On 5/10/2025 11:36 AM, Michael Niedermayer wrote:
> Fixes: Assertion n>=0 && n<=32 failed at ./libavcodec/get_bits.h:406
> Fixes: 398527871/clusterfuzz-testcase-minimized-ffmpeg_dem_IAMF_fuzzer-6602025714647040
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavformat/iamf_parse.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/libavformat/iamf_parse.c b/libavformat/iamf_parse.c
> index abedfdb0668..37fb25962c4 100644
> --- a/libavformat/iamf_parse.c
> +++ b/libavformat/iamf_parse.c
> @@ -304,6 +304,8 @@ static int update_extradata(AVCodecParameters *codecpar)
>           skip_bits(&gb, 4);
>           put_bits(&pb, 4, codecpar->ch_layout.nb_channels); // set channel config
>           ret = put_bits_left(&pb);
> +        if (ret < 0)
> +            return AVERROR_INVALIDDATA;
>           put_bits(&pb, ret, get_bits_long(&gb, ret));
>           flush_put_bits(&pb);

No, there's something wrong because the buffer for PutBytes is fixed and 
local. Maybe 5 bytes was not enough.

Will have a look.