[FFmpeg-devel] [PATCH 3/5] avcodec/xvididct: Fix integer overflow in idct_row()

[Michael Niedermayer]

Fixes: signed integer overflow: -1403461578 + -843974775 cannot be represented in type 'int'
Fixes: 60868/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG1VIDEO_fuzzer-4599793035378688

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/xvididct.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/libavcodec/xvididct.c b/libavcodec/xvididct.c
index f338901ab2..43ea927437 100644
--- a/libavcodec/xvididct.c
+++ b/libavcodec/xvididct.c
@@ -69,24 +69,24 @@ static int idct_row(short *in, const int *const tab, int rnd)
     if (!(right | in[4])) {
         const int k = c4 * in[0] + rnd;
         if (left) {
-            const int a0 = k + c2 * in[2];
-            const int a1 = k + c6 * in[2];
-            const int a2 = k - c6 * in[2];
-            const int a3 = k - c2 * in[2];
+            const unsigned a0 = k + c2 * in[2];
+            const unsigned a1 = k + c6 * in[2];
+            const unsigned a2 = k - c6 * in[2];
+            const unsigned a3 = k - c2 * in[2];
 
             const int b0 = c1 * in[1] + c3 * in[3];
             const int b1 = c3 * in[1] - c7 * in[3];
             const int b2 = c5 * in[1] - c1 * in[3];
             const int b3 = c7 * in[1] - c5 * in[3];
 
-            in[0] = (a0 + b0) >> ROW_SHIFT;
-            in[1] = (a1 + b1) >> ROW_SHIFT;
-            in[2] = (a2 + b2) >> ROW_SHIFT;
-            in[3] = (a3 + b3) >> ROW_SHIFT;
-            in[4] = (a3 - b3) >> ROW_SHIFT;
-            in[5] = (a2 - b2) >> ROW_SHIFT;
-            in[6] = (a1 - b1) >> ROW_SHIFT;
-            in[7] = (a0 - b0) >> ROW_SHIFT;
+            in[0] = (int)(a0 + b0) >> ROW_SHIFT;
+            in[1] = (int)(a1 + b1) >> ROW_SHIFT;
+            in[2] = (int)(a2 + b2) >> ROW_SHIFT;
+            in[3] = (int)(a3 + b3) >> ROW_SHIFT;
+            in[4] = (int)(a3 - b3) >> ROW_SHIFT;
+            in[5] = (int)(a2 - b2) >> ROW_SHIFT;
+            in[6] = (int)(a1 - b1) >> ROW_SHIFT;
+            in[7] = (int)(a0 - b0) >> ROW_SHIFT;
         } else {
             const int a0 = k >> ROW_SHIFT;
             if (a0) {
-- 
2.17.1