[PATCH 062/102] 8021q: fix a potential use-after-free

[Luis Henriques]

3.5.7.10 -stable review patch.  If anyone has any objections, please let me know.

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

From: Cong Wang <amwang at redhat.com>

commit 4a7df340ed1bac190c124c1601bfc10cde9fb4fb upstream.

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 at trash.net>
Cc: "David S. Miller" <davem at davemloft.net>
Signed-off-by: Cong Wang <amwang at redhat.com>
Acked-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 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 9096bcb..8bdc56d 100644
--- a/net/8021q/vlan.c
+++ b/net/8021q/vlan.c
@@ -86,13 +86,6 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 
 	grp = &vlan_info->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)
-		vlan_vid_del(real_dev, vlan_id);
-
 	grp->nr_vlan_devs--;
 
 	if (vlan->flags & VLAN_FLAG_GVRP)
@@ -108,6 +101,13 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
 	if (grp->nr_vlan_devs == 0)
 		vlan_gvrp_uninit_applicant(real_dev);
 
+	/* 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)
+		vlan_vid_del(real_dev, vlan_id);
+
 	/* Get rid of the vlan's reference to real_dev */
 	dev_put(real_dev);
 }
-- 
1.8.1.2