Re: [FFmpeg-devel] [PATCH 7/8] avcodec/vvc/cabac: Check k in kth_order_egk_decode()

[Nuo Mi <nuomi2021-at-gmail.com@ffmpeg.org>]

On Fri, Jun 20, 2025 at 8:40 AM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> The return value is int we can thus not handle 31 or more bits
>
> Fixes: integer overflow
> Fixes:
> 418396701/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VVC_fuzzer-4730994378997760
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by
> <https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by>:
> Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/vvc/cabac.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/libavcodec/vvc/cabac.c b/libavcodec/vvc/cabac.c
> index 6847ce59aff..78703cb065e 100644
> --- a/libavcodec/vvc/cabac.c
> +++ b/libavcodec/vvc/cabac.c
> @@ -937,6 +937,8 @@ static int kth_order_egk_decode(CABACContext *c, int k)
>
>      while (bit) {
>          bit = get_cabac_bypass(c);
> +        if (k >= 31)
> +            return AVERROR_PATCHWELCOME;
>
Hi Michael,
Thank you for the patch.

We may need to check the return value from ff_vvc_palette_predictor_run[1],
as it also uses kth_order_egk_decode

[1]: https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/vvc/ctu.c#L1860

         value += bit << k++;
>      }
>
> --
> 2.49.0
>
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