[FFmpeg-devel] [PATCH 1/5] avcodec/apedec: Fix 32bit int overflow in do_apply_filter()

[Tomas Härdin]

tis 2019-09-03 klockan 02:14 +0200 skrev Michael Niedermayer:
> Fixes: signed integer overflow: 2147480546 + 4096 cannot be represented in type 'int'
> Fixes: 16280/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5123442566758400
> 
> 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 490b11b94e..ed22f0f019 100644
> --- a/libavcodec/apedec.c
> +++ b/libavcodec/apedec.c
> @@ -1266,7 +1266,7 @@ static void do_apply_filter(APEContext *ctx, int version, APEFilter *f,
>                                                       f->delay - order,
>                                                       f->adaptcoeffs - order,
>                                                       order, APESIGN(*data));
> -        res = (res + (1 << (fracbits - 1))) >> fracbits;
> +        res = (int)(res + (1U << (fracbits - 1))) >> fracbits;

Does this mean the old code was decoding incorrectly, or is this just
an UB fix? (fixing UBs is good of course)

/Tomas