Extension:NoBogusUserpages

require_once( "extensions/NoBogusUserpages/NoBogusUserpages.php" );

$wgGroupPermissions['*'    ]['createbogususerpage'] = false;
$wgGroupPermissions['sysop']['createbogususerpage'] = true;

<?php
 /**
 * NoBogusUserpages
 * @package NoBogusUserpages
 * @author Daniel Friesen (http://www.wikia.com/wiki/User:Dantman) <dan_the_man@telus.net>
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License 2.0 or later
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */
 
if( !defined( 'MEDIAWIKI' ) ) die( "This is an extension to the MediaWiki package and cannot be run standalone." );
 
$wgExtensionCredits['other'][] = array (
        "name" => "NoBogusUserpages",
        "url" => "http://www.mediawiki.com/wiki/Extension:NoBogusUserpages",
        "author" => "[http://www.mediawiki.com/wiki/User:Dantman Daniel Friesen] [mailto:Daniel%20Friesen%20%3Cdan_the_man@telus.net%3E <dan_the_man@telus.net>]",
        "description" => "Restricts creation of userpages for which a user does not exist by those without rights to do so."
);
 
$wgAvailableRights[] = 'createbogususerpage';
$wgGroupPermissions['*'    ]['createbogususerpage'] = false;
$wgGroupPermissions['sysop']['createbogususerpage'] = true;
 
require_once( dirname(__FILE__).'/NoBogusUserpages.body.php' );
$wgExtensionFunctions[] = 'efNoBogusUserpagesSetup';
 
function efNoBogusUserpagesSetup() {
        global $wgMessageCache, $wgVersion;
 
        require_once( dirname(__FILE__).'/NoBogusUserpages.i18n.php' );
        $wgMessageCache->addMessagesByLang($messages);
 
        // Anything older than 1.6 wont' work.
        wfUseMW( '1.6' );
        if( version_compare( $wgVersion, '1.12a', '<' ) )
                // We are in pre 1.12, use the old hook.
                $wgHooks['userCan'][] = 'efNoBogusUserpagesUserCan';
        else
                // We are in 1.12, use the new hook which allows for a custom message.
                $wgHooks['getUserPermissionsErrors'][] = 'efNoBogusUserpagesUserCan';
}

<?php
 /**
 * NoBogusUserpages
 * @package NoBogusUserpages
 * @author Daniel Friesen (http://www.wikia.com/wiki/User:Dantman) <dan_the_man@telus.net>
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License 2.0 or later
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */
 
if( !defined( 'MEDIAWIKI' ) ) die( "This is an extension to the MediaWiki package and cannot be run standalone." );
 
function efNoBogusUserpagesUserCan( $title, $user, $action, $result ) {
        global $wgVersion;
        // If we're not in the user namespace,
        // or we're not trying to edit,
        // or the page already exists,
        // or we are allowed to create bogus userpages
        // then just let MediaWiki continue. 
        if( $title->getNamespace() != NS_USER
         || $action != 'create'
         || $user->isAllowed('createbogususerpage') ) return true;
        $userTitle = explode( '/', $title->getText(), 2 );
        $userName = $userTitle[0];
        // Don't block the creation of IP userpages if the page is for a IPv4 or IPv6 page.
        if( User::isIP($userName) || User::isIPv6($userName) ) return true;
        // Check if the user exists, if it says the user is anon,
        // but we know we're not on an ip page, then the user does not exist.
        // And therefore, we block creation.
        $user = User::newFromName( $userName );
        if( $user->isAnon() ) {
                // Output a value proper for the version of MW we're on.
                $result = version_compare( $wgVersion, '1.12a', '<' )
                        ? false
                        : 'badaccess-bogususerpage';
                return false;
        }
        return true;
}

<?php
 /**
 * NoBogusUserpages
 * @package NoBogusUserpages
 * @author Daniel Friesen (http://www.wikia.com/wiki/User:Dantman) <dan_the_man@telus.net>
 * @license http://www.gnu.org/copyleft/gpl.html GNU General Public License 2.0 or later
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
 */
 
if( !defined( 'MEDIAWIKI' ) ) die( "This is an extension to the MediaWiki package and cannot be run standalone." );
 
$messages = array(
        'en' => array(
                'badaccess-bogususerpage' => 'The user this userpage is meant for does not exist. You do not have the rights to be able to create a bogus userpage.'
        )
);