HID: lg-g15: cancel pending work on remove to fix a use-after-free

HID: lg-g15: cancel pending work on remove to fix a use-after-free

lg_g15_data is allocated with devm and holds a work item. The report
handlers schedule that work straight from device input.
lg_g15_event() and lg_g15_v2_event() do it on the backlight cycle key,
and lg_g510_leds_event() does it too. The worker dereferences the
lg_g15_data back through container_of.

The driver had no remove callback and never cancelled the work. So if a
report scheduled the work and the keyboard was then unplugged, devres
freed lg_g15_data while the work was still pending or running, and the
worker touched freed memory. This is a use-after-free. It is reachable
as a race on device unplug.

Add a remove callback that cancels the work before devres frees the
state. g15->work is only initialized for the models that schedule it
(G15, G15 v2, G510). The G13 and Z-10 leave it zeroed, so guard the
cancel on g15->work.func to avoid cancelling a work that was never set
up. The g15 NULL test mirrors the one already in lg_g15_raw_event().

Fixes: 97b741aba918 ("HID: lg-g15: Add keyboard and LCD backlight control")
Cc: stable@vger.kernel.org
Suggested-by: Hans de Goede <hansg@kernel.org>
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Reviewed-by: Hans de Goede <johannes.goede@oss.qualcomm.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>