ax25: Fix segfault after sock connection timeout

[ Upstream commit 8a367e74c0120ef68c8c70d5a025648c96626dff ]

The ax.25 socket connection timed out & the sock struct has been
previously taken down ie. sock struct is now a NULL pointer. Checking
the sock_flag causes the segfault.  Check if the socket struct pointer
is NULL before checking sock_flag. This segfault is seen in
timed out netrom connections.

Please submit to -stable.

Signed-off-by: Basil Gunn <basil@pacabunga.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/ax25/ax25_subr.c b/net/ax25/ax25_subr.c
index 655a7d4c96e1..983f0b5e14f1 100644
--- a/net/ax25/ax25_subr.c
+++ b/net/ax25/ax25_subr.c
@@ -264,7 +264,7 @@ void ax25_disconnect(ax25_cb *ax25, int reason)
 {
         ax25_clear_queues(ax25);
 
-        if (!sock_flag(ax25->sk, SOCK_DESTROY))
+        if (!ax25->sk || !sock_flag(ax25->sk, SOCK_DESTROY))
                 ax25_stop_heartbeat(ax25);
         ax25_stop_t1timer(ax25);
         ax25_stop_t2timer(ax25);