From 946272f8a5f73b249808d1fb8f30a25724864466 Mon Sep 17 00:00:00 2001 From: Yuchung Cheng Date: Wed, 31 May 2017 11:21:27 -0700 Subject: [PATCH] tcp: disallow cwnd undo when switching congestion control commit 44abafc4cc094214a99f860f778c48ecb23422fc upstream. When the sender switches its congestion control during loss recovery, if the recovery is spurious then it may incorrectly revert cwnd and ssthresh to the older values set by a previous congestion control. Consider a congestion control (like BBR) that does not use ssthresh and keeps it infinite: the connection may incorrectly revert cwnd to an infinite value when switching from BBR to another congestion control. This patch fixes it by disallowing such cwnd undo operation upon switching congestion control. Note that undo_marker is not reset s.t. the packets that were incorrectly marked lost would be corrected. We only avoid undoing the cwnd in tcp_undo_cwnd_reduction(). Signed-off-by: Yuchung Cheng Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Neal Cardwell Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller Signed-off-by: Willy Tarreau --- net/ipv4/tcp_cong.c | 1 + 1 file changed, 1 insertion(+) diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 019c2389a341..2ca6c080a4bc 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -95,6 +95,7 @@ void tcp_init_congestion_control(struct sock *sk) rcu_read_unlock(); } + tcp_sk(sk)->prior_ssthresh = 0; if (icsk->icsk_ca_ops->init) icsk->icsk_ca_ops->init(sk); } -- 2.20.1