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@niedermayer.cc>

diff --git a/libavcodec/vorbisdec.c b/libavcodec/vorbisdec.c
index 104dc86a13d6f10398662a077828514747e413c1..be6d1b2d219ae4316745d78e7e21dbb4300edcce 100644 (file)
--- 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) {