[PATCH RESEND net] cxgb4: fix use after free bugs caused by circular dependency problem

[Duoming Zhou]

The flower_stats_timer can schedule flower_stats_work and
flower_stats_work can also arm the flower_stats_timer. The
process is shown below:

----------- timer schedules work ------------
ch_flower_stats_cb() //timer handler
  schedule_work(&adap->flower_stats_work);

----------- work arms timer ------------
ch_flower_stats_handler() //workqueue callback function
  mod_timer(&adap->flower_stats_timer, ...);

When the cxgb4 device is detaching, the timer and workqueue
could still be rearmed. The process is shown below:

  (cleanup routine)           | (timer and workqueue routine)
remove_one()                  |
  free_some_resources()       | ch_flower_stats_cb() //timer
    cxgb4_cleanup_tc_flower() |   schedule_work()
      del_timer_sync()        |
                              | ch_flower_stats_handler() //workqueue
                              |   mod_timer()
      cancel_work_sync()      |
  kfree(adapter) //FREE       | ch_flower_stats_cb() //timer
                              |   adap->flower_stats_work //USE

This patch changes del_timer_sync() to timer_shutdown_sync(),
which could prevent rearming of the timer from the workqueue.

Fixes: e0f911c81e93 ("cxgb4: fetch stats for offloaded tc flower flows")
Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
 drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c
index dd9be229819..d3541159487 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_tc_flower.c
@@ -1135,7 +1135,7 @@ void cxgb4_cleanup_tc_flower(struct adapter *adap)
 		return;
 
 	if (adap->flower_stats_timer.function)
-		del_timer_sync(&adap->flower_stats_timer);
+		timer_shutdown_sync(&adap->flower_stats_timer);
 	cancel_work_sync(&adap->flower_stats_work);
 	rhashtable_destroy(&adap->flower_tbl);
 	adap->tc_flower_initialized = false;
-- 
2.17.1