[FFmpeg-cvslog] avcodec/alsdec: Fix invalid shift in multiply()

[Michael Niedermayer]

ffmpeg | branch: release/4.1 | Michael Niedermayer <michael at niedermayer.cc> | Thu Jun 20 19:09:11 2019 +0200| [9ede5cab3afae1473a63f148b15af9d88809e646] | committer: Michael Niedermayer

avcodec/alsdec: Fix invalid shift in multiply()

Fixes: shift exponent -24 is negative
Fixes: 15292/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5768533318828032

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 f30be1ec9856551d96f3876eec5f8b8abf456b81)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=9ede5cab3afae1473a63f148b15af9d88809e646
---

 libavcodec/alsdec.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index ca8701e6d0..891f742e7e 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -1379,6 +1379,9 @@ static SoftFloat_IEEE754 multiply(SoftFloat_IEEE754 a, SoftFloat_IEEE754 b) {
     mantissa_temp = (uint64_t)a.mant * (uint64_t)b.mant;
     mask_64       = (uint64_t)0x1 << 47;
 
+    if (!mantissa_temp)
+        return FLOAT_0;
+
     // Count the valid bit count
     while (!(mantissa_temp & mask_64) && mask_64) {
         bit_count--;