[FFmpeg-cvslog] avcodec/alsdec: fix undefined shift in multiply()

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Sun Jul  7 00:03:51 2019 +0200| [b880b3b236ddd00f85ea502b4c17a145fd26c790] | committer: Michael Niedermayer

avcodec/alsdec: fix undefined shift in multiply()

Fixes: left shift of negative value -6
Fixes: 15564/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_ALS_fuzzer-5701655938465792

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

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=b880b3b236ddd00f85ea502b4c17a145fd26c790
---

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

diff --git a/libavcodec/alsdec.c b/libavcodec/alsdec.c
index 8201deb366..6b5774175b 100644
--- a/libavcodec/alsdec.c
+++ b/libavcodec/alsdec.c
@@ -1416,7 +1416,7 @@ static SoftFloat_IEEE754 multiply(SoftFloat_IEEE754 a, SoftFloat_IEEE754 b) {
         return_val = 0x80000000U;
     }
 
-    return_val |= (a.exp + b.exp + bit_count - 47) << 23;
+    return_val |= ((unsigned)av_clip(a.exp + b.exp + bit_count - 47, -126, 127) << 23) & 0x7F800000;
     return_val |= mantissa;
     return av_bits2sf_ieee754(return_val);
 }