BUG#13427949

Automerged against latest mysql-5.5.

mysql-test/suite/rpl/r/rpl_connection.result

+include/master-slave.inc
+[connection master]
+call mtr.add_suppression(".*Invalid .* username when attempting to connect to the master server.*");
+include/stop_slave.inc
+CHANGE MASTER TO MASTER_USER= '', MASTER_PASSWORD= '';
+START SLAVE;
+include/wait_for_slave_io_error.inc [errno=1045, 1593]
+include/stop_slave.inc
+CHANGE MASTER TO MASTER_USER= 'root', MASTER_PASSWORD= '';
+START SLAVE;
+include/rpl_end.inc

mysql-test/suite/rpl/t/rpl_connection.test

+--source include/not_embedded.inc
+--source include/master-slave.inc
+--source include/have_binlog_format_mixed.inc
+
+#
+# BUG#13427949: CHANGE MASTER TO USER='' (EMPTY USER) CAUSES ERRORS ON VALGRING 
+#
+
+--connection slave
+call mtr.add_suppression(".*Invalid .* username when attempting to connect to the master server.*");
+
+
+# Assert that we disallow empty users and that no problem
+--source include/stop_slave.inc
+CHANGE MASTER TO MASTER_USER= '', MASTER_PASSWORD= '';
+START SLAVE;
+--let $slave_io_errno= 1045, 1593
+--source include/wait_for_slave_io_error.inc
+--source include/stop_slave.inc
+
+CHANGE MASTER TO MASTER_USER= 'root', MASTER_PASSWORD= '';
+START SLAVE;
+
+--source include/rpl_end.inc 

sql/slave.cc

@@ -4208,6 +4208,16 @@ static int connect_to_master(THD* thd, MYSQL* mysql, Master_info* mi,
   if (opt_plugin_dir_ptr && *opt_plugin_dir_ptr)
     mysql_options(mysql, MYSQL_PLUGIN_DIR, opt_plugin_dir_ptr);
 
+  /* we disallow empty users */
+  if (mi->user == NULL || mi->user[0] == 0)
+  {
+    mi->report(ERROR_LEVEL, ER_SLAVE_FATAL_ERROR,
+               ER(ER_SLAVE_FATAL_ERROR),
+               "Invalid (empty) username when attempting to "
+               "connect to the master server. Connection attempt "
+               "terminated.");
+    DBUG_RETURN(1);
+  }
   while (!(slave_was_killed = io_slave_killed(thd,mi)) &&
          (reconnect ? mysql_reconnect(mysql) != 0 :
           mysql_real_connect(mysql, mi->host, mi->user, mi->password, 0,
@@ -4336,7 +4346,9 @@ MYSQL *rpl_connect_master(MYSQL *mysql)
   /* This one is not strictly needed but we have it here for completeness */
   mysql_options(mysql, MYSQL_SET_CHARSET_DIR, (char *) charsets_dir);
 
-  if (io_slave_killed(thd, mi)
+  if (mi->user == NULL
+      || mi->user[0] == 0
+      || io_slave_killed(thd, mi)
       || !mysql_real_connect(mysql, mi->host, mi->user, mi->password, 0,
                              mi->port, 0, 0))
   {