Re: [FFmpeg-devel] [PATCH] lavc/vvc: Add check to num_multi_layer_olss

[Nuo Mi <nuomi2021@gmail.com>]

On Tue, Jan 30, 2024 at 5:41 PM <post@frankplowman.com> wrote:

> From: Frank Plowman <post@frankplowman.com>
>
> Check that vps_each_layer_is_an_ols_flag, which indicates that "at
> least one OLS specified by the VPS contains more than one layer," is
> set if num_multi_layer_olss is non-zero.
>
> Fixes:
> 65160/clusterfuzz-testcase-minimized-ffmpeg_BSF_VVC_METADATA_fuzzer-4665241535119360
>
> 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>:
> Frank Plowman <post@frankplowman.com>
> ---
>  libavcodec/cbs_h266_syntax_template.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/libavcodec/cbs_h266_syntax_template.c
> b/libavcodec/cbs_h266_syntax_template.c
> index 2f3478e5e1..37dc3acba0 100644
> --- a/libavcodec/cbs_h266_syntax_template.c
> +++ b/libavcodec/cbs_h266_syntax_template.c
> @@ -911,6 +911,8 @@ static int FUNC(vps) (CodedBitstreamContext *ctx,
> RWContext *rw,
>                  num_multi_layer_olss++;
>              }
>          }
> +        if (!current->vps_each_layer_is_an_ols_flag &&
> num_multi_layer_olss == 0)
> +            return AVERROR_INVALIDDATA;
>      }
>
> The specification does not provide information on how to obtain
TotalNumOlss (total_num_olss) when ols_mode_idc is set to 3.
Therefore, the earlier line "u(8, vps_num_ptls_minus1, 0, total_num_olss -
1)" is undefined.
We'd better return a patch welcome error instead of printing a warning
before vps_num_ptls_minus1 line

     for (i = 0; i <= current->vps_num_ptls_minus1; i++) {
> --
> 2.43.0
>
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