matroskadec: fix crash when parsing invalid mkv

CC: libav-stable@libav.org
Signed-off-by: Anton Khirnov <anton@khirnov.net>
(cherry picked from commit b8d7f3186e86234f6255f5e8ee9e98573b4d9a6e)
Signed-off-by: Anton Khirnov <anton@khirnov.net>

diff --git a/libavformat/matroskadec.c b/libavformat/matroskadec.c
index f384458..67df4b3 100644 (file)
--- a/libavformat/matroskadec.c
+++ b/libavformat/matroskadec.c
@@ -1825,8 +1825,12 @@ static int matroska_read_header(AVFormatContext *s)
     matroska->ctx = s;
 
     /* First read the EBML header. */
-    if (ebml_parse(matroska, ebml_syntax, &ebml) ||
-        ebml.version         > EBML_VERSION      ||
+    if (ebml_parse(matroska, ebml_syntax, &ebml) || !ebml.doctype) {
+        av_log(matroska->ctx, AV_LOG_ERROR, "EBML header parsing failed\n");
+        ebml_free(ebml_syntax, &ebml);
+        return AVERROR_INVALIDDATA;
+    }
+    if (ebml.version         > EBML_VERSION      ||
         ebml.max_size        > sizeof(uint64_t)  ||
         ebml.id_length       > sizeof(uint32_t)  ||
         ebml.doctype_version > 3) {