[FFmpeg-devel] [PATCH 2/4] avcodec/vc1_block: Fix integer overflow in AC rescaling in vc1_decode_i_block_adv()

[Michael Niedermayer]

Fixes: signed integer overflow: 50176 * 262144 cannot be represented in type 'int'
Fixes: 18629/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1IMAGE_fuzzer-5182370286403584

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/vc1_block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/vc1_block.c b/libavcodec/vc1_block.c
index 4c6dfaf6bf..a6673ad58a 100644
--- a/libavcodec/vc1_block.c
+++ b/libavcodec/vc1_block.c
@@ -889,7 +889,7 @@ static int vc1_decode_i_block_adv(VC1Context *v, int16_t block[64], int n,
                 q2 = FFABS(q2) * 2 + ((q2 < 0) ? 0 : v->halfpq) - 1;
             if (q2 && q1 != q2) {
                 for (k = 1; k < 8; k++)
-                    ac_val2[k] = (ac_val2[k] * q2 * ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
+                    ac_val2[k] = (int)(ac_val2[k] * q2 * (unsigned)ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
             }
             for (k = 1; k < 8; k++) {
                 block[k << sh] = ac_val2[k] * scale;
-- 
2.23.0