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

[Guenter Roeck]

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+rene...@sang-engineering.com>

Reviewed-by: Guenter Roeck <li...@roeck-us.net>

---
  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);