diff --git a/net/mptcp/options.c b/net/mptcp/options.c
new file mode 100644
index 0000000..64afe71
--- /dev/null
+++ b/net/mptcp/options.c
@@ -0,0 +1,1137 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#define pr_fmt(fmt) "MPTCP: " fmt
+
+#include <linux/kernel.h>
+#include <crypto/sha.h>
+#include <net/tcp.h>
+#include <net/mptcp.h>
+#include "protocol.h"
+#include "mib.h"
+
+static bool mptcp_cap_flag_sha256(u8 flags)
+{
+	return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
+}
+
+static void mptcp_parse_option(const struct sk_buff *skb,
+			       const unsigned char *ptr, int opsize,
+			       struct mptcp_options_received *mp_opt)
+{
+	u8 subtype = *ptr >> 4;
+	int expected_opsize;
+	u8 version;
+	u8 flags;
+
+	switch (subtype) {
+	case MPTCPOPT_MP_CAPABLE:
+		/* strict size checking */
+		if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
+			if (skb->len > tcp_hdr(skb)->doff << 2)
+				expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
+			else
+				expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
+		} else {
+			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
+				expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
+			else
+				expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
+		}
+		if (opsize != expected_opsize)
+			break;
+
+		/* try to be gentle vs future versions on the initial syn */
+		version = *ptr++ & MPTCP_VERSION_MASK;
+		if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
+			if (version != MPTCP_SUPPORTED_VERSION)
+				break;
+		} else if (version < MPTCP_SUPPORTED_VERSION) {
+			break;
+		}
+
+		flags = *ptr++;
+		if (!mptcp_cap_flag_sha256(flags) ||
+		    (flags & MPTCP_CAP_EXTENSIBILITY))
+			break;
+
+		/* RFC 6824, Section 3.1:
+		 * "For the Checksum Required bit (labeled "A"), if either
+		 * host requires the use of checksums, checksums MUST be used.
+		 * In other words, the only way for checksums not to be used
+		 * is if both hosts in their SYNs set A=0."
+		 *
+		 * Section 3.3.0:
+		 * "If a checksum is not present when its use has been
+		 * negotiated, the receiver MUST close the subflow with a RST as
+		 * it is considered broken."
+		 *
+		 * We don't implement DSS checksum - fall back to TCP.
+		 */
+		if (flags & MPTCP_CAP_CHECKSUM_REQD)
+			break;
+
+		mp_opt->mp_capable = 1;
+		if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
+			mp_opt->sndr_key = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
+			mp_opt->rcvr_key = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA) {
+			/* Section 3.1.:
+			 * "the data parameters in a MP_CAPABLE are semantically
+			 * equivalent to those in a DSS option and can be used
+			 * interchangeably."
+			 */
+			mp_opt->dss = 1;
+			mp_opt->use_map = 1;
+			mp_opt->mpc_map = 1;
+			mp_opt->data_len = get_unaligned_be16(ptr);
+			ptr += 2;
+		}
+		pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d",
+			 version, flags, opsize, mp_opt->sndr_key,
+			 mp_opt->rcvr_key, mp_opt->data_len);
+		break;
+
+	case MPTCPOPT_MP_JOIN:
+		mp_opt->mp_join = 1;
+		if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
+			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
+			mp_opt->join_id = *ptr++;
+			mp_opt->token = get_unaligned_be32(ptr);
+			ptr += 4;
+			mp_opt->nonce = get_unaligned_be32(ptr);
+			ptr += 4;
+			pr_debug("MP_JOIN bkup=%u, id=%u, token=%u, nonce=%u",
+				 mp_opt->backup, mp_opt->join_id,
+				 mp_opt->token, mp_opt->nonce);
+		} else if (opsize == TCPOLEN_MPTCP_MPJ_SYNACK) {
+			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
+			mp_opt->join_id = *ptr++;
+			mp_opt->thmac = get_unaligned_be64(ptr);
+			ptr += 8;
+			mp_opt->nonce = get_unaligned_be32(ptr);
+			ptr += 4;
+			pr_debug("MP_JOIN bkup=%u, id=%u, thmac=%llu, nonce=%u",
+				 mp_opt->backup, mp_opt->join_id,
+				 mp_opt->thmac, mp_opt->nonce);
+		} else if (opsize == TCPOLEN_MPTCP_MPJ_ACK) {
+			ptr += 2;
+			memcpy(mp_opt->hmac, ptr, MPTCPOPT_HMAC_LEN);
+			pr_debug("MP_JOIN hmac");
+		} else {
+			mp_opt->mp_join = 0;
+		}
+		break;
+
+	case MPTCPOPT_DSS:
+		pr_debug("DSS");
+		ptr++;
+
+		/* we must clear 'mpc_map' be able to detect MP_CAPABLE
+		 * map vs DSS map in mptcp_incoming_options(), and reconstruct
+		 * map info accordingly
+		 */
+		mp_opt->mpc_map = 0;
+		flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
+		mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
+		mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
+		mp_opt->use_map = (flags & MPTCP_DSS_HAS_MAP) != 0;
+		mp_opt->ack64 = (flags & MPTCP_DSS_ACK64) != 0;
+		mp_opt->use_ack = (flags & MPTCP_DSS_HAS_ACK);
+
+		pr_debug("data_fin=%d dsn64=%d use_map=%d ack64=%d use_ack=%d",
+			 mp_opt->data_fin, mp_opt->dsn64,
+			 mp_opt->use_map, mp_opt->ack64,
+			 mp_opt->use_ack);
+
+		expected_opsize = TCPOLEN_MPTCP_DSS_BASE;
+
+		if (mp_opt->use_ack) {
+			if (mp_opt->ack64)
+				expected_opsize += TCPOLEN_MPTCP_DSS_ACK64;
+			else
+				expected_opsize += TCPOLEN_MPTCP_DSS_ACK32;
+		}
+
+		if (mp_opt->use_map) {
+			if (mp_opt->dsn64)
+				expected_opsize += TCPOLEN_MPTCP_DSS_MAP64;
+			else
+				expected_opsize += TCPOLEN_MPTCP_DSS_MAP32;
+		}
+
+		/* RFC 6824, Section 3.3:
+		 * If a checksum is present, but its use had
+		 * not been negotiated in the MP_CAPABLE handshake,
+		 * the checksum field MUST be ignored.
+		 */
+		if (opsize != expected_opsize &&
+		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
+			break;
+
+		mp_opt->dss = 1;
+
+		if (mp_opt->use_ack) {
+			if (mp_opt->ack64) {
+				mp_opt->data_ack = get_unaligned_be64(ptr);
+				ptr += 8;
+			} else {
+				mp_opt->data_ack = get_unaligned_be32(ptr);
+				ptr += 4;
+			}
+
+			pr_debug("data_ack=%llu", mp_opt->data_ack);
+		}
+
+		if (mp_opt->use_map) {
+			if (mp_opt->dsn64) {
+				mp_opt->data_seq = get_unaligned_be64(ptr);
+				ptr += 8;
+			} else {
+				mp_opt->data_seq = get_unaligned_be32(ptr);
+				ptr += 4;
+			}
+
+			mp_opt->subflow_seq = get_unaligned_be32(ptr);
+			ptr += 4;
+
+			mp_opt->data_len = get_unaligned_be16(ptr);
+			ptr += 2;
+
+			pr_debug("data_seq=%llu subflow_seq=%u data_len=%u",
+				 mp_opt->data_seq, mp_opt->subflow_seq,
+				 mp_opt->data_len);
+		}
+
+		break;
+
+	case MPTCPOPT_ADD_ADDR:
+		mp_opt->echo = (*ptr++) & MPTCP_ADDR_ECHO;
+		if (!mp_opt->echo) {
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT)
+				mp_opt->family = MPTCP_ADDR_IPVERSION_4;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+			else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6 ||
+				 opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT)
+				mp_opt->family = MPTCP_ADDR_IPVERSION_6;
+#endif
+			else
+				break;
+		} else {
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT)
+				mp_opt->family = MPTCP_ADDR_IPVERSION_4;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+			else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE ||
+				 opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT)
+				mp_opt->family = MPTCP_ADDR_IPVERSION_6;
+#endif
+			else
+				break;
+		}
+
+		mp_opt->add_addr = 1;
+		mp_opt->addr_id = *ptr++;
+		pr_debug("ADD_ADDR: id=%d, echo=%d", mp_opt->addr_id, mp_opt->echo);
+		if (mp_opt->family == MPTCP_ADDR_IPVERSION_4) {
+			memcpy((u8 *)&mp_opt->addr.s_addr, (u8 *)ptr, 4);
+			ptr += 4;
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT) {
+				mp_opt->port = get_unaligned_be16(ptr);
+				ptr += 2;
+			}
+		}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		else {
+			memcpy(mp_opt->addr6.s6_addr, (u8 *)ptr, 16);
+			ptr += 16;
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT) {
+				mp_opt->port = get_unaligned_be16(ptr);
+				ptr += 2;
+			}
+		}
+#endif
+		if (!mp_opt->echo) {
+			mp_opt->ahmac = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		break;
+
+	case MPTCPOPT_RM_ADDR:
+		if (opsize != TCPOLEN_MPTCP_RM_ADDR_BASE)
+			break;
+
+		ptr++;
+
+		mp_opt->rm_addr = 1;
+		mp_opt->rm_id = *ptr++;
+		pr_debug("RM_ADDR: id=%d", mp_opt->rm_id);
+		break;
+
+	default:
+		break;
+	}
+}
+
+void mptcp_get_options(const struct sk_buff *skb,
+		       struct mptcp_options_received *mp_opt)
+{
+	const struct tcphdr *th = tcp_hdr(skb);
+	const unsigned char *ptr;
+	int length;
+
+	/* initialize option status */
+	mp_opt->mp_capable = 0;
+	mp_opt->mp_join = 0;
+	mp_opt->add_addr = 0;
+	mp_opt->ahmac = 0;
+	mp_opt->port = 0;
+	mp_opt->rm_addr = 0;
+	mp_opt->dss = 0;
+
+	length = (th->doff * 4) - sizeof(struct tcphdr);
+	ptr = (const unsigned char *)(th + 1);
+
+	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:
+			if (length < 2)
+				return;
+			opsize = *ptr++;
+			if (opsize < 2) /* "silly options" */
+				return;
+			if (opsize > length)
+				return;	/* don't parse partial options */
+			if (opcode == TCPOPT_MPTCP)
+				mptcp_parse_option(skb, ptr, opsize, mp_opt);
+			ptr += opsize - 2;
+			length -= opsize;
+		}
+	}
+}
+
+bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
+		       unsigned int *size, struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	/* we will use snd_isn to detect first pkt [re]transmission
+	 * in mptcp_established_options_mp()
+	 */
+	subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
+	if (subflow->request_mptcp) {
+		opts->suboptions = OPTION_MPTCP_MPC_SYN;
+		*size = TCPOLEN_MPTCP_MPC_SYN;
+		return true;
+	} else if (subflow->request_join) {
+		pr_debug("remote_token=%u, nonce=%u", subflow->remote_token,
+			 subflow->local_nonce);
+		opts->suboptions = OPTION_MPTCP_MPJ_SYN;
+		opts->join_id = subflow->local_id;
+		opts->token = subflow->remote_token;
+		opts->nonce = subflow->local_nonce;
+		opts->backup = subflow->request_bkup;
+		*size = TCPOLEN_MPTCP_MPJ_SYN;
+		return true;
+	}
+	return false;
+}
+
+/* MP_JOIN client subflow must wait for 4th ack before sending any data:
+ * TCP can't schedule delack timer before the subflow is fully established.
+ * MPTCP uses the delack timer to do 3rd ack retransmissions
+ */
+static void schedule_3rdack_retransmission(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
+	unsigned long timeout;
+
+	/* reschedule with a timeout above RTT, as we must look only for drop */
+	if (tp->srtt_us)
+		timeout = usecs_to_jiffies(tp->srtt_us >> (3 - 1));
+	else
+		timeout = TCP_TIMEOUT_INIT;
+	timeout += jiffies;
+
+	WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
+	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	icsk->icsk_ack.timeout = timeout;
+	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
+}
+
+static void clear_3rdack_retransmission(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	sk_stop_timer(sk, &icsk->icsk_delack_timer);
+	icsk->icsk_ack.timeout = 0;
+	icsk->icsk_ack.ato = 0;
+	icsk->icsk_ack.pending &= ~(ICSK_ACK_SCHED | ICSK_ACK_TIMER);
+}
+
+static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
+					 unsigned int *size,
+					 unsigned int remaining,
+					 struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_ext *mpext;
+	unsigned int data_len;
+
+	/* When skb is not available, we better over-estimate the emitted
+	 * options len. A full DSS option (28 bytes) is longer than
+	 * TCPOLEN_MPTCP_MPC_ACK_DATA(22) or TCPOLEN_MPTCP_MPJ_ACK(24), so
+	 * tell the caller to defer the estimate to
+	 * mptcp_established_options_dss(), which will reserve enough space.
+	 */
+	if (!skb)
+		return false;
+
+	/* MPC/MPJ needed only on 3rd ack packet */
+	if (subflow->fully_established ||
+	    subflow->snd_isn != TCP_SKB_CB(skb)->seq)
+		return false;
+
+	if (subflow->mp_capable) {
+		mpext = mptcp_get_ext(skb);
+		data_len = mpext ? mpext->data_len : 0;
+
+		/* we will check ext_copy.data_len in mptcp_write_options() to
+		 * discriminate between TCPOLEN_MPTCP_MPC_ACK_DATA and
+		 * TCPOLEN_MPTCP_MPC_ACK
+		 */
+		opts->ext_copy.data_len = data_len;
+		opts->suboptions = OPTION_MPTCP_MPC_ACK;
+		opts->sndr_key = subflow->local_key;
+		opts->rcvr_key = subflow->remote_key;
+
+		/* Section 3.1.
+		 * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
+		 * packets that start the first subflow of an MPTCP connection,
+		 * as well as the first packet that carries data
+		 */
+		if (data_len > 0)
+			*size = ALIGN(TCPOLEN_MPTCP_MPC_ACK_DATA, 4);
+		else
+			*size = TCPOLEN_MPTCP_MPC_ACK;
+
+		pr_debug("subflow=%p, local_key=%llu, remote_key=%llu map_len=%d",
+			 subflow, subflow->local_key, subflow->remote_key,
+			 data_len);
+
+		return true;
+	} else if (subflow->mp_join) {
+		opts->suboptions = OPTION_MPTCP_MPJ_ACK;
+		memcpy(opts->hmac, subflow->hmac, MPTCPOPT_HMAC_LEN);
+		*size = TCPOLEN_MPTCP_MPJ_ACK;
+		pr_debug("subflow=%p", subflow);
+
+		schedule_3rdack_retransmission(sk);
+		return true;
+	}
+	return false;
+}
+
+static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
+				 struct sk_buff *skb, struct mptcp_ext *ext)
+{
+	/* The write_seq value has already been incremented, so the actual
+	 * sequence number for the DATA_FIN is one less.
+	 */
+	u64 data_fin_tx_seq = READ_ONCE(mptcp_sk(subflow->conn)->write_seq) - 1;
+
+	if (!ext->use_map || !skb->len) {
+		/* RFC6824 requires a DSS mapping with specific values
+		 * if DATA_FIN is set but no data payload is mapped
+		 */
+		ext->data_fin = 1;
+		ext->use_map = 1;
+		ext->dsn64 = 1;
+		ext->data_seq = data_fin_tx_seq;
+		ext->subflow_seq = 0;
+		ext->data_len = 1;
+	} else if (ext->data_seq + ext->data_len == data_fin_tx_seq) {
+		/* If there's an existing DSS mapping and it is the
+		 * final mapping, DATA_FIN consumes 1 additional byte of
+		 * mapping space.
+		 */
+		ext->data_fin = 1;
+		ext->data_len++;
+	}
+}
+
+static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
+					  unsigned int *size,
+					  unsigned int remaining,
+					  struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	unsigned int dss_size = 0;
+	u64 snd_data_fin_enable;
+	struct mptcp_ext *mpext;
+	unsigned int ack_size;
+	bool ret = false;
+
+	mpext = skb ? mptcp_get_ext(skb) : NULL;
+	snd_data_fin_enable = READ_ONCE(msk->snd_data_fin_enable);
+
+	if (!skb || (mpext && mpext->use_map) || snd_data_fin_enable) {
+		unsigned int map_size;
+
+		map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;
+
+		remaining -= map_size;
+		dss_size = map_size;
+		if (mpext)
+			opts->ext_copy = *mpext;
+
+		if (skb && snd_data_fin_enable)
+			mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
+		ret = true;
+	}
+
+	/* passive sockets msk will set the 'can_ack' after accept(), even
+	 * if the first subflow may have the already the remote key handy
+	 */
+	opts->ext_copy.use_ack = 0;
+	if (!READ_ONCE(msk->can_ack)) {
+		*size = ALIGN(dss_size, 4);
+		return ret;
+	}
+
+	if (READ_ONCE(msk->use_64bit_ack)) {
+		ack_size = TCPOLEN_MPTCP_DSS_ACK64;
+		opts->ext_copy.data_ack = READ_ONCE(msk->ack_seq);
+		opts->ext_copy.ack64 = 1;
+	} else {
+		ack_size = TCPOLEN_MPTCP_DSS_ACK32;
+		opts->ext_copy.data_ack32 = (uint32_t)READ_ONCE(msk->ack_seq);
+		opts->ext_copy.ack64 = 0;
+	}
+	opts->ext_copy.use_ack = 1;
+
+	/* Add kind/length/subtype/flag overhead if mapping is not populated */
+	if (dss_size == 0)
+		ack_size += TCPOLEN_MPTCP_DSS_BASE;
+
+	dss_size += ack_size;
+
+	*size = ALIGN(dss_size, 4);
+	return true;
+}
+
+static u64 add_addr_generate_hmac(u64 key1, u64 key2, u8 addr_id,
+				  struct in_addr *addr)
+{
+	u8 hmac[SHA256_DIGEST_SIZE];
+	u8 msg[7];
+
+	msg[0] = addr_id;
+	memcpy(&msg[1], &addr->s_addr, 4);
+	msg[5] = 0;
+	msg[6] = 0;
+
+	mptcp_crypto_hmac_sha(key1, key2, msg, 7, hmac);
+
+	return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
+}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+static u64 add_addr6_generate_hmac(u64 key1, u64 key2, u8 addr_id,
+				   struct in6_addr *addr)
+{
+	u8 hmac[SHA256_DIGEST_SIZE];
+	u8 msg[19];
+
+	msg[0] = addr_id;
+	memcpy(&msg[1], &addr->s6_addr, 16);
+	msg[17] = 0;
+	msg[18] = 0;
+
+	mptcp_crypto_hmac_sha(key1, key2, msg, 19, hmac);
+
+	return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
+}
+#endif
+
+static bool mptcp_established_options_add_addr(struct sock *sk,
+					       unsigned int *size,
+					       unsigned int remaining,
+					       struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	struct mptcp_addr_info saddr;
+	bool echo;
+	int len;
+
+	if (!mptcp_pm_should_add_signal(msk) ||
+	    !(mptcp_pm_add_addr_signal(msk, remaining, &saddr, &echo)))
+		return false;
+
+	len = mptcp_add_addr_len(saddr.family, echo);
+	if (remaining < len)
+		return false;
+
+	*size = len;
+	opts->addr_id = saddr.id;
+	if (saddr.family == AF_INET) {
+		opts->suboptions |= OPTION_MPTCP_ADD_ADDR;
+		opts->addr = saddr.addr;
+		if (!echo) {
+			opts->ahmac = add_addr_generate_hmac(msk->local_key,
+							     msk->remote_key,
+							     opts->addr_id,
+							     &opts->addr);
+		}
+	}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else if (saddr.family == AF_INET6) {
+		opts->suboptions |= OPTION_MPTCP_ADD_ADDR6;
+		opts->addr6 = saddr.addr6;
+		if (!echo) {
+			opts->ahmac = add_addr6_generate_hmac(msk->local_key,
+							      msk->remote_key,
+							      opts->addr_id,
+							      &opts->addr6);
+		}
+	}
+#endif
+	pr_debug("addr_id=%d, ahmac=%llu, echo=%d", opts->addr_id, opts->ahmac, echo);
+
+	return true;
+}
+
+static bool mptcp_established_options_rm_addr(struct sock *sk,
+					      unsigned int *size,
+					      unsigned int remaining,
+					      struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	u8 rm_id;
+
+	if (!mptcp_pm_should_rm_signal(msk) ||
+	    !(mptcp_pm_rm_addr_signal(msk, remaining, &rm_id)))
+		return false;
+
+	if (remaining < TCPOLEN_MPTCP_RM_ADDR_BASE)
+		return false;
+
+	*size = TCPOLEN_MPTCP_RM_ADDR_BASE;
+	opts->suboptions |= OPTION_MPTCP_RM_ADDR;
+	opts->rm_id = rm_id;
+
+	pr_debug("rm_id=%d", opts->rm_id);
+
+	return true;
+}
+
+bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
+			       unsigned int *size, unsigned int remaining,
+			       struct mptcp_out_options *opts)
+{
+	unsigned int opt_size = 0;
+	bool ret = false;
+
+	opts->suboptions = 0;
+
+	if (unlikely(mptcp_check_fallback(sk)))
+		return false;
+
+	/* prevent adding of any MPTCP related options on reset packet
+	 * until we support MP_TCPRST/MP_FASTCLOSE
+	 */
+	if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
+		return false;
+
+	if (mptcp_established_options_mp(sk, skb, &opt_size, remaining, opts))
+		ret = true;
+	else if (mptcp_established_options_dss(sk, skb, &opt_size, remaining,
+					       opts))
+		ret = true;
+
+	/* we reserved enough space for the above options, and exceeding the
+	 * TCP option space would be fatal
+	 */
+	if (WARN_ON_ONCE(opt_size > remaining))
+		return false;
+
+	*size += opt_size;
+	remaining -= opt_size;
+	if (mptcp_established_options_add_addr(sk, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	} else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	}
+
+	return ret;
+}
+
+bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
+			  struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+
+	if (subflow_req->mp_capable) {
+		opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
+		opts->sndr_key = subflow_req->local_key;
+		*size = TCPOLEN_MPTCP_MPC_SYNACK;
+		pr_debug("subflow_req=%p, local_key=%llu",
+			 subflow_req, subflow_req->local_key);
+		return true;
+	} else if (subflow_req->mp_join) {
+		opts->suboptions = OPTION_MPTCP_MPJ_SYNACK;
+		opts->backup = subflow_req->backup;
+		opts->join_id = subflow_req->local_id;
+		opts->thmac = subflow_req->thmac;
+		opts->nonce = subflow_req->local_nonce;
+		pr_debug("req=%p, bkup=%u, id=%u, thmac=%llu, nonce=%u",
+			 subflow_req, opts->backup, opts->join_id,
+			 opts->thmac, opts->nonce);
+		*size = TCPOLEN_MPTCP_MPJ_SYNACK;
+		return true;
+	}
+	return false;
+}
+
+static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
+				    struct mptcp_subflow_context *subflow,
+				    struct sk_buff *skb,
+				    struct mptcp_options_received *mp_opt)
+{
+	/* here we can process OoO, in-window pkts, only in-sequence 4th ack
+	 * will make the subflow fully established
+	 */
+	if (likely(subflow->fully_established)) {
+		/* on passive sockets, check for 3rd ack retransmission
+		 * note that msk is always set by subflow_syn_recv_sock()
+		 * for mp_join subflows
+		 */
+		if (TCP_SKB_CB(skb)->seq == subflow->ssn_offset + 1 &&
+		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq &&
+		    subflow->mp_join && mp_opt->mp_join &&
+		    READ_ONCE(msk->pm.server_side))
+			tcp_send_ack(ssk);
+		goto fully_established;
+	}
+
+	/* we must process OoO packets before the first subflow is fully
+	 * established. OoO packets are instead a protocol violation
+	 * for MP_JOIN subflows as the peer must not send any data
+	 * before receiving the forth ack - cfr. RFC 8684 section 3.2.
+	 */
+	if (TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1) {
+		if (subflow->mp_join)
+			goto reset;
+		return subflow->mp_capable;
+	}
+
+	if (mp_opt->dss && mp_opt->use_ack) {
+		/* subflows are fully established as soon as we get any
+		 * additional ack.
+		 */
+		subflow->fully_established = 1;
+		WRITE_ONCE(msk->fully_established, true);
+		goto fully_established;
+	}
+
+	/* If the first established packet does not contain MP_CAPABLE + data
+	 * then fallback to TCP. Fallback scenarios requires a reset for
+	 * MP_JOIN subflows.
+	 */
+	if (!mp_opt->mp_capable) {
+		if (subflow->mp_join)
+			goto reset;
+		subflow->mp_capable = 0;
+		pr_fallback(msk);
+		__mptcp_do_fallback(msk);
+		return false;
+	}
+
+	if (unlikely(!READ_ONCE(msk->pm.server_side)))
+		pr_warn_once("bogus mpc option on established client sk");
+	mptcp_subflow_fully_established(subflow, mp_opt);
+
+fully_established:
+	if (likely(subflow->pm_notified))
+		return true;
+
+	subflow->pm_notified = 1;
+	if (subflow->mp_join) {
+		clear_3rdack_retransmission(ssk);
+		mptcp_pm_subflow_established(msk, subflow);
+	} else {
+		mptcp_pm_fully_established(msk);
+	}
+	return true;
+
+reset:
+	mptcp_subflow_reset(ssk);
+	return false;
+}
+
+static u64 expand_ack(u64 old_ack, u64 cur_ack, bool use_64bit)
+{
+	u32 old_ack32, cur_ack32;
+
+	if (use_64bit)
+		return cur_ack;
+
+	old_ack32 = (u32)old_ack;
+	cur_ack32 = (u32)cur_ack;
+	cur_ack = (old_ack & GENMASK_ULL(63, 32)) + cur_ack32;
+	if (unlikely(before(cur_ack32, old_ack32)))
+		return cur_ack + (1LL << 32);
+	return cur_ack;
+}
+
+static void update_una(struct mptcp_sock *msk,
+		       struct mptcp_options_received *mp_opt)
+{
+	u64 new_snd_una, snd_una, old_snd_una = atomic64_read(&msk->snd_una);
+	u64 write_seq = READ_ONCE(msk->write_seq);
+
+	/* avoid ack expansion on update conflict, to reduce the risk of
+	 * wrongly expanding to a future ack sequence number, which is way
+	 * more dangerous than missing an ack
+	 */
+	new_snd_una = expand_ack(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
+
+	/* ACK for data not even sent yet? Ignore. */
+	if (after64(new_snd_una, write_seq))
+		new_snd_una = old_snd_una;
+
+	while (after64(new_snd_una, old_snd_una)) {
+		snd_una = old_snd_una;
+		old_snd_una = atomic64_cmpxchg(&msk->snd_una, snd_una,
+					       new_snd_una);
+		if (old_snd_una == snd_una) {
+			mptcp_data_acked((struct sock *)msk);
+			break;
+		}
+	}
+}
+
+bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
+{
+	/* Skip if DATA_FIN was already received.
+	 * If updating simultaneously with the recvmsg loop, values
+	 * should match. If they mismatch, the peer is misbehaving and
+	 * we will prefer the most recent information.
+	 */
+	if (READ_ONCE(msk->rcv_data_fin) || !READ_ONCE(msk->first))
+		return false;
+
+	WRITE_ONCE(msk->rcv_data_fin_seq,
+		   expand_ack(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
+	WRITE_ONCE(msk->rcv_data_fin, 1);
+
+	return true;
+}
+
+static bool add_addr_hmac_valid(struct mptcp_sock *msk,
+				struct mptcp_options_received *mp_opt)
+{
+	u64 hmac = 0;
+
+	if (mp_opt->echo)
+		return true;
+
+	if (mp_opt->family == MPTCP_ADDR_IPVERSION_4)
+		hmac = add_addr_generate_hmac(msk->remote_key,
+					      msk->local_key,
+					      mp_opt->addr_id, &mp_opt->addr);
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else
+		hmac = add_addr6_generate_hmac(msk->remote_key,
+					       msk->local_key,
+					       mp_opt->addr_id, &mp_opt->addr6);
+#endif
+
+	pr_debug("msk=%p, ahmac=%llu, mp_opt->ahmac=%llu\n",
+		 msk, (unsigned long long)hmac,
+		 (unsigned long long)mp_opt->ahmac);
+
+	return hmac == mp_opt->ahmac;
+}
+
+void mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	struct mptcp_options_received mp_opt;
+	struct mptcp_ext *mpext;
+
+	if (__mptcp_check_fallback(msk))
+		return;
+
+	mptcp_get_options(skb, &mp_opt);
+	if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
+		return;
+
+	if (mp_opt.add_addr && add_addr_hmac_valid(msk, &mp_opt)) {
+		struct mptcp_addr_info addr;
+
+		addr.port = htons(mp_opt.port);
+		addr.id = mp_opt.addr_id;
+		if (mp_opt.family == MPTCP_ADDR_IPVERSION_4) {
+			addr.family = AF_INET;
+			addr.addr = mp_opt.addr;
+		}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		else if (mp_opt.family == MPTCP_ADDR_IPVERSION_6) {
+			addr.family = AF_INET6;
+			addr.addr6 = mp_opt.addr6;
+		}
+#endif
+		if (!mp_opt.echo) {
+			mptcp_pm_add_addr_received(msk, &addr);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
+		} else {
+			mptcp_pm_del_add_timer(msk, &addr);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
+		}
+		mp_opt.add_addr = 0;
+	}
+
+	if (mp_opt.rm_addr) {
+		mptcp_pm_rm_addr_received(msk, mp_opt.rm_id);
+		mp_opt.rm_addr = 0;
+	}
+
+	if (!mp_opt.dss)
+		return;
+
+	/* we can't wait for recvmsg() to update the ack_seq, otherwise
+	 * monodirectional flows will stuck
+	 */
+	if (mp_opt.use_ack)
+		update_una(msk, &mp_opt);
+
+	/* Zero-data-length packets are dropped by the caller and not
+	 * propagated to the MPTCP layer, so the skb extension does not
+	 * need to be allocated or populated. DATA_FIN information, if
+	 * present, needs to be updated here before the skb is freed.
+	 */
+	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
+		if (mp_opt.data_fin && mp_opt.data_len == 1 &&
+		    mptcp_update_rcv_data_fin(msk, mp_opt.data_seq, mp_opt.dsn64) &&
+		    schedule_work(&msk->work))
+			sock_hold(subflow->conn);
+
+		return;
+	}
+
+	mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
+	if (!mpext)
+		return;
+
+	memset(mpext, 0, sizeof(*mpext));
+
+	if (mp_opt.use_map) {
+		if (mp_opt.mpc_map) {
+			/* this is an MP_CAPABLE carrying MPTCP data
+			 * we know this map the first chunk of data
+			 */
+			mptcp_crypto_key_sha(subflow->remote_key, NULL,
+					     &mpext->data_seq);
+			mpext->data_seq++;
+			mpext->subflow_seq = 1;
+			mpext->dsn64 = 1;
+			mpext->mpc_map = 1;
+			mpext->data_fin = 0;
+		} else {
+			mpext->data_seq = mp_opt.data_seq;
+			mpext->subflow_seq = mp_opt.subflow_seq;
+			mpext->dsn64 = mp_opt.dsn64;
+			mpext->data_fin = mp_opt.data_fin;
+		}
+		mpext->data_len = mp_opt.data_len;
+		mpext->use_map = 1;
+	}
+}
+
+void mptcp_write_options(__be32 *ptr, struct mptcp_out_options *opts)
+{
+	if ((OPTION_MPTCP_MPC_SYN | OPTION_MPTCP_MPC_SYNACK |
+	     OPTION_MPTCP_MPC_ACK) & opts->suboptions) {
+		u8 len;
+
+		if (OPTION_MPTCP_MPC_SYN & opts->suboptions)
+			len = TCPOLEN_MPTCP_MPC_SYN;
+		else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions)
+			len = TCPOLEN_MPTCP_MPC_SYNACK;
+		else if (opts->ext_copy.data_len)
+			len = TCPOLEN_MPTCP_MPC_ACK_DATA;
+		else
+			len = TCPOLEN_MPTCP_MPC_ACK;
+
+		*ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
+				      MPTCP_SUPPORTED_VERSION,
+				      MPTCP_CAP_HMAC_SHA256);
+
+		if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
+		    opts->suboptions))
+			goto mp_capable_done;
+
+		put_unaligned_be64(opts->sndr_key, ptr);
+		ptr += 2;
+		if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
+			goto mp_capable_done;
+
+		put_unaligned_be64(opts->rcvr_key, ptr);
+		ptr += 2;
+		if (!opts->ext_copy.data_len)
+			goto mp_capable_done;
+
+		put_unaligned_be32(opts->ext_copy.data_len << 16 |
+				   TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
+		ptr += 1;
+	}
+
+mp_capable_done:
+	if (OPTION_MPTCP_ADD_ADDR & opts->suboptions) {
+		if (opts->ahmac)
+			*ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
+					      TCPOLEN_MPTCP_ADD_ADDR, 0,
+					      opts->addr_id);
+		else
+			*ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
+					      TCPOLEN_MPTCP_ADD_ADDR_BASE,
+					      MPTCP_ADDR_ECHO,
+					      opts->addr_id);
+		memcpy((u8 *)ptr, (u8 *)&opts->addr.s_addr, 4);
+		ptr += 1;
+		if (opts->ahmac) {
+			put_unaligned_be64(opts->ahmac, ptr);
+			ptr += 2;
+		}
+	}
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	if (OPTION_MPTCP_ADD_ADDR6 & opts->suboptions) {
+		if (opts->ahmac)
+			*ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
+					      TCPOLEN_MPTCP_ADD_ADDR6, 0,
+					      opts->addr_id);
+		else
+			*ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
+					      TCPOLEN_MPTCP_ADD_ADDR6_BASE,
+					      MPTCP_ADDR_ECHO,
+					      opts->addr_id);
+		memcpy((u8 *)ptr, opts->addr6.s6_addr, 16);
+		ptr += 4;
+		if (opts->ahmac) {
+			put_unaligned_be64(opts->ahmac, ptr);
+			ptr += 2;
+		}
+	}
+#endif
+
+	if (OPTION_MPTCP_RM_ADDR & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_RM_ADDR,
+				      TCPOLEN_MPTCP_RM_ADDR_BASE,
+				      0, opts->rm_id);
+	}
+
+	if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+				      TCPOLEN_MPTCP_MPJ_SYN,
+				      opts->backup, opts->join_id);
+		put_unaligned_be32(opts->token, ptr);
+		ptr += 1;
+		put_unaligned_be32(opts->nonce, ptr);
+		ptr += 1;
+	}
+
+	if (OPTION_MPTCP_MPJ_SYNACK & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+				      TCPOLEN_MPTCP_MPJ_SYNACK,
+				      opts->backup, opts->join_id);
+		put_unaligned_be64(opts->thmac, ptr);
+		ptr += 2;
+		put_unaligned_be32(opts->nonce, ptr);
+		ptr += 1;
+	}
+
+	if (OPTION_MPTCP_MPJ_ACK & opts->suboptions) {
+		*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+				      TCPOLEN_MPTCP_MPJ_ACK, 0, 0);
+		memcpy(ptr, opts->hmac, MPTCPOPT_HMAC_LEN);
+		ptr += 5;
+	}
+
+	if (opts->ext_copy.use_ack || opts->ext_copy.use_map) {
+		struct mptcp_ext *mpext = &opts->ext_copy;
+		u8 len = TCPOLEN_MPTCP_DSS_BASE;
+		u8 flags = 0;
+
+		if (mpext->use_ack) {
+			flags = MPTCP_DSS_HAS_ACK;
+			if (mpext->ack64) {
+				len += TCPOLEN_MPTCP_DSS_ACK64;
+				flags |= MPTCP_DSS_ACK64;
+			} else {
+				len += TCPOLEN_MPTCP_DSS_ACK32;
+			}
+		}
+
+		if (mpext->use_map) {
+			len += TCPOLEN_MPTCP_DSS_MAP64;
+
+			/* Use only 64-bit mapping flags for now, add
+			 * support for optional 32-bit mappings later.
+			 */
+			flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
+			if (mpext->data_fin)
+				flags |= MPTCP_DSS_DATA_FIN;
+		}
+
+		*ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);
+
+		if (mpext->use_ack) {
+			if (mpext->ack64) {
+				put_unaligned_be64(mpext->data_ack, ptr);
+				ptr += 2;
+			} else {
+				put_unaligned_be32(mpext->data_ack32, ptr);
+				ptr += 1;
+			}
+		}
+
+		if (mpext->use_map) {
+			put_unaligned_be64(mpext->data_seq, ptr);
+			ptr += 2;
+			put_unaligned_be32(mpext->subflow_seq, ptr);
+			ptr += 1;
+			put_unaligned_be32(mpext->data_len << 16 |
+					   TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
+		}
+	}
+}