[ci skip] Prepare 3.1.9 release
diff --git a/system/libraries/Session/drivers/Session_redis_driver.php b/system/libraries/Session/drivers/Session_redis_driver.php
index 413c30d..d7a5755 100644
--- a/system/libraries/Session/drivers/Session_redis_driver.php
+++ b/system/libraries/Session/drivers/Session_redis_driver.php
@@ -153,6 +153,8 @@
 			return $this->_success;
 		}
 
+		$this->php5_validate_id();
+
 		return $this->_fail();
 	}
 
@@ -310,6 +312,22 @@
 		return $this->_success;
 	}
 
+	// --------------------------------------------------------------------
+
+	/**
+	 * Validate ID
+	 *
+	 * Checks whether a session ID record exists server-side,
+	 * to enforce session.use_strict_mode.
+	 *
+	 * @param	string	$id
+	 * @return	bool
+	 */
+	public function validateId($id)
+	{
+		return (bool) $this->_redis->exists($this->_key_prefix.$id);
+	}
+
 	// ------------------------------------------------------------------------
 
 	/**