From: Wolfram Sang <wsa+renesas@sang-engineering.com>
Date: Tue, 28 Aug 2018 10:13:47 +0000 (+0200)
Subject: watchdog: core: fix null pointer dereference when releasing cdev
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=953b9dd7725bad55a922a35e75bff7bebf7b9978;p=linux.git

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 ffbdc4642ea55..f6c24b22b37c0 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);