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tcp: fix 0 divide in __tcp_select_window()

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syszkaller fuzzer was able to trigger a divide by zero, when
TCP window scaling is not enabled.

SO_RCVBUF can be used not only to increase sk_rcvbuf, also
to decrease it below current receive buffers utilization.

If mss is negative or 0, just return a zero TCP window.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov  <dvyukov@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2017-02-01 08:33:53 -08:00 committed by David S. Miller
parent 63117f09c7
commit 06425c308b
1 changed files with 4 additions and 2 deletions
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6
net/ipv4/tcp_output.c
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@ -2518,9 +2518,11 @@ u32 __tcp_select_window(struct sock *sk)
int full_space = min_t(int, tp->window_clamp, allowed_space);
int window;
if (mss > full_space)
if (unlikely(mss > full_space)) {
mss = full_space;
if (mss <= 0)
return 0;
}
if (free_space < (full_space >> 1)) {
icsk->icsk_ack.quick = 0;