Re: [FFmpeg-devel] [PATCH 3/4] avcodec/h263dec: Sanity check against minimal I/P frame size

From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 3/4] avcodec/h263dec: Sanity check against minimal I/P frame size
Date: Mon, 15 Aug 2022 21:04:09 +0200
Message-ID: <DB6PR0101MB2214A3267513FE5CD48FEAD78F689@DB6PR0101MB2214.eurprd01.prod.exchangelabs.com> (raw)
In-Reply-To: <20220815175927.8743-3-michael@niedermayer.cc>

Michael Niedermayer:
> Fixes: Timeout
> Fixes: 49718/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-4874987894341632
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/h263dec.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/libavcodec/h263dec.c b/libavcodec/h263dec.c
> index 8db0eccd89..c03a55a4fd 100644
> --- a/libavcodec/h263dec.c
> +++ b/libavcodec/h263dec.c
> @@ -553,6 +553,8 @@ retry:
>      avctx->has_b_frames = !s->low_delay;
>  
>      if (CONFIG_MPEG4_DECODER && avctx->codec_id == AV_CODEC_ID_MPEG4) {
> +        if (s->pict_type != AV_PICTURE_TYPE_B && s->mb_num/2 > get_bits_count(&s->gb))
> +            return AVERROR_INVALIDDATA;
>          if (ff_mpeg4_workaround_bugs(avctx) == 1)
>              goto retry;
>          if (s->studio_profile != (s->idsp.idct == NULL))

Is it possible that you wanted to use get_bits_left() here?

- Andreas
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