Input: alps - fix use-after-free bugs caused by dev3_register_work

The dev3_register_work delayed work item is initialized within
alps_reconnect() and scheduled upon receipt of the first bare
PS/2 packet from an external PS/2 device connected to the ALPS
touchpad. During device detachment, the original implementation
calls flush_workqueue() in psmouse_disconnect() to ensure
completion of dev3_register_work. However, the flush_workqueue()
in psmouse_disconnect() only blocks and waits for work items that
were already queued to the workqueue prior to its invocation. Any
work items submitted after flush_workqueue() is called are not
included in the set of tasks that the flush operation awaits.
This means that after flush_workqueue() has finished executing,
the dev3_register_work could still be scheduled. Although the
psmouse state is set to PSMOUSE_CMD_MODE in psmouse_disconnect(),
the scheduling of dev3_register_work remains unaffected.

The race condition can occur as follows:

CPU 0 (cleanup path) | CPU 1 (delayed work)
psmouse_disconnect() |
psmouse_set_state() |
flush_workqueue() | alps_report_bare_ps2_packet()
alps_disconnect() | psmouse_queue_work()
kfree(priv); // FREE | alps_register_bare_ps2_mouse()
| priv = container_of(work...); // USE
| priv->dev3 // USE

Add disable_delayed_work_sync() in alps_disconnect() to ensure
that dev3_register_work is properly canceled and prevented from
executing after the alps_data structure has been deallocated.

This bug is identified by static analysis.

Fixes: 04aae283ba6a ("Input: ALPS - do not mix trackstick and external PS/2 mouse data")
Cc: stable@kernel.org
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://patch.msgid.link/b57b0a9ccca51a3f06be141bfc02b9ffe69d1845.1765939397.git.duoming@zju.edu.cn
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>