[FFmpeg-devel] [PATCH 4/5] avcodec/mpegvideo_dec: Fix lowres=3 field select interlaced mpeg4 frame

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: [FFmpeg-devel] [PATCH 4/5] avcodec/mpegvideo_dec: Fix lowres=3 field select interlaced mpeg4 frame
Date: Sun, 13 Jul 2025 03:10:29 +0200
Message-ID: <20250713011030.1156550-4-michael@niedermayer.cc> (raw)
In-Reply-To: <20250713011030.1156550-1-michael@niedermayer.cc>

Fixes: out of array read in the chroma plane
Fixes: 428034092/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG4_DEC_fuzzer-5582608941776896.test

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
---
 libavcodec/mpegvideo_dec.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libavcodec/mpegvideo_dec.c b/libavcodec/mpegvideo_dec.c
index 4a54f6cd614..85e24c667e3 100644
--- a/libavcodec/mpegvideo_dec.c
+++ b/libavcodec/mpegvideo_dec.c
@@ -557,7 +557,7 @@ 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) - FFMAX(h, hc<<s->chroma_y_shift), 0)) {
+        (unsigned) src_y > FFMAX((v_edge_pos >> field_based) - (!!sy) - FFMAX(h, field_select + 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,
-- 
2.49.0

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