[FFmpeg-cvslog] avcodec/mpeg4videodec: Fix integer overflow in mpeg4_decode_studio_block()

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Fri Aug 23 00:23:52 2019 +0200| [0e4a0e962cb0e422d2a350b875fc1e38d7b842a3] | committer: Michael Niedermayer

avcodec/mpeg4videodec: Fix integer overflow in mpeg4_decode_studio_block()

Fixes: signed integer overflow: 24023040 * 112 cannot be represented in type 'int'
Fixes: 16570/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5173275211071488

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Kieran Kunhya <kierank at obe.tv>
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=0e4a0e962cb0e422d2a350b875fc1e38d7b842a3
---

 libavcodec/mpeg4videodec.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
index b6f2ae7b7b..25f528d59e 100644
--- a/libavcodec/mpeg4videodec.c
+++ b/libavcodec/mpeg4videodec.c
@@ -1826,6 +1826,7 @@ static int mpeg4_decode_studio_block(MpegEncContext *s, int32_t block[64], int n
     uint32_t flc;
     const int min = -1 *  (1 << (s->avctx->bits_per_raw_sample + 6));
     const int max =      ((1 << (s->avctx->bits_per_raw_sample + 6)) - 1);
+    int shift =  3 - s->dct_precision;
 
     mismatch = 1;
 
@@ -1921,7 +1922,7 @@ static int mpeg4_decode_studio_block(MpegEncContext *s, int32_t block[64], int n
             else
                 block[j] = flc;
         }
-        block[j] = ((8 * 2 * block[j] * quant_matrix[j] * s->qscale) >> s->dct_precision) / 32;
+        block[j] = ((block[j] * quant_matrix[j] * s->qscale) * (1 << shift)) / 16;
         block[j] = av_clip(block[j], min, max);
         mismatch ^= block[j];
     }