Re: [FFmpeg-devel] [PATCH v1] avcodec/cbs_vp8: Improve the bitstream position check

["Dai, Jianhui J" <jianhui.j.dai-at-intel.com@ffmpeg.org>]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of Dai,
> Jianhui J
> Sent: Thursday, January 25, 2024 8:54 AM
> To: ffmpeg-devel@ffmpeg.org
> Subject: [FFmpeg-devel] [PATCH v1] avcodec/cbs_vp8: Improve the bitstream
> position check
> 
> The VP8 compressed header may not be byte-aligned due to boolean coding. Use
> bitwise comparison to prevent the potential overread.
> 
> Signed-off-by: Jianhui Dai <jianhui.j.dai@intel.com>
> ---
>  libavcodec/cbs_vp8.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/cbs_vp8.c b/libavcodec/cbs_vp8.c index
> 065156c248..13acad3724 100644
> --- a/libavcodec/cbs_vp8.c
> +++ b/libavcodec/cbs_vp8.c
> @@ -327,9 +327,10 @@ static int cbs_vp8_read_unit(CodedBitstreamContext
> *ctx,
>      if (err < 0)
>          return err;
> 
> +    // Position may not be byte-aligned after compressed header; using bits
> +    // count comparison for accuracy.
>      pos = get_bits_count(&gbc);
> -    pos /= 8;
> -    av_assert0(pos <= unit->data_size);
> +    av_assert0(pos <= unit->data_size * 8);
> 
>      frame->data_ref = av_buffer_ref(unit->data_ref);
>      if (!frame->data_ref)

Ping reviewers to help to apply. 

The review history can be found here:
https://patchwork.ffmpeg.org/project/ffmpeg/patch/CH3PR11MB793797554CDB411074364733B1742@CH3PR11MB7937.namprd11.prod.outlook.com/

> --
> 2.25.1
> 
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