[FFmpeg-cvslog] avcodec/mpegvideo_dec: Check for existence of planes before accesses

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Sat Sep 30 18:07:58 2023 +0200| [3ede6cc0f18c3da842d18153b860d911bdbfbde9] | committer: Andreas Rheinhardt

avcodec/mpegvideo_dec: Check for existence of planes before accesses

Fixes segfaults with -debug +nomc -flags +gray (presuming
a build with --enable-gray).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=3ede6cc0f18c3da842d18153b860d911bdbfbde9
---

 libavcodec/mpegvideo_dec.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/libavcodec/mpegvideo_dec.c b/libavcodec/mpegvideo_dec.c
index aab2a4655a..c5e42e8ab6 100644
--- a/libavcodec/mpegvideo_dec.c
+++ b/libavcodec/mpegvideo_dec.c
@@ -249,10 +249,12 @@ static void gray_frame(AVFrame *frame)
 {
     int h_chroma_shift, v_chroma_shift;
 
-    av_pix_fmt_get_chroma_sub_sample(frame->format, &h_chroma_shift, &v_chroma_shift);
-
     for (int i = 0; i < frame->height; i++)
         memset(frame->data[0] + frame->linesize[0] * i, 0x80, frame->width);
+
+    if (!frame->data[1])
+        return;
+    av_pix_fmt_get_chroma_sub_sample(frame->format, &h_chroma_shift, &v_chroma_shift);
     for (int i = 0; i < AV_CEIL_RSHIFT(frame->height, v_chroma_shift); i++) {
         memset(frame->data[1] + frame->linesize[1] * i,
                0x80, AV_CEIL_RSHIFT(frame->width, h_chroma_shift));