watchdog: core: fix null pointer dereference when releasing cdev

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@sang-engineering.com>
Reviewed-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index ffbdc4642ea55cbe3dd6e6105e4b47c0d35bb163..f6c24b22b37c06ab1139b375bcb44e78a1f55be5 100644 (file)
--- 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);