tcp: Fix race in tcp_poll

[ Upstream commit a4d258036ed9b2a1811c3670c6099203a0f284a0 ]

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: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 0e22467e040df72719a3a9be47c56a6422a07956..dc6cffa8a9cf2961974cc3eafc14a57894eec2d0 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 548d575e6cc684673ef9c7a7a613e2f444ec509c..d83b4967cf68d99555798f6dcc9fab383c1a6c66 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4041,6 +4041,8 @@ 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);