Re: [FFmpeg-devel] [PATCH 2/4] avcodec/cbs_vp8: Do not use assert to check for end

From: James Almer <jamrial@gmail.com>
To: ffmpeg-devel@ffmpeg.org
Subject: Re: [FFmpeg-devel] [PATCH 2/4] avcodec/cbs_vp8: Do not use assert to check for end
Date: Sat, 16 Dec 2023 09:20:24 -0300
Message-ID: <67b46620-8a26-472b-93b9-29b51928464b@gmail.com> (raw)
In-Reply-To: <20231216121619.19436-2-michael@niedermayer.cc>

On 12/16/2023 9:16 AM, Michael Niedermayer wrote:
> Fixes: abort()
> Fixes: 64232/clusterfuzz-testcase-minimized-ffmpeg_BSF_TRACE_HEADERS_fuzzer-5417957987319808
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> ---
>   libavcodec/cbs_vp8.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/cbs_vp8.c b/libavcodec/cbs_vp8.c
> index 01d4b9cefef..b76cde98517 100644
> --- a/libavcodec/cbs_vp8.c
> +++ b/libavcodec/cbs_vp8.c
> @@ -329,7 +329,9 @@ static int cbs_vp8_read_unit(CodedBitstreamContext *ctx,
>   
>       pos = get_bits_count(&gbc);
>       pos /= 8;
> -    av_assert0(pos <= unit->data_size);
> +
> +    if (pos > unit->data_size)
> +        return AVERROR_INVALIDDATA;

Wouldn't this be hiding a bug in the parsing code? The assert is there 
to ensure no overread happened.

>   
>       frame->data_ref = av_buffer_ref(unit->data_ref);
>       if (!frame->data_ref)
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