Update Linux to v5.4.148

Sourced from [1]

[1] https://cdn.kernel.org/pub/linux/kernel/v5.x/linux-5.4.148.tar.gz

Change-Id: Ib3d26c5ba9b022e2e03533005c4fed4d7c30b61b
Signed-off-by: Olivier Deprez <olivier.deprez@arm.com>
diff --git a/include/net/ip.h b/include/net/ip.h
index a2c61c3..52abfc0 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -30,6 +30,7 @@
 #include <net/flow.h>
 #include <net/flow_dissector.h>
 #include <net/netns/hash.h>
+#include <net/lwtunnel.h>
 
 #define IPV4_MAX_PMTU		65535U		/* RFC 2675, Section 5.1 */
 #define IPV4_MIN_MTU		68			/* RFC 791 */
@@ -439,25 +440,34 @@
 						    bool forwarding)
 {
 	struct net *net = dev_net(dst->dev);
+	unsigned int mtu;
 
 	if (net->ipv4.sysctl_ip_fwd_use_pmtu ||
 	    ip_mtu_locked(dst) ||
 	    !forwarding)
 		return dst_mtu(dst);
 
-	return min(READ_ONCE(dst->dev->mtu), IP_MAX_MTU);
+	/* 'forwarding = true' case should always honour route mtu */
+	mtu = dst_metric_raw(dst, RTAX_MTU);
+	if (!mtu)
+		mtu = min(READ_ONCE(dst->dev->mtu), IP_MAX_MTU);
+
+	return mtu - lwtunnel_headroom(dst->lwtstate, mtu);
 }
 
 static inline unsigned int ip_skb_dst_mtu(struct sock *sk,
 					  const struct sk_buff *skb)
 {
+	unsigned int mtu;
+
 	if (!sk || !sk_fullsock(sk) || ip_sk_use_pmtu(sk)) {
 		bool forwarding = IPCB(skb)->flags & IPSKB_FORWARDED;
 
 		return ip_dst_mtu_maybe_forward(skb_dst(skb), forwarding);
 	}
 
-	return min(READ_ONCE(skb_dst(skb)->dev->mtu), IP_MAX_MTU);
+	mtu = min(READ_ONCE(skb_dst(skb)->dev->mtu), IP_MAX_MTU);
+	return mtu - lwtunnel_headroom(skb_dst(skb)->lwtstate, mtu);
 }
 
 struct dst_metrics *ip_fib_metrics_init(struct net *net, struct nlattr *fc_mx,
@@ -760,4 +770,9 @@
 int rtm_getroute_parse_ip_proto(struct nlattr *attr, u8 *ip_proto, u8 family,
 				struct netlink_ext_ack *extack);
 
+static inline bool inetdev_valid_mtu(unsigned int mtu)
+{
+	return likely(mtu >= IPV4_MIN_MTU);
+}
+
 #endif	/* _IP_H */