[FFmpeg-devel] [PATCH 1/6] avcodec/eatgq: : Check index increments in tgq_decode_block()

[Peter Ross]

On Thu, Jan 12, 2023 at 12:54:27AM +0100, Michael Niedermayer wrote:
> Fixes: out of array access
> Fixes: 48567/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_EATGQ_fuzzer-6743211456724992
> 
> 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/eatgq.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/libavcodec/eatgq.c b/libavcodec/eatgq.c
> index 89e9f20880..beb9f4d046 100644
> --- a/libavcodec/eatgq.c
> +++ b/libavcodec/eatgq.c
> @@ -56,7 +56,7 @@ static av_cold int tgq_decode_init(AVCodecContext *avctx)
>      return 0;
>  }
>  
> -static void tgq_decode_block(TgqContext *s, int16_t block[64], GetBitContext *gb)
> +static int tgq_decode_block(TgqContext *s, int16_t block[64], GetBitContext *gb)
>  {
>      const uint8_t *scantable = ff_zigzag_direct;
>      int i, j, value;
> @@ -64,6 +64,8 @@ static void tgq_decode_block(TgqContext *s, int16_t block[64], GetBitContext *gb
>      for (i = 1; i < 64;) {
>          switch (show_bits(gb, 3)) {
>          case 4:
> +            if (i >= 63)
> +                return AVERROR_INVALIDDATA;
>              block[scantable[i++]] = 0;
>          case 0:
>              block[scantable[i++]] = 0;
> @@ -73,6 +75,8 @@ static void tgq_decode_block(TgqContext *s, int16_t block[64], GetBitContext *gb
>          case 1:
>              skip_bits(gb, 2);
>              value = get_bits(gb, 6);
> +            if (value > 64 - i)
> +                return AVERROR_INVALIDDATA;
>              for (j = 0; j < value; j++)
>                  block[scantable[i++]] = 0;
>              break;
> @@ -100,6 +104,7 @@ static void tgq_decode_block(TgqContext *s, int16_t block[64], GetBitContext *gb
>          }
>      }
>      block[0] += 128 << 4;
> +    return 0;
>  }
>  
>  static void tgq_idct_put_mb(TgqContext *s, int16_t (*block)[64], AVFrame *frame,
> -- 
> 2.17.1

Hi Michael,

The return value of tgq_decode() is not checked anywhere.

Need to add something like:

-            tgq_decode_block(s, s->block[i], &gb);
+            if ((ret = tgq_decode_block(s, s->block[i], &gb)) < 0)
+                return ret;

(From earlier attempt at fixing this: https://patchwork.ffmpeg.org/project/ffmpeg/patch/1ab7c3994301a243fc64d59d6a08e3a2b364e411.1666774269.git.pross@xvid.org/)

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
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