Re: [PATCH v1 RFC] video/hdmi: Fix HDMI_VENDOR_INFOFRAME_SIZE

[Jani Nikula <jani.nikula@linux.intel.com>]

On Mon, 09 Jan 2023, Martin Blumenstingl <martin.blumenstingl@googlemail.com> wrote:
> When support for the HDMI vendor infoframe was introduced back with
> commit 7d27becb3532 ("video/hdmi: Introduce helpers for the HDMI vendor
> specific infoframe") it's payload size was either 5 or 6 bytes,
> depending on:
>   if (frame->s3d_struct >= HDMI_3D_STRUCTURE_SIDE_BY_SIDE_HALF)
> When true the size was 6 bytes, otherwise 5 bytes.
>
> Drivers that are using hdmi_infoframe_pack() are reserving 10 bytes (4
> bytes for the header and up to 6 bytes for the infoframe payload data)
> or more (exynos_hdmi reserves 25 bytes).
>
> Over time the frame payload length was reduced to 4 bytes. This however
> does not match the code from hdmi_hdmi_infoframe_pack() where ptr[8] and
> ptr[9] are written, which means the infoframe has to allow up to 6 bytes
> of payload data (considering that the header takes 4 bytes).
>
> Change HDMI_VENDOR_INFOFRAME_SIZE to 6 bytes so
> hdmi_vendor_infoframe_pack_only() can properly check the passed buffer
> size and avoid an out of bounds write to ptr[8] or ptr[9].
>
> Fixes: c5e69ab35c0d ("video/hdmi: Constify infoframe passed to the pack functions")
> Fixes: d43be2554b58 ("drivers: video: hdmi: cleanup coding style in video a bit")
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
> ---
> I'm not an expert on this topic and I'm not sure if the size still
> depends on that if condition from long time ago. So please share your
> thoughts.

I tried to look at this quickly, but it makes my brain hurt. I don't
think simply changing the size here is right either.

Cc: Ville.

BR,
Jani.



>
>
>  include/linux/hdmi.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
> index 2f4dcc8d060e..026c5ef5a1a5 100644
> --- a/include/linux/hdmi.h
> +++ b/include/linux/hdmi.h
> @@ -57,7 +57,7 @@ enum hdmi_infoframe_type {
>  #define HDMI_SPD_INFOFRAME_SIZE    25
>  #define HDMI_AUDIO_INFOFRAME_SIZE  10
>  #define HDMI_DRM_INFOFRAME_SIZE    26
> -#define HDMI_VENDOR_INFOFRAME_SIZE  4
> +#define HDMI_VENDOR_INFOFRAME_SIZE  6
>  
>  #define HDMI_INFOFRAME_SIZE(type)	\
>  	(HDMI_INFOFRAME_HEADER_SIZE + HDMI_ ## type ## _INFOFRAME_SIZE)

-- 
Jani Nikula, Intel Open Source Graphics Center