Re: [PATCH] usb: uvc: Fix 1-byte out-of-bounds read in uvc_parse_format()

[Ricardo Ribalda]

Hi Youngjun

On Tue, 10 Jun 2025 at 13:37, Youngjun Lee <yjjuny.lee@xxxxxxxxxxx> wrote:
>
> The buffer length check before calling uvc_parse_format() only ensured
> that the buffer has at least 3 bytes (buflen > 2), buf the function
> accesses buffer[3], requiring at least 4 bytes.
>
> This can lead to an out-of-bounds read if the buffer has exactly 3 bytes.
>
> Fix it by checking that the buffer has at least 4 bytes before passing it
> to uvc_parse_format().
>

You probably want to add:
Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
Cc: stable@xxxxxxxxxxxxxxx

> Signed-off-by: Youngjun Lee <yjjuny.lee@xxxxxxxxxxx>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index da24a655ab68..60367d9e1c05 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -729,7 +729,7 @@ static int uvc_parse_streaming(struct uvc_device *dev,
>         streaming->nformats = 0;
>
>         /* Parse the format descriptors. */
> -       while (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE) {
> +       while (buflen > 3 && buffer[1] == USB_DT_CS_INTERFACE) {
>                 switch (buffer[2]) {
>                 case UVC_VS_FORMAT_UNCOMPRESSED:
>                 case UVC_VS_FORMAT_MJPEG:
> --
> 2.43.0
>
>

I would have fixed it slightly different:

diff --git a/drivers/media/usb/uvc/uvc_driver.c
b/drivers/media/usb/uvc/uvc_driver.c
index 96eeb3aee546..1371a73e67e3 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -344,6 +344,9 @@ static int uvc_parse_format(struct uvc_device *dev,
        u8 ftype;
        int ret;

+       if (buflen < 4)
+               return -EINVAL;
+
        format->type = buffer[2];
        format->index = buffer[3];
        format->frames = frames;


I think it makes more sense to add the length check where it is going
to be used not on a caller function. If we every change
uvc_parse_format to read byte #5 we will probably miss the check on
uvc_parse_streaming()

-- 
Ricardo Ribalda