tcp: Fix race in tcp_poll

commit a4d258036ed9b2a1811c3670c6099203a0f284a0 upstream.

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>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1b409243cd0e32bb97f3f1dc712105ac3aace45f..3fa16d933fdee96e89a516b5208a1a6f0bff4074 100644 (file)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -388,8 +388,6 @@ 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
@@ -459,6 +457,11 @@ 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;
 }
 

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index f240f57b2199e0e7e801212742b152dae2060608..dd0c9af58ffce36da61ddb79afd7f3948c1fffc4 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4040,6 +4040,8 @@ static void tcp_reset(struct sock *sk)
        default:
                sk->sk_err = ECONNRESET;
        }
+       /* This barrier is coupled with smp_rmb() in tcp_poll() */
+       smp_wmb();
 
        if (!sock_flag(sk, SOCK_DEAD))
                sk->sk_error_report(sk);