[PATCH] core: fix free_netdev when register fails during notification call chain

[Daniel Lezcano <dlezcano@fr.ibm.com>]

Point 1:
The unregistering of a network device schedule a netdev_run_todo.
This function calls dev->destructor when it is set and the
destructor calls free_netdev.

Point 2:
In the case of an initialization of a network device the usual code
is:
  * alloc_netdev
  * register_netdev
     -> if this one fails, call free_netdev and exit with error.

Point 3:
In the register_netdevice function at the later state, when the device
is at the registered state, a call to the netdevice_notifiers is made.
If one of the notification falls into an error, a rollback to the
registered state is done using unregister_netdevice.

Conclusion:
When a network device fails to register during initialization because
one network subsystem returned an error during a notification call
chain, the network device is freed twice because of fact 1 and fact 2.
The second free_netdev will be done with an invalid pointer.

Proposed solution:
The following patch move all the code of unregister_netdevice *except*
the call to net_set_todo, to a new function "rollback_registered".

The following functions are changed in this way:
  * register_netdevice: calls rollback_registered when a notification fails
  * unregister_netdevice: calls rollback_register + net_set_todo, the call
                          order to net_set_todo is changed because it is the
                          latest now. Since it justs add an element to a 
list
                          that should not break anything.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
---
  net/core/dev.c |  112 
++++++++++++++++++++++++++++++---------------------------
  1 file changed, 59 insertions(+), 53 deletions(-)

Index: net-2.6/net/core/dev.c
===================================================================
--- net-2.6.orig/net/core/dev.c
+++ net-2.6/net/core/dev.c
@@ -3496,6 +3496,60 @@ static void net_set_todo(struct net_devi
      spin_unlock(&net_todo_list_lock);
  }

+static void rollback_registered(struct net_device *dev)
+{
+    BUG_ON(dev_boot_phase);
+    ASSERT_RTNL();
+
+    /* Some devices call without registering for initialization unwind. */
+    if (dev->reg_state == NETREG_UNINITIALIZED) {
+        printk(KERN_DEBUG "unregister_netdevice: device %s/%p never "
+                  "was registered\n", dev->name, dev);
+
+        WARN_ON(1);
+        return;
+    }
+
+    BUG_ON(dev->reg_state != NETREG_REGISTERED);
+
+    /* If device is running, close it first. */
+    dev_close(dev);
+
+    /* And unlink it from device chain. */
+    unlist_netdevice(dev);
+
+    dev->reg_state = NETREG_UNREGISTERING;
+
+    synchronize_net();
+
+    /* Shutdown queueing discipline. */
+    dev_shutdown(dev);
+
+
+    /* Notify protocols, that we are about to destroy
+       this device. They should clean all the things.
+    */
+    call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
+
+    /*
+     *    Flush the unicast and multicast chains
+     */
+    dev_addr_discard(dev);
+
+    if (dev->uninit)
+        dev->uninit(dev);
+
+    /* Notifier chain MUST detach us from master device. */
+    BUG_TRAP(!dev->master);
+
+    /* Remove entries from kobject tree */
+    netdev_unregister_kobject(dev);
+
+    synchronize_net();
+
+    dev_put(dev);
+}
+
  /**
   *    register_netdevice    - register a network device
   *    @dev: device to register
@@ -3633,8 +3687,10 @@ int register_netdevice(struct net_device
      /* Notify protocols, that a new device appeared. */
      ret = call_netdevice_notifiers(NETDEV_REGISTER, dev);
      ret = notifier_to_errno(ret);
-    if (ret)
-        unregister_netdevice(dev);
+    if (ret) {
+        rollback_registered(dev);
+        dev->reg_state = NETREG_UNREGISTERED;
+    }

  out:
      return ret;
@@ -3911,59 +3967,9 @@ void synchronize_net(void)

  void unregister_netdevice(struct net_device *dev)
  {
-    BUG_ON(dev_boot_phase);
-    ASSERT_RTNL();
-
-    /* Some devices call without registering for initialization unwind. */
-    if (dev->reg_state == NETREG_UNINITIALIZED) {
-        printk(KERN_DEBUG "unregister_netdevice: device %s/%p never "
-                  "was registered\n", dev->name, dev);
-
-        WARN_ON(1);
-        return;
-    }
-
-    BUG_ON(dev->reg_state != NETREG_REGISTERED);
-
-    /* If device is running, close it first. */
-    dev_close(dev);
-
-    /* And unlink it from device chain. */
-    unlist_netdevice(dev);
-
-    dev->reg_state = NETREG_UNREGISTERING;
-
-    synchronize_net();
-
-    /* Shutdown queueing discipline. */
-    dev_shutdown(dev);
-
-
-    /* Notify protocols, that we are about to destroy
-       this device. They should clean all the things.
-    */
-    call_netdevice_notifiers(NETDEV_UNREGISTER, dev);
-
-    /*
-     *    Flush the unicast and multicast chains
-     */
-    dev_addr_discard(dev);
-
-    if (dev->uninit)
-        dev->uninit(dev);
-
-    /* Notifier chain MUST detach us from master device. */
-    BUG_TRAP(!dev->master);
-
-    /* Remove entries from kobject tree */
-    netdev_unregister_kobject(dev);
-
+    rollback_registered(dev);
      /* Finish processing unregister after unlock */
      net_set_todo(dev);
-
-    synchronize_net();
-
-    dev_put(dev);
  }

  /**