[Devel] [PATCH rh7] af_unix: Guard against other == sk in unix_dgram_sendmsg

[Vasily Averin]

commit a5527dda344fff0514b7989ef7a755729769daa1
Author: Rainer Weikusat <rweikusat at mobileactivedefense.com>
Date:   Thu Feb 11 19:37:27 2016 +0000

    af_unix: Guard against other == sk in unix_dgram_sendmsg

    The unix_dgram_sendmsg routine use the following test

    if (unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {

    to determine if sk and other are in an n:1 association (either
    established via connect or by using sendto to send messages to an
    unrelated socket identified by address). This isn't correct as the
    specified address could have been bound to the sending socket itself or
    because this socket could have been connected to itself by the time of
    the unix_peer_get but disconnected before the unix_state_lock(other). In
    both cases, the if-block would be entered despite other == sk which
    might either block the sender unintentionally or lead to trying to unlock
    the same spin lock twice for a non-blocking send. Add a other != sk
    check to guard against this.

    Fixes: 7d267278a9ec ("unix: avoid use-after-free in ep_remove_wait_queue")
    Reported-By: Philipp Hahn <pmhahn at pmhahn.de>
    Signed-off-by: Rainer Weikusat <rweikusat at mobileactivedefense.com>
    Tested-by: Philipp Hahn <pmhahn at pmhahn.de>
    Signed-off-by: David S. Miller <davem at davemloft.net>

https://access.redhat.com/solutions/2176521
https://jira.sw.ru/browse/PSBM-43080
Signed-off-by: Vasily Averin <vvs at virtuozzo.com>
---
 net/unix/af_unix.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index d64141f..0e629f5 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1711,7 +1711,12 @@ restart_locked:
 			goto out_unlock;
 	}
 
-	if (unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
+	/* other == sk && unix_peer(other) != sk if
+	 * - unix_peer(sk) == NULL, destination address bound to sk
+	 * - unix_peer(sk) == sk by time of get but disconnected before lock
+	 */
+	if (other != sk &&
+	    unlikely(unix_peer(other) != sk && unix_recvq_full(other))) {
 		if (timeo) {
 			timeo = unix_wait_for_peer(other, timeo);
 
-- 
1.9.1