[FFmpeg-cvslog] avcodec/4xm: Check pre_gb in decode_i_block()

[Michael Niedermayer]

ffmpeg | branch: master | Michael Niedermayer <michael at niedermayer.cc> | Tue Mar  9 21:39:30 2021 +0100| [b87781649e2862d07fcb8d322289d89b47a530b6] | committer: Michael Niedermayer

avcodec/4xm: Check pre_gb in decode_i_block()

Fixes: Timeout
Fixes: 31257/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_FOURXM_fuzzer-5150866229297152

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=b87781649e2862d07fcb8d322289d89b47a530b6
---

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

diff --git a/libavcodec/4xm.c b/libavcodec/4xm.c
index 4d58b093f7..cbd8637763 100644
--- a/libavcodec/4xm.c
+++ b/libavcodec/4xm.c
@@ -499,8 +499,8 @@ static int decode_i_block(FourXContext *f, int16_t *block)
 {
     int code, i, j, level, val;
 
-    if (get_bits_left(&f->gb) < 2){
-        av_log(f->avctx, AV_LOG_ERROR, "%d bits left before decode_i_block()\n", get_bits_left(&f->gb));
+    if (get_bits_left(&f->pre_gb) < 2) {
+        av_log(f->avctx, AV_LOG_ERROR, "%d bits left before decode_i_block()\n", get_bits_left(&f->pre_gb));
         return AVERROR_INVALIDDATA;
     }