[FFmpeg-devel] [PATCH 4/5] avcodec/apedec: Fix integer overflow in intermediate

[Andreas Rheinhardt]

Michael Niedermayer:
> Fixes: signed integer overflow: 559334865 * 4 cannot be represented in type 'int'
> Fixes: 37929/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-6751932295806976
> 
> 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/apedec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
> index bf481ba3549..23318be0613 100644
> --- a/libavcodec/apedec.c
> +++ b/libavcodec/apedec.c
> @@ -1337,7 +1337,7 @@ static void do_apply_filter(APEContext *ctx, int version, APEFilter *f,
>              absres = FFABSU(res);
>              if (absres)
>                  *f->adaptcoeffs = APESIGN(res) *
> -                                  (8 << ((absres > f->avg * 3) + (absres > f->avg * 4 / 3)));
> +                                  (8 << ((absres > f->avg * 3) + (absres > f->avg * 4LL / 3)));
>                  /* equivalent to the following code
>                      if (absres <= f->avg * 4 / 3)
>                          *f->adaptcoeffs = APESIGN(res) * 8;
> 
How about using f->avg + f->avg / 3? Given that you haven't modified the
f->avg * 3 before, this should be save.

- Andreas