[FFmpeg-cvslog] avcodec/mpeg12dec: Do not put mpeg_f_code into an invalid state on error return

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Tue Aug 31 20:15:09 2021 +0200| [5a95abcce4d93f979e4b53f2220f7a54edd03312] | committer: Michael Niedermayer

avcodec/mpeg12dec: Do not put mpeg_f_code into an invalid state on error return

Fixes: invalid shift
Fixes: 37018/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_MPEG2VIDEO_fuzzer-5290280902328320

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=5a95abcce4d93f979e4b53f2220f7a54edd03312
---

 libavcodec/mpeg12dec.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavcodec/mpeg12dec.c b/libavcodec/mpeg12dec.c
index 49d865853b..507a271073 100644
--- a/libavcodec/mpeg12dec.c
+++ b/libavcodec/mpeg12dec.c
@@ -1538,6 +1538,10 @@ static int mpeg_decode_picture_coding_extension(Mpeg1Context *s1)
     s->mpeg_f_code[0][1] = get_bits(&s->gb, 4);
     s->mpeg_f_code[1][0] = get_bits(&s->gb, 4);
     s->mpeg_f_code[1][1] = get_bits(&s->gb, 4);
+    s->mpeg_f_code[0][0] += !s->mpeg_f_code[0][0];
+    s->mpeg_f_code[0][1] += !s->mpeg_f_code[0][1];
+    s->mpeg_f_code[1][0] += !s->mpeg_f_code[1][0];
+    s->mpeg_f_code[1][1] += !s->mpeg_f_code[1][1];
     if (!s->pict_type && s1->mpeg_enc_ctx_allocated) {
         av_log(s->avctx, AV_LOG_ERROR, "Missing picture start code\n");
         if (s->avctx->err_recognition & AV_EF_EXPLODE)
@@ -1553,10 +1557,6 @@ static int mpeg_decode_picture_coding_extension(Mpeg1Context *s1)
         s->current_picture.f->pict_type = s->pict_type;
         s->current_picture.f->key_frame = s->pict_type == AV_PICTURE_TYPE_I;
     }
-    s->mpeg_f_code[0][0] += !s->mpeg_f_code[0][0];
-    s->mpeg_f_code[0][1] += !s->mpeg_f_code[0][1];
-    s->mpeg_f_code[1][0] += !s->mpeg_f_code[1][0];
-    s->mpeg_f_code[1][1] += !s->mpeg_f_code[1][1];
 
     s->intra_dc_precision         = get_bits(&s->gb, 2);
     s->picture_structure          = get_bits(&s->gb, 2);