<?php
/**********************************************************************************
* Security.php                                                                    *
***********************************************************************************
* SMF: Simple Machines Forum                                                      *
* Open-Source Project Inspired by Zef Hemel (zef@zefhemel.com)                    *
* =============================================================================== *
* Software Version:           SMF 1.1                                             *
* Software by:                Simple Machines (http://www.simplemachines.org)     *
* Copyright 2006 by:          Simple Machines LLC (http://www.simplemachines.org) *
*           2001-2006 by:     Lewis Media (http://www.lewismedia.com)             *
* Support, News, Updates at:  http://www.simplemachines.org                       *
***********************************************************************************
* This program is free software; you may redistribute it and/or modify it under   *
* the terms of the provided license as published by Simple Machines LLC.          *
*                                                                                 *
* This program is distributed in the hope that it is and will be useful, but      *
* WITHOUT ANY WARRANTIES; without even any implied warranty of MERCHANTABILITY    *
* or FITNESS FOR A PARTICULAR PURPOSE.                                            *
*                                                                                 *
* See the "license.txt" file for details of the Simple Machines license.          *
* The latest version can always be found at http://www.simplemachines.org.        *
**********************************************************************************/
if (!defined('SMF'))
	die('Hacking attempt...');

/*	This file has the very important job of insuring forum security.  This
	task includes banning and permissions, namely.  It does this by providing
	the following functions:

	void validateSession()
		- makes sure the user is who they claim to be by requiring a
		  password to be typed in every hour.
		- is turned on and off by the securityDisable setting.
		- uses the adminLogin() function of Subs-Auth.php if they need to
		  login, which saves all request (post and get) data.

	void is_not_guest(string message = '')
		- checks if the user is currently a guest, and if so asks them to
		  login with a message telling them why.
		- message is what to tell them when asking them to login.

	void is_not_banned(bool force_check = false)
		- checks if the user is banned, and if so dies with an error.
		- caches this information for optimization purposes.
		- forces a recheck if force_check is true.

	void banPermissions()
		- applies any states of banning by removing permissions the user
		  cannot have.

	void log_ban(array ban_ids = array(), string email = null)
		- log the current user in the ban logs.
		- increment the hit counters for the specified ban ID's (if any.)

	void isBannedEmail(string email, string restriction, string error)
		- check if a given email is banned.
		- performs an immediate ban if the turns turns out positive.

	string checkSession(string type = 'post', string from_action = none,
			is_fatal = true)
		- checks the current session, verifying that the person is who he or
		  she should be.
		- also checks the referrer to make sure they didn't get sent here.
		- depends on the disableCheckUA setting, which is usually missing.
		- will check GET, POST, or REQUEST depending on the passed type.
		- also optionally checks the referring action if passed. (note that
		  the referring action must be by GET.)
		- returns the error message if is_fatal is false.

	bool checkSubmitOnce(string action, bool is_fatal = true)
		- registers a sequence number for a form.
		- checks whether a submitted sequence number is registered in the
		  current session.
		- depending on the value of is_fatal shows an error or returns true or
		  false.
		- frees a sequence number from the stack after it's been checked.
		- frees a sequence number without checking if action == 'free'.

	void setBit(string &string, int position, int value)
		- store a bit in a string at the given position fo string.

	bool getBit(string &string, int position)
		- read the bit stored in the string at a given position.
		- return true/false depending on the value of the bit.

	bool allowedTo(string permission, array boards = current)
		- checks whether the user is allowed to do permission. (ie. post_new.)
		- if boards is specified, checks those boards instead of the current
		  one.
		- always returns true if the user is an administrator.
		- returns true if he or she can do it, false otherwise.

	void isAllowedTo(string permission, array boards = current)
		- uses allowedTo() to check if the user is allowed to do permission.
		- checks the passed boards or current board for the permission.
		- if they are not, it loads the Errors language file and shows an
		  error using $txt['cannot_' . $permission].
		- if they are a guest and cannot do it, this calls is_not_guest().

	array boardsAllowedTo(string permission)
		- returns a list of boards on which the user is allowed to do the
		  specified permission.
		- returns an array with only a 0 in it if the user has permission
		  to do this on every board.
		- returns an empty array if he or she cannot do this on any board.
*/

// Check if the user is who he/she sais he is
function validateSession()
{
	global $modSettings, $sourcedir, $user_info, $sc;

	// We don't care if the option is off, because Guests should NEVER get past here.
	is_not_guest();

	// Is the security option off?  Or are they already logged in?
	if (!empty($modSettings['securityDisable']) || (!empty($_SESSION['admin_time']) && $_SESSION['admin_time'] + 3600 >= time()))
		return;

	require_once($sourcedir . '/Subs-Auth.php');

	// Hashed password, ahoy!
	if (isset($_POST['admin_hash_pass']) && strlen($_POST['admin_hash_pass']) == 40)
	{
		checkSession();

		$good_password = false;
		if (isset($modSettings['integrate_verify_password']) && function_exists($modSettings['integrate_verify_password']))
			if (call_user_func($modSettings['integrate_verify_password'], $user_info['username'], $_POST['admin_hash_pass'], true) === true)
				$good_password = true;

		if ($good_password || $_POST['admin_hash_pass'] == sha1($user_info['passwd'] . $sc))
		{
			$_SESSION['admin_time'] = time();
			return;
		}
	}
	// Posting the password... check it.
	if (isset($_POST['admin_pass']))
	{
		checkSession();

		$good_password = false;
		if (isset($modSettings['integrate_verify_password']) && function_exists($modSettings['integrate_verify_password']))
			if (call_user_func($modSettings['integrate_verify_password'], $user_info['username'], $_POST['admin_pass'], false) === true)
				$good_password = true;

		// Password correct?
		if ($good_password || sha1(strtolower($user_info['username']) . $_POST['admin_pass']) == $user_info['passwd'])
		{
			$_SESSION['admin_time'] = time();
			return;
		}
	}

	// Need to type in a password for that, man.
	adminLogin();
}

// Require a user who is logged in. (not a guest.)
function is_not_guest($message = '')
{
	global $user_info, $txt, $context;

	// Luckily, this person isn't a guest.
	if (!$user_info['is_guest'])
		return;

	// People always worry when they see people doing things they aren't actually doing...
	$_GET['action'] = '';
	$_GET['board'] = '';
	$_GET['topic'] = '';
	writeLog(true);

	// Just die.
	if (isset($_REQUEST['xml']))
		obExit(false);

	$_SESSION['login_url'] = $_SERVER['REQUEST_URL'];

	// Load the Login template and language file.
	loadLanguage('Login');
	loadTemplate('Login');

	// Use the kick_guest sub template...
	$context['kick_message'] = $message;
	$context['sub_template'] = 'kick_guest';
	$context['page_title'] = $txt[34];

	obExit();

	// We should never get to this point, but if we did we wouldn't know the user isn't a guest.
	trigger_error('Hacking attempt...', E_USER_ERROR);
}

// Do banning related stuff.  (ie. disallow access....)
function is_not_banned($forceCheck = false)
{
	global $txt, $db_prefix, $ID_MEMBER, $modSettings, $context, $user_info;
	global $sourcedir, $cookiename, $user_settings;

	// You cannot be banned if you are an admin - doesn't help if you log out.
	if ($user_info['is_admin'])
		return;

	// Only check the ban every so often. (to reduce load.)
	if ($forceCheck || !isset($_SESSION['ban']) || empty($modSettings['banLastUpdated']) || ($_SESSION['ban']['last_checked'] < $modSettings['banLastUpdated']) || $_SESSION['ban']['ID_MEMBER'] != $ID_MEMBER || $_SESSION['ban']['ip'] != $user_info['ip'] || $_SESSION['ban']['ip2'] != $user_info['ip2'] || (isset($user_info['email'], $_SESSION['ban']['email']) && $_SESSION['ban']['email'] != $user_info['email']))
	{
		// Innocent until proven guilty.  (but we know you are! :P)
		$_SESSION['ban'] = array(
			'last_checked' => time(),
			'ID_MEMBER' => $ID_MEMBER,
			'ip' => $user_info['ip'],
			'ip2' => $user_info['ip2'],
			'email' => $user_info['email'],
		);

		$ban_query = array();
		$flag_is_activated = false;

		// Check both IP addresses.
		foreach (array('ip', 'ip2') as $ip_number)
		{
			// Check if we have a valid IP address.
			if (preg_match('/^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/', $user_info[$ip_number], $ip_parts) == 1)
			{
				$ban_query[] = "(($ip_parts[1] BETWEEN bi.ip_low1 AND bi.ip_high1)
							AND ($ip_parts[2] BETWEEN bi.ip_low2 AND bi.ip_high2)
							AND ($ip_parts[3] BETWEEN bi.ip_low3 AND bi.ip_high3)
							AND ($ip_parts[4] BETWEEN bi.ip_low4 AND bi.ip_high4))";

				// IP was valid, maybe there's also a hostname...
				if (empty($modSettings['disableHostnameLookup']))
				{
					$hostname = host_from_ip($user_info[$ip_number]);
					if (strlen($hostname) > 0)
						$ban_query[] = "('" . addslashes($hostname) . "' LIKE bi.hostname)";
				}
			}
			// We use '255.255.255.255' for 'unknown' since it's not valid anyway.
			elseif ($user_info[$ip_number] == 'unknown')
				$ban_query[] = "(bi.ip_low1 = 255 AND bi.ip_high1 = 255
							AND bi.ip_low2 = 255 AND bi.ip_high2 = 255
							AND bi.ip_low3 = 255 AND bi.ip_high3 = 255
							AND bi.ip_low4 = 255 AND bi.ip_high4 = 255)";
		}

		// Is their email address banned?
		if (strlen($user_info['email']) != 0)
			$ban_query[] = "('" . addslashes($user_info['email']) . "' LIKE bi.email_address)";

		// How about this user?
		if (!$user_info['is_guest'] && !empty($ID_MEMBER))
			$ban_query[] = "bi.ID_MEMBER = $ID_MEMBER";

		// Check the ban, if there's information.
		if (!empty($ban_query))
		{
			$restrictions = array(
				'cannot_access',
				'cannot_login',
				'cannot_post',
				'cannot_register',
			);
			$request = db_query("
				SELECT bi.ID_BAN, bi.email_address, bi.ID_MEMBER, bg.cannot_access, bg.cannot_register,
					bg.cannot_post, bg.cannot_login, bg.reason
				FROM ({$db_prefix}ban_groups AS bg, {$db_prefix}ban_items AS bi)
				WHERE bg.ID_BAN_GROUP = bi.ID_BAN_GROUP
					AND (bg.expire_time IS NULL OR bg.expire_time > " . time() . ")
					AND (" . implode(' OR ', $ban_query) . ')', __FILE__, __LINE__);
			// Store every type of ban that applies to you in your session.
			while ($row = mysql_fetch_assoc($request))
			{
				foreach ($restrictions as $restriction)
					if (!empty($row[$restriction]))
					{
						$_SESSION['ban'][$restriction]['reason'] = $row['reason'];
						$_SESSION['ban'][$restriction]['ids'][] = $row['ID_BAN'];

						if (!$user_info['is_guest'] && $restriction == 'cannot_access' && ($row['ID_MEMBER'] == $ID_MEMBER || $row['email_address'] == $user_info['email']))
							$flag_is_activated = true;
					}
			}
			mysql_free_result($request);
		}

		// Mark the cannot_access and cannot_post bans as being 'hit'.
		if (isset($_SESSION['ban']['cannot_access']) || isset($_SESSION['ban']['cannot_post']))
			log_ban(array_merge(isset($_SESSION['ban']['cannot_access']) ? $_SESSION['ban']['cannot_access']['ids'] : array(), isset($_SESSION['ban']['cannot_post']) ? $_SESSION['ban']['cannot_post']['ids'] : array()));

		// If for whatever reason the is_activated flag seems wrong, do a little work to clear it up.
		if ($ID_MEMBER && (($user_settings['is_activated'] >= 10 && !$flag_is_activated)
			|| ($user_settings['is_activated'] < 10 && $flag_is_activated)))
		{
			require_once($sourcedir . '/ManageBans.php');
			updateBanMembers();
		}
	}

	// Hey, I know you! You're ehm...
	if (!isset($_SESSION['ban']['cannot_access']) && !empty($_COOKIE[$cookiename . '_']))
	{
		$bans = explode(',', $_COOKIE[$cookiename . '_']);
		foreach ($bans as $key => $value)
			$bans[$key] = (int) $value;
		$request = db_query("
			SELECT bi.ID_BAN, bg.reason
			FROM ({$db_prefix}ban_items AS bi, {$db_prefix}ban_groups AS bg)
			WHERE bg.ID_BAN_GROUP = bi.ID_BAN_GROUP
				AND (bg.expire_time IS NULL OR bg.expire_time > " . time() . ")
				AND bg.cannot_access = 1
				AND bi.ID_BAN IN (" . implode(', ', $bans) . ")
			LIMIT " . count($bans), __FILE__, __LINE__);
		while ($row = mysql_fetch_assoc($request))
		{
			$_SESSION['ban']['cannot_access']['ids'][] = $row['ID_BAN'];
			$_SESSION['ban']['cannot_access']['reason'] = $row['reason'];
		}
		mysql_free_result($request);

		// My mistake. Next time better.
		if (!isset($_SESSION['ban']['cannot_access']))
		{
			require_once($sourcedir . '/Subs-Auth.php');
			$cookie_url = url_parts(!empty($modSettings['localCookies']), !empty($modSettings['globalCookies']));
			setcookie($cookiename . '_', '', time() - 3600, $cookie_url[1], $cookie_url[0], 0);
		}
	}

	// If you're fully banned, it's end of the story for you.
	if (isset($_SESSION['ban']['cannot_access']))
	{
		// We don't wanna see you!
		if (!$user_info['is_guest'])
			db_query("
				DELETE FROM {$db_prefix}log_online
				WHERE ID_MEMBER = $ID_MEMBER
				LIMIT 1", __FILE__, __LINE__);

		// 'Log' the user out.  Can't have any funny business... (save the name!)
		$old_name = isset($user_info['name']) && $user_info['name'] != '' ? $user_info['name'] : $txt[28];
		$user_info['name'] = '';
		$user_info['username'] = '';
		$user_info['is_guest'] = true;
		$user_info['is_admin'] = false;
		$user_info['permissions'] = array();
		$ID_MEMBER = 0;
		$context['user'] = array(
			'id' => 0,
			'username' => '',
			'name' => $txt[28],
			'is_guest' => true,
			'is_logged' => false,
			'is_admin' => false,
			'is_mod' => false,
			'language' => $user_info['language']
		);

		// A goodbye present.
		require_once($sourcedir . '/Subs-Auth.php');
		$cookie_url = url_parts(!empty($modSettings['localCookies']), !empty($modSettings['globalCookies']));
		setcookie($cookiename . '_', implode(',', $_SESSION['ban']['cannot_access']['ids']), time() + 3153600, $cookie_url[1], $cookie_url[0], 0);

		// Don't scare anyone, now.
		$_GET['action'] = '';
		$_GET['board'] = '';
		$_GET['topic'] = '';
		writeLog(true);

		// You banned, sucka!
		fatal_error(sprintf($txt[430], $old_name) . (empty($_SESSION['ban']['cannot_access']['reason']) ? '' : '<br />' . $_SESSION['ban']['cannot_access']['reason']));

		// If we get here, something's gone wrong.... but let's try anyway.
		trigger_error('Hacking attempt...', E_USER_ERROR);
	}
	// You're not allowed to log in but yet you are. Let's fix that.
	elseif (isset($_SESSION['ban']['cannot_login']) && !$user_info['is_guest'])
	{
		// !!! Why doesn't this use the function made for logging bans?
		db_query("
			UPDATE {$db_prefix}ban_items
			SET hits = hits + 1
			WHERE ID_BAN IN (" . implode(', ', $_SESSION['ban']['cannot_login']['ids']) . ')', __FILE__, __LINE__);

		// Log this ban.
		db_query("
			INSERT INTO {$db_prefix}log_banned
				(ID_MEMBER, ip, email, logTime)
			VALUES ($ID_MEMBER, SUBSTRING('$user_info[ip]', 1, 16), SUBSTRING('$user_info[email]', 1, 255), " . time() . ')', __FILE__, __LINE__);

		// SMF's Wipe 'n Clean(r) erases all traces.
		$_GET['action'] = '';
		$_GET['board'] = '';
		$_GET['topic'] = '';
		writeLog(true);

		// Logged in, but not for long...
		require_once($sourcedir . '/LogInOut.php');
		Logout(true);
	}

	// Fix up the banning permissions.
	if (isset($user_info['permissions']))
		banPermissions();
}

// Fix permissions according to ban status.
function banPermissions()
{
	global $user_info;

	// Somehow they got here, at least take away all permissions...
	if (isset($_SESSION['ban']['cannot_access']))
		$user_info['permissions'] = array();
	// Okay, well, you can watch, but don't touch a thing.
	elseif (isset($_SESSION['ban']['cannot_post']))
	{
		$denied_permissions = array(
			'pm_send',
			'calendar_post', 'calendar_edit_own', 'calendar_edit_any',
			'poll_post',
			'poll_add_own', 'poll_add_any',
			'poll_edit_own', 'poll_edit_any',
			'poll_lock_own', 'poll_lock_any',
			'poll_remove_own', 'poll_remove_any',
			'manage_attachments', 'manage_smileys', 'manage_boards', 'admin_forum', 'manage_permissions',
			'moderate_forum', 'manage_membergroups', 'manage_bans', 'send_mail', 'edit_news',
			'profile_identity_any', 'profile_extra_any', 'profile_title_any',
			'post_new', 'post_reply_own', 'post_reply_any',
			'delete_own', 'delete_any', 'delete_replies',
			'make_sticky',
			'merge_any', 'split_any',
			'modify_own', 'modify_any', 'modify_replies',
			'move_any',
			'send_topic',
			'lock_own', 'lock_any',
			'remove_own', 'remove_any',
		);
		$user_info['permissions'] = array_diff($user_info['permissions'], $denied_permissions);
	}
}

// Log a ban in the database.
function log_ban($ban_ids = array(), $email = null)
{
	global $db_prefix, $user_info, $ID_MEMBER;

	// Don't log web accelerators, it's very confusing...
	if (isset($_SERVER['HTTP_X_MOZ']) && $_SERVER['HTTP_X_MOZ'] == 'prefetch')
		return;

	db_query("
		INSERT INTO {$db_prefix}log_banned
			(ID_MEMBER, ip, email, logTime)
		VALUES ($ID_MEMBER, SUBSTRING('$user_info[ip]', 1, 16), '" . ($email === null ? ($user_info['is_guest'] ? '' : $user_info['email']) : $email) . "', " . time() . ')', __FILE__, __LINE__);

	// One extra point for these bans.
	if (!empty($ban_ids))
		db_query("
			UPDATE {$db_prefix}ban_items
			SET hits = hits + 1
			WHERE ID_BAN IN (" . implode(', ', $ban_ids) . ')', __FILE__, __LINE__);
}

// Checks if a given email address might be banned.
function isBannedEmail($email, $restriction, $error)
{
	global $db_prefix, $txt;

	// Can't ban an empty email
	if (empty($email) || trim($email) == '')
		return;

	// Let's start with the bans based on your IP/hostname/memberID...
	$ban_ids = isset($_SESSION['ban'][$restriction]) ? $_SESSION['ban'][$restriction]['ids'] : array();
	$ban_reason = isset($_SESSION['ban'][$restriction]) ? $_SESSION['ban'][$restriction]['reason'] : '';

	// ...and add to that the email address you're trying to register.
	$request = db_query("
		SELECT bi.ID_BAN, bg.$restriction, bg.cannot_access, bg.reason
		FROM ({$db_prefix}ban_items AS bi, {$db_prefix}ban_groups AS bg)
		WHERE bg.ID_BAN_GROUP = bi.ID_BAN_GROUP
			AND '$email' LIKE bi.email_address
			AND (bg.$restriction = 1 OR bg.cannot_access = 1)", __FILE__, __LINE__);
	while ($row = mysql_fetch_assoc($request))
	{
		if (!empty($row['cannot_access']))
		{
			$_SESSION['ban']['cannot_access']['ids'][] = $row['ID_BAN'];
			$_SESSION['ban']['cannot_access']['reason'] = $row['reason'];
		}
		if (!empty($row[$restriction]))
		{
			$ban_ids[] = $row['ID_BAN'];
			$ban_reason = $row['reason'];
		}
	}
	mysql_free_result($request);

	// You're in biiig trouble.  Banned for the rest of this session!
	if (isset($_SESSION['ban']['cannot_access']))
	{
		log_ban($_SESSION['ban']['cannot_access']['ids']);
		$_SESSION['ban']['last_checked'] = time();

		fatal_error(sprintf($txt[430], $txt[28]) . $_SESSION['ban']['cannot_access']['reason'], false);
	}

	if (!empty($ban_ids))
	{
		// Log this ban for future reference.
		log_ban($ban_ids, $email);
		fatal_error($error . $ban_reason, false);
	}
}

// Make sure the user's correct session was passed, and they came from here. (type can be post, get, or request.)
function checkSession($type = 'post', $from_action = '', $is_fatal = true)
{
	global $sc, $modSettings, $boardurl;

	// Is it in as $_POST['sc']?
	if ($type == 'post' && (!isset($_POST['sc']) || $_POST['sc'] != $sc))
		$error = 'smf304';
	// How about $_GET['sesc']?
	elseif ($type == 'get' && (!isset($_GET['sesc']) || $_GET['sesc'] != $sc))
		$error = 'smf305';
	// Or can it be in either?
	elseif ($type == 'request' && (!isset($_GET['sesc']) || $_GET['sesc'] != $sc) && (!isset($_POST['sc']) || $_POST['sc'] != $sc))
		$error = 'smf305';

	// Verify that they aren't changing user agents on us - that could be bad.
	if ((!isset($_SESSION['USER_AGENT']) || $_SESSION['USER_AGENT'] != $_SERVER['HTTP_USER_AGENT']) && empty($modSettings['disableCheckUA']))
		$error = 'smf305';

	// Make sure a page with session check requirement is not being prefetched.
	if (isset($_SERVER['HTTP_X_MOZ']) && $_SERVER['HTTP_X_MOZ'] == 'prefetch')
	{
		ob_end_clean();
		header('HTTP/1.1 403 Forbidden');
		die;
	}

	// Check the referring site - it should be the same server at least!
	$referrer = isset($_SERVER['HTTP_REFERER']) ? @parse_url($_SERVER['HTTP_REFERER']) : array();
	if (!empty($referrer['host']))
	{
		if (strpos($_SERVER['HTTP_HOST'], ':') !== false)
			$real_host = substr($_SERVER['HTTP_HOST'], 0, strpos($_SERVER['HTTP_HOST'], ':'));
		else
			$real_host = $_SERVER['HTTP_HOST'];

		$parsed_url = parse_url($boardurl);

		// Are global cookies on?  If so, let's check them ;).
		if (!empty($modSettings['globalCookies']))
		{
			if (preg_match('~(?:[^\.]+\.)?([^\.]{3,}\..+)\z~i', $parsed_url['host'], $parts) == 1)
				$parsed_url['host'] = $parts[1];

			if (preg_match('~(?:[^\.]+\.)?([^\.]{3,}\..+)\z~i', $referrer['host'], $parts) == 1)
				$referrer['host'] = $parts[1];

			if (preg_match('~(?:[^\.]+\.)?([^\.]{3,}\..+)\z~i', $real_host, $parts) == 1)
				$real_host = $parts[1];
		}

		// Okay: referrer must either match parsed_url or real_host.
		if (isset($parsed_url['host']) && strtolower($referrer['host']) != strtolower($parsed_url['host']) && strtolower($referrer['host']) != strtolower($real_host))
		{
			$error = 'smf306';
			$log_error = true;
		}
	}

	// Well, first of all, if a from_action is specified you'd better have an old_url.
	if (!empty($from_action) && (!isset($_SESSION['old_url']) || preg_match('~[?;&]action=' . $from_action . '([;&]|$)~', $_SESSION['old_url']) == 0))
	{
		$error = 'smf306';
		$log_error = true;
	}

	if (strtolower($_SERVER['HTTP_USER_AGENT']) == 'hacker')
		fatal_error('Sound the alarm!  It\'s a hacker!  Close the castle gates!!', false);

	// Everything is ok, return an empty string.
	if (!isset($error))
		return '';
	// A session error occurred, show the error.
	elseif ($is_fatal)
		fatal_lang_error($error, isset($log_error));
	// A session error occurred, return the error to the calling function.
	else
		return $error;

	// We really should never fall through here, for very important reasons.  Let's make sure.
	trigger_error('Hacking attempt...', E_USER_ERROR);
}

// Check whether a form has been submitted twice.
function checkSubmitOnce($action, $is_fatal = true)
{
	global $context;

	if (!isset($_SESSION['forms']))
		$_SESSION['forms'] = array();

	// Register a form number and store it in the session stack. (use this on the page that has the form.)
	if ($action == 'register')
	{
		$context['form_sequence_number'] = 0;
		while (empty($context['form_sequence_number']) || in_array($context['form_sequence_number'], $_SESSION['forms']))
			$context['form_sequence_number'] = rand(1, 16000000);
	}
	// Check whether the submitted number can be found in the session.
	elseif ($action == 'check')
	{
		if (!isset($_REQUEST['seqnum']))
			return true;
		elseif (!in_array($_REQUEST['seqnum'], $_SESSION['forms']))
		{
			$_SESSION['forms'][] = (int) $_REQUEST['seqnum'];
			return true;
		}
		elseif ($is_fatal)
			fatal_lang_error('error_form_already_submitted', false);
		else
			return false;
	}
	// Don't check, just free the stack number.
	elseif ($action == 'free' && isset($_REQUEST['seqnum']) && in_array($_REQUEST['seqnum'], $_SESSION['forms']))	
		$_SESSION['forms'] = array_diff($_SESSION['forms'], array($_REQUEST['seqnum']));
	elseif ($action != 'free')
		trigger_error('checkSubmitOnce(): Invalid action \'' . $action . '\'', E_USER_WARNING);
}

// Check the user's permissions.
function allowedTo($permission, $boards = null)
{
	global $user_info, $db_prefix, $modSettings, $ID_MEMBER;

	// You're always allowed to do nothing. (unless you're a working man, MR. LAZY :P!)
	if (empty($permission))
		return true;

	// You're never allowed to do something if your data hasn't been loaded yet!
	if (empty($user_info))
		return false;

	// Administrators are supermen :P.
	if ($user_info['is_admin'])
		return true;

	// Are we checking the _current_ board, or some other boards?
	if ($boards === null)
	{
		// Check if they can do it.
		if (!is_array($permission) && in_array($permission, $user_info['permissions']))
			return true;
		// Search for any of a list of permissions.
		elseif (is_array($permission) && count(array_intersect($permission, $user_info['permissions'])) != 0)
			return true;
		// You aren't allowed, by default.
		else
			return false;
	}
	elseif (!is_array($boards))
		$boards = array($boards);

	// Determine which permission mode is still acceptable.
	if (empty($modSettings['permission_enable_by_board']) && !in_array('moderate_board', $user_info['permissions']))
	{
		// Make an array of the permission.
		$temp = is_array($permission) ? $permission : array($permission);

		if (in_array('post_reply_own', $temp) || in_array('post_reply_any', $temp))
			$max_allowable_mode = 3;
		elseif (in_array('post_new', $temp))
			$max_allowable_mode = 2;
		elseif (in_array('poll_post', $temp))
			$max_allowable_mode = 0;
	}

	$request = db_query("
		SELECT MIN(bp.addDeny) AS addDeny
		FROM ({$db_prefix}boards AS b, {$db_prefix}board_permissions AS bp)
			LEFT JOIN {$db_prefix}moderators AS mods ON (mods.ID_BOARD = b.ID_BOARD AND mods.ID_MEMBER = $ID_MEMBER)
		WHERE b.ID_BOARD IN (" . implode(', ', $boards) . ")" . (isset($max_allowable_mode) ? "
			AND b.permission_mode <= $max_allowable_mode" : '') . "
			AND bp.ID_BOARD = " . (empty($modSettings['permission_enable_by_board']) ? '0' : 'IF(b.permission_mode = 1, b.ID_BOARD, 0)') . "
			AND bp.ID_GROUP IN (" . implode(', ', $user_info['groups']) . ", 3)
			AND bp.permission " . (is_array($permission) ? "IN ('" . implode("', '", $permission) . "')" : " = '$permission'") . "
			AND (mods.ID_MEMBER IS NOT NULL OR bp.ID_GROUP != 3)
		GROUP BY b.ID_BOARD", __FILE__, __LINE__);

	// Make sure they can do it on all of the boards.
	if (mysql_num_rows($request) != count($boards))
		return false;

	$result = true;
	while ($row = mysql_fetch_assoc($request))
		$result &= !empty($row['addDeny']);
	mysql_free_result($request);

	// If the query returned 1, they can do it... otherwise, they can't.
	return $result;
}

// Fatal error if they cannot...
function isAllowedTo($permission, $boards = null)
{
	global $user_info, $txt;

	static $heavy_permissions = array(
		'admin_forum',
		'manage_attachments',
		'manage_smileys',
		'manage_boards',
		'edit_news',
		'moderate_forum',
		'manage_bans',
		'manage_membergroups',
		'manage_permissions',
	);

	// Make it an array, even if a string was passed.
	$permission = is_array($permission) ? $permission : array($permission);

	// Check the permission and return an error...
	if (!allowedTo($permission, $boards))
	{
		// Pick the last array entry as the permission shown as the error.
		$error_permission = array_shift($permission);

		// If they are a guest, show a login. (because the error might be gone if they do!)
		if ($user_info['is_guest'])
		{
			loadLanguage('Errors');
			is_not_guest($txt['cannot_' . $error_permission]);
		}

		// Clear the action because they aren't really doing that!
		$_GET['action'] = '';
		$_GET['board'] = '';
		$_GET['topic'] = '';
		writeLog(true);

		fatal_lang_error('cannot_' . $error_permission, false);

		// Getting this far is a really big problem, but let's try our best to prevent any cases...
		trigger_error('Hacking attempt...', E_USER_ERROR);
	}

	// If you're doing something on behalf of some "heavy" permissions, validate your session.
	// (take out the heavy permissions, and if you can't do anything but those, you need a validated session.)
	if (!allowedTo(array_diff($permission, $heavy_permissions), $boards))
		validateSession();
}

// Return the boards a user has a certain (board) permission on. (array(0) if all.)
function boardsAllowedTo($permission)
{
	global $db_prefix, $ID_MEMBER, $user_info, $modSettings;

	// Administrators are all powerful, sorry.
	if ($user_info['is_admin'])
		return array(0);

	// All groups the user is in except 'moderator'.
	$groups = array_diff($user_info['groups'], array(3));

	// With no local permissions, there might be some other restrictions.
	if (empty($modSettings['permission_enable_by_board']) && !in_array('moderate_board', $user_info['permissions']))
	{
		$needed_level = array(
			'post_reply_own' => 3,
			'post_reply_any' => 3,
			'post_new' => 2,
			'poll_post' => 0,
		);
		if (isset($needed_level[$permission]))
			$max_allowable_mode = $needed_level[$permission];
	}

	$request = db_query("
		SELECT b.ID_BOARD, b.permission_mode, bp.addDeny
		FROM ({$db_prefix}boards AS b, {$db_prefix}board_permissions AS bp)
			LEFT JOIN {$db_prefix}moderators AS mods ON (mods.ID_BOARD = b.ID_BOARD AND mods.ID_MEMBER = $ID_MEMBER)
		WHERE bp.ID_BOARD = " . (empty($modSettings['permission_enable_by_board']) ? '0' : 'IF(b.permission_mode = 1, b.ID_BOARD, 0)') . "
			AND bp.ID_GROUP IN (" . implode(', ', $groups) . ", 3)
			AND bp.permission = '$permission'" . (isset($max_allowable_mode) ? "
			AND (mods.ID_MEMBER IS NOT NULL OR b.permission_mode <= $max_allowable_mode)" : '') . "
			AND (mods.ID_MEMBER IS NOT NULL OR bp.ID_GROUP != 3)", __FILE__, __LINE__);
	$boards = array();
	$deny_boards = array();
	while ($row = mysql_fetch_assoc($request))
	{
		if (empty($row['addDeny']))
			$deny_boards[] = $row['ID_BOARD'];
		else
			$boards[] = $row['ID_BOARD'];
	}
	mysql_free_result($request);

	$boards = array_values(array_diff($boards, $deny_boards));

	return $boards;
}

// Grudge chickens out and puts this in for combatibility. This will be ripped out on day one for SMF 1.2 though ;)
function is_admin()
{
	isAllowedTo('admin_forum');
}

?>