From: Yuchung Cheng <ycheng@google.com>
Date: Tue, 1 Aug 2017 20:22:32 +0000 (-0700)
Subject: tcp: avoid setting cwnd to invalid ssthresh after cwnd reduction states
X-Git-Tag: archive/raspbian/4.9.51-1+rpi1~7^2~332
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=3914a7eccbc742ab87c5be1acd3006e051e33710;p=linux-4.9.git

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


[ 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.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 01336aa5f973..32c540145c17 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2560,8 +2560,8 @@ static inline void tcp_end_cwnd_reduction(struct sock *sk)
 		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;
 	}