linux-kernel - [PATCH] watchdog: Fix an invalid memory access in 'watchdog_cdev

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Message-Id: <dcb65e66acd1a50d65635b35d0d340846c7d10c7.1627575359.git.christophe.jaillet@wanadoo.fr>
Date:   Thu, 29 Jul 2021 18:16:58 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     wim@...ux-watchdog.org, linux@...ck-us.net, curtis.klein@....com
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>
Subject: [PATCH] watchdog: Fix an invalid memory access in 'watchdog_cdev_unregister()'

A few lines before 'watchdog_hrtimer_pretimeout_stop(wdd)', we explicitly
set 'wdd->wd_data' to NULL.
So, it is more than likely than this call will lead to an invalid
memory access.

Move this call before the 'wdd->wd_data = NULL;'

Fixes: 7b7d2fdc8c3e ("watchdog: Add hrtimer-based pretimeout feature")
Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
---
Completely untested!
Not sure at all, that it is the way to fix it.
---
 drivers/watchdog/watchdog_dev.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/watchdog/watchdog_dev.c b/drivers/watchdog/watchdog_dev.c
index 3bab32485273..ffd8f1a82355 100644
--- 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);
 }
-- 
2.30.2