watchdog: Fix NULL pointer dereference when releasing cdev

watchdog_hrtimer_pretimeout_stop needs the watchdog device to have a
valid pointer to the watchdog core data to stop the pretimeout hrtimer.
Therefore it needs to be called before the pointers are cleared in
watchdog_cdev_unregister.

Fixes: 7b7d2fdc8c3e ("watchdog: Add hrtimer-based pretimeout feature")
Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Curtis Klein <curtis.klein@hpe.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1624429583-5720-1-git-send-email-curtis.klein@hpe.com
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 5bf795c..f408967 100644 (file)
--- a/drivers/watchdog/watchdog_dev.c
+++ b/drivers/watchdog/watchdog_dev.c
@@ -1096,6 +1096,8 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
                watchdog_stop(wdd);
        }
 
+       watchdog_hrtimer_pretimeout_stop(wdd);
+
        mutex_lock(&wd_data->lock);
        wd_data->wdd = NULL;
        wdd->wd_data = NULL;
@@ -1103,7 +1105,6 @@ static void watchdog_cdev_unregister(struct watchdog_device *wdd)
 
        hrtimer_cancel(&wd_data->timer);
        kthread_cancel_work_sync(&wd_data->work);
-       watchdog_hrtimer_pretimeout_stop(wdd);
 
        put_device(&wd_data->dev);
 }