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

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Date:   Tue, 26 Oct 2021 11:55:05 +0100
From:   Kieran Bingham <kieran.bingham@...asonboard.com>
To:     Johan Hovold <johan@...nel.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: fix division by zero at stream start

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@...r.kernel.org      # 2.6.26
> Signed-off-by: Johan Hovold <johan@...nel.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@...asonboard.com>

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