * dropped its ofo queue, we will know this due to reneging detection.
+ */
+static void tcp_timeout_mark_lost(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb, *head;
+ bool is_reneg; /* is receiver reneging on SACKs? */
+
+ head = tcp_rtx_queue_head(sk);
+ is_reneg = head && (TCP_SKB_CB(head)->sacked & TCPCB_SACKED_ACKED);
+ if (is_reneg) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSACKRENEGING);
+ tp->sacked_out = 0;
+ /* Mark SACK reneging until we recover from this loss event. */
+ tp->is_sack_reneg = 1;
+ } else if (tcp_is_reno(tp)) {
+ tcp_reset_reno_sack(tp);
+ }
+
+ skb = head;
+ skb_rbtree_walk_from(skb) {
+ if (is_reneg)
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_ACKED;
+ else if (tcp_is_rack(sk) && skb != head &&
+ tcp_rack_skb_timeout(tp, skb, 0) > 0)
+ continue; /* Don't mark recently sent ones lost yet */
+ tcp_mark_skb_lost(sk, skb);
+ }
+ tcp_verify_left_out(tp);
+ tcp_clear_all_retrans_hints(tp);
+}
+
+/* Enter Loss state. */
+void tcp_enter_loss(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct net *net = sock_net(sk);
+ bool new_recovery = icsk->icsk_ca_state < TCP_CA_Recovery;
+
+ tcp_timeout_mark_lost(sk);
+
+ /* Reduce ssthresh if it has not yet been made inside this window. */
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
+ !after(tp->high_seq, tp->snd_una) ||
+ (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tp->prior_cwnd = tp->snd_cwnd;
+ tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
+ tcp_ca_event(sk, CA_EVENT_LOSS);
+ tcp_init_undo(tp);
+ }
+ tp->snd_cwnd = tcp_packets_in_flight(tp) + 1;
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+
+ /* Timeout in disordered state after receiving substantial DUPACKs
+ * suggests that the degree of reordering is over-estimated.
+ */
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder &&
+ tp->sacked_out >= net->ipv4.sysctl_tcp_reordering)
+ tp->reordering = min_t(unsigned int, tp->reordering,
+ net->ipv4.sysctl_tcp_reordering);
+ tcp_set_ca_state(sk, TCP_CA_Loss);
+ tp->high_seq = tp->snd_nxt;
+ tcp_ecn_queue_cwr(tp);
+
+ /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
+ * loss recovery is underway except recurring timeout(s) on
+ * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
+ */
+ tp->frto = net->ipv4.sysctl_tcp_frto &&
+ (new_recovery || icsk->icsk_retransmits) &&
+ !inet_csk(sk)->icsk_mtup.probe_size;
+}
+
+/* If ACK arrived pointing to a remembered SACK, it means that our
+ * remembered SACKs do not reflect real state of receiver i.e.
+ * receiver _host_ is heavily congested (or buggy).
+ *
+ * To avoid big spurious retransmission bursts due to transient SACK
+ * scoreboard oddities that look like reneging, we give the receiver a
+ * little time (max(RTT/2, 10ms)) to send us some more ACKs that will
+ * restore sanity to the SACK scoreboard. If the apparent reneging
+ * persists until this RTO then we'll clear the SACK scoreboard.
+ */
+static bool tcp_check_sack_reneging(struct sock *sk, int flag)
+{
+ if (flag & FLAG_SACK_RENEGING) {
+ struct tcp_sock *tp = tcp_sk(sk);
+ unsigned long delay = max(usecs_to_jiffies(tp->srtt_us >> 4),
+ msecs_to_jiffies(10));
+
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+ delay, TCP_RTO_MAX);
+ return true;
+ }
+ return false;
+}
+
+/* Heurestics to calculate number of duplicate ACKs. There's no dupACKs
+ * counter when SACK is enabled (without SACK, sacked_out is used for
+ * that purpose).
+ *
+ * With reordering, holes may still be in flight, so RFC3517 recovery
+ * uses pure sacked_out (total number of SACKed segments) even though
+ * it violates the RFC that uses duplicate ACKs, often these are equal
+ * but when e.g. out-of-window ACKs or packet duplication occurs,
+ * they differ. Since neither occurs due to loss, TCP should really
+ * ignore them.
+ */
+static inline int tcp_dupack_heuristics(const struct tcp_sock *tp)
+{
+ return tp->sacked_out + 1;
+}
+
+/* Linux NewReno/SACK/ECN state machine.
+ * --------------------------------------
+ *
+ * "Open" Normal state, no dubious events, fast path.
+ * "Disorder" In all the respects it is "Open",
+ * but requires a bit more attention. It is entered when
+ * we see some SACKs or dupacks. It is split of "Open"
+ * mainly to move some processing from fast path to slow one.
+ * "CWR" CWND was reduced due to some Congestion Notification event.
+ * It can be ECN, ICMP source quench, local device congestion.
+ * "Recovery" CWND was reduced, we are fast-retransmitting.
+ * "Loss" CWND was reduced due to RTO timeout or SACK reneging.
+ *
+ * tcp_fastretrans_alert() is entered:
+ * - each incoming ACK, if state is not "Open"
+ * - when arrived ACK is unusual, namely:
+ * * SACK
+ * * Duplicate ACK.
+ * * ECN ECE.
+ *
+ * Counting packets in flight is pretty simple.
+ *
+ * in_flight = packets_out - left_out + retrans_out
+ *
+ * packets_out is SND.NXT-SND.UNA counted in packets.
+ *
+ * retrans_out is number of retransmitted segments.
+ *
+ * left_out is number of segments left network, but not ACKed yet.
+ *
+ * left_out = sacked_out + lost_out
+ *
+ * sacked_out: Packets, which arrived to receiver out of order
+ * and hence not ACKed. With SACKs this number is simply
+ * amount of SACKed data. Even without SACKs
+ * it is easy to give pretty reliable estimate of this number,
+ * counting duplicate ACKs.
+ *
+ * lost_out: Packets lost by network. TCP has no explicit
+ * "loss notification" feedback from network (for now).
+ * It means that this number can be only _guessed_.
+ * Actually, it is the heuristics to predict lossage that
+ * distinguishes different algorithms.
+ *
+ * F.e. after RTO, when all the queue is considered as lost,
+ * lost_out = packets_out and in_flight = retrans_out.
+ *
+ * Essentially, we have now a few algorithms detecting
+ * lost packets.
+ *
+ * If the receiver supports SACK:
+ *
+ * RFC6675/3517: It is the conventional algorithm. A packet is
+ * considered lost if the number of higher sequence packets
+ * SACKed is greater than or equal the DUPACK thoreshold
+ * (reordering). This is implemented in tcp_mark_head_lost and
+ * tcp_update_scoreboard.
+ *
+ * RACK (draft-ietf-tcpm-rack-01): it is a newer algorithm
+ * (2017-) that checks timing instead of counting DUPACKs.
+ * Essentially a packet is considered lost if it's not S/ACKed
+ * after RTT + reordering_window, where both metrics are
+ * dynamically measured and adjusted. This is implemented in
+ * tcp_rack_mark_lost.
+ *
+ * If the receiver does not support SACK:
+ *
+ * NewReno (RFC6582): in Recovery we assume that one segment
+ * is lost (classic Reno). While we are in Recovery and
+ * a partial ACK arrives, we assume that one more packet
+ * is lost (NewReno). This heuristics are the same in NewReno
+ * and SACK.
+ *
+ * Really tricky (and requiring careful tuning) part of algorithm
+ * is hidden in functions tcp_time_to_recover() and tcp_xmit_retransmit_queue().
+ * The first determines the moment _when_ we should reduce CWND and,
+ * hence, slow down forward transmission. In fact, it determines the moment
+ * when we decide that hole is caused by loss, rather than by a reorder.
+ *
+ * tcp_xmit_retransmit_queue() decides, _what_ we should retransmit to fill
+ * holes, caused by lost packets.
+ *
+ * And the most logically complicated part of algorithm is undo
+ * heuristics. We detect false retransmits due to both too early
+ * fast retransmit (reordering) and underestimated RTO, analyzing
+ * timestamps and D-SACKs. When we detect that some segments were
+ * retransmitted by mistake and CWND reduction was wrong, we undo
+ * window reduction and abort recovery phase. This logic is hidden
+ * inside several functions named tcp_try_undo_<something>.
+ */
+
+/* This function decides, when we should leave Disordered state
+ * and enter Recovery phase, reducing congestion window.
+ *
+ * Main question: may we further continue forward transmission
+ * with the same cwnd?
+ */
+static bool tcp_time_to_recover(struct sock *sk, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Trick#1: The loss is proven. */
+ if (tp->lost_out)
+ return true;
+
+ /* Not-A-Trick#2 : Classic rule... */
+ if (!tcp_is_rack(sk) && tcp_dupack_heuristics(tp) > tp->reordering)
+ return true;
+
+ return false;
+}
+
+/* Detect loss in event "A" above by marking head of queue up as lost.
+ * For non-SACK(Reno) senders, the first "packets" number of segments
+ * are considered lost. For RFC3517 SACK, a segment is considered lost if it
+ * has at least tp->reordering SACKed seqments above it; "packets" refers to
+ * the maximum SACKed segments to pass before reaching this limit.
+ */
+static void tcp_mark_head_lost(struct sock *sk, int packets, int mark_head)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ int cnt, oldcnt, lost;
+ unsigned int mss;
+ /* Use SACK to deduce losses of new sequences sent during recovery */
+ const u32 loss_high = tcp_is_sack(tp) ? tp->snd_nxt : tp->high_seq;
+
+ WARN_ON(packets > tp->packets_out);
+ skb = tp->lost_skb_hint;
+ if (skb) {
+ /* Head already handled? */
+ if (mark_head && after(TCP_SKB_CB(skb)->seq, tp->snd_una))
+ return;
+ cnt = tp->lost_cnt_hint;
+ } else {
+ skb = tcp_rtx_queue_head(sk);
+ cnt = 0;
+ }
+
+ skb_rbtree_walk_from(skb) {
+ /* TODO: do this better */
+ /* this is not the most efficient way to do this... */
+ tp->lost_skb_hint = skb;
+ tp->lost_cnt_hint = cnt;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, loss_high))
+ break;
+
+ oldcnt = cnt;
+ if (tcp_is_reno(tp) ||
+ (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+ cnt += tcp_skb_pcount(skb);
+
+ if (cnt > packets) {
+ if (tcp_is_sack(tp) ||
+ (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED) ||
+ (oldcnt >= packets))
+ break;
+
+ mss = tcp_skb_mss(skb);
+ /* If needed, chop off the prefix to mark as lost. */
+ lost = (packets - oldcnt) * mss;
+ if (lost < skb->len &&
+ tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
+ lost, mss, GFP_ATOMIC) < 0)
+ break;
+ cnt = packets;
+ }
+
+ tcp_skb_mark_lost(tp, skb);
+
+ if (mark_head)
+ break;
+ }
+ tcp_verify_left_out(tp);
+}
+
+/* Account newly detected lost packet(s) */
+
+static void tcp_update_scoreboard(struct sock *sk, int fast_rexmit)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_is_sack(tp)) {
+ int sacked_upto = tp->sacked_out - tp->reordering;
+ if (sacked_upto >= 0)
+ tcp_mark_head_lost(sk, sacked_upto, 0);
+ else if (fast_rexmit)
+ tcp_mark_head_lost(sk, 1, 1);
+ }
+}
+
+static bool tcp_tsopt_ecr_before(const struct tcp_sock *tp, u32 when)
+{
+ return tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+ before(tp->rx_opt.rcv_tsecr, when);
+}
+
+/* skb is spurious retransmitted if the returned timestamp echo
+ * reply is prior to the skb transmission time
+ */
+static bool tcp_skb_spurious_retrans(const struct tcp_sock *tp,
+ const struct sk_buff *skb)
+{
+ return (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS) &&
+ tcp_tsopt_ecr_before(tp, tcp_skb_timestamp(skb));
+}
+
+/* Nothing was retransmitted or returned timestamp is less
+ * than timestamp of the first retransmission.
+ */
+static inline bool tcp_packet_delayed(const struct tcp_sock *tp)
+{
+ return !tp->retrans_stamp ||
+ tcp_tsopt_ecr_before(tp, tp->retrans_stamp);
+}
+
+/* Undo procedures. */
+
+/* We can clear retrans_stamp when there are no retransmissions in the
+ * window. It would seem that it is trivially available for us in
+ * tp->retrans_out, however, that kind of assumptions doesn't consider
+ * what will happen if errors occur when sending retransmission for the
+ * second time. ...It could the that such segment has only
+ * TCPCB_EVER_RETRANS set at the present time. It seems that checking
+ * the head skb is enough except for some reneging corner cases that
+ * are not worth the effort.
+ *
+ * Main reason for all this complexity is the fact that connection dying
+ * time now depends on the validity of the retrans_stamp, in particular,
+ * that successive retransmissions of a segment must not advance
+ * retrans_stamp under any conditions.
+ */
+static bool tcp_any_retrans_done(const struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+
+ if (tp->retrans_out)
+ return true;
+
+ skb = tcp_rtx_queue_head(sk);
+ if (unlikely(skb && TCP_SKB_CB(skb)->sacked & TCPCB_EVER_RETRANS))
+ return true;
+
+ return false;
+}
+
+static void DBGUNDO(struct sock *sk, const char *msg)
+{
+#if FASTRETRANS_DEBUG > 1
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_sock *inet = inet_sk(sk);
+
+ if (sk->sk_family == AF_INET) {
+ pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
+ msg,
+ &inet->inet_daddr, ntohs(inet->inet_dport),
+ tp->snd_cwnd, tcp_left_out(tp),
+ tp->snd_ssthresh, tp->prior_ssthresh,
+ tp->packets_out);
+ }
+#if IS_ENABLED(CONFIG_IPV6)
+ else if (sk->sk_family == AF_INET6) {
+ pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
+ msg,
+ &sk->sk_v6_daddr, ntohs(inet->inet_dport),
+ tp->snd_cwnd, tcp_left_out(tp),
+ tp->snd_ssthresh, tp->prior_ssthresh,
+ tp->packets_out);
+ }
+#endif
+#endif
+}
+
+static void tcp_undo_cwnd_reduction(struct sock *sk, bool unmark_loss)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (unmark_loss) {
+ struct sk_buff *skb;
+
+ skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
+ }
+ tp->lost_out = 0;
+ tcp_clear_all_retrans_hints(tp);
+ }
+
+ if (tp->prior_ssthresh) {
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
+
+ if (tp->prior_ssthresh > tp->snd_ssthresh) {
+ tp->snd_ssthresh = tp->prior_ssthresh;
+ tcp_ecn_withdraw_cwr(tp);
+ }
+ }
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+ tp->undo_marker = 0;
+ tp->rack.advanced = 1; /* Force RACK to re-exam losses */
+}
+
+static inline bool tcp_may_undo(const struct tcp_sock *tp)
+{
+ return tp->undo_marker && (!tp->undo_retrans || tcp_packet_delayed(tp));
+}
+
+/* People celebrate: "We love our President!" */
+static bool tcp_try_undo_recovery(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_may_undo(tp)) {
+ int mib_idx;
+
+ /* Happy end! We did not retransmit anything
+ * or our original transmission succeeded.
+ */
+ DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
+ tcp_undo_cwnd_reduction(sk, false);
+ if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
+ mib_idx = LINUX_MIB_TCPLOSSUNDO;
+ else
+ mib_idx = LINUX_MIB_TCPFULLUNDO;
+
+ NET_INC_STATS(sock_net(sk), mib_idx);
+ } else if (tp->rack.reo_wnd_persist) {
+ tp->rack.reo_wnd_persist--;
+ }
+ if (tp->snd_una == tp->high_seq && tcp_is_reno(tp)) {
+ /* Hold old state until something *above* high_seq
+ * is ACKed. For Reno it is MUST to prevent false
+ * fast retransmits (RFC2582). SACK TCP is safe. */
+ if (!tcp_any_retrans_done(sk))
+ tp->retrans_stamp = 0;
+ return true;
+ }
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ tp->is_sack_reneg = 0;
+ return false;
+}
+
+/* Try to undo cwnd reduction, because D-SACKs acked all retransmitted data */
+static bool tcp_try_undo_dsack(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tp->undo_marker && !tp->undo_retrans) {
+ tp->rack.reo_wnd_persist = min(TCP_RACK_RECOVERY_THRESH,
+ tp->rack.reo_wnd_persist + 1);
+ DBGUNDO(sk, "D-SACK");
+ tcp_undo_cwnd_reduction(sk, false);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
+ return true;
+ }
+ return false;
+}
+
+/* Undo during loss recovery after partial ACK or using F-RTO. */
+static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (frto_undo || tcp_may_undo(tp)) {
+ tcp_undo_cwnd_reduction(sk, true);
+
+ DBGUNDO(sk, "partial loss");
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
+ if (frto_undo)
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPSPURIOUSRTOS);
+ inet_csk(sk)->icsk_retransmits = 0;
+ if (frto_undo || tcp_is_sack(tp)) {
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ tp->is_sack_reneg = 0;
+ }
+ return true;
+ }
+ return false;
+}
+
+/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
+ * It computes the number of packets to send (sndcnt) based on packets newly
+ * delivered:
+ * 1) If the packets in flight is larger than ssthresh, PRR spreads the
+ * cwnd reductions across a full RTT.
+ * 2) Otherwise PRR uses packet conservation to send as much as delivered.
+ * But when the retransmits are acked without further losses, PRR
+ * slow starts cwnd up to ssthresh to speed up the recovery.
+ */
+static void tcp_init_cwnd_reduction(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tp->high_seq = tp->snd_nxt;
+ tp->tlp_high_seq = 0;
+ tp->snd_cwnd_cnt = 0;
+ tp->prior_cwnd = tp->snd_cwnd;
+ tp->prr_delivered = 0;
+ tp->prr_out = 0;
+ tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
+ tcp_ecn_queue_cwr(tp);
+}
+
+void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int sndcnt = 0;
+ int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
+
+ if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
+ return;
+
+ tp->prr_delivered += newly_acked_sacked;
+ if (delta < 0) {
+ u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
+ tp->prior_cwnd - 1;
+ sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
+ } else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
+ !(flag & FLAG_LOST_RETRANS)) {
+ sndcnt = min_t(int, delta,
+ max_t(int, tp->prr_delivered - tp->prr_out,
+ newly_acked_sacked) + 1);
+ } else {
+ sndcnt = min(delta, newly_acked_sacked);
+ }
+ /* Force a fast retransmit upon entering fast recovery */
+ sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
+ tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
+}
+
+static inline void tcp_end_cwnd_reduction(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (inet_csk(sk)->icsk_ca_ops->cong_control)
+ return;
+
+ /* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
+ if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
+ (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
+ tp->snd_cwnd = tp->snd_ssthresh;
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+ }
+ tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
+}
+
+/* Enter CWR state. Disable cwnd undo since congestion is proven with ECN */
+void tcp_enter_cwr(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tp->prior_ssthresh = 0;
+ if (inet_csk(sk)->icsk_ca_state < TCP_CA_CWR) {
+ tp->undo_marker = 0;
+ tcp_init_cwnd_reduction(sk);
+ tcp_set_ca_state(sk, TCP_CA_CWR);
+ }
+}
+EXPORT_SYMBOL(tcp_enter_cwr);
+
+static void tcp_try_keep_open(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int state = TCP_CA_Open;
+
+ if (tcp_left_out(tp) || tcp_any_retrans_done(sk))
+ state = TCP_CA_Disorder;
+
+ if (inet_csk(sk)->icsk_ca_state != state) {
+ tcp_set_ca_state(sk, state);
+ tp->high_seq = tp->snd_nxt;
+ }
+}
+
+static void tcp_try_to_open(struct sock *sk, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ tcp_verify_left_out(tp);
+
+ if (!tcp_any_retrans_done(sk))
+ tp->retrans_stamp = 0;
+
+ if (flag & FLAG_ECE)
+ tcp_enter_cwr(sk);
+
+ if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
+ tcp_try_keep_open(sk);
+ }
+}
+
+static void tcp_mtup_probe_failed(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ icsk->icsk_mtup.search_high = icsk->icsk_mtup.probe_size - 1;
+ icsk->icsk_mtup.probe_size = 0;
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPFAIL);
+}
+
+static void tcp_mtup_probe_success(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ /* FIXME: breaks with very large cwnd */
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tp->snd_cwnd = tp->snd_cwnd *
+ tcp_mss_to_mtu(sk, tp->mss_cache) /
+ icsk->icsk_mtup.probe_size;
+ tp->snd_cwnd_cnt = 0;
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+ tp->snd_ssthresh = tcp_current_ssthresh(sk);
+
+ icsk->icsk_mtup.search_low = icsk->icsk_mtup.probe_size;
+ icsk->icsk_mtup.probe_size = 0;
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPMTUPSUCCESS);
+}
+
+/* Do a simple retransmit without using the backoff mechanisms in
+ * tcp_timer. This is used for path mtu discovery.
+ * The socket is already locked here.
+ */
+void tcp_simple_retransmit(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *skb;
+ unsigned int mss = tcp_current_mss(sk);
+
+ skb_rbtree_walk(skb, &sk->tcp_rtx_queue) {
+ if (tcp_skb_seglen(skb) > mss &&
+ !(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
+ if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
+ TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
+ tp->retrans_out -= tcp_skb_pcount(skb);
+ }
+ tcp_skb_mark_lost_uncond_verify(tp, skb);
+ }
+ }
+
+ tcp_clear_retrans_hints_partial(tp);
+
+ if (!tp->lost_out)
+ return;
+
+ if (tcp_is_reno(tp))
+ tcp_limit_reno_sacked(tp);
+
+ tcp_verify_left_out(tp);
+
+ /* Don't muck with the congestion window here.
+ * Reason is that we do not increase amount of _data_
+ * in network, but units changed and effective
+ * cwnd/ssthresh really reduced now.
+ */
+ if (icsk->icsk_ca_state != TCP_CA_Loss) {
+ tp->high_seq = tp->snd_nxt;
+ tp->snd_ssthresh = tcp_current_ssthresh(sk);
+ tp->prior_ssthresh = 0;
+ tp->undo_marker = 0;
+ tcp_set_ca_state(sk, TCP_CA_Loss);
+ }
+ tcp_xmit_retransmit_queue(sk);
+}
+EXPORT_SYMBOL(tcp_simple_retransmit);
+
+void tcp_enter_recovery(struct sock *sk, bool ece_ack)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int mib_idx;
+
+ if (tcp_is_reno(tp))
+ mib_idx = LINUX_MIB_TCPRENORECOVERY;
+ else
+ mib_idx = LINUX_MIB_TCPSACKRECOVERY;
+
+ NET_INC_STATS(sock_net(sk), mib_idx);
+
+ tp->prior_ssthresh = 0;
+ tcp_init_undo(tp);
+
+ if (!tcp_in_cwnd_reduction(sk)) {
+ if (!ece_ack)
+ tp->prior_ssthresh = tcp_current_ssthresh(sk);
+ tcp_init_cwnd_reduction(sk);
+ }
+ tcp_set_ca_state(sk, TCP_CA_Recovery);
+}
+
+/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
+ * recovered or spurious. Otherwise retransmits more on partial ACKs.
+ */
+static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
+ int *rexmit)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ bool recovered = !before(tp->snd_una, tp->high_seq);
+
+ if ((flag & FLAG_SND_UNA_ADVANCED) &&
+ tcp_try_undo_loss(sk, false))
+ return;
+
+ if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
+ /* Step 3.b. A timeout is spurious if not all data are
+ * lost, i.e., never-retransmitted data are (s)acked.
+ */
+ if ((flag & FLAG_ORIG_SACK_ACKED) &&
+ tcp_try_undo_loss(sk, true))
+ return;
+
+ if (after(tp->snd_nxt, tp->high_seq)) {
+ if (flag & FLAG_DATA_SACKED || is_dupack)
+ tp->frto = 0; /* Step 3.a. loss was real */
+ } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
+ tp->high_seq = tp->snd_nxt;
+ /* Step 2.b. Try send new data (but deferred until cwnd
+ * is updated in tcp_ack()). Otherwise fall back to
+ * the conventional recovery.
+ */
+ if (!tcp_write_queue_empty(sk) &&
+ after(tcp_wnd_end(tp), tp->snd_nxt)) {
+ *rexmit = REXMIT_NEW;
+ return;
+ }
+ tp->frto = 0;
+ }
+ }
+
+ if (recovered) {
+ /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
+ tcp_try_undo_recovery(sk);
+ return;
+ }
+ if (tcp_is_reno(tp)) {
+ /* A Reno DUPACK means new data in F-RTO step 2.b above are
+ * delivered. Lower inflight to clock out (re)tranmissions.
+ */
+ if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
+ tcp_add_reno_sack(sk);
+ else if (flag & FLAG_SND_UNA_ADVANCED)
+ tcp_reset_reno_sack(tp);
+ }
+ *rexmit = REXMIT_LOST;
+}
+
+/* Undo during fast recovery after partial ACK. */
+static bool tcp_try_undo_partial(struct sock *sk, u32 prior_snd_una)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tp->undo_marker && tcp_packet_delayed(tp)) {
+ /* Plain luck! Hole if filled with delayed
+ * packet, rather than with a retransmit. Check reordering.
+ */
+ tcp_check_sack_reordering(sk, prior_snd_una, 1);
+
+ /* We are getting evidence that the reordering degree is higher
+ * than we realized. If there are no retransmits out then we
+ * can undo. Otherwise we clock out new packets but do not
+ * mark more packets lost or retransmit more.
+ */
+ if (tp->retrans_out)
+ return true;
+
+ if (!tcp_any_retrans_done(sk))
+ tp->retrans_stamp = 0;
+
+ DBGUNDO(sk, "partial recovery");
+ tcp_undo_cwnd_reduction(sk, true);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
+ tcp_try_keep_open(sk);
+ return true;
+ }
+ return false;
+}
+
+static void tcp_identify_packet_loss(struct sock *sk, int *ack_flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_rtx_queue_empty(sk))
+ return;
+
+ if (unlikely(tcp_is_reno(tp))) {
+ tcp_newreno_mark_lost(sk, *ack_flag & FLAG_SND_UNA_ADVANCED);
+ } else if (tcp_is_rack(sk)) {
+ u32 prior_retrans = tp->retrans_out;
+
+ tcp_rack_mark_lost(sk);
+ if (prior_retrans > tp->retrans_out)
+ *ack_flag |= FLAG_LOST_RETRANS;
+ }
+}
+
+static bool tcp_force_fast_retransmit(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ return after(tcp_highest_sack_seq(tp),
+ tp->snd_una + tp->reordering * tp->mss_cache);
+}
+
+/* Process an event, which can update packets-in-flight not trivially.
+ * Main goal of this function is to calculate new estimate for left_out,
+ * taking into account both packets sitting in receiver's buffer and
+ * packets lost by network.
+ *
+ * Besides that it updates the congestion state when packet loss or ECN
+ * is detected. But it does not reduce the cwnd, it is done by the
+ * congestion control later.
+ *
+ * It does _not_ decide what to send, it is made in function
+ * tcp_xmit_retransmit_queue().
+ */
+static void tcp_fastretrans_alert(struct sock *sk, const u32 prior_snd_una,
+ bool is_dupack, int *ack_flag, int *rexmit)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ int fast_rexmit = 0, flag = *ack_flag;
+ bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
+ tcp_force_fast_retransmit(sk));
+
+ if (!tp->packets_out && tp->sacked_out)
+ tp->sacked_out = 0;
+
+ /* Now state machine starts.
+ * A. ECE, hence prohibit cwnd undoing, the reduction is required. */
+ if (flag & FLAG_ECE)
+ tp->prior_ssthresh = 0;
+
+ /* B. In all the states check for reneging SACKs. */
+ if (tcp_check_sack_reneging(sk, flag))
+ return;
+
+ /* C. Check consistency of the current state. */
+ tcp_verify_left_out(tp);
+
+ /* D. Check state exit conditions. State can be terminated
+ * when high_seq is ACKed. */
+ if (icsk->icsk_ca_state == TCP_CA_Open) {
+ WARN_ON(tp->retrans_out != 0);
+ tp->retrans_stamp = 0;
+ } else if (!before(tp->snd_una, tp->high_seq)) {
+ switch (icsk->icsk_ca_state) {
+ case TCP_CA_CWR:
+ /* CWR is to be held something *above* high_seq
+ * is ACKed for CWR bit to reach receiver. */
+ if (tp->snd_una != tp->high_seq) {
+ tcp_end_cwnd_reduction(sk);
+ tcp_set_ca_state(sk, TCP_CA_Open);
+ }
+ break;
+
+ case TCP_CA_Recovery:
+ if (tcp_is_reno(tp))
+ tcp_reset_reno_sack(tp);
+ if (tcp_try_undo_recovery(sk))
+ return;
+ tcp_end_cwnd_reduction(sk);
+ break;
+ }
+ }
+
+ /* E. Process state. */
+ switch (icsk->icsk_ca_state) {
+ case TCP_CA_Recovery:
+ if (!(flag & FLAG_SND_UNA_ADVANCED)) {
+ if (tcp_is_reno(tp) && is_dupack)
+ tcp_add_reno_sack(sk);
+ } else {
+ if (tcp_try_undo_partial(sk, prior_snd_una))
+ return;
+ /* Partial ACK arrived. Force fast retransmit. */
+ do_lost = tcp_is_reno(tp) ||
+ tcp_force_fast_retransmit(sk);
+ }
+ if (tcp_try_undo_dsack(sk)) {
+ tcp_try_keep_open(sk);
+ return;
+ }
+ tcp_identify_packet_loss(sk, ack_flag);
+ break;
+ case TCP_CA_Loss:
+ tcp_process_loss(sk, flag, is_dupack, rexmit);
+ tcp_identify_packet_loss(sk, ack_flag);
+ if (!(icsk->icsk_ca_state == TCP_CA_Open ||
+ (*ack_flag & FLAG_LOST_RETRANS)))
+ return;
+ /* Change state if cwnd is undone or retransmits are lost */
+ /* fall through */
+ default:
+ if (tcp_is_reno(tp)) {
+ if (flag & FLAG_SND_UNA_ADVANCED)
+ tcp_reset_reno_sack(tp);
+ if (is_dupack)
+ tcp_add_reno_sack(sk);
+ }
+
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder)
+ tcp_try_undo_dsack(sk);
+
+ tcp_identify_packet_loss(sk, ack_flag);
+ if (!tcp_time_to_recover(sk, flag)) {
+ tcp_try_to_open(sk, flag);
+ return;
+ }
+
+ /* MTU probe failure: don't reduce cwnd */
+ if (icsk->icsk_ca_state < TCP_CA_CWR &&
+ icsk->icsk_mtup.probe_size &&
+ tp->snd_una == tp->mtu_probe.probe_seq_start) {
+ tcp_mtup_probe_failed(sk);
+ /* Restores the reduction we did in tcp_mtup_probe() */
+ tp->snd_cwnd++;
+ tcp_simple_retransmit(sk);
+ return;
+ }
+
+ /* Otherwise enter Recovery state */
+ tcp_enter_recovery(sk, (flag & FLAG_ECE));
+ fast_rexmit = 1;
+ }
+
+ if (!tcp_is_rack(sk) && do_lost)
+ tcp_update_scoreboard(sk, fast_rexmit);
+ *rexmit = REXMIT_LOST;
+}
+
+static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us, const int flag)
+{
+ u32 wlen = sock_net(sk)->ipv4.sysctl_tcp_min_rtt_wlen * HZ;
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if ((flag & FLAG_ACK_MAYBE_DELAYED) && rtt_us > tcp_min_rtt(tp)) {
+ /* If the remote keeps returning delayed ACKs, eventually
+ * the min filter would pick it up and overestimate the
+ * prop. delay when it expires. Skip suspected delayed ACKs.
+ */
+ return;
+ }
+ minmax_running_min(&tp->rtt_min, wlen, tcp_jiffies32,
+ rtt_us ? : jiffies_to_usecs(1));
+}
+
+static bool tcp_ack_update_rtt(struct sock *sk, const int flag,
+ long seq_rtt_us, long sack_rtt_us,
+ long ca_rtt_us, struct rate_sample *rs)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Prefer RTT measured from ACK's timing to TS-ECR. This is because
+ * broken middle-boxes or peers may corrupt TS-ECR fields. But
+ * Karn's algorithm forbids taking RTT if some retransmitted data
+ * is acked (RFC6298).
+ */
+ if (seq_rtt_us < 0)
+ seq_rtt_us = sack_rtt_us;
+
+ /* RTTM Rule: A TSecr value received in a segment is used to
+ * update the averaged RTT measurement only if the segment
+ * acknowledges some new data, i.e., only if it advances the
+ * left edge of the send window.
+ * See draft-ietf-tcplw-high-performance-00, section 3.3.
+ */
+ if (seq_rtt_us < 0 && tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+ flag & FLAG_ACKED) {
+ u32 delta = tcp_time_stamp(tp) - tp->rx_opt.rcv_tsecr;
+ u32 delta_us = delta * (USEC_PER_SEC / TCP_TS_HZ);
+
+ seq_rtt_us = ca_rtt_us = delta_us;
+ }
+ rs->rtt_us = ca_rtt_us; /* RTT of last (S)ACKed packet (or -1) */
+ if (seq_rtt_us < 0)
+ return false;
+
+ /* ca_rtt_us >= 0 is counting on the invariant that ca_rtt_us is
+ * always taken together with ACK, SACK, or TS-opts. Any negative
+ * values will be skipped with the seq_rtt_us < 0 check above.
+ */
+ tcp_update_rtt_min(sk, ca_rtt_us, flag);
+ tcp_rtt_estimator(sk, seq_rtt_us);
+ tcp_set_rto(sk);
+
+ /* RFC6298: only reset backoff on valid RTT measurement. */
+ inet_csk(sk)->icsk_backoff = 0;
+ return true;
+}
+
+/* Compute time elapsed between (last) SYNACK and the ACK completing 3WHS. */
+void tcp_synack_rtt_meas(struct sock *sk, struct request_sock *req)
+{
+ struct rate_sample rs;
+ long rtt_us = -1L;
+
+ if (req && !req->num_retrans && tcp_rsk(req)->snt_synack)
+ rtt_us = tcp_stamp_us_delta(tcp_clock_us(), tcp_rsk(req)->snt_synack);
+
+ tcp_ack_update_rtt(sk, FLAG_SYN_ACKED, rtt_us, -1L, rtt_us, &rs);
+}
+
+
+static void tcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ icsk->icsk_ca_ops->cong_avoid(sk, ack, acked);
+ tcp_sk(sk)->snd_cwnd_stamp = tcp_jiffies32;
+}
+
+/* Restart timer after forward progress on connection.
+ * RFC2988 recommends to restart timer to now+rto.
+ */
+void tcp_rearm_rto(struct sock *sk)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* If the retrans timer is currently being used by Fast Open
+ * for SYN-ACK retrans purpose, stay put.
+ */
+ if (tp->fastopen_rsk)
+ return;
+
+ if (!tp->packets_out) {
+ inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
+ } else {
+ u32 rto = inet_csk(sk)->icsk_rto;
+ /* Offset the time elapsed after installing regular RTO */
+ if (icsk->icsk_pending == ICSK_TIME_REO_TIMEOUT ||
+ icsk->icsk_pending == ICSK_TIME_LOSS_PROBE) {
+ s64 delta_us = tcp_rto_delta_us(sk);
+ /* delta_us may not be positive if the socket is locked
+ * when the retrans timer fires and is rescheduled.
+ */
+ rto = usecs_to_jiffies(max_t(int, delta_us, 1));
+ }
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto,
+ TCP_RTO_MAX);
+ }
+}
+
+/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
+static void tcp_set_xmit_timer(struct sock *sk)
+{
+ if (!tcp_schedule_loss_probe(sk, true))
+ tcp_rearm_rto(sk);
+}
+
+/* If we get here, the whole TSO packet has not been acked. */
+static u32 tcp_tso_acked(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 packets_acked;
+
+ BUG_ON(!after(TCP_SKB_CB(skb)->end_seq, tp->snd_una));
+
+ packets_acked = tcp_skb_pcount(skb);
+ if (tcp_trim_head(sk, skb, tp->snd_una - TCP_SKB_CB(skb)->seq))
+ return 0;
+ packets_acked -= tcp_skb_pcount(skb);
+
+ if (packets_acked) {
+ BUG_ON(tcp_skb_pcount(skb) == 0);
+ BUG_ON(!before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq));
+ }
+
+ return packets_acked;
+}
+
+static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
+ u32 prior_snd_una)
+{
+ const struct skb_shared_info *shinfo;
+
+ /* Avoid cache line misses to get skb_shinfo() and shinfo->tx_flags */
+ if (likely(!TCP_SKB_CB(skb)->txstamp_ack))
+ return;
+
+ shinfo = skb_shinfo(skb);
+ if (!before(shinfo->tskey, prior_snd_una) &&
+ before(shinfo->tskey, tcp_sk(sk)->snd_una)) {
+ tcp_skb_tsorted_save(skb) {
+ __skb_tstamp_tx(skb, NULL, sk, SCM_TSTAMP_ACK);
+ } tcp_skb_tsorted_restore(skb);
+ }
+}
+
+/* Remove acknowledged frames from the retransmission queue. If our packet
+ * is before the ack sequence we can discard it as it's confirmed to have
+ * arrived at the other end.
+ */
+static int tcp_clean_rtx_queue(struct sock *sk, u32 prior_fack,
+ u32 prior_snd_una,
+ struct tcp_sacktag_state *sack)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+ u64 first_ackt, last_ackt;
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 prior_sacked = tp->sacked_out;
+ u32 reord = tp->snd_nxt; /* lowest acked un-retx un-sacked seq */
+ struct sk_buff *skb, *next;
+ bool fully_acked = true;
+ long sack_rtt_us = -1L;
+ long seq_rtt_us = -1L;
+ long ca_rtt_us = -1L;
+ u32 pkts_acked = 0;
+ u32 last_in_flight = 0;
+ bool rtt_update;
+ int flag = 0;
+
+ first_ackt = 0;
+
+ for (skb = skb_rb_first(&sk->tcp_rtx_queue); skb; skb = next) {
+ struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+ const u32 start_seq = scb->seq;
+ u8 sacked = scb->sacked;
+ u32 acked_pcount;
+
+ tcp_ack_tstamp(sk, skb, prior_snd_una);
+
+ /* Determine how many packets and what bytes were acked, tso and else */
+ if (after(scb->end_seq, tp->snd_una)) {
+ if (tcp_skb_pcount(skb) == 1 ||
+ !after(tp->snd_una, scb->seq))
+ break;
+
+ acked_pcount = tcp_tso_acked(sk, skb);
+ if (!acked_pcount)
+ break;
+ fully_acked = false;
+ } else {
+ acked_pcount = tcp_skb_pcount(skb);
+ }
+
+ if (unlikely(sacked & TCPCB_RETRANS)) {
+ if (sacked & TCPCB_SACKED_RETRANS)
+ tp->retrans_out -= acked_pcount;
+ flag |= FLAG_RETRANS_DATA_ACKED;
+ } else if (!(sacked & TCPCB_SACKED_ACKED)) {
+ last_ackt = skb->skb_mstamp;
+ WARN_ON_ONCE(last_ackt == 0);
+ if (!first_ackt)
+ first_ackt = last_ackt;
+
+ last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
+ if (before(start_seq, reord))
+ reord = start_seq;
+ if (!after(scb->end_seq, tp->high_seq))
+ flag |= FLAG_ORIG_SACK_ACKED;
+ }
+
+ if (sacked & TCPCB_SACKED_ACKED) {
+ tp->sacked_out -= acked_pcount;
+ } else if (tcp_is_sack(tp)) {
+ tp->delivered += acked_pcount;
+ if (!tcp_skb_spurious_retrans(tp, skb))
+ tcp_rack_advance(tp, sacked, scb->end_seq,
+ skb->skb_mstamp);
+ }
+ if (sacked & TCPCB_LOST)
+ tp->lost_out -= acked_pcount;
+
+ tp->packets_out -= acked_pcount;
+ pkts_acked += acked_pcount;
+ tcp_rate_skb_delivered(sk, skb, sack->rate);
+
+ /* Initial outgoing SYN's get put onto the write_queue
+ * just like anything else we transmit. It is not
+ * true data, and if we misinform our callers that
+ * this ACK acks real data, we will erroneously exit
+ * connection startup slow start one packet too
+ * quickly. This is severely frowned upon behavior.
+ */
+ if (likely(!(scb->tcp_flags & TCPHDR_SYN))) {
+ flag |= FLAG_DATA_ACKED;
+ } else {
+ flag |= FLAG_SYN_ACKED;
+ tp->retrans_stamp = 0;
+ }
+
+ if (!fully_acked)
+ break;
+
+ next = skb_rb_next(skb);
+ if (unlikely(skb == tp->retransmit_skb_hint))
+ tp->retransmit_skb_hint = NULL;
+ if (unlikely(skb == tp->lost_skb_hint))
+ tp->lost_skb_hint = NULL;
+ tcp_rtx_queue_unlink_and_free(skb, sk);
+ }
+
+ if (!skb)
+ tcp_chrono_stop(sk, TCP_CHRONO_BUSY);
+
+ if (likely(between(tp->snd_up, prior_snd_una, tp->snd_una)))
+ tp->snd_up = tp->snd_una;
+
+ if (skb && (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
+ flag |= FLAG_SACK_RENEGING;
+
+ if (likely(first_ackt) && !(flag & FLAG_RETRANS_DATA_ACKED)) {
+ seq_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, first_ackt);
+ ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, last_ackt);
+
+ if (pkts_acked == 1 && last_in_flight < tp->mss_cache &&
+ last_in_flight && !prior_sacked && fully_acked &&
+ sack->rate->prior_delivered + 1 == tp->delivered &&
+ !(flag & (FLAG_CA_ALERT | FLAG_SYN_ACKED))) {
+ /* Conservatively mark a delayed ACK. It's typically
+ * from a lone runt packet over the round trip to
+ * a receiver w/o out-of-order or CE events.
+ */
+ flag |= FLAG_ACK_MAYBE_DELAYED;
+ }
+ }
+ if (sack->first_sackt) {
+ sack_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->first_sackt);
+ ca_rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, sack->last_sackt);
+ }
+ rtt_update = tcp_ack_update_rtt(sk, flag, seq_rtt_us, sack_rtt_us,
+ ca_rtt_us, sack->rate);
+
+ if (flag & FLAG_ACKED) {
+ flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
+ if (unlikely(icsk->icsk_mtup.probe_size &&
+ !after(tp->mtu_probe.probe_seq_end, tp->snd_una))) {
+ tcp_mtup_probe_success(sk);
+ }
+
+ if (tcp_is_reno(tp)) {
+ tcp_remove_reno_sacks(sk, pkts_acked);
+
+ /* If any of the cumulatively ACKed segments was
+ * retransmitted, non-SACK case cannot confirm that
+ * progress was due to original transmission due to
+ * lack of TCPCB_SACKED_ACKED bits even if some of
+ * the packets may have been never retransmitted.
+ */
+ if (flag & FLAG_RETRANS_DATA_ACKED)
+ flag &= ~FLAG_ORIG_SACK_ACKED;
+ } else {
+ int delta;
+
+ /* Non-retransmitted hole got filled? That's reordering */
+ if (before(reord, prior_fack))
+ tcp_check_sack_reordering(sk, reord, 0);
+
+ delta = prior_sacked - tp->sacked_out;
+ tp->lost_cnt_hint -= min(tp->lost_cnt_hint, delta);
+ }
+ } else if (skb && rtt_update && sack_rtt_us >= 0 &&
+ sack_rtt_us > tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp)) {
+ /* Do not re-arm RTO if the sack RTT is measured from data sent
+ * after when the head was last (re)transmitted. Otherwise the
+ * timeout may continue to extend in loss recovery.
+ */
+ flag |= FLAG_SET_XMIT_TIMER; /* set TLP or RTO timer */
+ }
+
+ if (icsk->icsk_ca_ops->pkts_acked) {
+ struct ack_sample sample = { .pkts_acked = pkts_acked,
+ .rtt_us = sack->rate->rtt_us,
+ .in_flight = last_in_flight };
+
+ icsk->icsk_ca_ops->pkts_acked(sk, &sample);
+ }
+
+#if FASTRETRANS_DEBUG > 0
+ WARN_ON((int)tp->sacked_out < 0);
+ WARN_ON((int)tp->lost_out < 0);
+ WARN_ON((int)tp->retrans_out < 0);
+ if (!tp->packets_out && tcp_is_sack(tp)) {
+ icsk = inet_csk(sk);
+ if (tp->lost_out) {
+ pr_debug("Leak l=%u %d\n",
+ tp->lost_out, icsk->icsk_ca_state);
+ tp->lost_out = 0;
+ }
+ if (tp->sacked_out) {
+ pr_debug("Leak s=%u %d\n",
+ tp->sacked_out, icsk->icsk_ca_state);
+ tp->sacked_out = 0;
+ }
+ if (tp->retrans_out) {
+ pr_debug("Leak r=%u %d\n",
+ tp->retrans_out, icsk->icsk_ca_state);
+ tp->retrans_out = 0;
+ }
+ }
+#endif
+ return flag;
+}
+
+static void tcp_ack_probe(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct sk_buff *head = tcp_send_head(sk);
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Was it a usable window open? */
+ if (!head)
+ return;
+ if (!after(TCP_SKB_CB(head)->end_seq, tcp_wnd_end(tp))) {
+ icsk->icsk_backoff = 0;
+ inet_csk_clear_xmit_timer(sk, ICSK_TIME_PROBE0);
+ /* Socket must be waked up by subsequent tcp_data_snd_check().
+ * This function is not for random using!
+ */
+ } else {
+ unsigned long when = tcp_probe0_when(sk, TCP_RTO_MAX);
+
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_PROBE0,
+ when, TCP_RTO_MAX);
+ }
+}
+
+static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
+{
+ return !(flag & FLAG_NOT_DUP) || (flag & FLAG_CA_ALERT) ||
+ inet_csk(sk)->icsk_ca_state != TCP_CA_Open;
+}
+
+/* Decide wheather to run the increase function of congestion control. */
+static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
+{
+ /* If reordering is high then always grow cwnd whenever data is
+ * delivered regardless of its ordering. Otherwise stay conservative
+ * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
+ * new SACK or ECE mark may first advance cwnd here and later reduce
+ * cwnd in tcp_fastretrans_alert() based on more states.
+ */
+ if (tcp_sk(sk)->reordering > sock_net(sk)->ipv4.sysctl_tcp_reordering)
+ return flag & FLAG_FORWARD_PROGRESS;
+
+ return flag & FLAG_DATA_ACKED;
+}
+
+/* The "ultimate" congestion control function that aims to replace the rigid
+ * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
+ * It's called toward the end of processing an ACK with precise rate
+ * information. All transmission or retransmission are delayed afterwards.
+ */
+static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
+ int flag, const struct rate_sample *rs)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (icsk->icsk_ca_ops->cong_control) {
+ icsk->icsk_ca_ops->cong_control(sk, rs);
+ return;
+ }
+
+ if (tcp_in_cwnd_reduction(sk)) {
+ /* Reduce cwnd if state mandates */
+ tcp_cwnd_reduction(sk, acked_sacked, flag);
+ } else if (tcp_may_raise_cwnd(sk, flag)) {
+ /* Advance cwnd if state allows */
+ tcp_cong_avoid(sk, ack, acked_sacked);
+ }
+ tcp_update_pacing_rate(sk);
+}
+
+/* Check that window update is acceptable.
+ * The function assumes that snd_una<=ack<=snd_next.
+ */
+static inline bool tcp_may_update_window(const struct tcp_sock *tp,
+ const u32 ack, const u32 ack_seq,
+ const u32 nwin)
+{
+ return after(ack, tp->snd_una) ||
+ after(ack_seq, tp->snd_wl1) ||
+ (ack_seq == tp->snd_wl1 && nwin > tp->snd_wnd);
+}
+
+/* If we update tp->snd_una, also update tp->bytes_acked */
+static void tcp_snd_una_update(struct tcp_sock *tp, u32 ack)
+{
+ u32 delta = ack - tp->snd_una;
+
+ sock_owned_by_me((struct sock *)tp);
+ tp->bytes_acked += delta;
+ tp->snd_una = ack;
+}
+
+/* If we update tp->rcv_nxt, also update tp->bytes_received */
+static void tcp_rcv_nxt_update(struct tcp_sock *tp, u32 seq)
+{
+ u32 delta = seq - tp->rcv_nxt;
+
+ sock_owned_by_me((struct sock *)tp);
+ tp->bytes_received += delta;
+ tp->rcv_nxt = seq;
+}
+
+/* Update our send window.
+ *
+ * Window update algorithm, described in RFC793/RFC1122 (used in linux-2.2
+ * and in FreeBSD. NetBSD's one is even worse.) is wrong.
+ */
+static int tcp_ack_update_window(struct sock *sk, const struct sk_buff *skb, u32 ack,
+ u32 ack_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ int flag = 0;
+ u32 nwin = ntohs(tcp_hdr(skb)->window);
+
+ if (likely(!tcp_hdr(skb)->syn))
+ nwin <<= tp->rx_opt.snd_wscale;
+
+ if (tcp_may_update_window(tp, ack, ack_seq, nwin)) {
+ flag |= FLAG_WIN_UPDATE;
+ tcp_update_wl(tp, ack_seq);
+
+ if (tp->snd_wnd != nwin) {
+ tp->snd_wnd = nwin;
+
+ /* Note, it is the only place, where
+ * fast path is recovered for sending TCP.
+ */
+ tp->pred_flags = 0;
+ tcp_fast_path_check(sk);
+
+ if (!tcp_write_queue_empty(sk))
+ tcp_slow_start_after_idle_check(sk);
+
+ if (nwin > tp->max_window) {
+ tp->max_window = nwin;
+ tcp_sync_mss(sk, inet_csk(sk)->icsk_pmtu_cookie);
+ }
+ }
+ }
+
+ tcp_snd_una_update(tp, ack);
+
+ return flag;
+}
+
+static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
+ u32 *last_oow_ack_time)
+{
+ if (*last_oow_ack_time) {
+ s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
+
+ if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
+ NET_INC_STATS(net, mib_idx);
+ return true; /* rate-limited: don't send yet! */
+ }
+ }
+
+ *last_oow_ack_time = tcp_jiffies32;
+
+ return false; /* not rate-limited: go ahead, send dupack now! */
+}
+
+/* Return true if we're currently rate-limiting out-of-window ACKs and
+ * thus shouldn't send a dupack right now. We rate-limit dupacks in
+ * response to out-of-window SYNs or ACKs to mitigate ACK loops or DoS
+ * attacks that send repeated SYNs or ACKs for the same connection. To
+ * do this, we do not send a duplicate SYNACK or ACK if the remote
+ * endpoint is sending out-of-window SYNs or pure ACKs at a high rate.
+ */
+bool tcp_oow_rate_limited(struct net *net, const struct sk_buff *skb,
+ int mib_idx, u32 *last_oow_ack_time)
+{
+ /* Data packets without SYNs are not likely part of an ACK loop. */
+ if ((TCP_SKB_CB(skb)->seq != TCP_SKB_CB(skb)->end_seq) &&
+ !tcp_hdr(skb)->syn)
+ return false;
+
+ return __tcp_oow_rate_limited(net, mib_idx, last_oow_ack_time);
+}
+
+/* RFC 5961 7 [ACK Throttling] */
+static void tcp_send_challenge_ack(struct sock *sk, const struct sk_buff *skb)
+{
+ /* unprotected vars, we dont care of overwrites */
+ static u32 challenge_timestamp;
+ static unsigned int challenge_count;
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct net *net = sock_net(sk);
+ u32 count, now;
+
+ /* First check our per-socket dupack rate limit. */
+ if (__tcp_oow_rate_limited(net,
+ LINUX_MIB_TCPACKSKIPPEDCHALLENGE,
+ &tp->last_oow_ack_time))
+ return;
+
+ /* Then check host-wide RFC 5961 rate limit. */
+ now = jiffies / HZ;
+ if (now != challenge_timestamp) {
+ u32 ack_limit = net->ipv4.sysctl_tcp_challenge_ack_limit;
+ u32 half = (ack_limit + 1) >> 1;
+
+ challenge_timestamp = now;
+ WRITE_ONCE(challenge_count, half + prandom_u32_max(ack_limit));
+ }
+ count = READ_ONCE(challenge_count);
+ if (count > 0) {
+ WRITE_ONCE(challenge_count, count - 1);
+ NET_INC_STATS(net, LINUX_MIB_TCPCHALLENGEACK);
+ tcp_send_ack(sk);
+ }
+}
+
+static void tcp_store_ts_recent(struct tcp_sock *tp)
+{
+ tp->rx_opt.ts_recent = tp->rx_opt.rcv_tsval;
+ tp->rx_opt.ts_recent_stamp = ktime_get_seconds();
+}
+
+static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
+{
+ if (tp->rx_opt.saw_tstamp && !after(seq, tp->rcv_wup)) {
+ /* PAWS bug workaround wrt. ACK frames, the PAWS discard
+ * extra check below makes sure this can only happen
+ * for pure ACK frames. -DaveM
+ *
+ * Not only, also it occurs for expired timestamps.
+ */
+
+ if (tcp_paws_check(&tp->rx_opt, 0))
+ tcp_store_ts_recent(tp);
+ }
+}
+
+/* This routine deals with acks during a TLP episode.
+ * We mark the end of a TLP episode on receiving TLP dupack or when
+ * ack is after tlp_high_seq.
+ * Ref: loss detection algorithm in draft-dukkipati-tcpm-tcp-loss-probe.
+ */
+static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (before(ack, tp->tlp_high_seq))
+ return;
+
+ if (flag & FLAG_DSACKING_ACK) {
+ /* This DSACK means original and TLP probe arrived; no loss */
+ tp->tlp_high_seq = 0;
+ } else if (after(ack, tp->tlp_high_seq)) {
+ /* ACK advances: there was a loss, so reduce cwnd. Reset
+ * tlp_high_seq in tcp_init_cwnd_reduction()
+ */
+ tcp_init_cwnd_reduction(sk);
+ tcp_set_ca_state(sk, TCP_CA_CWR);
+ tcp_end_cwnd_reduction(sk);
+ tcp_try_keep_open(sk);
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPLOSSPROBERECOVERY);
+ } else if (!(flag & (FLAG_SND_UNA_ADVANCED |
+ FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
+ /* Pure dupack: original and TLP probe arrived; no loss */
+ tp->tlp_high_seq = 0;
+ }
+}
+
+static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
+{
+ const struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (icsk->icsk_ca_ops->in_ack_event)
+ icsk->icsk_ca_ops->in_ack_event(sk, flags);
+}
+
+/* Congestion control has updated the cwnd already. So if we're in
+ * loss recovery then now we do any new sends (for FRTO) or
+ * retransmits (for CA_Loss or CA_recovery) that make sense.
+ */
+static void tcp_xmit_recovery(struct sock *sk, int rexmit)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (rexmit == REXMIT_NONE)
+ return;
+
+ if (unlikely(rexmit == 2)) {
+ __tcp_push_pending_frames(sk, tcp_current_mss(sk),
+ TCP_NAGLE_OFF);
+ if (after(tp->snd_nxt, tp->high_seq))
+ return;
+ tp->frto = 0;
+ }
+ tcp_xmit_retransmit_queue(sk);
+}
+
+/* Returns the number of packets newly acked or sacked by the current ACK */
+static u32 tcp_newly_delivered(struct sock *sk, u32 prior_delivered, int flag)
+{
+ const struct net *net = sock_net(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 delivered;
+
+ delivered = tp->delivered - prior_delivered;
+ NET_ADD_STATS(net, LINUX_MIB_TCPDELIVERED, delivered);
+ if (flag & FLAG_ECE) {
+ tp->delivered_ce += delivered;
+ NET_ADD_STATS(net, LINUX_MIB_TCPDELIVEREDCE, delivered);
+ }
+ return delivered;
+}
+
+/* This routine deals with incoming acks, but not outgoing ones. */
+static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct tcp_sacktag_state sack_state;
+ struct rate_sample rs = { .prior_delivered = 0 };
+ u32 prior_snd_una = tp->snd_una;
+ bool is_sack_reneg = tp->is_sack_reneg;
+ u32 ack_seq = TCP_SKB_CB(skb)->seq;
+ u32 ack = TCP_SKB_CB(skb)->ack_seq;
+ bool is_dupack = false;
+ int prior_packets = tp->packets_out;
+ u32 delivered = tp->delivered;
+ u32 lost = tp->lost;
+ int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
+ u32 prior_fack;
+
+ sack_state.first_sackt = 0;
+ sack_state.rate = &rs;
+
+ /* We very likely will need to access rtx queue. */
+ prefetch(sk->tcp_rtx_queue.rb_node);
+
+ /* If the ack is older than previous acks
+ * then we can probably ignore it.
+ */
+ if (before(ack, prior_snd_una)) {
+ /* RFC 5961 5.2 [Blind Data Injection Attack].[Mitigation] */
+ if (before(ack, prior_snd_una - tp->max_window)) {
+ if (!(flag & FLAG_NO_CHALLENGE_ACK))
+ tcp_send_challenge_ack(sk, skb);
+ return -1;
+ }
+ goto old_ack;
+ }
+
+ /* If the ack includes data we haven't sent yet, discard
+ * this segment (RFC793 Section 3.9).
+ */
+ if (after(ack, tp->snd_nxt))
+ goto invalid_ack;
+
+ if (after(ack, prior_snd_una)) {
+ flag |= FLAG_SND_UNA_ADVANCED;
+ icsk->icsk_retransmits = 0;
+
+#if IS_ENABLED(CONFIG_TLS_DEVICE)
+ if (static_branch_unlikely(&clean_acked_data_enabled))
+ if (icsk->icsk_clean_acked)
+ icsk->icsk_clean_acked(sk, ack);
+#endif
+ }
+
+ prior_fack = tcp_is_sack(tp) ? tcp_highest_sack_seq(tp) : tp->snd_una;
+ rs.prior_in_flight = tcp_packets_in_flight(tp);
+
+ /* ts_recent update must be made after we are sure that the packet
+ * is in window.
+ */
+ if (flag & FLAG_UPDATE_TS_RECENT)
+ tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
+ if (!(flag & FLAG_SLOWPATH) && after(ack, prior_snd_una)) {
+ /* Window is constant, pure forward advance.
+ * No more checks are required.
+ * Note, we use the fact that SND.UNA>=SND.WL2.
+ */
+ tcp_update_wl(tp, ack_seq);
+ tcp_snd_una_update(tp, ack);
+ flag |= FLAG_WIN_UPDATE;
+
+ tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPACKS);
+ } else {
+ u32 ack_ev_flags = CA_ACK_SLOWPATH;
+
+ if (ack_seq != TCP_SKB_CB(skb)->end_seq)
+ flag |= FLAG_DATA;
+ else
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPUREACKS);
+
+ flag |= tcp_ack_update_window(sk, skb, ack, ack_seq);
+
+ if (TCP_SKB_CB(skb)->sacked)
+ flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
+ &sack_state);
+
+ if (tcp_ecn_rcv_ecn_echo(tp, tcp_hdr(skb))) {
+ flag |= FLAG_ECE;
+ ack_ev_flags |= CA_ACK_ECE;
+ }
+
+ if (flag & FLAG_WIN_UPDATE)
+ ack_ev_flags |= CA_ACK_WIN_UPDATE;
+
+ tcp_in_ack_event(sk, ack_ev_flags);
+ }
+
+ /* We passed data and got it acked, remove any soft error
+ * log. Something worked...
+ */
+ sk->sk_err_soft = 0;
+ icsk->icsk_probes_out = 0;
+ tp->rcv_tstamp = tcp_jiffies32;
+ if (!prior_packets)
+ goto no_queue;
+
+ /* See if we can take anything off of the retransmit queue. */
+ flag |= tcp_clean_rtx_queue(sk, prior_fack, prior_snd_una, &sack_state);
+
+ tcp_rack_update_reo_wnd(sk, &rs);
+
+ if (tp->tlp_high_seq)
+ tcp_process_tlp_ack(sk, ack, flag);
+ /* If needed, reset TLP/RTO timer; RACK may later override this. */
+ if (flag & FLAG_SET_XMIT_TIMER)
+ tcp_set_xmit_timer(sk);
+
+ if (tcp_ack_is_dubious(sk, flag)) {
+ is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
+ tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ &rexmit);
+ }
+
+ if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP))
+ sk_dst_confirm(sk);
+
+ delivered = tcp_newly_delivered(sk, delivered, flag);
+ lost = tp->lost - lost; /* freshly marked lost */
+ rs.is_ack_delayed = !!(flag & FLAG_ACK_MAYBE_DELAYED);
+ tcp_rate_gen(sk, delivered, lost, is_sack_reneg, sack_state.rate);
+ tcp_cong_control(sk, ack, delivered, flag, sack_state.rate);
+ tcp_xmit_recovery(sk, rexmit);
+ return 1;
+
+no_queue:
+ /* If data was DSACKed, see if we can undo a cwnd reduction. */
+ if (flag & FLAG_DSACKING_ACK) {
+ tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ &rexmit);
+ tcp_newly_delivered(sk, delivered, flag);
+ }
+ /* If this ack opens up a zero window, clear backoff. It was
+ * being used to time the probes, and is probably far higher than
+ * it needs to be for normal retransmission.
+ */
+ tcp_ack_probe(sk);
+
+ if (tp->tlp_high_seq)
+ tcp_process_tlp_ack(sk, ack, flag);
+ return 1;
+
+invalid_ack:
+ SOCK_DEBUG(sk, "Ack %u after %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
+ return -1;
+
+old_ack:
+ /* If data was SACKed, tag it and see if we should send more data.
+ * If data was DSACKed, see if we can undo a cwnd reduction.
+ */
+ if (TCP_SKB_CB(skb)->sacked) {
+ flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
+ &sack_state);
+ tcp_fastretrans_alert(sk, prior_snd_una, is_dupack, &flag,
+ &rexmit);
+ tcp_newly_delivered(sk, delivered, flag);
+ tcp_xmit_recovery(sk, rexmit);
+ }
+
+ SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);
+ return 0;
+}
+
+static void tcp_parse_fastopen_option(int len, const unsigned char *cookie,
+ bool syn, struct tcp_fastopen_cookie *foc,
+ bool exp_opt)
+{
+ /* Valid only in SYN or SYN-ACK with an even length. */
+ if (!foc || !syn || len < 0 || (len & 1))
+ return;
+
+ if (len >= TCP_FASTOPEN_COOKIE_MIN &&
+ len <= TCP_FASTOPEN_COOKIE_MAX)
+ memcpy(foc->val, cookie, len);
+ else if (len != 0)
+ len = -1;
+ foc->len = len;
+ foc->exp = exp_opt;
+}
+
+static void smc_parse_options(const struct tcphdr *th,
+ struct tcp_options_received *opt_rx,
+ const unsigned char *ptr,
+ int opsize)
+{
+#if IS_ENABLED(CONFIG_SMC)
+ if (static_branch_unlikely(&tcp_have_smc)) {
+ if (th->syn && !(opsize & 1) &&
+ opsize >= TCPOLEN_EXP_SMC_BASE &&
+ get_unaligned_be32(ptr) == TCPOPT_SMC_MAGIC)
+ opt_rx->smc_ok = 1;
+ }
+#endif
+}
+
+/* Look for tcp options. Normally only called on SYN and SYNACK packets.
+ * But, this can also be called on packets in the established flow when
+ * the fast version below fails.
+ */
+void tcp_parse_options(const struct net *net,
+ const struct sk_buff *skb,
+ struct tcp_options_received *opt_rx, int estab,
+ struct tcp_fastopen_cookie *foc)
+{
+ const unsigned char *ptr;
+ const struct tcphdr *th = tcp_hdr(skb);
+ int length = (th->doff * 4) - sizeof(struct tcphdr);
+
+ ptr = (const unsigned char *)(th + 1);
+ opt_rx->saw_tstamp = 0;
+
+ while (length > 0) {
+ int opcode = *ptr++;
+ int opsize;
+
+ switch (opcode) {
+ case TCPOPT_EOL:
+ return;
+ case TCPOPT_NOP: /* Ref: RFC 793 section 3.1 */
+ length--;
+ continue;
+ default:
+ opsize = *ptr++;
+ if (opsize < 2) /* "silly options" */
+ return;
+ if (opsize > length)
+ return; /* don't parse partial options */
+ switch (opcode) {
+ case TCPOPT_MSS:
+ if (opsize == TCPOLEN_MSS && th->syn && !estab) {
+ u16 in_mss = get_unaligned_be16(ptr);
+ if (in_mss) {
+ if (opt_rx->user_mss &&
+ opt_rx->user_mss < in_mss)
+ in_mss = opt_rx->user_mss;
+ opt_rx->mss_clamp = in_mss;
+ }
+ }
+ break;
+ case TCPOPT_WINDOW:
+ if (opsize == TCPOLEN_WINDOW && th->syn &&
+ !estab && net->ipv4.sysctl_tcp_window_scaling) {
+ __u8 snd_wscale = *(__u8 *)ptr;
+ opt_rx->wscale_ok = 1;
+ if (snd_wscale > TCP_MAX_WSCALE) {
+ net_info_ratelimited("%s: Illegal window scaling value %d > %u received\n",
+ __func__,
+ snd_wscale,
+ TCP_MAX_WSCALE);
+ snd_wscale = TCP_MAX_WSCALE;
+ }
+ opt_rx->snd_wscale = snd_wscale;
+ }
+ break;
+ case TCPOPT_TIMESTAMP:
+ if ((opsize == TCPOLEN_TIMESTAMP) &&
+ ((estab && opt_rx->tstamp_ok) ||
+ (!estab && net->ipv4.sysctl_tcp_timestamps))) {
+ opt_rx->saw_tstamp = 1;
+ opt_rx->rcv_tsval = get_unaligned_be32(ptr);
+ opt_rx->rcv_tsecr = get_unaligned_be32(ptr + 4);
+ }
+ break;
+ case TCPOPT_SACK_PERM:
+ if (opsize == TCPOLEN_SACK_PERM && th->syn &&
+ !estab && net->ipv4.sysctl_tcp_sack) {
+ opt_rx->sack_ok = TCP_SACK_SEEN;
+ tcp_sack_reset(opt_rx);
+ }
+ break;
+
+ case TCPOPT_SACK:
+ if ((opsize >= (TCPOLEN_SACK_BASE + TCPOLEN_SACK_PERBLOCK)) &&
+ !((opsize - TCPOLEN_SACK_BASE) % TCPOLEN_SACK_PERBLOCK) &&
+ opt_rx->sack_ok) {
+ TCP_SKB_CB(skb)->sacked = (ptr - 2) - (unsigned char *)th;
+ }
+ break;
+#ifdef CONFIG_TCP_MD5SIG
+ case TCPOPT_MD5SIG:
+ /*
+ * The MD5 Hash has already been
+ * checked (see tcp_v{4,6}_do_rcv()).
+ */
+ break;
+#endif
+ case TCPOPT_FASTOPEN:
+ tcp_parse_fastopen_option(
+ opsize - TCPOLEN_FASTOPEN_BASE,
+ ptr, th->syn, foc, false);
+ break;
+
+ case TCPOPT_EXP:
+ /* Fast Open option shares code 254 using a
+ * 16 bits magic number.
+ */
+ if (opsize >= TCPOLEN_EXP_FASTOPEN_BASE &&
+ get_unaligned_be16(ptr) ==
+ TCPOPT_FASTOPEN_MAGIC)
+ tcp_parse_fastopen_option(opsize -
+ TCPOLEN_EXP_FASTOPEN_BASE,
+ ptr + 2, th->syn, foc, true);
+ else
+ smc_parse_options(th, opt_rx, ptr,
+ opsize);
+ break;
+
+ }
+ ptr += opsize-2;
+ length -= opsize;
+ }
+ }
+}
+EXPORT_SYMBOL(tcp_parse_options);
+
+static bool tcp_parse_aligned_timestamp(struct tcp_sock *tp, const struct tcphdr *th)
+{
+ const __be32 *ptr = (const __be32 *)(th + 1);
+
+ if (*ptr == htonl((TCPOPT_NOP << 24) | (TCPOPT_NOP << 16)
+ | (TCPOPT_TIMESTAMP << 8) | TCPOLEN_TIMESTAMP)) {
+ tp->rx_opt.saw_tstamp = 1;
+ ++ptr;
+ tp->rx_opt.rcv_tsval = ntohl(*ptr);
+ ++ptr;
+ if (*ptr)
+ tp->rx_opt.rcv_tsecr = ntohl(*ptr) - tp->tsoffset;
+ else
+ tp->rx_opt.rcv_tsecr = 0;
+ return true;
+ }
+ return false;
+}
+
+/* Fast parse options. This hopes to only see timestamps.
+ * If it is wrong it falls back on tcp_parse_options().
+ */
+static bool tcp_fast_parse_options(const struct net *net,
+ const struct sk_buff *skb,
+ const struct tcphdr *th, struct tcp_sock *tp)
+{
+ /* In the spirit of fast parsing, compare doff directly to constant
+ * values. Because equality is used, short doff can be ignored here.
+ */
+ if (th->doff == (sizeof(*th) / 4)) {
+ tp->rx_opt.saw_tstamp = 0;
+ return false;
+ } else if (tp->rx_opt.tstamp_ok &&
+ th->doff == ((sizeof(*th) + TCPOLEN_TSTAMP_ALIGNED) / 4)) {
+ if (tcp_parse_aligned_timestamp(tp, th))
+ return true;
+ }
+
+ tcp_parse_options(net, skb, &tp->rx_opt, 1, NULL);
+ if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
+ tp->rx_opt.rcv_tsecr -= tp->tsoffset;
+
+ return true;
+}
+
+#ifdef CONFIG_TCP_MD5SIG
+/*
+ * Parse MD5 Signature option
+ */
+const u8 *tcp_parse_md5sig_option(const struct tcphdr *th)
+{
+ int length = (th->doff << 2) - sizeof(*th);
+ const u8 *ptr = (const u8 *)(th + 1);
+
+ /* If not enough data remaining, we can short cut */
+ while (length >= TCPOLEN_MD5SIG) {
+ int opcode = *ptr++;
+ int opsize;
+
+ switch (opcode) {
+ case TCPOPT_EOL:
+ return NULL;
+ case TCPOPT_NOP:
+ length--;
+ continue;
+ default:
+ opsize = *ptr++;
+ if (opsize < 2 || opsize > length)
+ return NULL;
+ if (opcode == TCPOPT_MD5SIG)
+ return opsize == TCPOLEN_MD5SIG ? ptr : NULL;
+ }
+ ptr += opsize - 2;
+ length -= opsize;
+ }
+ return NULL;
+}
+EXPORT_SYMBOL(tcp_parse_md5sig_option);
+#endif
+
+/* Sorry, PAWS as specified is broken wrt. pure-ACKs -DaveM
+ *
+ * It is not fatal. If this ACK does _not_ change critical state (seqs, window)
+ * it can pass through stack. So, the following predicate verifies that
+ * this segment is not used for anything but congestion avoidance or
+ * fast retransmit. Moreover, we even are able to eliminate most of such
+ * second order effects, if we apply some small "replay" window (~RTO)
+ * to timestamp space.
+ *
+ * All these measures still do not guarantee that we reject wrapped ACKs
+ * on networks with high bandwidth, when sequence space is recycled fastly,
+ * but it guarantees that such events will be very rare and do not affect
+ * connection seriously. This doesn't look nice, but alas, PAWS is really
+ * buggy extension.
+ *
+ * [ Later note. Even worse! It is buggy for segments _with_ data. RFC
+ * states that events when retransmit arrives after original data are rare.
+ * It is a blatant lie. VJ forgot about fast retransmit! 8)8) It is
+ * the biggest problem on large power networks even with minor reordering.
+ * OK, let's give it small replay window. If peer clock is even 1hz, it is safe
+ * up to bandwidth of 18Gigabit/sec. 8) ]
+ */
+
+static int tcp_disordered_ack(const struct sock *sk, const struct sk_buff *skb)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ const struct tcphdr *th = tcp_hdr(skb);
+ u32 seq = TCP_SKB_CB(skb)->seq;
+ u32 ack = TCP_SKB_CB(skb)->ack_seq;
+
+ return (/* 1. Pure ACK with correct sequence number. */
+ (th->ack && seq == TCP_SKB_CB(skb)->end_seq && seq == tp->rcv_nxt) &&
+
+ /* 2. ... and duplicate ACK. */
+ ack == tp->snd_una &&
+
+ /* 3. ... and does not update window. */
+ !tcp_may_update_window(tp, ack, seq, ntohs(th->window) << tp->rx_opt.snd_wscale) &&
+
+ /* 4. ... and sits in replay window. */
+ (s32)(tp->rx_opt.ts_recent - tp->rx_opt.rcv_tsval) <= (inet_csk(sk)->icsk_rto * 1024) / HZ);
+}
+
+static inline bool tcp_paws_discard(const struct sock *sk,
+ const struct sk_buff *skb)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ return !tcp_paws_check(&tp->rx_opt, TCP_PAWS_WINDOW) &&
+ !tcp_disordered_ack(sk, skb);
+}
+
+/* Check segment sequence number for validity.
+ *
+ * Segment controls are considered valid, if the segment
+ * fits to the window after truncation to the window. Acceptability
+ * of data (and SYN, FIN, of course) is checked separately.
+ * See tcp_data_queue(), for example.
+ *
+ * Also, controls (RST is main one) are accepted using RCV.WUP instead
+ * of RCV.NXT. Peer still did not advance his SND.UNA when we
+ * delayed ACK, so that hisSND.UNA<=ourRCV.WUP.
+ * (borrowed from freebsd)
+ */
+
+static inline bool tcp_sequence(const struct tcp_sock *tp, u32 seq, u32 end_seq)
+{
+ return !before(end_seq, tp->rcv_wup) &&
+ !after(seq, tp->rcv_nxt + tcp_receive_window(tp));
+}
+
+/* When we get a reset we do this. */
+void tcp_reset(struct sock *sk)
+{
+ trace_tcp_receive_reset(sk);
+
+ /* We want the right error as BSD sees it (and indeed as we do). */
+ switch (sk->sk_state) {
+ case TCP_SYN_SENT:
+ sk->sk_err = ECONNREFUSED;
+ break;
+ case TCP_CLOSE_WAIT:
+ sk->sk_err = EPIPE;
+ break;
+ case TCP_CLOSE:
+ return;
+ default:
+ sk->sk_err = ECONNRESET;
+ }
+ /* This barrier is coupled with smp_rmb() in tcp_poll() */
+ smp_wmb();
+
+ tcp_write_queue_purge(sk);
+ tcp_done(sk);
+
+ if (!sock_flag(sk, SOCK_DEAD))
+ sk->sk_error_report(sk);
+}
+
+/*
+ * Process the FIN bit. This now behaves as it is supposed to work
+ * and the FIN takes effect when it is validly part of sequence
+ * space. Not before when we get holes.
+ *
+ * If we are ESTABLISHED, a received fin moves us to CLOSE-WAIT
+ * (and thence onto LAST-ACK and finally, CLOSE, we never enter
+ * TIME-WAIT)
+ *
+ * If we are in FINWAIT-1, a received FIN indicates simultaneous
+ * close and we go into CLOSING (and later onto TIME-WAIT)
+ *
+ * If we are in FINWAIT-2, a received FIN moves us to TIME-WAIT.
+ */
+void tcp_fin(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ inet_csk_schedule_ack(sk);
+
+ sk->sk_shutdown |= RCV_SHUTDOWN;
+ sock_set_flag(sk, SOCK_DONE);
+
+ switch (sk->sk_state) {
+ case TCP_SYN_RECV:
+ case TCP_ESTABLISHED:
+ /* Move to CLOSE_WAIT */
+ tcp_set_state(sk, TCP_CLOSE_WAIT);
+ inet_csk(sk)->icsk_ack.pingpong = 1;
+ break;
+
+ case TCP_CLOSE_WAIT:
+ case TCP_CLOSING:
+ /* Received a retransmission of the FIN, do
+ * nothing.
+ */
+ break;
+ case TCP_LAST_ACK:
+ /* RFC793: Remain in the LAST-ACK state. */
+ break;
+
+ case TCP_FIN_WAIT1:
+ /* This case occurs when a simultaneous close
+ * happens, we must ack the received FIN and
+ * enter the CLOSING state.
+ */
+ tcp_send_ack(sk);
+ tcp_set_state(sk, TCP_CLOSING);
+ break;
+ case TCP_FIN_WAIT2:
+ /* Received a FIN -- send ACK and enter TIME_WAIT. */
+ tcp_send_ack(sk);
+ tcp_time_wait(sk, TCP_TIME_WAIT, 0);
+ break;
+ default:
+ /* Only TCP_LISTEN and TCP_CLOSE are left, in these
+ * cases we should never reach this piece of code.
+ */
+ pr_err("%s: Impossible, sk->sk_state=%d\n",
+ __func__, sk->sk_state);
+ break;
+ }
+
+ /* It _is_ possible, that we have something out-of-order _after_ FIN.
+ * Probably, we should reset in this case. For now drop them.
+ */
+ skb_rbtree_purge(&tp->out_of_order_queue);
+ if (tcp_is_sack(tp))
+ tcp_sack_reset(&tp->rx_opt);
+ sk_mem_reclaim(sk);
+
+ if (!sock_flag(sk, SOCK_DEAD)) {
+ sk->sk_state_change(sk);
+
+ /* Do not send POLL_HUP for half duplex close. */
+ if (sk->sk_shutdown == SHUTDOWN_MASK ||
+ sk->sk_state == TCP_CLOSE)
+ sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
+ else
+ sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
+ }
+}
+
+static inline bool tcp_sack_extend(struct tcp_sack_block *sp, u32 seq,
+ u32 end_seq)
+{
+ if (!after(seq, sp->end_seq) && !after(sp->start_seq, end_seq)) {
+ if (before(seq, sp->start_seq))
+ sp->start_seq = seq;
+ if (after(end_seq, sp->end_seq))
+ sp->end_seq = end_seq;
+ return true;
+ }
+ return false;
+}
+
+static void tcp_dsack_set(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
+ int mib_idx;
+
+ if (before(seq, tp->rcv_nxt))
+ mib_idx = LINUX_MIB_TCPDSACKOLDSENT;
+ else
+ mib_idx = LINUX_MIB_TCPDSACKOFOSENT;
+
+ NET_INC_STATS(sock_net(sk), mib_idx);
+
+ tp->rx_opt.dsack = 1;
+ tp->duplicate_sack[0].start_seq = seq;
+ tp->duplicate_sack[0].end_seq = end_seq;
+ }
+}
+
+static void tcp_dsack_extend(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (!tp->rx_opt.dsack)
+ tcp_dsack_set(sk, seq, end_seq);
+ else
+ tcp_sack_extend(tp->duplicate_sack, seq, end_seq);
+}
+
+static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+ tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
+
+ if (tcp_is_sack(tp) && sock_net(sk)->ipv4.sysctl_tcp_dsack) {
+ u32 end_seq = TCP_SKB_CB(skb)->end_seq;
+
+ if (after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))
+ end_seq = tp->rcv_nxt;
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, end_seq);
+ }
+ }
+
+ tcp_send_ack(sk);
+}
+
+/* These routines update the SACK block as out-of-order packets arrive or
+ * in-order packets close up the sequence space.
+ */
+static void tcp_sack_maybe_coalesce(struct tcp_sock *tp)
+{
+ int this_sack;
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ struct tcp_sack_block *swalk = sp + 1;
+
+ /* See if the recent change to the first SACK eats into
+ * or hits the sequence space of other SACK blocks, if so coalesce.
+ */
+ for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;) {
+ if (tcp_sack_extend(sp, swalk->start_seq, swalk->end_seq)) {
+ int i;
+
+ /* Zap SWALK, by moving every further SACK up by one slot.
+ * Decrease num_sacks.
+ */
+ tp->rx_opt.num_sacks--;
+ for (i = this_sack; i < tp->rx_opt.num_sacks; i++)
+ sp[i] = sp[i + 1];
+ continue;
+ }
+ this_sack++, swalk++;
+ }
+}
+
+static void tcp_sack_new_ofo_skb(struct sock *sk, u32 seq, u32 end_seq)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ int cur_sacks = tp->rx_opt.num_sacks;
+ int this_sack;
+
+ if (!cur_sacks)
+ goto new_sack;
+
+ for (this_sack = 0; this_sack < cur_sacks; this_sack++, sp++) {
+ if (tcp_sack_extend(sp, seq, end_seq)) {
+ /* Rotate this_sack to the first one. */
+ for (; this_sack > 0; this_sack--, sp--)
+ swap(*sp, *(sp - 1));
+ if (cur_sacks > 1)
+ tcp_sack_maybe_coalesce(tp);
+ return;
+ }
+ }
+
+ /* Could not find an adjacent existing SACK, build a new one,
+ * put it at the front, and shift everyone else down. We
+ * always know there is at least one SACK present already here.
+ *
+ * If the sack array is full, forget about the last one.
+ */
+ if (this_sack >= TCP_NUM_SACKS) {
+ if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
+ tcp_send_ack(sk);
+ this_sack--;
+ tp->rx_opt.num_sacks--;
+ sp--;
+ }
+ for (; this_sack > 0; this_sack--, sp--)
+ *sp = *(sp - 1);
+
+new_sack:
+ /* Build the new head SACK, and we're done. */
+ sp->start_seq = seq;
+ sp->end_seq = end_seq;
+ tp->rx_opt.num_sacks++;
+}
+
+/* RCV.NXT advances, some SACKs should be eaten. */
+
+static void tcp_sack_remove(struct tcp_sock *tp)
+{
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ int num_sacks = tp->rx_opt.num_sacks;
+ int this_sack;
+
+ /* Empty ofo queue, hence, all the SACKs are eaten. Clear. */
+ if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
+ tp->rx_opt.num_sacks = 0;
+ return;
+ }
+
+ for (this_sack = 0; this_sack < num_sacks;) {
+ /* Check if the start of the sack is covered by RCV.NXT. */
+ if (!before(tp->rcv_nxt, sp->start_seq)) {
+ int i;
+
+ /* RCV.NXT must cover all the block! */
+ WARN_ON(before(tp->rcv_nxt, sp->end_seq));
+
+ /* Zap this SACK, by moving forward any other SACKS. */
+ for (i = this_sack+1; i < num_sacks; i++)
+ tp->selective_acks[i-1] = tp->selective_acks[i];
+ num_sacks--;
+ continue;
+ }
+ this_sack++;
+ sp++;
+ }
+ tp->rx_opt.num_sacks = num_sacks;
+}
+
+/**
+ * tcp_try_coalesce - try to merge skb to prior one
+ * @sk: socket
+ * @dest: destination queue
+ * @to: prior buffer
+ * @from: buffer to add in queue
+ * @fragstolen: pointer to boolean
+ *
+ * Before queueing skb @from after @to, try to merge them
+ * to reduce overall memory use and queue lengths, if cost is small.
+ * Packets in ofo or receive queues can stay a long time.
+ * Better try to coalesce them right now to avoid future collapses.
+ * Returns true if caller should free @from instead of queueing it
+ */
+static bool tcp_try_coalesce(struct sock *sk,
+ struct sk_buff *to,
+ struct sk_buff *from,
+ bool *fragstolen)
+{
+ int delta;
+
+ *fragstolen = false;
+
+ /* Its possible this segment overlaps with prior segment in queue */
+ if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
+ return false;
+
+#ifdef CONFIG_TLS_DEVICE
+ if (from->decrypted != to->decrypted)
+ return false;
+#endif
+
+ if (!skb_try_coalesce(to, from, fragstolen, &delta))
+ return false;
+
+ atomic_add(delta, &sk->sk_rmem_alloc);
+ sk_mem_charge(sk, delta);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
+ TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
+ TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
+ TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
+
+ if (TCP_SKB_CB(from)->has_rxtstamp) {
+ TCP_SKB_CB(to)->has_rxtstamp = true;
+ to->tstamp = from->tstamp;
+ skb_hwtstamps(to)->hwtstamp = skb_hwtstamps(from)->hwtstamp;
+ }
+
+ return true;
+}
+
+static bool tcp_ooo_try_coalesce(struct sock *sk,
+ struct sk_buff *to,
+ struct sk_buff *from,
+ bool *fragstolen)
+{
+ bool res = tcp_try_coalesce(sk, to, from, fragstolen);
+
+ /* In case tcp_drop() is called later, update to->gso_segs */
+ if (res) {
+ u32 gso_segs = max_t(u16, 1, skb_shinfo(to)->gso_segs) +
+ max_t(u16, 1, skb_shinfo(from)->gso_segs);
+
+ skb_shinfo(to)->gso_segs = min_t(u32, gso_segs, 0xFFFF);
+ }
+ return res;
+}
+
+static void tcp_drop(struct sock *sk, struct sk_buff *skb)
+{
+ sk_drops_add(sk, skb);
+ __kfree_skb(skb);
+}
+
+/* This one checks to see if we can put data from the
+ * out_of_order queue into the receive_queue.
+ */
+static void tcp_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ __u32 dsack_high = tp->rcv_nxt;
+ bool fin, fragstolen, eaten;
+ struct sk_buff *skb, *tail;
+ struct rb_node *p;
+
+ p = rb_first(&tp->out_of_order_queue);
+ while (p) {
+ skb = rb_to_skb(p);
+ if (after(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
+ break;
+
+ if (before(TCP_SKB_CB(skb)->seq, dsack_high)) {
+ __u32 dsack = dsack_high;
+ if (before(TCP_SKB_CB(skb)->end_seq, dsack_high))
+ dsack_high = TCP_SKB_CB(skb)->end_seq;
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb)->seq, dsack);
+ }
+ p = rb_next(p);
+ rb_erase(&skb->rbnode, &tp->out_of_order_queue);
+
+ if (unlikely(!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt))) {
+ SOCK_DEBUG(sk, "ofo packet was already received\n");
+ tcp_drop(sk, skb);
+ continue;
+ }
+ SOCK_DEBUG(sk, "ofo requeuing : rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq);
+
+ tail = skb_peek_tail(&sk->sk_receive_queue);
+ eaten = tail && tcp_try_coalesce(sk, tail, skb, &fragstolen);
+ tcp_rcv_nxt_update(tp, TCP_SKB_CB(skb)->end_seq);
+ fin = TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN;
+ if (!eaten)
+ __skb_queue_tail(&sk->sk_receive_queue, skb);
+ else
+ kfree_skb_partial(skb, fragstolen);
+
+ if (unlikely(fin)) {
+ tcp_fin(sk);
+ /* tcp_fin() purges tp->out_of_order_queue,
+ * so we must end this loop right now.
+ */
+ break;
+ }
+ }
+}
+
+static bool tcp_prune_ofo_queue(struct sock *sk);
+static int tcp_prune_queue(struct sock *sk);
+
+static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
+ unsigned int size)
+{
+ if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
+ !sk_rmem_schedule(sk, skb, size)) {
+
+ if (tcp_prune_queue(sk) < 0)
+ return -1;
+
+ while (!sk_rmem_schedule(sk, skb, size)) {
+ if (!tcp_prune_ofo_queue(sk))
+ return -1;
+ }
+ }
+ return 0;
+}
+
+static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct rb_node **p, *parent;
+ struct sk_buff *skb1;
+ u32 seq, end_seq;
+ bool fragstolen;
+
+ tcp_ecn_check_ce(sk, skb);
+
+ if (unlikely(tcp_try_rmem_schedule(sk, skb, skb->truesize))) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFODROP);
+ tcp_drop(sk, skb);
+ return;
+ }
+
+ /* Disable header prediction. */
+ tp->pred_flags = 0;
+ inet_csk_schedule_ack(sk);
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOQUEUE);
+ seq = TCP_SKB_CB(skb)->seq;
+ end_seq = TCP_SKB_CB(skb)->end_seq;
+ SOCK_DEBUG(sk, "out of order segment: rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, seq, end_seq);
+
+ p = &tp->out_of_order_queue.rb_node;
+ if (RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
+ /* Initial out of order segment, build 1 SACK. */
+ if (tcp_is_sack(tp)) {
+ tp->rx_opt.num_sacks = 1;
+ tp->selective_acks[0].start_seq = seq;
+ tp->selective_acks[0].end_seq = end_seq;
+ }
+ rb_link_node(&skb->rbnode, NULL, p);
+ rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
+ tp->ooo_last_skb = skb;
+ goto end;
+ }
+
+ /* In the typical case, we are adding an skb to the end of the list.
+ * Use of ooo_last_skb avoids the O(Log(N)) rbtree lookup.
+ */
+ if (tcp_ooo_try_coalesce(sk, tp->ooo_last_skb,
+ skb, &fragstolen)) {
+coalesce_done:
+ tcp_grow_window(sk, skb);
+ kfree_skb_partial(skb, fragstolen);
+ skb = NULL;
+ goto add_sack;
+ }
+ /* Can avoid an rbtree lookup if we are adding skb after ooo_last_skb */
+ if (!before(seq, TCP_SKB_CB(tp->ooo_last_skb)->end_seq)) {
+ parent = &tp->ooo_last_skb->rbnode;
+ p = &parent->rb_right;
+ goto insert;
+ }
+
+ /* Find place to insert this segment. Handle overlaps on the way. */
+ parent = NULL;
+ while (*p) {
+ parent = *p;
+ skb1 = rb_to_skb(parent);
+ if (before(seq, TCP_SKB_CB(skb1)->seq)) {
+ p = &parent->rb_left;
+ continue;
+ }
+ if (before(seq, TCP_SKB_CB(skb1)->end_seq)) {
+ if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
+ /* All the bits are present. Drop. */
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPOFOMERGE);
+ tcp_drop(sk, skb);
+ skb = NULL;
+ tcp_dsack_set(sk, seq, end_seq);
+ goto add_sack;
+ }
+ if (after(seq, TCP_SKB_CB(skb1)->seq)) {
+ /* Partial overlap. */
+ tcp_dsack_set(sk, seq, TCP_SKB_CB(skb1)->end_seq);
+ } else {
+ /* skb's seq == skb1's seq and skb covers skb1.
+ * Replace skb1 with skb.
+ */
+ rb_replace_node(&skb1->rbnode, &skb->rbnode,
+ &tp->out_of_order_queue);
+ tcp_dsack_extend(sk,
+ TCP_SKB_CB(skb1)->seq,
+ TCP_SKB_CB(skb1)->end_seq);
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPOFOMERGE);
+ tcp_drop(sk, skb1);
+ goto merge_right;
+ }
+ } else if (tcp_ooo_try_coalesce(sk, skb1,
+ skb, &fragstolen)) {
+ goto coalesce_done;
+ }
+ p = &parent->rb_right;
+ }
+insert:
+ /* Insert segment into RB tree. */
+ rb_link_node(&skb->rbnode, parent, p);
+ rb_insert_color(&skb->rbnode, &tp->out_of_order_queue);
+
+merge_right:
+ /* Remove other segments covered by skb. */
+ while ((skb1 = skb_rb_next(skb)) != NULL) {
+ if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
+ break;
+ if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
+ end_seq);
+ break;
+ }
+ rb_erase(&skb1->rbnode, &tp->out_of_order_queue);
+ tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
+ TCP_SKB_CB(skb1)->end_seq);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPOFOMERGE);
+ tcp_drop(sk, skb1);
+ }
+ /* If there is no skb after us, we are the last_skb ! */
+ if (!skb1)
+ tp->ooo_last_skb = skb;
+
+add_sack:
+ if (tcp_is_sack(tp))
+ tcp_sack_new_ofo_skb(sk, seq, end_seq);
+end:
+ if (skb) {
+ tcp_grow_window(sk, skb);
+ skb_condense(skb);
+ skb_set_owner_r(skb, sk);
+ }
+}
+
+static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,
+ bool *fragstolen)
+{
+ int eaten;
+ struct sk_buff *tail = skb_peek_tail(&sk->sk_receive_queue);
+
+ __skb_pull(skb, hdrlen);
+ eaten = (tail &&
+ tcp_try_coalesce(sk, tail,
+ skb, fragstolen)) ? 1 : 0;
+ tcp_rcv_nxt_update(tcp_sk(sk), TCP_SKB_CB(skb)->end_seq);
+ if (!eaten) {
+ __skb_queue_tail(&sk->sk_receive_queue, skb);
+ skb_set_owner_r(skb, sk);
+ }
+ return eaten;
+}
+
+int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size)
+{
+ struct sk_buff *skb;
+ int err = -ENOMEM;
+ int data_len = 0;
+ bool fragstolen;
+
+ if (size == 0)
+ return 0;
+
+ if (size > PAGE_SIZE) {
+ int npages = min_t(size_t, size >> PAGE_SHIFT, MAX_SKB_FRAGS);
+
+ data_len = npages << PAGE_SHIFT;
+ size = data_len + (size & ~PAGE_MASK);
+ }
+ skb = alloc_skb_with_frags(size - data_len, data_len,
+ PAGE_ALLOC_COSTLY_ORDER,
+ &err, sk->sk_allocation);
+ if (!skb)
+ goto err;
+
+ skb_put(skb, size - data_len);
+ skb->data_len = data_len;
+ skb->len = size;
+
+ if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
+ goto err_free;
+ }
+
+ err = skb_copy_datagram_from_iter(skb, 0, &msg->msg_iter, size);
+ if (err)
+ goto err_free;
+
+ TCP_SKB_CB(skb)->seq = tcp_sk(sk)->rcv_nxt;
+ TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(skb)->seq + size;
+ TCP_SKB_CB(skb)->ack_seq = tcp_sk(sk)->snd_una - 1;
+
+ if (tcp_queue_rcv(sk, skb, 0, &fragstolen)) {
+ WARN_ON_ONCE(fragstolen); /* should not happen */
+ __kfree_skb(skb);
+ }
+ return size;
+
+err_free:
+ kfree_skb(skb);
+err:
+ return err;
+
+}
+
+void tcp_data_ready(struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+ int avail = tp->rcv_nxt - tp->copied_seq;
+
+ if (avail < sk->sk_rcvlowat && !sock_flag(sk, SOCK_DONE))
+ return;
+
+ sk->sk_data_ready(sk);
+}
+
+static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ bool fragstolen;
+ int eaten;
+
+ if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
+ __kfree_skb(skb);
+ return;
+ }
+ skb_dst_drop(skb);
+ __skb_pull(skb, tcp_hdr(skb)->doff * 4);
+
+ tcp_ecn_accept_cwr(sk, skb);
+
+ tp->rx_opt.dsack = 0;
+
+ /* Queue data for delivery to the user.
+ * Packets in sequence go to the receive queue.
+ * Out of sequence packets to the out_of_order_queue.
+ */
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt) {
+ if (tcp_receive_window(tp) == 0) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
+ goto out_of_window;
+ }
+
+ /* Ok. In sequence. In window. */
+queue_and_out:
+ if (skb_queue_len(&sk->sk_receive_queue) == 0)
+ sk_forced_mem_schedule(sk, skb->truesize);
+ else if (tcp_try_rmem_schedule(sk, skb, skb->truesize)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
+ goto drop;
+ }
+
+ eaten = tcp_queue_rcv(sk, skb, 0, &fragstolen);
+ if (skb->len)
+ tcp_event_data_recv(sk, skb);
+ if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
+ tcp_fin(sk);
+
+ if (!RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
+ tcp_ofo_queue(sk);
+
+ /* RFC5681. 4.2. SHOULD send immediate ACK, when
+ * gap in queue is filled.
+ */
+ if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
+ inet_csk(sk)->icsk_ack.pending |= ICSK_ACK_NOW;
+ }
+
+ if (tp->rx_opt.num_sacks)
+ tcp_sack_remove(tp);
+
+ tcp_fast_path_check(sk);
+
+ if (eaten > 0)
+ kfree_skb_partial(skb, fragstolen);
+ if (!sock_flag(sk, SOCK_DEAD))
+ tcp_data_ready(sk);
+ return;
+ }
+
+ if (!after(TCP_SKB_CB(skb)->end_seq, tp->rcv_nxt)) {
+ /* A retransmit, 2nd most common case. Force an immediate ack. */
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOST);
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq);
+
+out_of_window:
+ tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
+ inet_csk_schedule_ack(sk);
+drop:
+ tcp_drop(sk, skb);
+ return;
+ }
+
+ /* Out of window. F.e. zero window probe. */
+ if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt + tcp_receive_window(tp)))
+ goto out_of_window;
+
+ if (before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt)) {
+ /* Partial packet, seq < rcv_next < end_seq */
+ SOCK_DEBUG(sk, "partial packet: rcv_next %X seq %X - %X\n",
+ tp->rcv_nxt, TCP_SKB_CB(skb)->seq,
+ TCP_SKB_CB(skb)->end_seq);
+
+ tcp_dsack_set(sk, TCP_SKB_CB(skb)->seq, tp->rcv_nxt);
+
+ /* If window is closed, drop tail of packet. But after
+ * remembering D-SACK for its head made in previous line.
+ */
+ if (!tcp_receive_window(tp)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPZEROWINDOWDROP);
+ goto out_of_window;
+ }
+ goto queue_and_out;
+ }
+
+ tcp_data_queue_ofo(sk, skb);
+}
+
+static struct sk_buff *tcp_skb_next(struct sk_buff *skb, struct sk_buff_head *list)
+{
+ if (list)
+ return !skb_queue_is_last(list, skb) ? skb->next : NULL;
+
+ return skb_rb_next(skb);
+}
+
+static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
+ struct sk_buff_head *list,
+ struct rb_root *root)
+{
+ struct sk_buff *next = tcp_skb_next(skb, list);
+
+ if (list)
+ __skb_unlink(skb, list);
+ else
+ rb_erase(&skb->rbnode, root);
+
+ __kfree_skb(skb);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVCOLLAPSED);
+
+ return next;
+}
+
+/* Insert skb into rb tree, ordered by TCP_SKB_CB(skb)->seq */
+void tcp_rbtree_insert(struct rb_root *root, struct sk_buff *skb)
+{
+ struct rb_node **p = &root->rb_node;
+ struct rb_node *parent = NULL;
+ struct sk_buff *skb1;
+
+ while (*p) {
+ parent = *p;
+ skb1 = rb_to_skb(parent);
+ if (before(TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb1)->seq))
+ p = &parent->rb_left;
+ else
+ p = &parent->rb_right;
+ }
+ rb_link_node(&skb->rbnode, parent, p);
+ rb_insert_color(&skb->rbnode, root);
+}
+
+/* Collapse contiguous sequence of skbs head..tail with
+ * sequence numbers start..end.
+ *
+ * If tail is NULL, this means until the end of the queue.
+ *
+ * Segments with FIN/SYN are not collapsed (only because this
+ * simplifies code)
+ */
+static void
+tcp_collapse(struct sock *sk, struct sk_buff_head *list, struct rb_root *root,
+ struct sk_buff *head, struct sk_buff *tail, u32 start, u32 end)
+{
+ struct sk_buff *skb = head, *n;
+ struct sk_buff_head tmp;
+ bool end_of_skbs;
+
+ /* First, check that queue is collapsible and find
+ * the point where collapsing can be useful.
+ */
+restart:
+ for (end_of_skbs = true; skb != NULL && skb != tail; skb = n) {
+ n = tcp_skb_next(skb, list);
+
+ /* No new bits? It is possible on ofo queue. */
+ if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+ skb = tcp_collapse_one(sk, skb, list, root);
+ if (!skb)
+ break;
+ goto restart;
+ }
+
+ /* The first skb to collapse is:
+ * - not SYN/FIN and
+ * - bloated or contains data before "start" or
+ * overlaps to the next one.
+ */
+ if (!(TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)) &&
+ (tcp_win_from_space(sk, skb->truesize) > skb->len ||
+ before(TCP_SKB_CB(skb)->seq, start))) {
+ end_of_skbs = false;
+ break;
+ }
+
+ if (n && n != tail &&
+ TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(n)->seq) {
+ end_of_skbs = false;
+ break;
+ }
+
+ /* Decided to skip this, advance start seq. */
+ start = TCP_SKB_CB(skb)->end_seq;
+ }
+ if (end_of_skbs ||
+ (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
+ return;
+
+ __skb_queue_head_init(&tmp);
+
+ while (before(start, end)) {
+ int copy = min_t(int, SKB_MAX_ORDER(0, 0), end - start);
+ struct sk_buff *nskb;
+
+ nskb = alloc_skb(copy, GFP_ATOMIC);
+ if (!nskb)
+ break;
+
+ memcpy(nskb->cb, skb->cb, sizeof(skb->cb));
+#ifdef CONFIG_TLS_DEVICE
+ nskb->decrypted = skb->decrypted;
+#endif
+ TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(nskb)->end_seq = start;
+ if (list)
+ __skb_queue_before(list, skb, nskb);
+ else
+ __skb_queue_tail(&tmp, nskb); /* defer rbtree insertion */
+ skb_set_owner_r(nskb, sk);
+
+ /* Copy data, releasing collapsed skbs. */
+ while (copy > 0) {
+ int offset = start - TCP_SKB_CB(skb)->seq;
+ int size = TCP_SKB_CB(skb)->end_seq - start;
+
+ BUG_ON(offset < 0);
+ if (size > 0) {
+ size = min(copy, size);
+ if (skb_copy_bits(skb, offset, skb_put(nskb, size), size))
+ BUG();
+ TCP_SKB_CB(nskb)->end_seq += size;
+ copy -= size;
+ start += size;
+ }
+ if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
+ skb = tcp_collapse_one(sk, skb, list, root);
+ if (!skb ||
+ skb == tail ||
+ (TCP_SKB_CB(skb)->tcp_flags & (TCPHDR_SYN | TCPHDR_FIN)))
+ goto end;
+#ifdef CONFIG_TLS_DEVICE
+ if (skb->decrypted != nskb->decrypted)
+ goto end;
+#endif
+ }
+ }
+ }
+end:
+ skb_queue_walk_safe(&tmp, skb, n)
+ tcp_rbtree_insert(root, skb);
+}
+
+/* Collapse ofo queue. Algorithm: select contiguous sequence of skbs
+ * and tcp_collapse() them until all the queue is collapsed.
+ */
+static void tcp_collapse_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 range_truesize, sum_tiny = 0;
+ struct sk_buff *skb, *head;
+ u32 start, end;
+
+ skb = skb_rb_first(&tp->out_of_order_queue);
+new_range:
+ if (!skb) {
+ tp->ooo_last_skb = skb_rb_last(&tp->out_of_order_queue);
+ return;
+ }
+ start = TCP_SKB_CB(skb)->seq;
+ end = TCP_SKB_CB(skb)->end_seq;
+ range_truesize = skb->truesize;
+
+ for (head = skb;;) {
+ skb = skb_rb_next(skb);
+
+ /* Range is terminated when we see a gap or when
+ * we are at the queue end.
+ */
+ if (!skb ||
+ after(TCP_SKB_CB(skb)->seq, end) ||
+ before(TCP_SKB_CB(skb)->end_seq, start)) {
+ /* Do not attempt collapsing tiny skbs */
+ if (range_truesize != head->truesize ||
+ end - start >= SKB_WITH_OVERHEAD(SK_MEM_QUANTUM)) {
+ tcp_collapse(sk, NULL, &tp->out_of_order_queue,
+ head, skb, start, end);
+ } else {
+ sum_tiny += range_truesize;
+ if (sum_tiny > sk->sk_rcvbuf >> 3)
+ return;
+ }
+ goto new_range;
+ }
+
+ range_truesize += skb->truesize;
+ if (unlikely(before(TCP_SKB_CB(skb)->seq, start)))
+ start = TCP_SKB_CB(skb)->seq;
+ if (after(TCP_SKB_CB(skb)->end_seq, end))
+ end = TCP_SKB_CB(skb)->end_seq;
+ }
+}
+
+/*
+ * Clean the out-of-order queue to make room.
+ * We drop high sequences packets to :
+ * 1) Let a chance for holes to be filled.
+ * 2) not add too big latencies if thousands of packets sit there.
+ * (But if application shrinks SO_RCVBUF, we could still end up
+ * freeing whole queue here)
+ * 3) Drop at least 12.5 % of sk_rcvbuf to avoid malicious attacks.
+ *
+ * Return true if queue has shrunk.
+ */
+static bool tcp_prune_ofo_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct rb_node *node, *prev;
+ int goal;
+
+ if (RB_EMPTY_ROOT(&tp->out_of_order_queue))
+ return false;
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_OFOPRUNED);
+ goal = sk->sk_rcvbuf >> 3;
+ node = &tp->ooo_last_skb->rbnode;
+ do {
+ prev = rb_prev(node);
+ rb_erase(node, &tp->out_of_order_queue);
+ goal -= rb_to_skb(node)->truesize;
+ tcp_drop(sk, rb_to_skb(node));
+ if (!prev || goal <= 0) {
+ sk_mem_reclaim(sk);
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
+ !tcp_under_memory_pressure(sk))
+ break;
+ goal = sk->sk_rcvbuf >> 3;
+ }
+ node = prev;
+ } while (node);
+ tp->ooo_last_skb = rb_to_skb(prev);
+
+ /* Reset SACK state. A conforming SACK implementation will
+ * do the same at a timeout based retransmit. When a connection
+ * is in a sad state like this, we care only about integrity
+ * of the connection not performance.
+ */
+ if (tp->rx_opt.sack_ok)
+ tcp_sack_reset(&tp->rx_opt);
+ return true;
+}
+
+/* Reduce allocated memory if we can, trying to get
+ * the socket within its memory limits again.
+ *
+ * Return less than zero if we should start dropping frames
+ * until the socket owning process reads some of the data
+ * to stabilize the situation.
+ */
+static int tcp_prune_queue(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ SOCK_DEBUG(sk, "prune_queue: c=%x\n", tp->copied_seq);
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_PRUNECALLED);
+
+ if (atomic_read(&sk->sk_rmem_alloc) >= sk->sk_rcvbuf)
+ tcp_clamp_window(sk);
+ else if (tcp_under_memory_pressure(sk))
+ tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
+
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
+ return 0;
+
+ tcp_collapse_ofo_queue(sk);
+ if (!skb_queue_empty(&sk->sk_receive_queue))
+ tcp_collapse(sk, &sk->sk_receive_queue, NULL,
+ skb_peek(&sk->sk_receive_queue),
+ NULL,
+ tp->copied_seq, tp->rcv_nxt);
+ sk_mem_reclaim(sk);
+
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
+ return 0;
+
+ /* Collapsing did not help, destructive actions follow.
+ * This must not ever occur. */
+
+ tcp_prune_ofo_queue(sk);
+
+ if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
+ return 0;
+
+ /* If we are really being abused, tell the caller to silently
+ * drop receive data on the floor. It will get retransmitted
+ * and hopefully then we'll have sufficient space.
+ */
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_RCVPRUNED);
+
+ /* Massive buffer overcommit. */
+ tp->pred_flags = 0;
+ return -1;
+}
+
+static bool tcp_should_expand_sndbuf(const struct sock *sk)
+{
+ const struct tcp_sock *tp = tcp_sk(sk);
+
+ /* If the user specified a specific send buffer setting, do
+ * not modify it.
+ */
+ if (sk->sk_userlocks & SOCK_SNDBUF_LOCK)
+ return false;
+
+ /* If we are under global TCP memory pressure, do not expand. */
+ if (tcp_under_memory_pressure(sk))
+ return false;
+
+ /* If we are under soft global TCP memory pressure, do not expand. */
+ if (sk_memory_allocated(sk) >= sk_prot_mem_limits(sk, 0))
+ return false;
+
+ /* If we filled the congestion window, do not expand. */
+ if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
+ return false;
+
+ return true;
+}
+
+/* When incoming ACK allowed to free some skb from write_queue,
+ * we remember this event in flag SOCK_QUEUE_SHRUNK and wake up socket
+ * on the exit from tcp input handler.
+ *
+ * PROBLEM: sndbuf expansion does not work well with largesend.
+ */
+static void tcp_new_space(struct sock *sk)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ if (tcp_should_expand_sndbuf(sk)) {
+ tcp_sndbuf_expand(sk);
+ tp->snd_cwnd_stamp = tcp_jiffies32;
+ }
+
+ sk->sk_write_space(sk);
+}
+
+static void tcp_check_space(struct sock *sk)
+{
+ if (sock_flag(sk, SOCK_QUEUE_SHRUNK)) {
+ sock_reset_flag(sk, SOCK_QUEUE_SHRUNK);
+ /* pairs with tcp_poll() */
+ smp_mb();
+ if (sk->sk_socket &&
+ test_bit(SOCK_NOSPACE, &sk->sk_socket->flags)) {
+ tcp_new_space(sk);
+ if (!test_bit(SOCK_NOSPACE, &sk->sk_socket->flags))
+ tcp_chrono_stop(sk, TCP_CHRONO_SNDBUF_LIMITED);
+ }
+ }
+}
+
+static inline void tcp_data_snd_check(struct sock *sk)
+{
+ tcp_push_pending_frames(sk);
+ tcp_check_space(sk);
+}
+
+/*
+ * Check if sending an ack is needed.
+ */
+static void __tcp_ack_snd_check(struct sock *sk, int ofo_possible)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ unsigned long rtt, delay;
+
+ /* More than one full frame received... */
+ if (((tp->rcv_nxt - tp->rcv_wup) > inet_csk(sk)->icsk_ack.rcv_mss &&
+ /* ... and right edge of window advances far enough.
+ * (tcp_recvmsg() will send ACK otherwise).
+ * If application uses SO_RCVLOWAT, we want send ack now if
+ * we have not received enough bytes to satisfy the condition.
+ */
+ (tp->rcv_nxt - tp->copied_seq < sk->sk_rcvlowat ||
+ __tcp_select_window(sk) >= tp->rcv_wnd)) ||
+ /* We ACK each frame or... */
+ tcp_in_quickack_mode(sk) ||
+ /* Protocol state mandates a one-time immediate ACK */
+ inet_csk(sk)->icsk_ack.pending & ICSK_ACK_NOW) {
+send_now:
+ tcp_send_ack(sk);
+ return;
+ }
+
+ if (!ofo_possible || RB_EMPTY_ROOT(&tp->out_of_order_queue)) {
+ tcp_send_delayed_ack(sk);
+ return;
+ }
+
+ if (!tcp_is_sack(tp) ||
+ tp->compressed_ack >= sock_net(sk)->ipv4.sysctl_tcp_comp_sack_nr)
+ goto send_now;
+
+ if (tp->compressed_ack_rcv_nxt != tp->rcv_nxt) {
+ tp->compressed_ack_rcv_nxt = tp->rcv_nxt;
+ if (tp->compressed_ack > TCP_FASTRETRANS_THRESH)
+ NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
+ tp->compressed_ack - TCP_FASTRETRANS_THRESH);
+ tp->compressed_ack = 0;
+ }
+
+ if (++tp->compressed_ack <= TCP_FASTRETRANS_THRESH)
+ goto send_now;
+
+ if (hrtimer_is_queued(&tp->compressed_ack_timer))
+ return;
+
+ /* compress ack timer : 5 % of rtt, but no more than tcp_comp_sack_delay_ns */
+
+ rtt = tp->rcv_rtt_est.rtt_us;
+ if (tp->srtt_us && tp->srtt_us < rtt)
+ rtt = tp->srtt_us;
+
+ delay = min_t(unsigned long, sock_net(sk)->ipv4.sysctl_tcp_comp_sack_delay_ns,
+ rtt * (NSEC_PER_USEC >> 3)/20);
+ sock_hold(sk);
+ hrtimer_start(&tp->compressed_ack_timer, ns_to_ktime(delay),
+ HRTIMER_MODE_REL_PINNED_SOFT);
+}
+
+static inline void tcp_ack_snd_check(struct sock *sk)
+{
+ if (!inet_csk_ack_scheduled(sk)) {
+ /* We sent a data segment already. */
+ return;
+ }
+ __tcp_ack_snd_check(sk, 1);
+}
+
+/*
+ * This routine is only called when we have urgent data
+ * signaled. Its the 'slow' part of tcp_urg. It could be
+ * moved inline now as tcp_urg is only called from one
+ * place. We handle URGent data wrong. We have to - as
+ * BSD still doesn't use the correction from RFC961.
+ * For 1003.1g we should support a new option TCP_STDURG to permit
+ * either form (or just set the sysctl tcp_stdurg).
+ */
+
+static void tcp_check_urg(struct sock *sk, const struct tcphdr *th)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ u32 ptr = ntohs(th->urg_ptr);
+
+ if (ptr && !sock_net(sk)->ipv4.sysctl_tcp_stdurg)
+ ptr--;
+ ptr += ntohl(th->seq);
+
+ /* Ignore urgent data that we've already seen and read. */
+ if (after(tp->copied_seq, ptr))
+ return;
+
+ /* Do not replay urg ptr.
+ *
+ * NOTE: interesting situation not covered by specs.
+ * Misbehaving sender may send urg ptr, pointing to segment,
+ * which we already have in ofo queue. We are not able to fetch
+ * such data and will stay in TCP_URG_NOTYET until will be eaten
+ * by recvmsg(). Seems, we are not obliged to handle such wicked
+ * situations. But it is worth to think about possibility of some
+ * DoSes using some hypothetical application level deadlock.
+ */
+ if (before(ptr, tp->rcv_nxt))
+ return;
+
+ /* Do we already have a newer (or duplicate) urgent pointer? */
+ if (tp->urg_data && !after(ptr, tp->urg_seq))
+ return;
+
+ /* Tell the world about our new urgent pointer. */
+ sk_send_sigurg(sk);
+
+ /* We may be adding urgent data when the last byte read was
+ * urgent. To do this requires some care. We cannot just ignore
+ * tp->copied_seq since we would read the last urgent byte again
+ * as data, nor can we alter copied_seq until this data arrives
+ * or we break the semantics of SIOCATMARK (and thus sockatmark())
+ *
+ * NOTE. Double Dutch. Rendering to plain English: author of comment
+ * above did something sort of send("A", MSG_OOB); send("B", MSG_OOB);
+ * and expect that both A and B disappear from stream. This is _wrong_.
+ * Though this happens in BSD with high probability, this is occasional.
+ * Any application relying on this is buggy. Note also, that fix "works"
+ * only in this artificial test. Insert some normal data between A and B and we will
+ * decline of BSD again. Verdict: it is better to remove to trap
+ * buggy users.
+ */
+ if (tp->urg_seq == tp->copied_seq && tp->urg_data &&
+ !sock_flag(sk, SOCK_URGINLINE) && tp->copied_seq != tp->rcv_nxt) {
+ struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
+ tp->copied_seq++;
+ if (skb && !before(tp->copied_seq, TCP_SKB_CB(skb)->end_seq)) {
+ __skb_unlink(skb, &sk->sk_receive_queue);
+ __kfree_skb(skb);
+ }
+ }
+
+ tp->urg_data = TCP_URG_NOTYET;
+ tp->urg_seq = ptr;
+
+ /* Disable header prediction. */
+ tp->pred_flags = 0;
+}
+
+/* This is the 'fast' part of urgent handling. */
+static void tcp_urg(struct sock *sk, struct sk_buff *skb, const struct tcphdr *th)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ /* Check if we get a new urgent pointer - normally not. */
+ if (th->urg)
+ tcp_check_urg(sk, th);
+
+ /* Do we wait for any urgent data? - normally not... */
+ if (tp->urg_data == TCP_URG_NOTYET) {
+ u32 ptr = tp->urg_seq - ntohl(th->seq) + (th->doff * 4) -
+ th->syn;
+
+ /* Is the urgent pointer pointing into this packet? */
+ if (ptr < skb->len) {
+ u8 tmp;
+ if (skb_copy_bits(skb, ptr, &tmp, 1))
+ BUG();
+ tp->urg_data = TCP_URG_VALID | tmp;
+ if (!sock_flag(sk, SOCK_DEAD))
+ sk->sk_data_ready(sk);
+ }
+ }
+}
+
+/* Accept RST for rcv_nxt - 1 after a FIN.
+ * When tcp connections are abruptly terminated from Mac OSX (via ^C), a
+ * FIN is sent followed by a RST packet. The RST is sent with the same
+ * sequence number as the FIN, and thus according to RFC 5961 a challenge
+ * ACK should be sent. However, Mac OSX rate limits replies to challenge
+ * ACKs on the closed socket. In addition middleboxes can drop either the
+ * challenge ACK or a subsequent RST.
+ */
+static bool tcp_reset_check(const struct sock *sk, const struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+
+ return unlikely(TCP_SKB_CB(skb)->seq == (tp->rcv_nxt - 1) &&
+ (1 << sk->sk_state) & (TCPF_CLOSE_WAIT | TCPF_LAST_ACK |
+ TCPF_CLOSING));
+}
+
+/* Does PAWS and seqno based validation of an incoming segment, flags will
+ * play significant role here.
+ */
+static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th, int syn_inerr)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ bool rst_seq_match = false;
+
+ /* RFC1323: H1. Apply PAWS check first. */
+ if (tcp_fast_parse_options(sock_net(sk), skb, th, tp) &&
+ tp->rx_opt.saw_tstamp &&
+ tcp_paws_discard(sk, skb)) {
+ if (!th->rst) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_PAWSESTABREJECTED);
+ if (!tcp_oow_rate_limited(sock_net(sk), skb,
+ LINUX_MIB_TCPACKSKIPPEDPAWS,
+ &tp->last_oow_ack_time))
+ tcp_send_dupack(sk, skb);
+ goto discard;
+ }
+ /* Reset is accepted even if it did not pass PAWS. */
+ }
+
+ /* Step 1: check sequence number */
+ if (!tcp_sequence(tp, TCP_SKB_CB(skb)->seq, TCP_SKB_CB(skb)->end_seq)) {
+ /* RFC793, page 37: "In all states except SYN-SENT, all reset
+ * (RST) segments are validated by checking their SEQ-fields."
+ * And page 69: "If an incoming segment is not acceptable,
+ * an acknowledgment should be sent in reply (unless the RST
+ * bit is set, if so drop the segment and return)".
+ */
+ if (!th->rst) {
+ if (th->syn)
+ goto syn_challenge;
+ if (!tcp_oow_rate_limited(sock_net(sk), skb,
+ LINUX_MIB_TCPACKSKIPPEDSEQ,
+ &tp->last_oow_ack_time))
+ tcp_send_dupack(sk, skb);
+ } else if (tcp_reset_check(sk, skb)) {
+ tcp_reset(sk);
+ }
+ goto discard;
+ }
+
+ /* Step 2: check RST bit */
+ if (th->rst) {
+ /* RFC 5961 3.2 (extend to match against (RCV.NXT - 1) after a
+ * FIN and SACK too if available):
+ * If seq num matches RCV.NXT or (RCV.NXT - 1) after a FIN, or
+ * the right-most SACK block,
+ * then
+ * RESET the connection
+ * else
+ * Send a challenge ACK
+ */
+ if (TCP_SKB_CB(skb)->seq == tp->rcv_nxt ||
+ tcp_reset_check(sk, skb)) {
+ rst_seq_match = true;
+ } else if (tcp_is_sack(tp) && tp->rx_opt.num_sacks > 0) {
+ struct tcp_sack_block *sp = &tp->selective_acks[0];
+ int max_sack = sp[0].end_seq;
+ int this_sack;
+
+ for (this_sack = 1; this_sack < tp->rx_opt.num_sacks;
+ ++this_sack) {
+ max_sack = after(sp[this_sack].end_seq,
+ max_sack) ?
+ sp[this_sack].end_seq : max_sack;
+ }
+
+ if (TCP_SKB_CB(skb)->seq == max_sack)
+ rst_seq_match = true;
+ }
+
+ if (rst_seq_match)
+ tcp_reset(sk);
+ else {
+ /* Disable TFO if RST is out-of-order
+ * and no data has been received
+ * for current active TFO socket
+ */
+ if (tp->syn_fastopen && !tp->data_segs_in &&
+ sk->sk_state == TCP_ESTABLISHED)
+ tcp_fastopen_active_disable(sk);
+ tcp_send_challenge_ack(sk, skb);
+ }
+ goto discard;
+ }
+
+ /* step 3: check security and precedence [ignored] */
+
+ /* step 4: Check for a SYN
+ * RFC 5961 4.2 : Send a challenge ack
+ */
+ if (th->syn) {
+syn_challenge:
+ if (syn_inerr)
+ TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);
+ tcp_send_challenge_ack(sk, skb);
+ goto discard;
+ }
+
+ return true;
+
+discard:
+ tcp_drop(sk, skb);
+ return false;
+}
+
+/*
+ * TCP receive function for the ESTABLISHED state.
+ *
+ * It is split into a fast path and a slow path. The fast path is
+ * disabled when:
+ * - A zero window was announced from us - zero window probing
+ * is only handled properly in the slow path.
+ * - Out of order segments arrived.
+ * - Urgent data is expected.
+ * - There is no buffer space left
+ * - Unexpected TCP flags/window values/header lengths are received
+ * (detected by checking the TCP header against pred_flags)
+ * - Data is sent in both directions. Fast path only supports pure senders
+ * or pure receivers (this means either the sequence number or the ack
+ * value must stay constant)
+ * - Unexpected TCP option.
+ *
+ * When these conditions are not satisfied it drops into a standard
+ * receive procedure patterned after RFC793 to handle all cases.
+ * The first three cases are guaranteed by proper pred_flags setting,
+ * the rest is checked inline. Fast processing is turned on in
+ * tcp_data_queue when everything is OK.
+ */
+void tcp_rcv_established(struct sock *sk, struct sk_buff *skb)
+{
+ const struct tcphdr *th = (const struct tcphdr *)skb->data;
+ struct tcp_sock *tp = tcp_sk(sk);
+ unsigned int len = skb->len;
+
+ /* TCP congestion window tracking */
+ trace_tcp_probe(sk, skb);
+
+ tcp_mstamp_refresh(tp);
+ if (unlikely(!sk->sk_rx_dst))
+ inet_csk(sk)->icsk_af_ops->sk_rx_dst_set(sk, skb);
+ /*
+ * Header prediction.
+ * The code loosely follows the one in the famous
+ * "30 instruction TCP receive" Van Jacobson mail.
+ *
+ * Van's trick is to deposit buffers into socket queue
+ * on a device interrupt, to call tcp_recv function
+ * on the receive process context and checksum and copy
+ * the buffer to user space. smart...
+ *
+ * Our current scheme is not silly either but we take the
+ * extra cost of the net_bh soft interrupt processing...
+ * We do checksum and copy also but from device to kernel.
+ */
+
+ tp->rx_opt.saw_tstamp = 0;
+
+ /* pred_flags is 0xS?10 << 16 + snd_wnd
+ * if header_prediction is to be made
+ * 'S' will always be tp->tcp_header_len >> 2
+ * '?' will be 0 for the fast path, otherwise pred_flags is 0 to
+ * turn it off (when there are holes in the receive
+ * space for instance)
+ * PSH flag is ignored.
+ */
+
+ if ((tcp_flag_word(th) & TCP_HP_BITS) == tp->pred_flags &&
+ TCP_SKB_CB(skb)->seq == tp->rcv_nxt &&
+ !after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
+ int tcp_header_len = tp->tcp_header_len;
+
+ /* Timestamp header prediction: tcp_header_len
+ * is automatically equal to th->doff*4 due to pred_flags
+ * match.
+ */
+
+ /* Check timestamp */
+ if (tcp_header_len == sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) {
+ /* No? Slow path! */
+ if (!tcp_parse_aligned_timestamp(tp, th))
+ goto slow_path;
+
+ /* If PAWS failed, check it more carefully in slow path */
+ if ((s32)(tp->rx_opt.rcv_tsval - tp->rx_opt.ts_recent) < 0)
+ goto slow_path;
+
+ /* DO NOT update ts_recent here, if checksum fails
+ * and timestamp was corrupted part, it will result
+ * in a hung connection since we will drop all
+ * future packets due to the PAWS test.
+ */
+ }
+
+ if (len <= tcp_header_len) {
+ /* Bulk data transfer: sender */
+ if (len == tcp_header_len) {
+ /* Predicted packet is in window by definition.
+ * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+ * Hence, check seq<=rcv_wup reduces to:
+ */
+ if (tcp_header_len ==
+ (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
+ tp->rcv_nxt == tp->rcv_wup)
+ tcp_store_ts_recent(tp);
+
+ /* We know that such packets are checksummed
+ * on entry.
+ */
+ tcp_ack(sk, skb, 0);
+ __kfree_skb(skb);
+ tcp_data_snd_check(sk);
+ /* When receiving pure ack in fast path, update
+ * last ts ecr directly instead of calling
+ * tcp_rcv_rtt_measure_ts()
+ */
+ tp->rcv_rtt_last_tsecr = tp->rx_opt.rcv_tsecr;
+ return;
+ } else { /* Header too small */
+ TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+ goto discard;
+ }
+ } else {
+ int eaten = 0;
+ bool fragstolen = false;
+
+ if (tcp_checksum_complete(skb))
+ goto csum_error;
+
+ if ((int)skb->truesize > sk->sk_forward_alloc)
+ goto step5;
+
+ /* Predicted packet is in window by definition.
+ * seq == rcv_nxt and rcv_wup <= rcv_nxt.
+ * Hence, check seq<=rcv_wup reduces to:
+ */
+ if (tcp_header_len ==
+ (sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED) &&
+ tp->rcv_nxt == tp->rcv_wup)
+ tcp_store_ts_recent(tp);
+
+ tcp_rcv_rtt_measure_ts(sk, skb);
+
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPHPHITS);
+
+ /* Bulk data transfer: receiver */
+ eaten = tcp_queue_rcv(sk, skb, tcp_header_len,
+ &fragstolen);
+
+ tcp_event_data_recv(sk, skb);
+
+ if (TCP_SKB_CB(skb)->ack_seq != tp->snd_una) {
+ /* Well, only one small jumplet in fast path... */
+ tcp_ack(sk, skb, FLAG_DATA);
+ tcp_data_snd_check(sk);
+ if (!inet_csk_ack_scheduled(sk))
+ goto no_ack;
+ }
+
+ __tcp_ack_snd_check(sk, 0);
+no_ack:
+ if (eaten)
+ kfree_skb_partial(skb, fragstolen);
+ tcp_data_ready(sk);
+ return;
+ }
+ }
+
+slow_path:
+ if (len < (th->doff << 2) || tcp_checksum_complete(skb))
+ goto csum_error;
+
+ if (!th->ack && !th->rst && !th->syn)
+ goto discard;
+
+ /*
+ * Standard slow path.
+ */
+
+ if (!tcp_validate_incoming(sk, skb, th, 1))
+ return;
+
+step5:
+ if (tcp_ack(sk, skb, FLAG_SLOWPATH | FLAG_UPDATE_TS_RECENT) < 0)
+ goto discard;
+
+ tcp_rcv_rtt_measure_ts(sk, skb);
+
+ /* Process urgent data. */
+ tcp_urg(sk, skb, th);
+
+ /* step 7: process the segment text */
+ tcp_data_queue(sk, skb);
+
+ tcp_data_snd_check(sk);
+ tcp_ack_snd_check(sk);
+ return;
+
+csum_error:
+ TCP_INC_STATS(sock_net(sk), TCP_MIB_CSUMERRORS);
+ TCP_INC_STATS(sock_net(sk), TCP_MIB_INERRS);
+
+discard:
+ tcp_drop(sk, skb);
+}
+EXPORT_SYMBOL(tcp_rcv_established);
+
+void tcp_finish_connect(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ tcp_set_state(sk, TCP_ESTABLISHED);
+ icsk->icsk_ack.lrcvtime = tcp_jiffies32;
+
+ if (skb) {
+ icsk->icsk_af_ops->sk_rx_dst_set(sk, skb);
+ security_inet_conn_established(sk, skb);
+ sk_mark_napi_id(sk, skb);
+ }
+
+ tcp_init_transfer(sk, BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB);
+
+ /* Prevent spurious tcp_cwnd_restart() on first data
+ * packet.
+ */
+ tp->lsndtime = tcp_jiffies32;
+
+ if (sock_flag(sk, SOCK_KEEPOPEN))
+ inet_csk_reset_keepalive_timer(sk, keepalive_time_when(tp));
+
+ if (!tp->rx_opt.snd_wscale)
+ __tcp_fast_path_on(tp, tp->snd_wnd);
+ else
+ tp->pred_flags = 0;
+}
+
+static bool tcp_rcv_fastopen_synack(struct sock *sk, struct sk_buff *synack,
+ struct tcp_fastopen_cookie *cookie)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct sk_buff *data = tp->syn_data ? tcp_rtx_queue_head(sk) : NULL;
+ u16 mss = tp->rx_opt.mss_clamp, try_exp = 0;
+ bool syn_drop = false;
+
+ if (mss == tp->rx_opt.user_mss) {
+ struct tcp_options_received opt;
+
+ /* Get original SYNACK MSS value if user MSS sets mss_clamp */
+ tcp_clear_options(&opt);
+ opt.user_mss = opt.mss_clamp = 0;
+ tcp_parse_options(sock_net(sk), synack, &opt, 0, NULL);
+ mss = opt.mss_clamp;
+ }
+
+ if (!tp->syn_fastopen) {
+ /* Ignore an unsolicited cookie */
+ cookie->len = -1;
+ } else if (tp->total_retrans) {
+ /* SYN timed out and the SYN-ACK neither has a cookie nor
+ * acknowledges data. Presumably the remote received only
+ * the retransmitted (regular) SYNs: either the original
+ * SYN-data or the corresponding SYN-ACK was dropped.
+ */
+ syn_drop = (cookie->len < 0 && data);
+ } else if (cookie->len < 0 && !tp->syn_data) {
+ /* We requested a cookie but didn't get it. If we did not use
+ * the (old) exp opt format then try so next time (try_exp=1).
+ * Otherwise we go back to use the RFC7413 opt (try_exp=2).
+ */
+ try_exp = tp->syn_fastopen_exp ? 2 : 1;
+ }
+
+ tcp_fastopen_cache_set(sk, mss, cookie, syn_drop, try_exp);
+
+ if (data) { /* Retransmit unacked data in SYN */
+ skb_rbtree_walk_from(data) {
+ if (__tcp_retransmit_skb(sk, data, 1))
+ break;
+ }
+ tcp_rearm_rto(sk);
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_TCPFASTOPENACTIVEFAIL);
+ return true;
+ }
+ tp->syn_data_acked = tp->syn_data;
+ if (tp->syn_data_acked) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPFASTOPENACTIVE);
+ /* SYN-data is counted as two separate packets in tcp_ack() */
+ if (tp->delivered > 1)
+ --tp->delivered;
+ }
+
+ tcp_fastopen_add_skb(sk, synack);
+
+ return false;
+}
+
+static void smc_check_reset_syn(struct tcp_sock *tp)
+{
+#if IS_ENABLED(CONFIG_SMC)
+ if (static_branch_unlikely(&tcp_have_smc)) {
+ if (tp->syn_smc && !tp->rx_opt.smc_ok)
+ tp->syn_smc = 0;
+ }
+#endif
+}
+
+static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
+ const struct tcphdr *th)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct tcp_fastopen_cookie foc = { .len = -1 };
+ int saved_clamp = tp->rx_opt.mss_clamp;
+ bool fastopen_fail;
+
+ tcp_parse_options(sock_net(sk), skb, &tp->rx_opt, 0, &foc);
+ if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
+ tp->rx_opt.rcv_tsecr -= tp->tsoffset;
+
+ if (th->ack) {
+ /* rfc793:
+ * "If the state is SYN-SENT then
+ * first check the ACK bit
+ * If the ACK bit is set
+ * If SEG.ACK =< ISS, or SEG.ACK > SND.NXT, send
+ * a reset (unless the RST bit is set, if so drop
+ * the segment and return)"
+ */
+ if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
+ after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
+ goto reset_and_undo;
+
+ if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
+ !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
+ tcp_time_stamp(tp))) {
+ NET_INC_STATS(sock_net(sk),
+ LINUX_MIB_PAWSACTIVEREJECTED);
+ goto reset_and_undo;
+ }
+
+ /* Now ACK is acceptable.
+ *
+ * "If the RST bit is set
+ * If the ACK was acceptable then signal the user "error:
+ * connection reset", drop the segment, enter CLOSED state,
+ * delete TCB, and return."
+ */
+
+ if (th->rst) {
+ tcp_reset(sk);
+ goto discard;
+ }
+
+ /* rfc793:
+ * "fifth, if neither of the SYN or RST bits is set then
+ * drop the segment and return."
+ *
+ * See note below!
+ * --ANK(990513)
+ */
+ if (!th->syn)
+ goto discard_and_undo;
+
+ /* rfc793:
+ * "If the SYN bit is on ...
+ * are acceptable then ...
+ * (our SYN has been ACKed), change the connection
+ * state to ESTABLISHED..."
+ */
+
+ tcp_ecn_rcv_synack(tp, th);
+
+ tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
+ tcp_ack(sk, skb, FLAG_SLOWPATH);
+
+ /* Ok.. it's good. Set up sequence numbers and
+ * move to established.
+ */
+ tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+ tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+
+ /* RFC1323: The window in SYN & SYN/ACK segments is
+ * never scaled.
+ */
+ tp->snd_wnd = ntohs(th->window);
+
+ if (!tp->rx_opt.wscale_ok) {
+ tp->rx_opt.snd_wscale = tp->rx_opt.rcv_wscale = 0;
+ tp->window_clamp = min(tp->window_clamp, 65535U);
+ }
+
+ if (tp->rx_opt.saw_tstamp) {
+ tp->rx_opt.tstamp_ok = 1;
+ tp->tcp_header_len =
+ sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
+ tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
+ tcp_store_ts_recent(tp);
+ } else {
+ tp->tcp_header_len = sizeof(struct tcphdr);
+ }
+
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ tcp_initialize_rcv_mss(sk);
+
+ /* Remember, tcp_poll() does not lock socket!
+ * Change state from SYN-SENT only after copied_seq
+ * is initialized. */
+ tp->copied_seq = tp->rcv_nxt;
+
+ smc_check_reset_syn(tp);
+
+ smp_mb();
+
+ tcp_finish_connect(sk, skb);
+
+ fastopen_fail = (tp->syn_fastopen || tp->syn_data) &&
+ tcp_rcv_fastopen_synack(sk, skb, &foc);
+
+ if (!sock_flag(sk, SOCK_DEAD)) {
+ sk->sk_state_change(sk);
+ sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
+ }
+ if (fastopen_fail)
+ return -1;
+ if (sk->sk_write_pending ||
+ icsk->icsk_accept_queue.rskq_defer_accept ||
+ icsk->icsk_ack.pingpong) {
+ /* Save one ACK. Data will be ready after
+ * several ticks, if write_pending is set.
+ *
+ * It may be deleted, but with this feature tcpdumps
+ * look so _wonderfully_ clever, that I was not able
+ * to stand against the temptation 8) --ANK
+ */
+ inet_csk_schedule_ack(sk);
+ tcp_enter_quickack_mode(sk, TCP_MAX_QUICKACKS);
+ inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
+ TCP_DELACK_MAX, TCP_RTO_MAX);
+
+discard:
+ tcp_drop(sk, skb);
+ return 0;
+ } else {
+ tcp_send_ack(sk);
+ }
+ return -1;
+ }
+
+ /* No ACK in the segment */
+
+ if (th->rst) {
+ /* rfc793:
+ * "If the RST bit is set
+ *
+ * Otherwise (no ACK) drop the segment and return."
+ */
+
+ goto discard_and_undo;
+ }
+
+ /* PAWS check. */
+ if (tp->rx_opt.ts_recent_stamp && tp->rx_opt.saw_tstamp &&
+ tcp_paws_reject(&tp->rx_opt, 0))
+ goto discard_and_undo;
+
+ if (th->syn) {
+ /* We see SYN without ACK. It is attempt of
+ * simultaneous connect with crossed SYNs.
+ * Particularly, it can be connect to self.
+ */
+ tcp_set_state(sk, TCP_SYN_RECV);
+
+ if (tp->rx_opt.saw_tstamp) {
+ tp->rx_opt.tstamp_ok = 1;
+ tcp_store_ts_recent(tp);
+ tp->tcp_header_len =
+ sizeof(struct tcphdr) + TCPOLEN_TSTAMP_ALIGNED;
+ } else {
+ tp->tcp_header_len = sizeof(struct tcphdr);
+ }
+
+ tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+ tp->copied_seq = tp->rcv_nxt;
+ tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
+
+ /* RFC1323: The window in SYN & SYN/ACK segments is
+ * never scaled.
+ */
+ tp->snd_wnd = ntohs(th->window);
+ tp->snd_wl1 = TCP_SKB_CB(skb)->seq;
+ tp->max_window = tp->snd_wnd;
+
+ tcp_ecn_rcv_syn(tp, th);
+
+ tcp_mtup_init(sk);
+ tcp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+ tcp_initialize_rcv_mss(sk);
+
+ tcp_send_synack(sk);
+#if 0
+ /* Note, we could accept data and URG from this segment.
+ * There are no obstacles to make this (except that we must
+ * either change tcp_recvmsg() to prevent it from returning data
+ * before 3WHS completes per RFC793, or employ TCP Fast Open).
+ *
+ * However, if we ignore data in ACKless segments sometimes,
+ * we have no reasons to accept it sometimes.
+ * Also, seems the code doing it in step6 of tcp_rcv_state_process
+ * is not flawless. So, discard packet for sanity.
+ * Uncomment this return to process the data.
+ */
+ return -1;
+#else
+ goto discard;
+#endif
+ }
+ /* "fifth, if neither of the SYN or RST bits is set then
+ * drop the segment and return."
+ */
+
+discard_and_undo:
+ tcp_clear_options(&tp->rx_opt);
+ tp->rx_opt.mss_clamp = saved_clamp;
+ goto discard;
+
+reset_and_undo:
+ tcp_clear_options(&tp->rx_opt);
+ tp->rx_opt.mss_clamp = saved_clamp;
+ return 1;
+}
+
+/*
+ * This function implements the receiving procedure of RFC 793 for
+ * all states except ESTABLISHED and TIME_WAIT.
+ * It's called from both tcp_v4_rcv and tcp_v6_rcv and should be
+ * address independent.
+ */
+
+int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct inet_connection_sock *icsk = inet_csk(sk);
+ const struct tcphdr *th = tcp_hdr(skb);
+ struct request_sock *req;
+ int queued = 0;
+ bool acceptable;
+
+ switch (sk->sk_state) {
+ case TCP_CLOSE:
+ goto discard;
+
+ case TCP_LISTEN:
+ if (th->ack)
+ return 1;
+
+ if (th->rst)
+ goto discard;
+
+ if (th->syn) {
+ if (th->fin)
+ goto discard;
+ /* It is possible that we process SYN packets from backlog,
+ * so we need to make sure to disable BH and RCU right there.
+ */
+ rcu_read_lock();
+ local_bh_disable();
+ acceptable = icsk->icsk_af_ops->conn_request(sk, skb) >= 0;
+ local_bh_enable();
+ rcu_read_unlock();
+
+ if (!acceptable)
+ return 1;
+ consume_skb(skb);
+ return 0;
+ }
+ goto discard;
+
+ case TCP_SYN_SENT:
+ tp->rx_opt.saw_tstamp = 0;
+ tcp_mstamp_refresh(tp);
+ queued = tcp_rcv_synsent_state_process(sk, skb, th);
+ if (queued >= 0)
+ return queued;
+
+ /* Do step6 onward by hand. */
+ tcp_urg(sk, skb, th);
+ __kfree_skb(skb);
+ tcp_data_snd_check(sk);
+ return 0;
+ }
+
+ tcp_mstamp_refresh(tp);
+ tp->rx_opt.saw_tstamp = 0;
+ req = tp->fastopen_rsk;
+ if (req) {
+ bool req_stolen;
+
+ WARN_ON_ONCE(sk->sk_state != TCP_SYN_RECV &&
+ sk->sk_state != TCP_FIN_WAIT1);
+
+ if (!tcp_check_req(sk, skb, req, true, &req_stolen))
+ goto discard;
+ }
+
+ if (!th->ack && !th->rst && !th->syn)
+ goto discard;
+
+ if (!tcp_validate_incoming(sk, skb, th, 0))
+ return 0;
+
+ /* step 5: check the ACK field */
+ acceptable = tcp_ack(sk, skb, FLAG_SLOWPATH |
+ FLAG_UPDATE_TS_RECENT |
+ FLAG_NO_CHALLENGE_ACK) > 0;
+
+ if (!acceptable) {
+ if (sk->sk_state == TCP_SYN_RECV)
+ return 1; /* send one RST */
+ tcp_send_challenge_ack(sk, skb);
+ goto discard;
+ }
+ switch (sk->sk_state) {
+ case TCP_SYN_RECV:
+ tp->delivered++; /* SYN-ACK delivery isn't tracked in tcp_ack */
+ if (!tp->srtt_us)
+ tcp_synack_rtt_meas(sk, req);
+
+ /* Once we leave TCP_SYN_RECV, we no longer need req
+ * so release it.
+ */
+ if (req) {
+ inet_csk(sk)->icsk_retransmits = 0;
+ reqsk_fastopen_remove(sk, req, false);
+ /* Re-arm the timer because data may have been sent out.
+ * This is similar to the regular data transmission case
+ * when new data has just been ack'ed.
+ *
+ * (TFO) - we could try to be more aggressive and
+ * retransmitting any data sooner based on when they
+ * are sent out.
+ */
+ tcp_rearm_rto(sk);
+ } else {
+ tcp_init_transfer(sk, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB);
+ tp->copied_seq = tp->rcv_nxt;
+ }
+ smp_mb();
+ tcp_set_state(sk, TCP_ESTABLISHED);
+ sk->sk_state_change(sk);
+
+ /* Note, that this wakeup is only for marginal crossed SYN case.
+ * Passively open sockets are not waked up, because
+ * sk->sk_sleep == NULL and sk->sk_socket == NULL.
+ */
+ if (sk->sk_socket)
+ sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
+
+ tp->snd_una = TCP_SKB_CB(skb)->ack_seq;
+ tp->snd_wnd = ntohs(th->window) << tp->rx_opt.snd_wscale;
+ tcp_init_wl(tp, TCP_SKB_CB(skb)->seq);
+
+ if (tp->rx_opt.tstamp_ok)
+ tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
+
+ if (!inet_csk(sk)->icsk_ca_ops->cong_control)
+ tcp_update_pacing_rate(sk);
+
+ /* Prevent spurious tcp_cwnd_restart() on first data packet */
+ tp->lsndtime = tcp_jiffies32;
+
+ tcp_initialize_rcv_mss(sk);
+ tcp_fast_path_on(tp);
+ break;
+
+ case TCP_FIN_WAIT1: {
+ int tmo;
+
+ /* If we enter the TCP_FIN_WAIT1 state and we are a
+ * Fast Open socket and this is the first acceptable
+ * ACK we have received, this would have acknowledged
+ * our SYNACK so stop the SYNACK timer.
+ */
+ if (req) {
+ /* We no longer need the request sock. */
+ reqsk_fastopen_remove(sk, req, false);
+ tcp_rearm_rto(sk);
+ }
+ if (tp->snd_una != tp->write_seq)
+ break;
+
+ tcp_set_state(sk, TCP_FIN_WAIT2);
+ sk->sk_shutdown |= SEND_SHUTDOWN;
+
+ sk_dst_confirm(sk);
+
+ if (!sock_flag(sk, SOCK_DEAD)) {
+ /* Wake up lingering close() */
+ sk->sk_state_change(sk);
+ break;
+ }
+
+ if (tp->linger2 < 0) {
+ tcp_done(sk);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ return 1;
+ }
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
+ /* Receive out of order FIN after close() */
+ if (tp->syn_fastopen && th->fin)
+ tcp_fastopen_active_disable(sk);
+ tcp_done(sk);
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ return 1;
+ }
+
+ tmo = tcp_fin_time(sk);
+ if (tmo > TCP_TIMEWAIT_LEN) {
+ inet_csk_reset_keepalive_timer(sk, tmo - TCP_TIMEWAIT_LEN);
+ } else if (th->fin || sock_owned_by_user(sk)) {
+ /* Bad case. We could lose such FIN otherwise.
+ * It is not a big problem, but it looks confusing
+ * and not so rare event. We still can lose it now,
+ * if it spins in bh_lock_sock(), but it is really
+ * marginal case.
+ */
+ inet_csk_reset_keepalive_timer(sk, tmo);
+ } else {
+ tcp_time_wait(sk, TCP_FIN_WAIT2, tmo);
+ goto discard;
+ }
+ break;
+ }
+
+ case TCP_CLOSING:
+ if (tp->snd_una == tp->write_seq) {
+ tcp_time_wait(sk, TCP_TIME_WAIT, 0);
+ goto discard;
+ }
+ break;
+
+ case TCP_LAST_ACK:
+ if (tp->snd_una == tp->write_seq) {
+ tcp_update_metrics(sk);
+ tcp_done(sk);
+ goto discard;
+ }
+ break;
+ }
+
+ /* step 6: check the URG bit */
+ tcp_urg(sk, skb, th);
+
+ /* step 7: process the segment text */
+ switch (sk->sk_state) {
+ case TCP_CLOSE_WAIT:
+ case TCP_CLOSING:
+ case TCP_LAST_ACK:
+ if (!before(TCP_SKB_CB(skb)->seq, tp->rcv_nxt))
+ break;
+ /* fall through */
+ case TCP_FIN_WAIT1:
+ case TCP_FIN_WAIT2:
+ /* RFC 793 says to queue data in these states,
+ * RFC 1122 says we MUST send a reset.
+ * BSD 4.4 also does reset.
+ */
+ if (sk->sk_shutdown & RCV_SHUTDOWN) {
+ if (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq &&
+ after(TCP_SKB_CB(skb)->end_seq - th->fin, tp->rcv_nxt)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPABORTONDATA);
+ tcp_reset(sk);
+ return 1;
+ }
+ }
+ /* Fall through */
+ case TCP_ESTABLISHED:
+ tcp_data_queue(sk, skb);
+ queued = 1;
+ break;
+ }
+
+ /* tcp_data could move socket to TIME-WAIT */
+ if (sk->sk_state != TCP_CLOSE) {
+ tcp_data_snd_check(sk);
+ tcp_ack_snd_check(sk);
+ }
+
+ if (!queued) {
+discard:
+ tcp_drop(sk, skb);
+ }
+ return 0;
+}
+EXPORT_SYMBOL(tcp_rcv_state_process);
+
+static inline void pr_drop_req(struct request_sock *req, __u16 port, int family)
+{
+ struct inet_request_sock *ireq = inet_rsk(req);
+
+ if (family == AF_INET)
+ net_dbg_ratelimited("drop open request from %pI4/%u\n",
+ &ireq->ir_rmt_addr, port);
+#if IS_ENABLED(CONFIG_IPV6)
+ else if (family == AF_INET6)
+ net_dbg_ratelimited("drop open request from %pI6/%u\n",
+ &ireq->ir_v6_rmt_addr, port);
+#endif
+}
+
+/* RFC3168 : 6.1.1 SYN packets must not have ECT/ECN bits set
+ *
+ * If we receive a SYN packet with these bits set, it means a
+ * network is playing bad games with TOS bits. In order to
+ * avoid possible false congestion notifications, we disable
+ * TCP ECN negotiation.
+ *
+ * Exception: tcp_ca wants ECN. This is required for DCTCP
+ * congestion control: Linux DCTCP asserts ECT on all packets,
+ * including SYN, which is most optimal solution; however,
+ * others, such as FreeBSD do not.
+ */
+static void tcp_ecn_create_request(struct request_sock *req,
+ const struct sk_buff *skb,
+ const struct sock *listen_sk,
+ const struct dst_entry *dst)
+{
+ const struct tcphdr *th = tcp_hdr(skb);
+ const struct net *net = sock_net(listen_sk);
+ bool th_ecn = th->ece && th->cwr;
+ bool ect, ecn_ok;
+ u32 ecn_ok_dst;
+
+ if (!th_ecn)
+ return;
+
+ ect = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
+ ecn_ok_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
+ ecn_ok = net->ipv4.sysctl_tcp_ecn || ecn_ok_dst;
+
+ if ((!ect && ecn_ok) || tcp_ca_needs_ecn(listen_sk) ||
+ (ecn_ok_dst & DST_FEATURE_ECN_CA) ||
+ tcp_bpf_ca_needs_ecn((struct sock *)req))
+ inet_rsk(req)->ecn_ok = 1;
+}
+
+static void tcp_openreq_init(struct request_sock *req,
+ const struct tcp_options_received *rx_opt,
+ struct sk_buff *skb, const struct sock *sk)
+{
+ struct inet_request_sock *ireq = inet_rsk(req);
+
+ req->rsk_rcv_wnd = 0; /* So that tcp_send_synack() knows! */
+ req->cookie_ts = 0;
+ tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
+ tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+ tcp_rsk(req)->snt_synack = tcp_clock_us();
+ tcp_rsk(req)->last_oow_ack_time = 0;
+ req->mss = rx_opt->mss_clamp;
+ req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
+ ireq->tstamp_ok = rx_opt->tstamp_ok;
+ ireq->sack_ok = rx_opt->sack_ok;
+ ireq->snd_wscale = rx_opt->snd_wscale;
+ ireq->wscale_ok = rx_opt->wscale_ok;
+ ireq->acked = 0;
+ ireq->ecn_ok = 0;
+ ireq->ir_rmt_port = tcp_hdr(skb)->source;
+ ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
+ ireq->ir_mark = inet_request_mark(sk, skb);
+#if IS_ENABLED(CONFIG_SMC)
+ ireq->smc_ok = rx_opt->smc_ok;
+#endif
+}
+
+struct request_sock *inet_reqsk_alloc(const struct request_sock_ops *ops,
+ struct sock *sk_listener,
+ bool attach_listener)
+{
+ struct request_sock *req = reqsk_alloc(ops, sk_listener,
+ attach_listener);
+
+ if (req) {
+ struct inet_request_sock *ireq = inet_rsk(req);
+
+ ireq->ireq_opt = NULL;
+#if IS_ENABLED(CONFIG_IPV6)
+ ireq->pktopts = NULL;
+#endif
+ atomic64_set(&ireq->ir_cookie, 0);
+ ireq->ireq_state = TCP_NEW_SYN_RECV;
+ write_pnet(&ireq->ireq_net, sock_net(sk_listener));
+ ireq->ireq_family = sk_listener->sk_family;
+ }
+
+ return req;
+}
+EXPORT_SYMBOL(inet_reqsk_alloc);
+
+/*
+ * Return true if a syncookie should be sent
+ */
+static bool tcp_syn_flood_action(const struct sock *sk,
+ const struct sk_buff *skb,
+ const char *proto)
+{
+ struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
+ const char *msg = "Dropping request";
+ bool want_cookie = false;
+ struct net *net = sock_net(sk);
+
+#ifdef CONFIG_SYN_COOKIES
+ if (net->ipv4.sysctl_tcp_syncookies) {
+ msg = "Sending cookies";
+ want_cookie = true;
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDOCOOKIES);
+ } else
+#endif
+ __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPREQQFULLDROP);
+
+ if (!queue->synflood_warned &&
+ net->ipv4.sysctl_tcp_syncookies != 2 &&
+ xchg(&queue->synflood_warned, 1) == 0)
+ net_info_ratelimited("%s: Possible SYN flooding on port %d. %s. Check SNMP counters.\n",
+ proto, ntohs(tcp_hdr(skb)->dest), msg);
+
+ return want_cookie;
+}
+
+static void tcp_reqsk_record_syn(const struct sock *sk,
+ struct request_sock *req,
+ const struct sk_buff *skb)
+{
+ if (tcp_sk(sk)->save_syn) {
+ u32 len = skb_network_header_len(skb) + tcp_hdrlen(skb);
+ u32 *copy;
+
+ copy = kmalloc(len + sizeof(u32), GFP_ATOMIC);
+ if (copy) {
+ copy[0] = len;
+ memcpy(©[1], skb_network_header(skb), len);
+ req->saved_syn = copy;
+ }
+ }
+}
+
+int tcp_conn_request(struct request_sock_ops *rsk_ops,
+ const struct tcp_request_sock_ops *af_ops,
+ struct sock *sk, struct sk_buff *skb)
+{
+ struct tcp_fastopen_cookie foc = { .len = -1 };
+ __u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
+ struct tcp_options_received tmp_opt;
+ struct tcp_sock *tp = tcp_sk(sk);
+ struct net *net = sock_net(sk);
+ struct sock *fastopen_sk = NULL;
+ struct request_sock *req;
+ bool want_cookie = false;
+ struct dst_entry *dst;
+ struct flowi fl;
+
+ /* TW buckets are converted to open requests without
+ * limitations, they conserve resources and peer is
+ * evidently real one.
+ */
+ if ((net->ipv4.sysctl_tcp_syncookies == 2 ||
+ inet_csk_reqsk_queue_is_full(sk)) && !isn) {
+ want_cookie = tcp_syn_flood_action(sk, skb, rsk_ops->slab_name);
+ if (!want_cookie)
+ goto drop;
+ }
+
+ if (sk_acceptq_is_full(sk)) {
+ NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+ goto drop;
+ }
+
+ req = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
+ if (!req)
+ goto drop;
+
+ tcp_rsk(req)->af_specific = af_ops;
+ tcp_rsk(req)->ts_off = 0;
+
+ tcp_clear_options(&tmp_opt);
+ tmp_opt.mss_clamp = af_ops->mss_clamp;
+ tmp_opt.user_mss = tp->rx_opt.user_mss;
+ tcp_parse_options(sock_net(sk), skb, &tmp_opt, 0,
+ want_cookie ? NULL : &foc);
+
+ if (want_cookie && !tmp_opt.saw_tstamp)
+ tcp_clear_options(&tmp_opt);
+
+ if (IS_ENABLED(CONFIG_SMC) && want_cookie)
+ tmp_opt.smc_ok = 0;
+
+ tmp_opt.tstamp_ok = tmp_opt.saw_tstamp;
+ tcp_openreq_init(req, &tmp_opt, skb, sk);
+ inet_rsk(req)->no_srccheck = inet_sk(sk)->transparent;
+
+ /* Note: tcp_v6_init_req() might override ir_iif for link locals */
+ inet_rsk(req)->ir_iif = inet_request_bound_dev_if(sk, skb);
+
+ af_ops->init_req(req, sk, skb);
+
+ if (security_inet_conn_request(sk, skb, req))
+ goto drop_and_free;
+
+ if (tmp_opt.tstamp_ok)
+ tcp_rsk(req)->ts_off = af_ops->init_ts_off(net, skb);
+
+ dst = af_ops->route_req(sk, &fl, req);
+ if (!dst)
+ goto drop_and_free;
+
+ if (!want_cookie && !isn) {
+ /* Kill the following clause, if you dislike this way. */
+ if (!net->ipv4.sysctl_tcp_syncookies &&
+ (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
+ (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
+ !tcp_peer_is_proven(req, dst)) {
+ /* Without syncookies last quarter of
+ * backlog is filled with destinations,
+ * proven to be alive.
+ * It means that we continue to communicate
+ * to destinations, already remembered
+ * to the moment of synflood.
+ */
+ pr_drop_req(req, ntohs(tcp_hdr(skb)->source),
+ rsk_ops->family);
+ goto drop_and_release;
+ }
+
+ isn = af_ops->init_seq(skb);
+ }
+
+ tcp_ecn_create_request(req, skb, sk, dst);
+
+ if (want_cookie) {
+ isn = cookie_init_sequence(af_ops, sk, skb, &req->mss);
+ req->cookie_ts = tmp_opt.tstamp_ok;
+ if (!tmp_opt.tstamp_ok)
+ inet_rsk(req)->ecn_ok = 0;
+ }
+
+ tcp_rsk(req)->snt_isn = isn;
+ tcp_rsk(req)->txhash = net_tx_rndhash();
+ tcp_openreq_init_rwin(req, sk, dst);
+ sk_rx_queue_set(req_to_sk(req), skb);
+ if (!want_cookie) {
+ tcp_reqsk_record_syn(sk, req, skb);
+ fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
+ }
+ if (fastopen_sk) {
+ af_ops->send_synack(fastopen_sk, dst, &fl, req,
+ &foc, TCP_SYNACK_FASTOPEN);
+ /* Add the child socket directly into the accept queue */
+ inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
+ sk->sk_data_ready(sk);
+ bh_unlock_sock(fastopen_sk);
+ sock_put(fastopen_sk);
+ } else {
+ tcp_rsk(req)->tfo_listener = false;
+ if (!want_cookie)
+ inet_csk_reqsk_queue_hash_add(sk, req,
+ tcp_timeout_init((struct sock *)req));
+ af_ops->send_synack(sk, dst, &fl, req, &foc,
+ !want_cookie ? TCP_SYNACK_NORMAL :
+ TCP_SYNACK_COOKIE);
+ if (want_cookie) {
+ reqsk_free(req);
+ return 0;
+ }
+ }
+ reqsk_put(req);
+ return 0;
+
+drop_and_release:
+ dst_release(dst);
+drop_and_free:
+ reqsk_free(req);
+drop:
+ tcp_listendrop(sk);
+ return 0;
+}
+EXPORT_SYMBOL(tcp_conn_request);