Re: [PATCH] media: v4l2-ctrls: document expected validation scope

[Jacopo Mondi <jacopo.mondi@ideasonboard.com>]

Hi Linus

On Wed, Jul 01, 2026 at 10:11:20AM +0200, Linus Walleij wrote:
> After discussion on the mailing list it became clear that these
> validations are not expected to be exhaustive.
>
> Link: https://lore.kernel.org/linux-media/20260629133209.GG3054459@killaraus.ideasonboard.com/

The above linked discussion is about parameters buffers, which can
indeed contain large sets of data.

I'm not sure the same applies to extended controls ?

> Signed-off-by: Linus Walleij <linusw@kernel.org>
> ---
>  Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> index b8698b85bd80..58184b6e386f 100644
> --- a/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> +++ b/Documentation/userspace-api/media/v4l/vidioc-g-ext-ctrls.rst
> @@ -118,6 +118,18 @@ correct. This prevents the situation where only some of the controls
>  were set/get. Only low-level errors (e. g. a failed i2c command) can
>  still cause this situation.
>
> +The validation of controls is not expected to be exhaustive, for example
> +custom controls under ``V4L2_CTRL_CLASS_USER`` would become very voluminous.
> +The expected behaviour is to reject settings that could:
> +
> +1. Pose stability issues, such as turning the hardware unresponsive requiring
> +   a hard reset, such controls must be rejected.
> +
> +2. Pose security issues, such as compromising unrelated kernel-contained
> +   data to userspace.
> +
> +Extended validation of control values should be performed in userspace.
> +
>  .. tabularcolumns:: |p{6.8cm}|p{4.0cm}|p{6.5cm}|
>
>  .. c:type:: v4l2_ext_control
>
> ---
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> change-id: 20260701-v4l2-doc-c60195d38d00
>
> Best regards,
> --
> Linus Walleij <linusw@kernel.org>
>