Support for Firewalld

Firewalld [1] is a firewall managing daemon with D-Bus interface.

What sort of problem are we trying to solve with this ?

Firewalld internally also executes iptables/ip6tables to change firewall settings.
It might happen on systems where both docker and firewalld are running
concurrently, that both of them try to call iptables at the same time.
The result is that the second one fails because the first one is holding a xtables lock.
One workaround is to use --wait/-w option in both
docker & firewalld when calling iptables.
It's already been done in both upstreams:
b315c380f4
b3b451d6f8
But it'd still be better if docker used firewalld when it's running.

Other problem the firewalld support would solve is that
iptables/firewalld service's restart flushes all firewall rules
previously added by docker.
See next patch for possible solution.

This patch utilizes firewalld's D-Bus interface.
If firewalld is running, we call direct.passthrough() [2] method instead
of executing iptables directly.
direct.passthrough() takes the same arguments as iptables tool itself
and passes them through to iptables tool.
It might be better to use other methods, like direct.addChain and
direct.addRule [3] so it'd be more intergrated with firewalld, but
that'd make the patch much bigger.
If firewalld is not running, everything works as before.

[1] http://www.firewalld.org/
[2] https://jpopelka.fedorapeople.org/firewalld/doc/firewalld.dbus.html#FirewallD1.direct.Methods.passthrough
[3] https://jpopelka.fedorapeople.org/firewalld/doc/firewalld.dbus.html#FirewallD1.direct.Methods.addChain
    https://jpopelka.fedorapeople.org/firewalld/doc/firewalld.dbus.html#FirewallD1.direct.Methods.addRule

Signed-off-by: Jiri Popelka <jpopelka@redhat.com>

iptables/firewalld.go

@@ -0,0 +1,94 @@
+package iptables
+
+import (
+	"github.com/Sirupsen/logrus"
+	"github.com/godbus/dbus"
+)
+
+type IPV string
+
+const (
+	Iptables  IPV = "ipv4"
+	Ip6tables IPV = "ipv6"
+	Ebtables  IPV = "eb"
+)
+const (
+	dbusInterface = "org.fedoraproject.FirewallD1"
+	dbusPath      = "/org/fedoraproject/FirewallD1"
+)
+
+// Conn is a connection to firewalld dbus endpoint.
+type Conn struct {
+	sysconn *dbus.Conn
+	sysobj  *dbus.Object
+	signal  chan *dbus.Signal
+}
+
+var (
+	connection       *Conn
+	firewalldRunning bool // is Firewalld service running
+)
+
+func FirewalldInit() {
+	var err error
+
+	connection, err = newConnection()
+
+	if err != nil {
+		logrus.Errorf("Failed to connect to D-Bus system bus: %s", err)
+	}
+
+	firewalldRunning = checkRunning()
+}
+
+// New() establishes a connection to the system bus.
+func newConnection() (*Conn, error) {
+	c := new(Conn)
+	if err := c.initConnection(); err != nil {
+		return nil, err
+	}
+
+	return c, nil
+}
+
+// Innitialize D-Bus connection.
+func (c *Conn) initConnection() error {
+	var err error
+
+	c.sysconn, err = dbus.SystemBus()
+	if err != nil {
+		return err
+	}
+
+	// This never fails, even if the service is not running atm.
+	c.sysobj = c.sysconn.Object(dbusInterface, dbus.ObjectPath(dbusPath))
+
+	return nil
+}
+
+// Call some remote method to see whether the service is actually running.
+func checkRunning() bool {
+	var zone string
+	var err error
+
+	if connection != nil {
+		err = connection.sysobj.Call(dbusInterface+".getDefaultZone", 0).Store(&zone)
+		logrus.Infof("Firewalld running: %t", err == nil)
+		return err == nil
+	}
+	logrus.Info("Firewalld not running")
+	return false
+}
+
+// Firewalld's passthrough method simply passes args through to iptables/ip6tables
+func Passthrough(ipv IPV, args ...string) ([]byte, error) {
+	var output string
+
+	logrus.Debugf("Firewalld passthrough: %s, %s", ipv, args)
+	err := connection.sysobj.Call(dbusInterface+".direct.passthrough", 0, ipv, args).Store(&output)
+	if output != "" {
+		logrus.Debugf("passthrough output: %s", output)
+	}
+
+	return []byte(output), err
+}

iptables/iptables.go

@@ -275,6 +275,13 @@ func Exists(table Table, chain string, rule ...string) bool {
 
 // Call 'iptables' system command, passing supplied arguments
 func Raw(args ...string) ([]byte, error) {
+	if firewalldRunning {
+		output, err := Passthrough(Iptables, args...)
+		if err == nil || !strings.Contains(err.Error(), "was not provided by any .service files") {
+			return output, err
+		}
+
+	}
 
 	if err := initCheck(); err != nil {
 		return nil, err