media: streamzap: fix race between device disconnection and urb callback

Syzkaller has reported a general protection fault at function
ir_raw_event_store_with_filter(). This crash is caused by a NULL pointer
dereference of dev->raw pointer, even though it is checked for NULL in
the same function, which means there is a race condition. It occurs due
to the incorrect order of actions in the streamzap_disconnect() function:
rc_unregister_device() is called before usb_kill_urb(). The dev->raw
pointer is freed and set to NULL in rc_unregister_device(), and only
after that usb_kill_urb() waits for in-progress requests to finish.

If rc_unregister_device() is called while streamzap_callback() handler is
not finished, this can lead to accessing freed resources. Thus
rc_unregister_device() should be called after usb_kill_urb().

Found by Linux Verification Center (linuxtesting.org) with Syzkaller.

Fixes: 8e9e60640067 ("V4L/DVB: staging/lirc: port lirc_streamzap to ir-core")
Cc: [e-mail]
Reported-by: [e-mail]
Closes: https://syzkaller.appspot.com/bug?extid=34008406ee9a31b13c73
Signed-off-by: Murad Masimov <[e-mail]>
Signed-off-by: Sean Young <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/rc/streamzap.c

···
 	if (!sz)
 		return;
 
-	rc_unregister_device(sz->rdev);
 	usb_kill_urb(sz->urb_in);
+	rc_unregister_device(sz->rdev);
 	usb_free_urb(sz->urb_in);
 	usb_free_coherent(usbdev, sz->buf_in_len, sz->buf_in, sz->dma_in);