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

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

net/ipv4/tcp.c

+5 −2
Original line number Diff line number Diff line
@@ -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);

net/ipv4/tcp_input.c

+2 −0
Original line number Diff line number Diff line
@@ -4048,6 +4048,8 @@ 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);