usb: gadget: uvc: fix list double add in uvcg_video_pump

commit 96163f8 upstream.

A panic can occur if the endpoint becomes disabled and the
uvcg_video_pump adds the request back to the req_free list after it has
already been queued to the endpoint. The endpoint complete will add the
request back to the req_free list. Invalidate the local request handle
once it's been queued.

<6>[  246.796704][T13726] configfs-gadget gadget: uvc: uvc_function_set_alt(1, 0)
<3>[  246.797078][   T26] list_add double add: new=ffffff878bee5c40, prev=ffffff878bee5c40, next=ffffff878b0f0a90.
<6>[  246.797213][   T26] ------------[ cut here ]------------
<2>[  246.797224][   T26] kernel BUG at lib/list_debug.c:31!
<6>[  246.807073][   T26] Call trace:
<6>[  246.807180][   T26]  uvcg_video_pump+0x364/0x38c
<6>[  246.807366][   T26]  process_one_work+0x2a4/0x544
<6>[  246.807394][   T26]  worker_thread+0x350/0x784
<6>[  246.807442][   T26]  kthread+0x2ac/0x320

Fixes: f9897ec ("usb: gadget: uvc: only pump video data if necessary")
Cc: stable@vger.kernel.org
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dan Vacura <w36195@motorola.com>
Link: https://lore.kernel.org/r/20220617163154.16621-1-w36195@motorola.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/gadget/function/uvc_video.c

@@ -415,6 +415,9 @@ static void uvcg_video_pump(struct work_struct *work)
 			uvcg_queue_cancel(queue, 0);
 			break;
 		}
+
+		/* Endpoint now owns the request */
+		req = NULL;
 		video->req_int_count++;
 	}