MDL-63183 auth: Login protection

CSRF protection for the login form. The authenticate_user_login function was extended to validate the token (in \core\session\manager) but by default it does not perform the extra validation. Existing uses of this function from auth plugins and features like "change password" will continue to work without changes. New config value $CFG->disablelogintoken can bypass this check.
2018-10-23 12:29:30 +08:00
parent e3602a5a0a
commit 52b50073fc
12 changed files with 192 additions and 6 deletions
@@ -46,6 +46,9 @@ class manager {
    /** @var bool $sessionactive Is the session active? */
    protected static $sessionactive = null;

+    /** @var string $logintokenkey Key used to get and store request protection for login form. */
+    protected static $logintokenkey = 'core_auth_login';
+
    /**
     * Start user session.
     *
@@ -906,4 +909,102 @@ class manager {
        )));
    }

+    /**
+     * Generate a new login token and store it in the session.
+     *
+     * @return array The current login state.
+     */
+    private static function create_login_token() {
+        global $SESSION;
+
+        $state = [
+            'token' => random_string(32),
+            'created' => time() // Server time - not user time.
+        ];
+
+        if (!isset($SESSION->logintoken)) {
+            $SESSION->logintoken = [];
+        }
+
+        // Overwrite any previous values.
+        $SESSION->logintoken[self::$logintokenkey] = $state;
+
+        return $state;
+    }
+
+    /**
+     * Get the current login token or generate a new one.
+     *
+     * All login forms generated from Moodle must include a login token
+     * named "logintoken" with the value being the result of this function.
+     * Logins will be rejected if they do not include this token as well as
+     * the username and password fields.
+     *
+     * @return string The current login token.
+     */
+    public static function get_login_token() {
+        global $CFG, $SESSION;
+
+        $state = false;
+
+        if (!isset($SESSION->logintoken)) {
+            $SESSION->logintoken = [];
+        }
+
+        if (array_key_exists(self::$logintokenkey, $SESSION->logintoken)) {
+            $state = $SESSION->logintoken[self::$logintokenkey];
+        }
+        if (empty($state)) {
+            $state = self::create_login_token();
+        }
+
+        // Check token lifespan.
+        if ($state['created'] < (time() - $CFG->sessiontimeout)) {
+            $state = self::create_login_token();
+        }
+
+        // Return the current session login token.
+        if (array_key_exists('token', $state)) {
+            return $state['token'];
+        } else {
+            return false;
+        }
+    }
+
+    /**
+     * Check the submitted value against the stored login token.
+     *
+     * @param mixed $token The value submitted in the login form that we are validating.
+     *                     If false is passed for the token, this function will always return true.
+     * @return boolean If the submitted token is valid.
+     */
+    public static function validate_login_token($token = false) {
+        global $CFG;
+
+        if (!empty($CFG->alternateloginurl) || !empty($CFG->disablelogintoken)) {
+            // An external login page cannot generate the login token we need to protect CSRF on
+            // login requests.
+            // Other custom login workflows may skip this check by setting disablelogintoken in config.
+            return true;
+        }
+        if ($token === false) {
+            // authenticate_user_login is a core function was extended to validate tokens.
+            // For existing uses other than the login form it does not
+            // validate that a token was generated.
+            // Some uses that do not validate the token are login/token.php,
+            // or an auth plugin like auth/ldap/auth.php.
+            return true;
+        }
+
+        $currenttoken = self::get_login_token();
+
+        // We need to clean the login token so the old one is not valid again.
+        self::create_login_token();
+
+        if ($currenttoken !== $token) {
+            // Fail the login.
+            return false;
+        }
+        return true;
+    }
 }