[PATCH] NET: Fix race condition about network device name allocation.

Kenji Kaneshige found this race between device removal and
registration.  On unregister it is possible for the old device to
exist, because sysfs file is still open.  A new device with 'eth%d'
will select the same name, but sysfs kobject register will fial.

The following changes the shutdown order slightly. It hold a removes
the sysfs entries earlier (on unregister_netdevice), but holds a
kobject reference.  Then when todo runs the actual last put free
happens.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
[chrisw: backport to 2.6.20]
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

diff --git a/net/core/dev.c b/net/core/dev.c
index 2a587b861620617056c7cec16a8d1f9523752b90..3c3d383d24c2355bf5f236293928141c2859f487 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3138,7 +3138,6 @@ void netdev_run_todo(void)
                        continue;
                }
 
-               netdev_unregister_sysfs(dev);
                dev->reg_state = NETREG_UNREGISTERED;
 
                netdev_wait_allrefs(dev);
@@ -3149,11 +3148,11 @@ void netdev_run_todo(void)
                BUG_TRAP(!dev->ip6_ptr);
                BUG_TRAP(!dev->dn_ptr);
 
-               /* It must be the very last action,
-                * after this 'dev' may point to freed up memory.
-                */
                if (dev->destructor)
                        dev->destructor(dev);
+
+               /* Free network device */
+               kobject_put(&dev->class_dev.kobj);
        }
 
 out:
@@ -3310,6 +3309,9 @@ int unregister_netdevice(struct net_device *dev)
        /* Notifier chain MUST detach us from master device. */
        BUG_TRAP(!dev->master);
 
+       /* Remove entries from sysfs */
+       netdev_unregister_sysfs(dev);
+
        /* Finish processing unregister after unlock */
        net_set_todo(dev);
 

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index f47f319bb7dc2ae78b02e5f97f2d84519e686710..c60fe3b86bb69dbe9c9b18b5c43256f87213b466 100644 (file)
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -440,9 +440,15 @@ static struct class net_class = {
 #endif
 };
 
+/* Delete sysfs entries but hold kobject reference until after all
+ * netdev references are gone.
+ */
 void netdev_unregister_sysfs(struct net_device * net)
 {
-       class_device_del(&(net->class_dev));
+       struct class_device *dev = &(net->class_dev);
+
+       kobject_get(&dev->kobj);
+       class_device_del(dev);
 }
 
 /* Create sysfs entries for network device. */