[FFmpeg-devel] [PATCH 2/2] avcodec/cdtoons: Fix off by 4 check on diff_size

[Paul B Mahol]

Are you sure this is correct?
Does asan reports exactly overread by 4?

On 2/20/20, Michael Niedermayer <michael at niedermayer.cc> wrote:
> Fixes: out of array read
> Fixes:
> 20742/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_CDTOONS_fuzzer-5738148607033344
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/cdtoons.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavcodec/cdtoons.c b/libavcodec/cdtoons.c
> index dc4fa6bf0b..d5dce6351f 100644
> --- a/libavcodec/cdtoons.c
> +++ b/libavcodec/cdtoons.c
> @@ -269,7 +269,7 @@ static int cdtoons_decode_frame(AVCodecContext *avctx,
> void *data,
>                  diff_size  = bytestream_get_be32(&buf);
>                  width      = bytestream_get_be16(&buf);
>                  height     = bytestream_get_be16(&buf);
> -                if (diff_size < 4 || diff_size - 4 > eod - buf) {
> +                if (diff_size < 8 || diff_size - 4 > eod - buf) {
>                      av_log(avctx, AV_LOG_WARNING, "Ran (seriously) out of
> data for Diff frame data.\n");
>                      return AVERROR_INVALIDDATA;
>                  }
> --
> 2.17.1
>
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