8021q: fix a potential use-after-free

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>

diff --git a/net/8021q/vlan.c b/net/8021q/vlan.c
index a187144..85addcd 100644 (file)
--- 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_MVRP)
@@ -114,6 +107,13 @@ void unregister_vlan_dev(struct net_device *dev, struct list_head *head)
                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);
 }