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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Hulk Robot <hulkci@huawei.com>,
        Zou Wei <zou_wei@huawei.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.9 213/245] watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()
Date:   Mon, 19 Jul 2021 16:52:35 +0200
Message-Id: <20210719144947.280808156@linuxfoundation.org>
In-Reply-To: <20210719144940.288257948@linuxfoundation.org>
References: <20210719144940.288257948@linuxfoundation.org>
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From: Zou Wei <zou_wei@huawei.com>

[ Upstream commit 90b7c141132244e8e49a34a4c1e445cce33e07f4 ]

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@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/1620716691-108460-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 1cfd3f6a13d5..08500db8324f 100644
--- a/drivers/watchdog/sc520_wdt.c
+++ b/drivers/watchdog/sc520_wdt.c
@@ -190,7 +190,7 @@ 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);
-- 
2.30.2