linux-kernel - Re: [PATCH] usb: gadget: uvc: fix list double add in uvcg_video

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Date:   Fri, 17 Jun 2022 15:51:08 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Dan Vacura <w36195@...orola.com>
Cc:     linux-usb@...r.kernel.org, stable@...r.kernel.org,
        Felipe Balbi <balbi@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Paul Elder <paul.elder@...asonboard.com>,
        Michael Grzeschik <m.grzeschik@...gutronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: gadget: uvc: fix list double add in uvcg_video_pump

Hi Dan,

Thank you for the patch.

On Wed, Jun 15, 2022 at 10:09:15PM -0500, Dan Vacura wrote:
> 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.

Good catch !

> <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: f9897ec0f6d3 ("usb: gadget: uvc: only pump video data if necessary")
> Cc: stable@...r.kernel.org
> Signed-off-by: Dan Vacura <w36195@...orola.com>
> ---
>  drivers/usb/gadget/function/uvc_video.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/usb/gadget/function/uvc_video.c b/drivers/usb/gadget/function/uvc_video.c
> index 93f42c7f800d..59e2f51b53a5 100644
> --- a/drivers/usb/gadget/function/uvc_video.c
> +++ b/drivers/usb/gadget/function/uvc_video.c
> @@ -427,6 +427,9 @@ static void uvcg_video_pump(struct work_struct *work)
>  		if (ret < 0) {
>  			uvcg_queue_cancel(queue, 0);
>  			break;
> +		} else {
> +			/* Endpoint now owns the request */
> +			req = NULL;
>  		}
>  		video->req_int_count++;

I'd write it as

		if (ret < 0) {
			uvcg_queue_cancel(queue, 0);
			break;
		}

		/* Endpoint now owns the request. */
		req = NULL;
		video->req_int_count++;

Apart from that,

Reviewed-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>

>  	}

-- 
Regards,

Laurent Pinchart