[FFmpeg-devel] [PATCH 4/4] avcodec/apedec: Fix multiple integer overflows in filter_3800()

[Reimar Döffinger]

On 16.06.2019, at 12:30, Lynne <dev at lynne.ee> wrote:

> Jun 16, 2019, 10:57 AM by michael at niedermayer.cc:
> 
>> Fixes: left shift of negative value -4
>> Fixes: signed integer overflow: -15091694 * 167 cannot be represented in type 'int'
>> Fixes: signed integer overflow: 1898547155 + 453967445 cannot be represented in type 'int'
>> Fixes: 15258/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5759095564402688
>> 
>> 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 | 16 ++++++++--------
>> 1 file changed, 8 insertions(+), 8 deletions(-)
>> 
>> diff --git a/libavcodec/apedec.c b/libavcodec/apedec.c
>> index 61ebfdafd5..f1bfc634c2 100644
>> --- a/libavcodec/apedec.c
>> +++ b/libavcodec/apedec.c
>> @@ -859,22 +859,22 @@ static av_always_inline int filter_3800(APEPredictor *p,
>> return predictionA;
>> }
>> d2 =  p->buf[delayA];
>> -    d1 = (p->buf[delayA] - p->buf[delayA - 1]) << 1;
>> -    d0 =  p->buf[delayA] + ((p->buf[delayA - 2] - p->buf[delayA - 1]) << 3);
>> +    d1 = (p->buf[delayA] - p->buf[delayA - 1]) * 2;
>> +    d0 =  p->buf[delayA] + ((p->buf[delayA - 2] - p->buf[delayA - 1]) * 8);
>> d3 =  p->buf[delayB] * 2 - p->buf[delayB - 1];
>> d4 =  p->buf[delayB];
>> 
>> -    predictionA = d0 * p->coeffsA[filter][0] +
>> -                  d1 * p->coeffsA[filter][1] +
>> -                  d2 * p->coeffsA[filter][2];
>> +    predictionA = d0 * (unsigned)p->coeffsA[filter][0] +
>> +                  d1 * (unsigned)p->coeffsA[filter][1] +
>> +                  d2 * (unsigned)p->coeffsA[filter][2];
>> 
>> sign = APESIGN(decoded);
>> p->coeffsA[filter][0] += (((d0 >> 30) & 2) - 1) * sign;
>> p->coeffsA[filter][1] += (((d1 >> 28) & 8) - 4) * sign;
>> p->coeffsA[filter][2] += (((d2 >> 28) & 8) - 4) * sign;
>> 
>> -    predictionB = d3 * p->coeffsB[filter][0] -
>> -                  d4 * p->coeffsB[filter][1];
>> +    predictionB = d3 * (unsigned)p->coeffsB[filter][0] -
>> +                  d4 * (unsigned)p->coeffsB[filter][1];
>> p->lastA[filter] = decoded + (predictionA >> 11);
>> sign = APESIGN(p->lastA[filter]);
>> p->coeffsB[filter][0] += (((d3 >> 29) & 4) - 2) * sign;
>> @@ -902,7 +902,7 @@ static void long_filter_high_3800(int32_t *buffer, int order, int shift, int len
>> dotprod = 0;
>> sign = APESIGN(buffer[i]);
>> for (j = 0; j < order; j++) {
>> -            dotprod += delay[j] * coeffs[j];
>> +            dotprod += delay[j] * (unsigned)coeffs[j];
>> coeffs[j] += ((delay[j] >> 31) | 1) * sign;
>> }
>> buffer[i] -= dotprod >> shift;
>> 
> 
> This code is DSP, overflows should be allowed in case input is corrupt.

Then get the C standard changed or use a different language.
But in C overflows on signed types absolutely are not Ok.