[FFmpeg-devel] [PATCH] avcodec/bonk: Check step

[Rémi Denis-Courmont]

Le sunnuntaina 2. lokakuuta 2022, 18.43.23 EEST Michael Niedermayer a écrit :
> Fixes: signed integer overflow: 2040812214 + 255101526 cannot be represented
> in type 'int' Fixes:
> 51323/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BONK_fuzzer-4791481
> 067503616
> 
> 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/bonk.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/libavcodec/bonk.c b/libavcodec/bonk.c
> index 409694f710d..32f7c9b9bdb 100644
> --- a/libavcodec/bonk.c
> +++ b/libavcodec/bonk.c
> @@ -187,6 +187,9 @@ static int intlist_read(BonkContext *s, int *buf, int
> entries, int base_2_part) if (!dominant)
>                  n_zeros += steplet;
> 
> +            if (step > INT_MAX/9*8)
> +                return AVERROR_INVALIDDATA;
> +
>              step += step / 8;
>          } else if (steplet > 0) {
>              int actual_run = read_uint_max(s, steplet - 1);

No problem with this patch *specifically* but wouldn't it be more effective to 
fix that sort of issue with checked arithmetic, e.g. something like:

        if (av_ckd_add(&step, step, step / 8))
            return AVERROR_INVALIDDATA;

...especially on 64-bit systems whence this is really just an add. This also 
avoids having to figure out what the exact boundary value is.

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