avformat/mxfdec: Fix DoS issues in mxf_read_index_entry_array()

Fixes: 20170829A.mxf

Co-Author: 张洪亮(望初)" <wangchu.zhl@alibaba-inc.com>
Found-by: Xiaohei and Wangchu from Alibaba Security Team
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/mxfdec.c

@@ -899,6 +899,8 @@ static int mxf_read_index_entry_array(AVIOContext *pb, MXFIndexTableSegment *seg
     segment->nb_index_entries = avio_rb32(pb);
 
     length = avio_rb32(pb);
+    if(segment->nb_index_entries && length < 11)
+        return AVERROR_INVALIDDATA;
 
     if (!(segment->temporal_offset_entries=av_calloc(segment->nb_index_entries, sizeof(*segment->temporal_offset_entries))) ||
         !(segment->flag_entries          = av_calloc(segment->nb_index_entries, sizeof(*segment->flag_entries))) ||
@@ -909,6 +911,8 @@ static int mxf_read_index_entry_array(AVIOContext *pb, MXFIndexTableSegment *seg
     }
 
     for (i = 0; i < segment->nb_index_entries; i++) {
+        if(avio_feof(pb))
+            return AVERROR_INVALIDDATA;
         segment->temporal_offset_entries[i] = avio_r8(pb);
         avio_r8(pb);                                        /* KeyFrameOffset */
         segment->flag_entries[i] = avio_r8(pb);