[PATCH AUTOSEL 4.4 07/12] watchdog: Fix possible use-after-free by calling del_timer_sync()

[Sasha Levin]

From: Zou Wei <zou_wei at huawei.com>

[ Upstream commit d0212f095ab56672f6f36aabc605bda205e1e0bf ]

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 at huawei.com>
Signed-off-by: Zou Wei <zou_wei at huawei.com>
Reviewed-by: Guenter Roeck <linux at roeck-us.net>
Acked-by: Vladimir Zapolskiy <vz at mleia.com>
Link: https://lore.kernel.org/r/1620802676-19701-1-git-send-email-zou_wei@huawei.com
Signed-off-by: Guenter Roeck <linux at roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim at linux-watchdog.org>
Signed-off-by: Sasha Levin <sashal at kernel.org>
---
 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 ab7b8b185d99..fbdc0f32e666 100644
--- a/drivers/watchdog/lpc18xx_wdt.c
+++ b/drivers/watchdog/lpc18xx_wdt.c
@@ -309,7 +309,7 @@ static int lpc18xx_wdt_remove(struct platform_device *pdev)
 	unregister_restart_handler(&lpc18xx_wdt->restart_handler);
 
 	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);
diff --git a/drivers/watchdog/w83877f_wdt.c b/drivers/watchdog/w83877f_wdt.c
index f0483c75ed32..4b52cf321747 100644
--- 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);
 
-- 
2.30.2