[FFmpeg-cvslog] avcodec/vorbisdec: fix FASTDIV usage for vr_type == 2

[Michael Niedermayer]

ffmpeg | branch: release/4.2 | Michael Niedermayer <michael at niedermayer.cc> | Fri Sep  6 12:06:30 2019 +0200| [5b44aec196e6951ecf3dbc0bc0bef91f09e98df8] | committer: Michael Niedermayer

avcodec/vorbisdec: fix FASTDIV usage for vr_type == 2

This reverts a hunk from f1ca40ee00402102046fc7e59606651930436b0e

Fixes: out of array read
Fixes: 16924/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_VORBIS_fuzzer-5157893162139648

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 722fd4696583cc984700eaec4745922ae177b2da)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=5b44aec196e6951ecf3dbc0bc0bef91f09e98df8
---

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

diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c
index 104dc86a13..be6d1b2d21 100644
--- a/libavcodec/vorbisdec.c
+++ b/libavcodec/vorbisdec.c
@@ -1513,7 +1513,7 @@ static av_always_inline int vorbis_residue_decode_internal(vorbis_context *vc,
                                 }
 
                             } else if (vr_type == 2) {
-                                unsigned voffs_div = FASTDIV(voffset << 1, ch <<1);
+                                unsigned voffs_div = ch == 1 ? voffset : FASTDIV(voffset, ch);
                                 unsigned voffs_mod = voffset - voffs_div * ch;
 
                                 for (k = 0; k < step; ++k) {