Bug#11764602 ASSERTION IN

FORMAT_DESCRIPTION_LOG_EVENT::CALC_SERVER_VERSION_SPLIT

Problem: When reading a Format_description_log_event, it supposes MySQL
version is always valid and DBUG_ASSERTION is used check the version number.
However, user may give a wrong binlog offset, even give a faked binary event
which includes an invalid MySQL version. This will cause server crash.

Fix: The assertions are removed and an error will be reported if MySQL
version in Format_description_log_event is invalid.

sql/log_event.cc

@@ -4205,7 +4205,6 @@ Format_description_log_event::do_shall_skip(Relay_log_info *rli)
    into 'server_version_split':
    X.Y.Zabc (X,Y,Z numbers, a not a digit) -> {X,Y,Z}
    X.Yabc -> {X,Y,0}
-   Xabc -> {X,0,0}
    'server_version_split' is then used for lookups to find if the server which
    created this event has some known bug.
 */
@@ -4216,10 +4215,21 @@ void Format_description_log_event::calc_server_version_split()
   for (uint i= 0; i<=2; i++)
   {
     number= strtoul(p, &r, 10);
-    server_version_split[i]= (uchar)number;
-    DBUG_ASSERT(number < 256); // fit in uchar
+    /*
+      It is an invalid version if any version number greater than 255 or
+      first number is not followed by '.'.
+    */
+    if (number < 256 && (*r == '.' || i != 0))
+      server_version_split[i]= (uchar)number;
+    else
+    {
+      server_version_split[0]= 0;
+      server_version_split[1]= 0;
+      server_version_split[2]= 0;
+      break;
+    }
+
     p= r;
-    DBUG_ASSERT(!((i == 0) && (*r != '.'))); // should be true in practice
     if (*r == '.')
       p++; // skip the dot
   }

sql/log_event.h

@@ -969,7 +969,7 @@ class Log_event
     return thd ? thd->db : 0;
   }
 #else
-  Log_event() : temp_buf(0) {}
+  Log_event() : temp_buf(0), flags(0) {}
     /* avoid having to link mysqlbinlog against libpthread */
   static Log_event* read_log_event(IO_CACHE* file,
                                    const Format_description_log_event
@@ -2244,12 +2244,26 @@ class Format_description_log_event: public Start_log_event_v3
 #ifndef MYSQL_CLIENT
   bool write(IO_CACHE* file);
 #endif
-  bool is_valid() const
+  bool header_is_valid() const
   {
     return ((common_header_len >= ((binlog_version==1) ? OLD_HEADER_LEN :
                                    LOG_EVENT_MINIMAL_HEADER_LEN)) &&
             (post_header_len != NULL));
   }
+
+  bool version_is_valid() const
+  {
+    /* It is invalid only when all version numbers are 0 */
+    return !(server_version_split[0] == 0 &&
+             server_version_split[1] == 0 &&
+             server_version_split[2] == 0);
+  }
+
+  bool is_valid() const
+  {
+    return header_is_valid() && version_is_valid();
+  }
+
   int get_data_size()
   {
     /*