Input: lkkbd - disable pending work before freeing device

lkkbd_interrupt() schedules lk->tq via schedule_work(), and the work
handler lkkbd_reinit() dereferences the lkkbd structure and its
serio/input_dev fields.

lkkbd_disconnect() and error paths in lkkbd_connect() free the lkkbd
structure without preventing the reinit work from being queued again
until serio_close() returns. This can allow the work handler to run
after the structure has been freed, leading to a potential use-after-free.

Use disable_work_sync() instead of cancel_work_sync() to ensure the
reinit work cannot be re-queued, and call it both in lkkbd_disconnect()
and in lkkbd_connect() error paths after serio_open().

Signed-off-by: Minseong Kim <ii4gsp@gmail.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20251212052314.16139-1-ii4gsp@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Author: ii4gsp

drivers/input/keyboard/lkkbd.c

@@ -670,7 +670,8 @@ static int lkkbd_connect(struct serio *serio, struct serio_driver *drv)
 
 	return 0;
 
- fail3:	serio_close(serio);
+ fail3:	disable_work_sync(&lk->tq);
+	serio_close(serio);
  fail2:	serio_set_drvdata(serio, NULL);
  fail1:	input_free_device(input_dev);
 	kfree(lk);
@@ -684,6 +685,8 @@ static void lkkbd_disconnect(struct serio *serio)
 {
 	struct lkkbd *lk = serio_get_drvdata(serio);
 
+	disable_work_sync(&lk->tq);
+
 	input_get_device(lk->dev);
 	input_unregister_device(lk->dev);
 	serio_close(serio);