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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
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

7
net/ipv4/tcp.c
View file

@ -386,8 +386,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait)
*/ */
mask = 0; mask = 0;
if (sk->sk_err)
mask = POLLERR;
/* /*
* POLLHUP is certainly not done right. But poll() doesn't * 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) if (tp->urg_data & TCP_URG_VALID)
mask |= POLLPRI; mask |= POLLPRI;
} }
/* This barrier is coupled with smp_wmb() in tcp_reset() */
smp_rmb();
if (sk->sk_err)
mask |= POLLERR;
return mask; return mask;
} }
EXPORT_SYMBOL(tcp_poll); EXPORT_SYMBOL(tcp_poll);

2
net/ipv4/tcp_input.c
View file

@ -4048,6 +4048,8 @@ static void tcp_reset(struct sock *sk)
default: default:
sk->sk_err = ECONNRESET; sk->sk_err = ECONNRESET;
} }
/* This barrier is coupled with smp_rmb() in tcp_poll() */
smp_wmb();
if (!sock_flag(sk, SOCK_DEAD)) if (!sock_flag(sk, SOCK_DEAD))
sk->sk_error_report(sk); sk->sk_error_report(sk);