[FFmpeg-devel] [PATCH 1/4] avcodec/mpegvideo_dec: Check for existence of planes before accesses

From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
To: ffmpeg-devel@ffmpeg.org
Cc: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Subject: [FFmpeg-devel] [PATCH 1/4] avcodec/mpegvideo_dec: Check for existence of planes before accesses
Date: Sat, 30 Sep 2023 20:02:17 +0200
Message-ID: <AS8P250MB0744CC369A3887A6A38474498FC7A@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM> (raw)

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

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
---
 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 7aa46a4e25..77d90104f6 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));
-- 
2.34.1

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