[FFmpeg-devel] [PATCH] avcodec/mobiclip: Check quantizer before table setup

[Paul B Mahol]

On Fri, Sep 11, 2020 at 01:19:59AM +0200, Michael Niedermayer wrote:
> Fixes: index -1 out of bounds for type 'const uint8_t [6][16]'
> Fixes: out of array read
> Fixes: shift exponent -21 is negative
> Fixes: 25422/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MOBICLIP_fuzzer-5748258226569216
> Fixes: shift exponent 8039082 is too large for 32-bit type 'int'
> Fixes: 25430/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MOBICLIP_fuzzer-5698567770210304
> 
> 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/mobiclip.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/mobiclip.c b/libavcodec/mobiclip.c
> index d147eddbae..13f0edc89d 100644
> --- a/libavcodec/mobiclip.c
> +++ b/libavcodec/mobiclip.c
> @@ -1323,6 +1323,10 @@ static int mobiclip_decode(AVCodecContext *avctx, void *data,
>          }
>      } else {
>          MotionXY *motion = s->motion;
> +        int quantizer = s->quantizer + get_se_golomb(gb);
> +
> +        if (quantizer < 12 || quantizer > 161)

>From where this numbers come?
I think this is too aggressive.

> +            return AVERROR_INVALIDDATA;
>  
>          memset(motion, 0, s->motion_size);
>  
> @@ -1330,7 +1334,7 @@ static int mobiclip_decode(AVCodecContext *avctx, void *data,
>          frame->key_frame = 0;
>          s->dct_tab_idx = 0;
>  
> -        setup_qtables(avctx, s->quantizer + get_se_golomb(gb));
> +        setup_qtables(avctx, quantizer);
>          for (int y = 0; y < avctx->height; y += 16) {
>              for (int x = 0; x < avctx->width; x += 16) {
>                  int idx;
> -- 
> 2.17.1
> 
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