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MDL-48498 core_files: curl_security_helper_base and implementation

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Base class and core implementation providing a means to check URLs
against the curl security admin settings entries.
This commit is contained in:
Jake Dallimore
2016-11-08 15:11:15 +08:00
parent 067268942c
commit f6d9efefaa
4 changed files with 611 additions and 0 deletions
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lib/classes/files/curl_security_helper.php
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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle 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 3 of the License, or
// (at your option) any later version.
//
// Moodle 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 Moodle. If not, see <http://www.gnu.org/licenses/>.
/**
* Contains a class providing functions used to check the host/port black/whitelists for curl.
*
* @package core
* @copyright 2016 Jake Dallimore
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @author Jake Dallimore <[email protected]>
*/
namespace core\files;
use core\ip_utils;
defined('MOODLE_INTERNAL') || exit();
/**
* Host and port checking for curl.
*
* This class provides a means to check URL/host/port against the system-level cURL security entries.
* It does not provide a means to add URLs, hosts or ports to the black/white lists; this is configured manually
* via the site admin section of Moodle (See: 'Site admin' > 'Security' > 'HTTP Security').
*
* This class is currently used by the 'curl' wrapper class in lib/filelib.php.
* Depends on:
* core\ip_utils (several functions)
* moodlelib (clean_param)
*
* @package core
* @copyright 2016 Jake Dallimore
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @author Jake Dallimore <[email protected]>
*/
class curl_security_helper extends curl_security_helper_base {
/**
* @var array of supported transport schemes and their respective default ports.
*/
protected $transportschemes = [
'http' => 80,
'https' => 443
];
/**
* Checks whether the given URL is blacklisted by checking its address and port number against the black/white lists.
* The behaviour of this function can be classified as strict, as it returns true for URLs which are invalid or
* could not be parsed, as well as those valid URLs which were found in the blacklist.
*
* @param string $urlstring the URL to check.
* @return bool true if the URL is blacklisted or invalid and false if the URL is not blacklisted.
*/
public function url_is_blocked($urlstring) {
// If no config data is present, then all hosts/ports are allowed.
if (!$this->is_enabled()) {
return false;
}
// Try to parse the URL to get the 'host' and 'port' components.
try {
$url = new \moodle_url($urlstring);
$parsed['scheme'] = $url->get_scheme();
$parsed['host'] = $url->get_host();
$parsed['port'] = $url->get_port();
} catch (\moodle_exception $e) {
// Moodle exception is thrown if the $urlstring is invalid. Treat as blocked.
return true;
}
// The port will be empty unless explicitly set in the $url (uncommon), so try to infer it from the supported schemes.
if (!$parsed['port'] && $parsed['scheme'] && isset($this->transportschemes[$parsed['scheme']])) {
$parsed['port'] = $this->transportschemes[$parsed['scheme']];
}
if ($parsed['port'] && $parsed['host']) {
// Check the host and port against the blacklist/whitelist entries.
return $this->host_is_blocked($parsed['host']) || $this->port_is_blocked($parsed['port']);
}
return true;
}
/**
* Returns a string message describing a blocked URL. E.g. 'This URL is blocked'.
*
* @return string the string error.
*/
public function get_blocked_url_string() {
return get_string('curlsecurityurlblocked', 'admin');
}
/**
* Checks whether the host portion of a url is blocked.
* The host portion may be a FQDN, IPv4 address or a IPv6 address wrapped in square brackets, as per standard URL notation.
* E.g.
* images.example.com
* 127.0.0.1
* [0.0.0.0.0.0.0.1]
* The method logic is as follows:
* 1. Check the host component against the list of IPv4/IPv6 addresses and ranges.
* - This will perform a DNS forward lookup if required.
* 2. Check the host component against the list of domain names and wildcard domain names.
* - This will perform a DNS reverse lookup if required.
*
* @param string $host the host component of the URL to check against the blacklist.
* @return bool true if the host is both valid and blocked, false otherwise.
*/
protected function host_is_blocked($host) {
if (!$this->is_enabled() || empty($host) || !is_string($host)) {
return false;
}
// Fix for square brackets in the 'host' portion of the URL (only occurs if an IPv6 address is specified).
$host = str_replace(array('[', ']'), '', $host); // RFC3986, section 3.2.2.
$blacklistedhosts = $this->get_blacklisted_hosts_by_category();
if (ip_utils::is_ip_address($host)) {
if ($this->address_explicitly_blocked($host)) {
return true;
}
// Only perform a reverse lookup if there is a point to it (i.e. we have rules to check against).
if ($blacklistedhosts['domain'] || $blacklistedhosts['domainwildcard']) {
$hostname = gethostbyaddr($host); // DNS reverse lookup - supports both IPv4 and IPv6 address formats.
if ($hostname !== $host && $this->host_explicitly_blocked($hostname)) {
return true;
}
}
} else if (ip_utils::is_domain_name($host)) {
if ($this->host_explicitly_blocked($host)) {
return true;
}
// Only perform a forward lookup if there are IP rules to check against.
if ($blacklistedhosts['ipv4'] || $blacklistedhosts['ipv6']) {
$hostip = gethostbyname($host); // DNS forward lookup - only returns IPv4 addresses!
if ($hostip !== $host && $this->address_explicitly_blocked($hostip)) {
return true;
}
}
}
return false;
}
/**
* Checks whether the given port is blocked, as determined by its absence on the ports whitelist.
* Ports are assumed to be blocked unless found in the whitelist.
*
* @param integer|string $port the port to check against the ports whitelist.
* @return bool true if the port is blocked, false otherwise.
*/
protected function port_is_blocked($port) {
$portnum = intval($port);
// Intentionally block port 0 and below and check the int cast was valid.
if (empty($port) || (string)$portnum !== (string)$port || $port < 0) {
return true;
}
$allowedports = $this->get_whitelisted_ports();
return !empty($allowedports) && !in_array($portnum, $allowedports);
}
/**
* Convenience method to check whether we have any entries in the host blacklist or ports whitelist admin settings.
* If no entries are found at all, the assumption is that the blacklist is disabled entirely.
*
* @return bool true if one or more entries exist, false otherwise.
*/
public function is_enabled() {
return (!empty($this->get_whitelisted_ports()) || !empty($this->get_blacklisted_hosts()));
}
/**
* Checks whether the input address is blocked by at any of the IPv4 or IPv6 address rules.
*
* @param string $addr the ip address to check.
* @return bool true if the address is covered by an entry in the blacklist, false otherwise.
*/
protected function address_explicitly_blocked($addr) {
$blockedhosts = $this->get_blacklisted_hosts_by_category();
$iphostsblocked = array_merge($blockedhosts['ipv4'], $blockedhosts['ipv6']);
return address_in_subnet($addr, implode(',', $iphostsblocked));
}
/**
* Checks whether the input hostname is blocked by any of the domain/wildcard rules.
*
* @param string $host the hostname to check
* @return bool true if the host is covered by an entry in the blacklist, false otherwise.
*/
protected function host_explicitly_blocked($host) {
$blockedhosts = $this->get_blacklisted_hosts_by_category();
$domainhostsblocked = array_merge($blockedhosts['domain'], $blockedhosts['domainwildcard']);
return ip_utils::is_domain_in_allowed_list($host, $domainhostsblocked);
}
/**
* Helper to get all entries from the admin setting, as an array, sorted by classification.
* Classifications include 'ipv4', 'ipv6', 'domain', 'domainwildcard'.
*
* @return array of host/domain/ip entries from the 'curlsecurityblockedhosts' config.
*/
protected function get_blacklisted_hosts_by_category() {
// For each of the admin setting entries, check and place in the correct section of the config array.
$config = ['ipv6' => [], 'ipv4' => [], 'domain' => [], 'domainwildcard' => []];
$entries = $this->get_blacklisted_hosts();
foreach ($entries as $entry) {
if (ip_utils::is_ipv6_address($entry) || ip_utils::is_ipv6_range($entry)) {
$config['ipv6'][] = $entry;
} else if (ip_utils::is_ipv4_address($entry) || ip_utils::is_ipv4_range($entry)) {
$config['ipv4'][] = $entry;
} else if (ip_utils::is_domain_name($entry)) {
$config['domain'][] = $entry;
} else if (ip_utils::is_domain_matching_pattern($entry)) {
$config['domainwildcard'][] = $entry;
}
}
return $config;
}
/**
* Helper that returns the whitelisted ports, as defined in the 'curlsecurityallowedport' setting.
*
* @return array the array of whitelisted ports.
*/
protected function get_whitelisted_ports() {
global $CFG;
return array_filter(explode("\n", $CFG->curlsecurityallowedport), function($entry) {
return !empty($entry);
});
}
/**
* Helper that returns the blacklisted hosts, as defined in the 'curlsecurityblockedhosts' setting.
*
* @return array the array of blacklisted host entries.
*/
protected function get_blacklisted_hosts() {
global $CFG;
return array_filter(array_map('trim', explode("\n", $CFG->curlsecurityblockedhosts)), function($entry) {
return !empty($entry);
});
}
}
lib/classes/files/curl_security_helper_base.php
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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle 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 3 of the License, or
// (at your option) any later version.
//
// Moodle 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 Moodle. If not, see <http://www.gnu.org/licenses/>.
/**
* Contains an abstract base class definition for curl security helpers.
*
* @package core
* @copyright 2016 Jake Dallimore
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @author Jake Dallimore <[email protected]>
*/
namespace core\files;
defined('MOODLE_INTERNAL') || exit();
/**
* Security helper for the curl class.
*
* This class is intended as a base class for all curl security helpers. A curl security helper should provide a means to check
* a URL to determine whether curl should be allowed to request its content. It must also be able to return a simple string to
* explain that the URL is blocked, e.g. 'This URL is blocked'.
*
* Curl security helpers are currently used by the 'curl' wrapper class in lib/filelib.php.
*
* This class depends on:
* - nothing.
*
* @package core
* @copyright 2016 Jake Dallimore
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
* @author Jake Dallimore <[email protected]>
*/
abstract class curl_security_helper_base {
/**
* Check whether the input url should be blocked or not.
*
* @param string $url the url to check.
* @return bool true if the url is deemed to be blocked, false otherwise.
*/
abstract public function url_is_blocked($url);
/**
* Returns a string, explaining that a URL is blocked.
*
* @return string the lang string indicating that the url has been blocked.
*/
abstract public function get_blocked_url_string();
}