[FFmpeg-cvslog] avcodec/ac3dec: Fix: runtime error: index -1 out of bounds for type 'INTFLOAT [2]'

[Michael Niedermayer]

ffmpeg | branch: release/3.3 | Michael Niedermayer <michael at niedermayer.cc> | Sun May 14 14:42:45 2017 +0200| [09912081519438de5f48a5f1bc3846fb3ef1af02] | committer: Michael Niedermayer

avcodec/ac3dec: Fix: runtime error: index -1 out of bounds for type 'INTFLOAT [2]'

It seems dual mono with a LFE channel is not forbidden

Fixes: 1570/clusterfuzz-testcase-minimized-6455337349545984

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/targets/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
(cherry picked from commit c55e637072b694a1db40e21948d218bfa2e744bb)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=09912081519438de5f48a5f1bc3846fb3ef1af02
---

 libavcodec/ac3dec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/ac3dec.c b/libavcodec/ac3dec.c
index bd6f1478ac..148f058fa2 100644
--- a/libavcodec/ac3dec.c
+++ b/libavcodec/ac3dec.c
@@ -1389,7 +1389,7 @@ static int decode_audio_block(AC3DecodeContext *s, int blk)
     for (ch = 1; ch <= s->channels; ch++) {
         int audio_channel = 0;
         INTFLOAT gain;
-        if (s->channel_mode == AC3_CHMODE_DUALMONO)
+        if (s->channel_mode == AC3_CHMODE_DUALMONO && ch <= 2)
             audio_channel = 2-ch;
         if (s->heavy_compression && s->compression_exists[audio_channel])
             gain = s->heavy_dynamic_range[audio_channel];