8021q: fix a potential use-after-free

[ Upstream commit 4a7df340 ]

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@trash.net>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

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);
 }