linux-kernel - [56/74] 8021q: fix a potential use-after-free

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Date:	Sun, 07 Apr 2013 23:45:42 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Eric Dumazet" <edumazet@...gle.com>,
	"Patrick McHardy" <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>,
	"Cong Wang" <amwang@...hat.com>
Subject: [56/74] 8021q: fix a potential use-after-free

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

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

From: Cong Wang <amwang@...hat.com>

[ Upstream commit 4a7df340ed1bac190c124c1601bfc10cde9fb4fb ]

vlan_vid_del() could possibly free ->vlan_info after a RCU grace
period, however, we may still refer to the freed memory area
by 'grp' pointer. Found by code inspection.

This patch moves vlan_vid_del() as behind as possible.

Cc: Patrick McHardy <kaber@...sh.net>
Cc: "David S. Miller" <davem@...emloft.net>
Signed-off-by: Cong Wang <amwang@...hat.com>
Acked-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/8021q/vlan.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index 5471628..963f285 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -110,13 +110,6 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 	grp = rtnl_dereference(real_dev->vlgrp);
 	BUG_ON(!grp);
 
-	/* Take it out of our own structures, but be sure to interlock with
-	 * HW accelerating devices or SW vlan input packet processing if
-	 * VLAN is not 0 (leave it there for 802.1p).
-	 */
-	if (vlan_id && (real_dev->features & NETIF_F_HW_VLAN_FILTER))
-		ops->ndo_vlan_rx_kill_vid(real_dev, vlan_id);
-
 	grp->nr_vlans--;
 
 	if (vlan->flags & VLAN_FLAG_GVRP)
@@ -139,6 +132,13 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 		call_rcu(&grp->rcu, vlan_rcu_free);
 	}
 
+	/* Take it out of our own structures, but be sure to interlock with
+	 * HW accelerating devices or SW vlan input packet processing if
+	 * VLAN is not 0 (leave it there for 802.1p).
+	 */
+	if (vlan_id && (real_dev->features & NETIF_F_HW_VLAN_FILTER))
+		ops->ndo_vlan_rx_kill_vid(real_dev, vlan_id);
+
 	/* Get rid of the vlan's reference to real_dev */
 	dev_put(real_dev);
 }

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