Re: [FFmpeg-devel] [PATCH v2 7/7] avcodec: add AV_CODEC_FLAG_CLEAR

["Ronald S. Bultje" <rsbultje@gmail.com>]

Hi,

On Wed, Dec 6, 2023 at 3:23 AM Marton Balint <cus@passwd.hu> wrote:

> Signed-off-by: Marton Balint <cus@passwd.hu>
> ---
>  doc/APIchanges             |  3 +++
>  doc/codecs.texi            | 14 ++++++++++++++
>  libavcodec/avcodec.h       |  4 ++++
>  libavcodec/decode.c        |  6 ++++++
>  libavcodec/options_table.h |  1 +
>  libavcodec/version.h       |  2 +-
>  6 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/doc/APIchanges b/doc/APIchanges
> index 416e2bec5e..f839504a64 100644
> --- a/doc/APIchanges
> +++ b/doc/APIchanges
> @@ -2,6 +2,9 @@ The last version increases of all libraries were on
> 2023-02-09
>
>  API changes, most recent first:
>
> +2023-12-xx - xxxxxxxxxxx - lavc 60.36.100 - avcodec.h
> +  Add AV_CODEC_FLAG_CLEAR.
> +
>  2023-12-xx - xxxxxxxxxxx - lavu 58.33.100 - imgutils.h
>    Add av_image_fill_color()
>
> diff --git a/doc/codecs.texi b/doc/codecs.texi
> index 5b950b4560..0504a535f2 100644
> --- a/doc/codecs.texi
> +++ b/doc/codecs.texi
> @@ -76,6 +76,20 @@ Apply interlaced motion estimation.
>  Use closed gop.
>  @item output_corrupt
>  Output even potentially corrupted frames.
> +@item clear
> +Clear the contents of the video buffer before decoding the next picture
> to it.
> +
> +Usually if only a part of a picture is affected by a decode error then the
> +decoder (if it implements error concealment) tries to hide it by
> interpolating
> +pixels from neighbouring areas or in some cases from the previous frame.
> Even
> +without error concealment it is quite likely that the affected area will
> +contain pixels from an earlier frame, due to frame pooling.
>

No comment on the patch itself, but wouldn't our users (and the C standard
itself) consider it a security issue to return stale (or worse:
uninitialized) data while pretending that it's safe to access?

I thought touching uninitialized data was UB.

Ronald
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