Re: [PATCH 1/2] watchdog: core: fix null pointer dereference when releasing cdev

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On 08/28/2018 03:13 AM, Wolfram Sang wrote:
watchdog_stop() calls watchdog_update_worker() which needs a valid
wdd->wd_data pointer. So, when unregistering the cdev, clear the
pointers after we call watchdog_stop(), not before.

Fixes: bb292ac1c602 ("watchdog: Introduce watchdog_stop_on_unregister helper")
Signed-off-by: Wolfram Sang <wsa+renesas@xxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Guenter Roeck <linux@xxxxxxxxxxxx>

---
  drivers/watchdog/watchdog_dev.c | 10 +++++-----
  1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index ffbdc4642ea5..f6c24b22b37c 100644
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -1019,16 +1019,16 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
  		old_wd_data = NULL;
  	}
- mutex_lock(&wd_data->lock);
-	wd_data->wdd = NULL;
-	wdd->wd_data = NULL;
-	mutex_unlock(&wd_data->lock);
-
  	if (watchdog_active(wdd) &&
  	    test_bit(WDOG_STOP_ON_UNREGISTER, &wdd->status)) {
  		watchdog_stop(wdd);
  	}
+ mutex_lock(&wd_data->lock);
+	wd_data->wdd = NULL;
+	wdd->wd_data = NULL;
+	mutex_unlock(&wd_data->lock);
+
  	hrtimer_cancel(&wd_data->timer);
  	kthread_cancel_work_sync(&wd_data->work);




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