watchdog: Fix race condition in registration code
A race condition exists when registering the first watchdog device.
Sequence of events:
- watchdog_register_device calls watchdog_dev_register
- watchdog_dev_register creates the watchdog misc device by calling
misc_register.
At that time, the matching character device (/dev/watchdog0) does not yet
exist, and old_wdd is not set either.
- Userspace gets an event and opens /dev/watchdog
- watchdog_open is called and sets wdd = old_wdd, which is still NULL,
and tries to dereference it. This causes the kernel to panic.
Seen with systemd trying to open /dev/watchdog immediately after
it was created.
Reported-by: Arkadiusz Miskiewicz <arekm@maven.pl>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Tested-by: Arkadiusz Miskiewicz <arekm@maven.pl>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
1 file changed