[FFmpeg-cvslog] avcodec/vc1_block: Fix undefined behavior in ac prediction rescaling
Michael Niedermayer
git at videolan.org
Sat Nov 23 00:30:36 EET 2019
ffmpeg | branch: release/3.4 | Michael Niedermayer <michael at niedermayer.cc> | Thu Oct 31 15:00:32 2019 +0100| [313af229425799e15f0d810cbec1af65e5293a8a] | committer: Michael Niedermayer
avcodec/vc1_block: Fix undefined behavior in ac prediction rescaling
The intermediates are required to fit in 12bit (8.1.3.9 Coefficient Scaling)
See SMPTE 421M-2006 and Amendment 1-2007
Fixes: signed integer overflow: -20691 * 262144 cannot be represented in type 'int'
Fixes: 18479/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VC1_fuzzer-5128912371187712
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit 7fc1baf0ca83ef06014878290339a59735603959)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=313af229425799e15f0d810cbec1af65e5293a8a
---
libavcodec/vc1_block.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/libavcodec/vc1_block.c b/libavcodec/vc1_block.c
index 51a2f41316..b4a674978f 100644
--- a/libavcodec/vc1_block.c
+++ b/libavcodec/vc1_block.c
@@ -1013,10 +1013,10 @@ static int vc1_decode_intra_block(VC1Context *v, int16_t block[64], int n,
return AVERROR_INVALIDDATA;
if (dc_pred_dir) { // left
for (k = 1; k < 8; k++)
- block[k << v->left_blk_sh] += (ac_val[k] * q2 * ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
+ block[k << v->left_blk_sh] += (int)(ac_val[k] * q2 * (unsigned)ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
} else { //top
for (k = 1; k < 8; k++)
- block[k << v->top_blk_sh] += (ac_val[k + 8] * q2 * ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
+ block[k << v->top_blk_sh] += (int)(ac_val[k + 8] * q2 * (unsigned)ff_vc1_dqscale[q1 - 1] + 0x20000) >> 18;
}
} else {
if (dc_pred_dir) { // left
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