[FFmpeg-cvslog] avcodec/mpeg12dec: Don't adapt (last|next)_pic.linesize for field pics

[Andreas Rheinhardt]

ffmpeg | branch: master | Andreas Rheinhardt <andreas.rheinhardt at outlook.com> | Mon Jun 24 01:38:17 2024 +0200| [5a30b45c0fe4abaaf69ca8e465bf8113fee23626] | committer: Andreas Rheinhardt

avcodec/mpeg12dec: Don't adapt (last|next)_pic.linesize for field pics

These values are not read anywhere. Furthermore, since commit
fe6037fd04db8837dcdb9013f9c4ad4e7eb0592e the linesize values
of the MPVWorkPictures were wrong for subsequent fields
in a chain of B-pictures (as they are always doubled and no longer
based upon the frame-linesizes) which can eventually lead to overflow.

Finally, it makes no real sense to ever double the linesize
of the reference pictures at all: Even when the current picture
is a field, it can still reference both fields of reference
pictures and therefore the linesize should allow to address
both fields (for the same reason, data is not offset for
reference pictures).

libavcodec/mpeg12dec.c:1304:41: runtime error: signed integer overflow: 4611686018427387904 * 2 cannot be represented in type 'long'

issue: 69732/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEGVIDEO_fuzzer-5123551179374592

Reviewed-by: Michael Niedermayer <michael at niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at outlook.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=5a30b45c0fe4abaaf69ca8e465bf8113fee23626
---

 libavcodec/mpeg12dec.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
index 09befdcc64..bb0a769e49 100644
--- a/libavcodec/mpeg12dec.c
+++ b/libavcodec/mpeg12dec.c
@@ -1278,8 +1278,6 @@ static int mpeg_field_start(Mpeg1Context *s1, const uint8_t *buf, int buf_size)
                                                     s->cur_pic.linesize[i]);
                 }
                 s->cur_pic.linesize[i]  *= 2;
-                s->last_pic.linesize[i] *= 2;
-                s->next_pic.linesize[i] *= 2;
             }
         }