From a4ecb15a2432880353d0de4a35204ab8b65b8751 Mon Sep 17 00:00:00 2001 From: "Cui, Cheng" Date: Fri, 17 Feb 2017 17:04:55 +0000 Subject: [PATCH] tcp: accommodate sequence number to a peer's shrunk receive window caused by precision loss in window scaling Prevent sending out a left-shifted sequence number from a Linux sender in response to a peer's shrunk receive-window caused by losing least significant bits in window-scaling. Cc: "David S. Miller" Cc: Alexey Kuznetsov Cc: James Morris Cc: Hideaki YOSHIFUJI Cc: Patrick McHardy Signed-off-by: Cheng Cui Acked-by: Eric Dumazet Signed-off-by: David S. Miller --- net/ipv4/tcp_output.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 61f272a99a49..22548b5f05cb 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -83,7 +83,8 @@ static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb) tcp_skb_pcount(skb)); } -/* SND.NXT, if window was not shrunk. +/* SND.NXT, if window was not shrunk or the amount of shrunk was less than one + * window scaling factor due to loss of precision. * If window has been shrunk, what should we make? It is not clear at all. * Using SND.UNA we will fail to open window, SND.NXT is out of window. :-( * Anything in between SND.UNA...SND.UNA+SND.WND also can be already @@ -93,7 +94,9 @@ static inline __u32 tcp_acceptable_seq(const struct sock *sk) { const struct tcp_sock *tp = tcp_sk(sk); - if (!before(tcp_wnd_end(tp), tp->snd_nxt)) + if (!before(tcp_wnd_end(tp), tp->snd_nxt) || + (tp->rx_opt.wscale_ok && + ((tp->snd_nxt - tcp_wnd_end(tp)) < (1 << tp->rx_opt.rcv_wscale)))) return tp->snd_nxt; else return tcp_wnd_end(tp); -- 2.30.2