[PATCH] net/bridge/br_if.c: fix possible use-after-free in port_carrier_check()

[Oleg Nesterov <oleg@tv-sign.ru>]

If del_nbp()->cancel_delayed_work(carrier_check) fails, port_carrier_check()
may run later and access an already freed container (struct net_bridge_port).

With this patch, carrier_check owns a reference to "struct net_bridge_port",
not net_device, so it is always safe to acces the container.

port_carrier_check() uses p->dev->br_port == NULL as indication that net_bridge_port
is under destruction. Otherwise it assumes that p->dev->br_port == p.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-By: David Howells <dhowells@redhat.com>

--- WQ/net/bridge/br_if.c~5_bridge_uaf	2007-02-18 23:06:15.000000000 +0300
+++ WQ/net/bridge/br_if.c	2007-02-20 00:59:54.000000000 +0300
@@ -83,14 +83,14 @@ static void port_carrier_check(struct wo
 	struct net_device *dev;
 	struct net_bridge *br;
 
-	dev = container_of(work, struct net_bridge_port,
-			   carrier_check.work)->dev;
+	p = container_of(work, struct net_bridge_port, carrier_check.work);
 
 	rtnl_lock();
-	p = dev->br_port;
-	if (!p)
-		goto done;
 	br = p->br;
+	dev = p->dev;
+
+	if (!dev->br_port)
+		goto done;
 
 	if (netif_carrier_ok(dev))
 		p->path_cost = port_cost(dev);
@@ -107,14 +107,16 @@ static void port_carrier_check(struct wo
 		spin_unlock_bh(&br->lock);
 	}
 done:
-	dev_put(dev);
 	rtnl_unlock();
+	kobject_put(&p->kobj);
 }
 
 static void release_nbp(struct kobject *kobj)
 {
 	struct net_bridge_port *p
 		= container_of(kobj, struct net_bridge_port, kobj);
+
+	dev_put(p->dev);
 	kfree(p);
 }
 
@@ -127,12 +129,6 @@ static struct kobj_type brport_ktype = {
 
 static void destroy_nbp(struct net_bridge_port *p)
 {
-	struct net_device *dev = p->dev;
-
-	p->br = NULL;
-	p->dev = NULL;
-	dev_put(dev);
-
 	kobject_put(&p->kobj);
 }
 
@@ -162,7 +158,7 @@ static void del_nbp(struct net_bridge_po
 	dev_set_promiscuity(dev, -1);
 
 	if (cancel_delayed_work(&p->carrier_check))
-		dev_put(dev);
+		kobject_put(&p->kobj);
 
 	spin_lock_bh(&br->lock);
 	br_stp_disable_port(p);
@@ -446,7 +442,7 @@ int br_add_if(struct net_bridge *br, str
 	br_stp_recalculate_bridge_id(br);
 	br_features_recompute(br);
 	if (schedule_delayed_work(&p->carrier_check, BR_PORT_DEBOUNCE))
-		dev_hold(dev);
+		kobject_get(&p->kobj);
 
 	spin_unlock_bh(&br->lock);