Commit a4d25803 authored by Tom Marshall's avatar Tom Marshall Committed by David S. Miller

tcp: Fix race in tcp_poll

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: default avatarTom Marshall <tdm.code@gmail.com>
Signed-off-by: default avatarEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 9828e6e6
...@@ -386,8 +386,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait) ...@@ -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) ...@@ -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);
......
...@@ -4048,6 +4048,8 @@ static void tcp_reset(struct sock *sk) ...@@ -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);
......
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