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tcp: accommodate sequence number to a peer's shrunk receive window caused by precision loss in window scaling

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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" <davem@davemloft.net>
Cc: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Cc: James Morris <jmorris@namei.org>
Cc: Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>
Cc: Patrick McHardy <kaber@trash.net>
Signed-off-by: Cheng Cui <Cheng.Cui@netapp.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Cui, Cheng 2017-02-17 17:04:55 +00:00 committed by David S. Miller
parent e606519ec3
commit a4ecb15a24
1 changed files with 5 additions and 2 deletions
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7
net/ipv4/tcp_output.c
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@ -83,7 +83,8 @@ static void tcp_event_new_data_sent(struct sock *sk, const struct sk_buff *skb)
tcp_skb_pcount(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. * 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. :-( * 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 * 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); 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; return tp->snd_nxt;
else else
return tcp_wnd_end(tp); return tcp_wnd_end(tp);