[FFmpeg-devel] [PATCH 4/4] avcodec/vorbisdec: fix FASTDIV usage for vr_type == 2

[Michael Niedermayer]

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>
---
 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) {
-- 
2.23.0