Re: [FFmpeg-devel] [PATCH 3/3] avutil/opt: Preserve nb_channels in opt_free

[James Almer <jamrial@gmail.com>]

On 4/29/2024 9:48 PM, Michael Niedermayer wrote:
> Fixes: division by 0
> Fixes: decoder modifying demuxer channels on failure
> Fixes: -sseof -5 -i zgclab/ffmpeg_crash/poc3
> 
> Found-by: Wang Dawei and Zhou Geng, from Zhongguancun Laboratory
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavutil/opt.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/libavutil/opt.c b/libavutil/opt.c
> index ecbf7efe5fb..24c08e4bc06 100644
> --- a/libavutil/opt.c
> +++ b/libavutil/opt.c
> @@ -132,9 +132,11 @@ static void opt_free_elem(const AVOption *o, void *ptr)
>           av_dict_free((AVDictionary **)ptr);
>           break;
>   
> -    case AV_OPT_TYPE_CHLAYOUT:
> +    case AV_OPT_TYPE_CHLAYOUT: {
> +        int nb_channels = ((AVChannelLayout *)ptr)->nb_channels;
>           av_channel_layout_uninit((AVChannelLayout *)ptr);
> -        break;
> +        ((AVChannelLayout *)ptr)->nb_channels = nb_channels;
> +        break;}
>   
>       default:
>           break;

A little bit of context would be helpful here. What's using nb_channels 
after av_opt_free was called and where?
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