l2tp: protect tunnel->del_work by ref_count

There is a small chance that tunnel_free() is called before tunnel->del_work scheduled
resulting in a zero pointer dereference.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Acked-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 2 deletions

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index f6b090df3930..afca2eb4dfa7 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1319,7 +1319,7 @@ static void l2tp_tunnel_del_work(struct work_struct *work)
         tunnel = container_of(work, struct l2tp_tunnel, del_work);
         sk = l2tp_tunnel_sock_lookup(tunnel);
         if (!sk)
-                return;
+                goto out;
 
         sock = sk->sk_socket;
 
@@ -1341,6 +1341,8 @@ static void l2tp_tunnel_del_work(struct work_struct *work)
         }
 
         l2tp_tunnel_sock_put(sk);
+out:
+        l2tp_tunnel_dec_refcount(tunnel);
 }
 
 /* Create a socket for the tunnel, if one isn't set up by
@@ -1636,8 +1638,13 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
  */
 int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
 {
+        l2tp_tunnel_inc_refcount(tunnel);
         l2tp_tunnel_closeall(tunnel);
-        return (false == queue_work(l2tp_wq, &tunnel->del_work));
+        if (false == queue_work(l2tp_wq, &tunnel->del_work)) {
+                l2tp_tunnel_dec_refcount(tunnel);
+                return 1;
+        }
+        return 0;
 }
 EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);