linux-kernel - [PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt

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Message-ID: <1620716691-108460-1-git-send-email-zou_wei@huawei.com>
Date:   Tue, 11 May 2021 15:04:51 +0800
From:   Zou Wei <zou_wei@...wei.com>
To:     <wim@...ux-watchdog.org>, <linux@...ck-us.net>
CC:     <linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Zou Wei <zou_wei@...wei.com>
Subject: [PATCH -next] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

This module's remove path calls del_timer(). However, that function
does not wait until the timer handler finishes. This means that the
timer handler may still be running after the driver's remove function
has finished, which would result in a use-after-free.

Fix by calling del_timer_sync(), which makes sure the timer handler
has finished, and unable to re-schedule itself.

Reported-by: Hulk Robot <hulkci@...wei.com>
Signed-off-by: Zou Wei <zou_wei@...wei.com>
---
 drivers/watchdog/sc520_wdt.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/watchdog/sc520_wdt.c b/drivers/watchdog/sc520_wdt.c
index e66e6b9..ca65468 100644
--- a/drivers/watchdog/sc520_wdt.c
+++ b/drivers/watchdog/sc520_wdt.c
@@ -186,7 +186,7 @@ static int wdt_startup(void)
 static int wdt_turnoff(void)
 {
 	/* Stop the timer */
-	del_timer(&timer);
+	del_timer_sync(&timer);
 
 	/* Stop the watchdog */
 	wdt_config(0);
-- 
2.6.2