watchdog: Fix possible use-after-free by calling del_timer_sync()

stable inclusion
from stable-v4.19.198
commit ecd620e0fb1ff7f78fdb593379b2e6938c99707a
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9RL1P
CVE: CVE-2021-47321

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ecd620e0fb1ff7f78fdb593379b2e6938c99707a



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[ Upstream commit d0212f09 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>