Re: [FFmpeg-devel] [PATCH 01/11] avcodec/adpcm: Fix integer overflow in intermediate in ADPCM_XMD

[Paul B Mahol <onemda@gmail.com>]

On Sun, Apr 16, 2023 at 6:48 PM Michael Niedermayer <michael@niedermayer.cc>
wrote:

> Fixes: runtime error: signed integer overflow: 2140143616 + 254665816
> cannot be represented in type 'int'
> Fixes:
> 45982/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ADPCM_XMD_fuzzer-6690181676924928
>
> As a sideeffect this simplifies the equation, the high bits are different
> after this but only
> the low 16bits are stored and used in later steps.
> The change is untested as there are no fate testcases, no sample files on
> the server, no links on
> the mailing list and no reports on trac referencing this format that i
> could find.
>
> Found-by: continuous fuzzing process
> https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
> Signed-off-by
> <https://github.com/google/oss-fuzz/tree/master/projects/ffmpegSigned-off-by>:
> Michael Niedermayer <michael@niedermayer.cc>
> ---
>  libavcodec/adpcm.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/adpcm.c b/libavcodec/adpcm.c
> index 451696932d1..d8f334cf5a0 100644
> --- a/libavcodec/adpcm.c
> +++ b/libavcodec/adpcm.c
> @@ -1579,11 +1579,11 @@ static int adpcm_decode_frame(AVCodecContext
> *avctx, AVFrame *frame,
>                      nibble[0] = sign_extend(byte & 15, 4);
>                      nibble[1] = sign_extend(byte >> 4, 4);
>
> -                    out[2+n*2] = (nibble[0]*(scale<<14) +
> (history[0]*29336) - (history[1]*13136)) >> 14;
> +                    out[2+n*2  ] = nibble[0]*scale + ((history[0]*3667 -
> history[1]*1642) >> 11);
>

Please commit this with no extra spaces added.

Here is sample: https://0x0.st/H8Le.xmd


>                      history[1] = history[0];
>                      history[0] = out[2+n*2];
>
> -                    out[2+n*2+1] = (nibble[1]*(scale<<14) +
> (history[0]*29336) - (history[1]*13136)) >> 14;
> +                    out[2+n*2+1] = nibble[1]*scale + ((history[0]*3667 -
> history[1]*1642) >> 11);
>                      history[1] = history[0];
>                      history[0] = out[2+n*2+1];
>                  }
> --
> 2.17.1
>
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