[FFmpeg-devel] [PATCH 1/2] avcodec/apedec: Fix integer overflows in predictor_update_3930()

[Michael Niedermayer]

Fixes: signed integer overflow: 1074134419 - -1075212485 cannot be represented in type 'int'
Fixes: 43273/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-4706880883130368

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 b932263012e..607304fe363 100644
--- a/libavcodec/apedec.c
+++ b/libavcodec/apedec.c
@@ -1088,13 +1088,13 @@ static av_always_inline int predictor_update_3930(APEPredictor *p,
                                                   const int delayA)
 {
     int32_t predictionA, sign;
-    int32_t d0, d1, d2, d3;
+    uint32_t d0, d1, d2, d3;
 
     p->buf[delayA]     = p->lastA[filter];
     d0 = p->buf[delayA    ];
-    d1 = p->buf[delayA    ] - p->buf[delayA - 1];
-    d2 = p->buf[delayA - 1] - p->buf[delayA - 2];
-    d3 = p->buf[delayA - 2] - p->buf[delayA - 3];
+    d1 = p->buf[delayA    ] - (unsigned)p->buf[delayA - 1];
+    d2 = p->buf[delayA - 1] - (unsigned)p->buf[delayA - 2];
+    d3 = p->buf[delayA - 2] - (unsigned)p->buf[delayA - 3];
 
     predictionA = d0 * p->coeffsA[filter][0] +
                   d1 * p->coeffsA[filter][1] +
@@ -1105,10 +1105,10 @@ static av_always_inline int predictor_update_3930(APEPredictor *p,
     p->filterA[filter] = p->lastA[filter] + ((int)(p->filterA[filter] * 31U) >> 5);
 
     sign = APESIGN(decoded);
-    p->coeffsA[filter][0] += ((d0 < 0) * 2 - 1) * sign;
-    p->coeffsA[filter][1] += ((d1 < 0) * 2 - 1) * sign;
-    p->coeffsA[filter][2] += ((d2 < 0) * 2 - 1) * sign;
-    p->coeffsA[filter][3] += ((d3 < 0) * 2 - 1) * sign;
+    p->coeffsA[filter][0] += (((int32_t)d0 < 0) * 2 - 1) * sign;
+    p->coeffsA[filter][1] += (((int32_t)d1 < 0) * 2 - 1) * sign;
+    p->coeffsA[filter][2] += (((int32_t)d2 < 0) * 2 - 1) * sign;
+    p->coeffsA[filter][3] += (((int32_t)d3 < 0) * 2 - 1) * sign;
 
     return p->filterA[filter];
 }
-- 
2.17.1