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    Subject[PATCH 5.13 165/351] watchdog: Fix possible use-after-free in wdt_startup()
    Date
    From: Zou Wei <zou_wei@huawei.com>

    [ Upstream commit c08a6b31e4917034f0ed0cb457c3bb209576f542 ]

    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/1620716495-108352-1-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/sbc60xxwdt.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/watchdog/sbc60xxwdt.c b/drivers/watchdog/sbc60xxwdt.c
    index a947a63fb44a..7b974802dfc7 100644
    --- a/drivers/watchdog/sbc60xxwdt.c
    +++ b/drivers/watchdog/sbc60xxwdt.c
    @@ -146,7 +146,7 @@ static void wdt_startup(void)
    static void wdt_turnoff(void)
    {
    /* Stop the timer */
    - del_timer(&timer);
    + del_timer_sync(&timer);
    inb_p(wdt_stop);
    pr_info("Watchdog timer is now disabled...\n");
    }
    --
    2.30.2


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