[FFmpeg-cvslog] avcodec/mpegvideo_dec: consider interlaced lowres 4:2:0 chroma in edge emulation check better

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Thu Jun  8 15:47:37 2023 +0200| [d7d3f1af2ab23cae1b2fc36afafc9872bc633808] | committer: Michael Niedermayer

avcodec/mpegvideo_dec: consider interlaced lowres 4:2:0 chroma in edge emulation check better

Fixes: out of array read
Fixes: 59673/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG1VIDEO_fuzzer-5194311374077952

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=d7d3f1af2ab23cae1b2fc36afafc9872bc633808
---

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

diff --git a/libavcodec/mpegvideo_dec.c b/libavcodec/mpegvideo_dec.c
index 765ccd0ba4..c87ca77ae6 100644
--- a/libavcodec/mpegvideo_dec.c
+++ b/libavcodec/mpegvideo_dec.c
@@ -640,6 +640,7 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
     const int s_mask     = (2 << lowres) - 1;
     const int h_edge_pos = s->h_edge_pos >> lowres;
     const int v_edge_pos = s->v_edge_pos >> lowres;
+    int hc = s->chroma_y_shift ? (h+1-bottom_field)>>1 : h;
     linesize   = s->current_picture.f->linesize[0] << field_based;
     uvlinesize = s->current_picture.f->linesize[1] << field_based;
 
@@ -702,7 +703,7 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
     ptr_cr = ref_picture[2] + uvsrc_y * uvlinesize + uvsrc_x;
 
     if ((unsigned) src_x > FFMAX( h_edge_pos - (!!sx) - 2 * block_s,       0) || uvsrc_y<0 ||
-        (unsigned) src_y > FFMAX((v_edge_pos >> field_based) - (!!sy) - h, 0)) {
+        (unsigned) src_y > FFMAX((v_edge_pos >> field_based) - (!!sy) - FFMAX(h, hc<<s->chroma_y_shift), 0)) {
         s->vdsp.emulated_edge_mc(s->sc.edge_emu_buffer, ptr_y,
                                  linesize >> field_based, linesize >> field_based,
                                  17, 17 + field_based,
@@ -747,7 +748,6 @@ static av_always_inline void mpeg_motion_lowres(MpegEncContext *s,
     pix_op[lowres - 1](dest_y, ptr_y, linesize, h, sx, sy);
 
     if (!CONFIG_GRAY || !(s->avctx->flags & AV_CODEC_FLAG_GRAY)) {
-        int hc = s->chroma_y_shift ? (h+1-bottom_field)>>1 : h;
         uvsx = (uvsx << 2) >> lowres;
         uvsy = (uvsy << 2) >> lowres;
         if (hc) {