[PATCH net] ethernet: ixgb: fix use after free bugs caused by circular dependency problem

[Duoming Zhou]

The watchdog_timer can schedule tx_timeout_task and tx_timeout_task
can also arm watchdog_timer. The process is shown below:

----------- timer schedules work ------------
ixgb_watchdog() //timer handler
  schedule_work(&adapter->tx_timeout_task)

----------- work arms timer ------------
ixgb_tx_timeout_task() //workqueue callback function
  ixgb_up()
    mod_timer(&adapter->watchdog_timer,...)

When ixgb device is detaching, the timer and workqueue
could still be rearmed. The process is shown below:

  (cleanup routine)           |  (timer and workqueue routine)
ixgb_remove()                 |
                              | ixgb_tx_timeout_task() //workqueue
                              |   ixgb_up()
                              |     mod_timer()
  cancel_work_sync()          |
  free_netdev(netdev) //FREE  | ixgb_watchdog() //timer
                              |   netif_carrier_ok(netdev) //USE

This patch adds timer_shutdown_sync() in ixgb_remove(), which
could prevent rearming of the timer from the workqueue.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/net/ethernet/intel/ixgb/ixgb_main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/ethernet/intel/ixgb/ixgb_main.c b/drivers/net/ethernet/intel/ixgb/ixgb_main.c
index b4d47e7a76c..6ce3601904b 100644
--- a/drivers/net/ethernet/intel/ixgb/ixgb_main.c
+++ b/drivers/net/ethernet/intel/ixgb/ixgb_main.c
@@ -516,6 +516,7 @@ ixgb_remove(struct pci_dev *pdev)
 	struct net_device *netdev = pci_get_drvdata(pdev);
 	struct ixgb_adapter *adapter = netdev_priv(netdev);
 
+	timer_shutdown_sync(&adapter->watchdog_timer);
 	cancel_work_sync(&adapter->tx_timeout_task);
 
 	unregister_netdev(netdev);
-- 
2.17.1