From d0212f095ab56672f6f36aabc605bda205e1e0bf Mon Sep 17 00:00:00 2001
From: Zou Wei <zou_wei@huawei.com>
Date: Wed, 12 May 2021 14:57:56 +0800
Subject: [PATCH] watchdog: Fix possible use-after-free by calling del_timer_sync()
Git-commit: d0212f095ab56672f6f36aabc605bda205e1e0bf
Patch-mainline: v5.14-rc1
References: git-fixes

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@huawei.com>
Signed-off-by: Zou Wei <zou_wei@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Link: https://lore.kernel.org/r/1620802676-19701-1-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>
Acked-by: Takashi Iwai <tiwai@suse.de>

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

--- a/drivers/watchdog/lpc18xx_wdt.c
+++ b/drivers/watchdog/lpc18xx_wdt.c
@@ -300,7 +300,7 @@ static int lpc18xx_wdt_remove(struct pla
 	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);
 
 	watchdog_unregister_device(&lpc18xx_wdt->wdt_dev);
 	clk_disable_unprepare(lpc18xx_wdt->wdt_clk);
--- a/drivers/watchdog/w83877f_wdt.c
+++ b/drivers/watchdog/w83877f_wdt.c
@@ -170,7 +170,7 @@ static void wdt_startup(void)
 static void wdt_turnoff(void)
 {
 	/* Stop the timer */
-	del_timer(&timer);
+	del_timer_sync(&timer);
 
 	wdt_change(WDT_DISABLE);