[FFmpeg-devel] [PATCH 2/2] avcodec/binkdsp: Fix integer overflows in idct

[Peter Ross]

On Tue, Jun 18, 2019 at 02:55:02PM +0200, Michael Niedermayer wrote:
> Fixes: signed integer overflow: 3784 * 682038 cannot be represented in type 'int'
> Fixes: 15265/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BINK_fuzzer-5088311799971840
> Fixes: 15268/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_BINK_fuzzer-5666502344179712
> 
> 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/binkdsp.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/libavcodec/binkdsp.c b/libavcodec/binkdsp.c
> index 9d70e2326f..a357d31672 100644
> --- a/libavcodec/binkdsp.c
> +++ b/libavcodec/binkdsp.c
> @@ -33,20 +33,22 @@
>  #define A3  3784
>  #define A4 -5352
>  
> +#define MUL(X,Y) ((int)((unsigned)(X) * (Y)) >> 11)
> +
>  #define IDCT_TRANSFORM(dest,s0,s1,s2,s3,s4,s5,s6,s7,d0,d1,d2,d3,d4,d5,d6,d7,munge,src) {\
>      const int a0 = (src)[s0] + (src)[s4]; \
>      const int a1 = (src)[s0] - (src)[s4]; \
>      const int a2 = (src)[s2] + (src)[s6]; \
> -    const int a3 = (A1*((src)[s2] - (src)[s6])) >> 11; \
> +    const int a3 = MUL(A1, (src)[s2] - (src)[s6]); \
>      const int a4 = (src)[s5] + (src)[s3]; \
>      const int a5 = (src)[s5] - (src)[s3]; \
>      const int a6 = (src)[s1] + (src)[s7]; \
>      const int a7 = (src)[s1] - (src)[s7]; \
>      const int b0 = a4 + a6; \
> -    const int b1 = (A3*(a5 + a7)) >> 11; \
> -    const int b2 = ((A4*a5) >> 11) - b0 + b1; \
> -    const int b3 = (A1*(a6 - a4) >> 11) - b2; \
> -    const int b4 = ((A2*a7) >> 11) + b3 - b1; \
> +    const int b1 = MUL(A3, a5 + a7); \
> +    const int b2 = MUL(A4, a5) - b0 + b1; \
> +    const int b3 = MUL(A1, a6 - a4) - b2; \
> +    const int b4 = MUL(A2, a7) + b3 - b1; \
>      (dest)[d0] = munge(a0+a2   +b0); \
>      (dest)[d1] = munge(a1+a3-a2+b2); \
>      (dest)[d2] = munge(a1-a3+a2+b3); \
> -- 
> 2.21.0

approve both parts 1 & 2.

have also tested these changes against my pile of reference binkb files.

-- Peter
(A907 E02F A6E5 0CD2 34CD 20D2 6760 79C5 AC40 DD6B)
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