linux-kernel - [PATCH -next] watchdog: Fix possible use-after-free by calling del_timer

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Message-ID: <1620802676-19701-1-git-send-email-zou_wei@huawei.com>
Date:   Wed, 12 May 2021 14:57:56 +0800
From:   Zou Wei <zou_wei@...wei.com>
To:     <wim@...ux-watchdog.org>, <linux@...ck-us.net>, <vz@...ia.com>
CC:     <linux-watchdog@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, Zou Wei <zou_wei@...wei.com>
Subject: [PATCH -next] watchdog: Fix possible use-after-free by calling del_timer_sync()

This driver'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/lpc18xx_wdt.c | 2 +-
 drivers/watchdog/w83877f_wdt.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/lpc18xx_wdt.c b/drivers/watchdog/lpc18xx_wdt.c
index 78cf11c..60b6d74 100644
--- a/drivers/watchdog/lpc18xx_wdt.c
+++ b/drivers/watchdog/lpc18xx_wdt.c
@@ -292,7 +292,7 @@ static int lpc18xx_wdt_remove(struct platform_device *pdev)
 	struct lpc18xx_wdt_dev *lpc18xx_wdt = platform_get_drvdata(pdev);
 
 	dev_warn(&pdev->dev, "I quit now, hardware will probably reboot!\n");
-	del_timer(&lpc18xx_wdt->timer);
+	del_timer_sync(&lpc18xx_wdt->timer);
 
 	return 0;
 }
diff --git a/drivers/watchdog/w83877f_wdt.c b/drivers/watchdog/w83877f_wdt.c
index 5772cc5..f265086 100644
--- a/drivers/watchdog/w83877f_wdt.c
+++ b/drivers/watchdog/w83877f_wdt.c
@@ -166,7 +166,7 @@ static void wdt_startup(void)
 static void wdt_turnoff(void)
 {
 	/* Stop the timer */
-	del_timer(&timer);
+	del_timer_sync(&timer);
 
 	wdt_change(WDT_DISABLE);
 
-- 
2.6.2