[FFmpeg-devel] [PATCH 3/3] avcodec/mlpdec: Check quant_step_size against huff_lsbs

[wm4]

On Sat, 20 May 2017 23:01:04 +0200
Michael Niedermayer <michael at niedermayer.cc> wrote:

> This reorders the operations so as to avoid computations with the above arguments
> before they have been initialized.
> Fixes part of 1708/clusterfuzz-testcase-minimized-5035111957397504
> 
> Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/mlpdec.c | 34 +++++++++++++++++++++++++---------
>  1 file changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/libavcodec/mlpdec.c b/libavcodec/mlpdec.c
> index c0a23c5f0d..11be380d27 100644
> --- a/libavcodec/mlpdec.c
> +++ b/libavcodec/mlpdec.c
> @@ -825,8 +825,6 @@ static int read_channel_params(MLPDecodeContext *m, unsigned int substr,
>          return AVERROR_INVALIDDATA;
>      }
>  
> -    cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
> -
>      return 0;
>  }
>  
> @@ -838,7 +836,8 @@ static int read_decoding_params(MLPDecodeContext *m, GetBitContext *gbp,
>  {
>      SubStream *s = &m->substream[substr];
>      unsigned int ch;
> -    int ret;
> +    int ret = 0;
> +    unsigned recompute_sho = 0;
>  
>      if (s->param_presence_flags & PARAM_PRESENCE)
>          if (get_bits1(gbp))
> @@ -878,19 +877,36 @@ static int read_decoding_params(MLPDecodeContext *m, GetBitContext *gbp,
>      if (s->param_presence_flags & PARAM_QUANTSTEP)
>          if (get_bits1(gbp))
>              for (ch = 0; ch <= s->max_channel; ch++) {
> -                ChannelParams *cp = &s->channel_params[ch];
> -
>                  s->quant_step_size[ch] = get_bits(gbp, 4);
>  
> -                cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
> +                recompute_sho |= 1<<ch;
>              }
>  
>      for (ch = s->min_channel; ch <= s->max_channel; ch++)
> -        if (get_bits1(gbp))
> +        if (get_bits1(gbp)) {
> +            recompute_sho |= 1<<ch;
>              if ((ret = read_channel_params(m, substr, gbp, ch)) < 0)
> -                return ret;
> +                goto fail;
> +        }
>  
> -    return 0;
> +


> +fail:
> +    for (ch = 0; ch <= s->max_channel; ch++) {
> +        if (recompute_sho & (1<<ch)) {
> +            ChannelParams *cp = &s->channel_params[ch];
> +
> +            if (cp->codebook > 0 && cp->huff_lsbs < s->quant_step_size[ch]) {
> +                if (ret >= 0) {
> +                    av_log(m->avctx, AV_LOG_ERROR, "quant_step_size larger than huff_lsbs\n");
> +                    ret = AVERROR_INVALIDDATA;
> +                }
> +                s->quant_step_size[ch] = 0;
> +            }
> +
> +            cp->sign_huff_offset = calculate_sign_huff(m, substr, ch);
> +        }
> +    }
> +    return ret;

What's all this stuff for?

>  }
>  
>  #define MSB_MASK(bits)  (-1u << (bits))