[FFmpeg-devel] [PATCH 2/2] avcodec/zmbv: Check that the decompressed data is large enough to contain MVs or an intra frame

Paul B Mahol onemda at gmail.com
Mon Sep 17 22:39:01 EEST 2018


On 9/17/18, Michael Niedermayer <michael at niedermayer.cc> wrote:
> Fixes: Timeout
> Fixes:
> 10182/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ZMBV_fuzzer-6245951174344704
>
> 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/zmbv.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/libavcodec/zmbv.c b/libavcodec/zmbv.c
> index 177993d0a6..0c2daf47c2 100644
> --- a/libavcodec/zmbv.c
> +++ b/libavcodec/zmbv.c
> @@ -409,6 +409,7 @@ static int decode_frame(AVCodecContext *avctx, void
> *data, int *got_frame, AVPac
>      int zret = Z_OK; // Zlib return code
>      int len = buf_size;
>      int hi_ver, lo_ver, ret;
> +    int min_size;
>
>      /* parse header */
>      if (len < 1)
> @@ -510,7 +511,11 @@ static int decode_frame(AVCodecContext *avctx, void
> *data, int *got_frame, AVPac
>          memset(c->prev, 0, avctx->width * avctx->height * (c->bpp / 8));
>          c->decode_intra= decode_intra;
>      }
> -
> +    if (c->flags & ZMBV_KEYFRAME) {
> +        min_size = avctx->width * avctx->height * (c->bpp / 8);

Do you have proof this is really minimal possible thing zlib can
compress single frame?
If not, Drop. It.

> +    } else {
> +        min_size = (c->bx * c->by * 2 + 3) & ~3;
> +    }
>      if (!c->decode_intra) {
>          av_log(avctx, AV_LOG_ERROR, "Error! Got no format or no
> keyframe!\n");
>          return AVERROR_INVALIDDATA;
> @@ -539,6 +544,10 @@ static int decode_frame(AVCodecContext *avctx, void
> *data, int *got_frame, AVPac
>          }
>          c->decomp_len = c->zstream.total_out;
>      }
> +    if (min_size > c->decomp_len) {
> +        av_log(avctx, AV_LOG_ERROR, "input too small\n");
> +        return AVERROR_INVALIDDATA;
> +    }
>      if (c->flags & ZMBV_KEYFRAME) {
>          frame->key_frame = 1;
>          frame->pict_type = AV_PICTURE_TYPE_I;
> --
> 2.18.0
>
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