net/x25: Fix x25_neigh refcnt leak when x25 disconnect

commit 4becb7e upstream.

x25_connect() invokes x25_get_neigh(), which returns a reference of the
specified x25_neigh object to "x25->neighbour" with increased refcnt.

When x25 connect success and returns, the reference still be hold by
"x25->neighbour", so the refcount should be decreased in
x25_disconnect() to keep refcount balanced.

The reference counting issue happens in x25_disconnect(), which forgets
to decrease the refcnt increased by x25_get_neigh() in x25_connect(),
causing a refcnt leak.

Fix this issue by calling x25_neigh_put() before x25_disconnect()
returns.

Signed-off-by: Xiyu Yang <[email protected]>
Signed-off-by: Xin Tan <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: sherlly

net/x25/x25_subr.c

@@ -363,6 +363,10 @@ void x25_disconnect(struct sock *sk, int reason, unsigned char cause,
 		x25->neighbour = NULL;
 		read_unlock_bh(&x25_list_lock);
 	}
+	read_lock_bh(&x25_list_lock);
+	x25_neigh_put(x25->neighbour);
+	x25->neighbour = NULL;
+	read_unlock_bh(&x25_list_lock);
 }
 
 /*