[FFmpeg-devel] [PATCH 2/3] avcodec/siren: Check available bits at frame start

[James Almer]

On 9/28/2021 7:28 PM, Michael Niedermayer wrote:
> Fixes: Timeout
> Fixes: 39089/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MSNSIREN_fuzzer-6677219854909440
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Suggested-by: James Almer <jamrial at gmail.com>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>   libavcodec/siren.c | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/siren.c b/libavcodec/siren.c
> index 7f084172a4c..8c9628e2d8e 100644
> --- a/libavcodec/siren.c
> +++ b/libavcodec/siren.c
> @@ -447,6 +447,8 @@ static int decode_envelope(SirenContext *s, GetBitContext *gb,
>           int index = 0;
>   
>           do {
> +            if (get_bits_left(gb) < 4)

If the idea is that there will be enough bits to read rate_control after 
this function returns, then this should also take into account the 
get_bits1() below.

> +                return AVERROR_INVALIDDATA;
>               index = differential_decoder_tree[i - 1][index][get_bits1(gb)];
>           } while (index > 0);
>   
> @@ -727,9 +729,11 @@ static int siren_decode(AVCodecContext *avctx, void *data,
>   
>       skip_bits(gb, s->sample_rate_bits);
>   
> -    decode_envelope(s, gb, s->number_of_regions,
> +    ret = decode_envelope(s, gb, s->number_of_regions,
>                       s->decoder_standard_deviation,
>                       s->absolute_region_power_index, s->esf_adjustment);
> +    if (ret < 0)
> +        return ret;
>   
>       rate_control = get_bits(gb, 4);
>   
>