Patch "tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states" has been added to the 4.12-stable tree

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

tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states

to the 4.12-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-avoid-setting-cwnd-to-invalid-ssthresh-after-cwnd-reduction-states.patch
and it can be found in the queue-4.12 subdirectory.

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

From: Yuchung Cheng <[email protected]>
Date: Tue, 1 Aug 2017 13:22:32 -0700
Subject: tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states

From: Yuchung Cheng <[email protected]>

[ Upstream commit ed254971edea92c3ac5c67c6a05247a92aa6075e ]

If the sender switches the congestion control during ECN-triggered cwnd-reduction state (CA_CWR), upon exiting recovery cwnd is set to the ssthresh value calculated by the previous congestion control. If the previous congestion control is BBR that always keep ssthresh to TCP_INIFINITE_SSTHRESH, cwnd ends up being infinite. The safe step is to avoid assigning invalid ssthresh value when recovery ends.

---
 net/ipv4/tcp_input.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -2517,8 +2517,8 @@ static inline void tcp_end_cwnd_reductio
 		return;
 
 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
-	if (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR ||
-	    (tp->undo_marker && tp->snd_ssthresh < TCP_INFINITE_SSTHRESH)) {
+	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_time_stamp;
 	}

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

queue-4.12/tcp-avoid-setting-cwnd-to-invalid-ssthresh-after-cwnd-reduction-states.patch queue-4.12/tcp-fastopen-tcp_connect-must-refresh-the-route.patch queue-4.12/net-fix-keepalive-code-vs-tcp_fastopen_connect.patch