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A reboot notifier, which stops the WDT by calling the stop hook without
any check, would be registered when we set WDOG_STOP_ON_REBOOT flag.
Howerer we allow the WDT driver to omit the stop hook since commit
"d0684c8a93549" ("watchdog: Make stop function optional") and provide
a module parameter for user that controls the WDOG_STOP_ON_REBOOT flag
in commit 9232c80659 ("watchdog: Add stop_on_reboot parameter to
control reboot policy"). Together that commits make user potential to
insert a watchdog driver that don't provide a stop hook but with the
stop_on_reboot parameter set, then dereferencing of null pointer occurs
on system reboot.
Check the stop hook before registering the reboot notifier to fix the
issue.
Fixes: d0684c8a93 ("watchdog: Make stop function optional")
Signed-off-by: Wang Wensheng <wangwensheng4@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20201109130512.28121-1-wangwensheng4@huawei.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.