avcodec/h264_metadata_bsf: Check nb_units before accessing the first in h264_metadata...

Fixes: null pointer dereference
Fixes: 29835/clusterfuzz-testcase-minimized-ffmpeg_BSF_H264_METADATA_fuzzer-4712125383704576
Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

diff --git a/libavcodec/h264_metadata_bsf.c b/libavcodec/h264_metadata_bsf.c
index c3a63f357810ef21a53cd22f8f23e1bffb7fcd62..6e58c0be1d499f74065dd4bb577381f2a95412c5 100644 (file)
--- a/libavcodec/h264_metadata_bsf.c
+++ b/libavcodec/h264_metadata_bsf.c
@@ -462,7 +462,7 @@ static int h264_metadata_update_fragment(AVBSFContext *bsf, AVPacket *pkt,
     int err, i, has_sps, seek_point;
 
     // If an AUD is present, it must be the first NAL unit.
-    if (au->units[0].type == H264_NAL_AUD) {
+    if (au->nb_units && au->units[0].type == H264_NAL_AUD) {
         if (ctx->aud == BSF_ELEMENT_REMOVE)
             ff_cbs_delete_unit(au, 0);
     } else {