Re: [PATCH] media: uvcvideo: fix division by zero at stream start

Kieran Bingham
2021-10-26T10:55:12Z

Quoting Johan Hovold (2021-10-26 10:55:11)
> Add the missing bulk-endpoint max-packet sanity check to probe() to
> avoid division by zero in uvc_alloc_urb_buffers() in case a malicious
> device has broken descriptors (or when doing descriptor fuzz testing).
>
> Note that USB core will reject URBs submitted for endpoints with zero
> wMaxPacketSize but that drivers doing packet-size calculations still
> need to handle this (cf. commit 2548288b4fb0 ("USB: Fix: Don't skip
> endpoint descriptors with maxpacket=0")).
>
> Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
> Cc: stable@vger.kernel.org # 2.6.26
> Signed-off-by: Johan Hovold <johan@kernel.org>
> ---
> drivers/media/usb/uvc/uvc_video.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
> index e16464606b14..85ac5c1081b6 100644
> --- a/drivers/media/usb/uvc/uvc_video.c
> +++ b/drivers/media/usb/uvc/uvc_video.c
> @@ -1958,6 +1958,10 @@ static int uvc_video_start_transfer(struct uvc_streaming *stream,
> if (ep == NULL)
> return -EIO;
>
> + /* Reject broken descriptors. */
> + if (usb_endpoint_maxp(&ep->desc) == 0)
> + return -EIO;

Is there any value in identifying this with a specific return code like
-ENODATA?

But either way, this seems sane.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> +
> ret = uvc_init_video_bulk(stream, ep, gfp_flags);
> }
>
> --
> 2.32.0
>