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tcp: Fix race in tcp_poll

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If a RST comes in immediately after checking sk->sk_err, tcp_poll will
return POLLIN but not POLLOUT.  Fix this by checking sk->sk_err at the end
of tcp_poll.  Additionally, ensure the correct order of operations on SMP
machines with memory barriers.

Signed-off-by: Tom Marshall <tdm.code@gmail.com>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Tom Marshall
2010-09-20 15:42:05 -07:00
committed by David S. Miller
parent 9828e6e6e3
commit a4d258036e
2 changed files with 7 additions and 2 deletions
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7
net/ipv4/tcp.c
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@@ -386,8 +386,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
*/
mask = 0;
if (sk->sk_err)
mask = POLLERR;
/*
* POLLHUP is certainly not done right. But poll() doesn't
@@ -457,6 +455,11 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
if (tp->urg_data & TCP_URG_VALID)
mask |= POLLPRI;
}
/* This barrier is coupled with smp_wmb() in tcp_reset() */
smp_rmb();
if (sk->sk_err)
mask |= POLLERR;
return mask;
}
EXPORT_SYMBOL(tcp_poll);