[3.16.y-ckt stable] Patch "l2tp: protect tunnel->del_work by ref_count" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    l2tp: protect tunnel->del_work by ref_count

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt19.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 7f0c8958137af6a431b8f462d715b2d430e9cf1f Mon Sep 17 00:00:00 2001
From: Alexander Couzens <lynxis at fe80.eu>
Date: Mon, 28 Sep 2015 11:32:42 +0200
Subject: l2tp: protect tunnel->del_work by ref_count

commit 06a15f51cf3618e32a73871ee6a547ef7fd902b5 upstream.

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 at fe80.eu>
Acked-by: James Chapman <jchapman at katalix.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/l2tp/l2tp_core.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c
index bea259043205..0c6a8f18b0fc 100644
--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1318,7 +1318,7 @@ 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;

@@ -1339,6 +1339,8 @@ 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
@@ -1673,8 +1675,13 @@ 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);