linux-kernel - [PATCH 3.16 246/346] l2tp: fix use-after-free during module unload

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Date:   Mon, 14 Nov 2016 00:14:20 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Sabrina Dubroca" <sd@...asysnail.net>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 246/346] l2tp: fix use-after-free during module unload

3.16.39-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sabrina Dubroca <sd@...asysnail.net>

commit 2f86953e7436c9b9a4690909c5e2db24799e173b upstream.

Tunnel deletion is delayed by both a workqueue (l2tp_tunnel_delete -> wq
 -> l2tp_tunnel_del_work) and RCU (sk_destruct -> RCU ->
l2tp_tunnel_destruct).

By the time l2tp_tunnel_destruct() runs to destroy the tunnel and finish
destroying the socket, the private data reserved via the net_generic
mechanism has already been freed, but l2tp_tunnel_destruct() actually
uses this data.

Make sure tunnel deletion for the netns has completed before returning
from l2tp_exit_net() by first flushing the tunnel removal workqueue, and
then waiting for RCU callbacks to complete.

Fixes: 167eb17e0b17 ("l2tp: create tunnel sockets in the right namespace")
Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/l2tp/l2tp_core.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/net/l2tp/l2tp_core.c
+++ b/net/l2tp/l2tp_core.c
@@ -1892,6 +1892,9 @@ static __net_exit void l2tp_exit_net(str
 		(void)l2tp_tunnel_delete(tunnel);
 	}
 	rcu_read_unlock_bh();
+
+	flush_workqueue(l2tp_wq);
+	rcu_barrier();
 }
 
 static struct pernet_operations l2tp_net_ops = {