watchdog: sc520_wdt: Fix possible use-after-free in wdt_turnoff()

stable inclusion
from stable-v4.19.198
commit 522e75ed63f67e815d4ec0deace67df22d9ce78e
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I9S3H8
CVE: CVE-2021-47323

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.19.y&id=522e75ed63f67e815d4ec0deace67df22d9ce78e



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[ Upstream commit 90b7c141 ]

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/1620716691-108460-1-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: Yu Liao <liaoyu15@huawei.com>