Patch "tcp: fastopen: tcp_connect() must refresh the route" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

tcp: fastopen: tcp_connect() must refresh the route

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tcp-fastopen-tcp_connect-must-refresh-the-route.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Tue, 8 Aug 2017 01:41:58 -0700
Subject: tcp: fastopen: tcp_connect() must refresh the route

From: Eric Dumazet <[email protected]>

[ Upstream commit 8ba60924710cde564a3905588b6219741d6356d0 ]

With new TCP_FASTOPEN_CONNECT socket option, there is a possibility to call tcp_connect() while socket sk_dst_cache is either NULL or invalid.

+0 socket(..., SOCK_STREAM, IPPROTO_TCP) = 4
+0 fcntl(4, F_SETFL, O_RDWR|O_NONBLOCK) = 0
+0 setsockopt(4, SOL_TCP, TCP_FASTOPEN_CONNECT, [1], 4) = 0 +0 connect(4, ..., ...) = 0

<< sk->sk_dst_cache becomes obsolete, or even set to NULL >>

+1 sendto(4, ..., 1000, MSG_FASTOPEN, ..., ...) = 1000

We need to refresh the route otherwise bad things can happen, especially when syzkaller is running on the host :/

---
 net/ipv4/tcp_output.c |    3 +++
 1 file changed, 3 insertions(+)

@@ -3344,6 +3344,9 @@ int tcp_connect(struct sock *sk)
 	struct sk_buff *buff;
 	int err;
 
+	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
+		return -EHOSTUNREACH; /* Routing failure or similar. */
+
 	tcp_connect_init(sk);
 
 	if (unlikely(tp->repair)) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/tcp-avoid-setting-cwnd-to-invalid-ssthresh-after-cwnd-reduction-states.patch queue-4.9/tcp-fastopen-tcp_connect-must-refresh-the-route.patch queue-4.9/net-fix-keepalive-code-vs-tcp_fastopen_connect.patch