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

[Oleg Nesterov]

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 <[EMAIL PROTECTED]>
Acked-By: David Howells <[EMAIL PROTECTED]>

--- 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);
 

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