[FFmpeg-cvslog] avcodec/mpeg4videodec: consider lowres in dest_pcm[]

[Michael Niedermayer]

ffmpeg | branch: release/5.1 | Michael Niedermayer <michael at niedermayer.cc> | Sun Jul 23 19:01:37 2023 +0200| [10dfb498ea42974e6523f2862775886045db9b48] | committer: Michael Niedermayer

avcodec/mpeg4videodec: consider lowres in dest_pcm[]

Fixes: out of array access
Fixes: 59999/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_fuzzer-5767982157266944

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 d48476183fad230c8e457b2f314f8e136b973c4e)
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=10dfb498ea42974e6523f2862775886045db9b48
---

 libavcodec/mpeg4videodec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/mpeg4videodec.c b/libavcodec/mpeg4videodec.c
index b04ec1388e..46c6f9026b 100644
--- a/libavcodec/mpeg4videodec.c
+++ b/libavcodec/mpeg4videodec.c
@@ -123,7 +123,7 @@ void ff_mpeg4_decode_studio(MpegEncContext *s, uint8_t *dest_y, uint8_t *dest_cb
             int hsub = i ? s->chroma_x_shift : 0;
             int lowres = s->avctx->lowres;
             int step = 1 << lowres;
-            dest_pcm[i] += (linesize[i] / 2) * ((16 >> vsub) - 1);
+            dest_pcm[i] += (linesize[i] / 2) * ((16 >> vsub + lowres) - 1);
             for (int h = (16 >> (vsub + lowres)) - 1; h >= 0; h--){
                 for (int w = (16 >> (hsub + lowres)) - 1, idx = 0; w >= 0; w--, idx += step)
                     dest_pcm[i][w] = src[idx];