From Jimbojw.com

<?php //

/*
 * EditOnlyYourOwnPage.php - Allows users to edit their own pages.
 * @author Jim R. Wilson
 * @version 0.1
 * @copyright Copyright (C) 2007 Jim R. Wilson
 * @license The MIT License - http://www.opensource.org/licenses/mit-license.php 
 * -----------------------------------------------------------------------
 * Description:
 *     This is a MediaWiki extension which restricts non-sysop users to only edit 
 *     their own  pages, talk pages, or subpages thereof regardless of other permissions.
 * Requirements:
 *     MediaWiki 1.6.x, 1.9.x, 1.10.x or higher
 *     PHP 4.x, 5.x or higher.
 * Installation:
 *     1. Drop this script (EditOnlyYourOwnPage.php) in $IP/extensions
 *         Note: $IP is your MediaWiki install dir.
 *     2. Enable the extension by adding this line to your LocalSettings.php:
 *         require_once('extensions/EditOnlyYourOwnPage.php');
 * Version Notes:
 *     version 0.1:
 *         Initial release.
 * -----------------------------------------------------------------------
 * Copyright (c) 2007 Jim R. Wilson
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy 
 * of this software and associated documentation files (the "Software"), to deal 
 * in the Software without restriction, including without limitation the rights to 
 * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of 
 * the Software, and to permit persons to whom the Software is furnished to do 
 * so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in all 
 * copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 
 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT 
 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, 
 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING 
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR 
 * OTHER DEALINGS IN THE SOFTWARE. 
 * -----------------------------------------------------------------------
 */
 
# Confirm MW environment
if (defined('MEDIAWIKI')) {
 
# Credits
$wgExtensionCredits['other'][] = array(
    'name'=>'EditOnlyYourOwnPage',
    'author'=>'Jim R. Wilson - wilson.jim.r<at>gmail.com',
    'url'=>'http://jimbojw.com/wiki/index.php?title=EditOnlyYourOwnPage',
    'description'=>'Prevents users from editing anything other than their own pages.',
    'version'=>'0.1'
);
 
# Attach Hook
$wgHooks['userCan'][] = 'EditOnlyYourOwnPage';
 
/**
 * Allow edit action if user attempts to edit their own page, their own talk page or subpages
 * Usage: $wgHooks['userCan'][] = 'EditOnlyYourOwnPage';
 * @param Title $title Title of the article. (passed by reference)
 * @param User $user User attempting action on article - presumably $wgUser. (passed by reference)
 * @param String $action Action being taken on article. (passed by value)
 * @param Mixed $result The result of processing. (passed by reference)
 * @return Boolean Always true so other extensions have a chance to process 'userCan'
 */
function EditOnlyYourOwnPage(&$title, &$user, $action, &$result) {
 
    # Check for edit or create action and sysop membership
    if (
        ($action!='edit' &&
        $action!='create') ||
        in_array('sysop', $user->getGroups())
    ) return true;
 
    # Check for User (or User_Talk) namespace
    if (
        $title->getNamespace()!=NS_USER &&  
        $title->getNamespace()!=NS_USER_TALK
    ) {
        $result = false;
        return false;
    }
 
    # Check if the page name matches or starts with the username
    $name = $user->getName();
    $text = $title->getText();
    if (
        $name==$text ||
        preg_match('/^'.preg_quote($name).'\\//', $text)
    ) {
        $result = true;
        return true;
    }
    
    # User is trying to edit another user's page or talk page
    $result = false;
    return false;
}
 
} # End MW Environment wrapper
//