Add ct expect support (#272)

expr/ct.go

@@ -194,3 +194,74 @@ func (c *CtHelper) unmarshal(fam byte, data []byte) error {
 	}
 	return ad.Err()
 }
+
+// From https://git.netfilter.org/libnftnl/tree/include/linux/netfilter/nf_tables.h?id=be0bae0ad31b0adb506f96de083f52a2bd0d4fbf#n1601
+// Currently not available in sys/unix
+const (
+	NFTA_CT_EXPECT_L3PROTO = 0x01
+	NFTA_CT_EXPECT_L4PROTO = 0x02
+	NFTA_CT_EXPECT_DPORT   = 0x03
+	NFTA_CT_EXPECT_TIMEOUT = 0x04
+	NFTA_CT_EXPECT_SIZE    = 0x05
+)
+
+type CtExpect struct {
+	L3Proto uint16
+	L4Proto uint8
+	DPort   uint16
+	Timeout uint32
+	Size    uint8
+}
+
+func (c *CtExpect) marshal(fam byte) ([]byte, error) {
+	exprData, err := c.marshalData(fam)
+	if err != nil {
+		return nil, err
+	}
+
+	return netlink.MarshalAttributes([]netlink.Attribute{
+		{Type: unix.NFTA_EXPR_NAME, Data: []byte("ctexpect\x00")},
+		{Type: unix.NLA_F_NESTED | unix.NFTA_EXPR_DATA, Data: exprData},
+	})
+}
+
+func (c *CtExpect) marshalData(fam byte) ([]byte, error) {
+	// all elements except l3proto must be defined
+	// per https://git.netfilter.org/nftables/tree/doc/stateful-objects.txt?id=db70959a5ccf2952b218f51c3d529e186a5a43bb#n119
+	// from man page: l3proto is derived from the table family by default
+	exprData := []netlink.Attribute{
+		{Type: NFTA_CT_EXPECT_L4PROTO, Data: []byte{c.L4Proto}},
+		{Type: NFTA_CT_EXPECT_DPORT, Data: binaryutil.BigEndian.PutUint16(c.DPort)},
+		{Type: NFTA_CT_EXPECT_TIMEOUT, Data: binaryutil.BigEndian.PutUint32(c.Timeout)},
+		{Type: NFTA_CT_EXPECT_SIZE, Data: []byte{c.Size}},
+	}
+
+	if c.L3Proto != 0 {
+		attr := netlink.Attribute{Type: NFTA_CT_EXPECT_L3PROTO, Data: binaryutil.BigEndian.PutUint16(c.L3Proto)}
+		exprData = append(exprData, attr)
+	}
+	return netlink.MarshalAttributes(exprData)
+}
+
+func (c *CtExpect) unmarshal(fam byte, data []byte) error {
+	ad, err := netlink.NewAttributeDecoder(data)
+	if err != nil {
+		return err
+	}
+	ad.ByteOrder = binary.BigEndian
+	for ad.Next() {
+		switch ad.Type() {
+		case NFTA_CT_EXPECT_L3PROTO:
+			c.L3Proto = ad.Uint16()
+		case NFTA_CT_EXPECT_L4PROTO:
+			c.L4Proto = ad.Uint8()
+		case NFTA_CT_EXPECT_DPORT:
+			c.DPort = ad.Uint16()
+		case NFTA_CT_EXPECT_TIMEOUT:
+			c.Timeout = ad.Uint32()
+		case NFTA_CT_EXPECT_SIZE:
+			c.Size = ad.Uint8()
+		}
+	}
+	return ad.Err()
+}

expr/expr.go

@@ -201,6 +201,8 @@ func exprFromName(name string) Any {
 		e = &CtHelper{}
 	case "synproxy":
 		e = &SynProxy{}
+	case "ctexpect":
+		e = &CtExpect{}
 	}
 	return e
 }

nftables_test.go

@@ -1428,7 +1428,6 @@ func TestSynProxyObject(t *testing.T) {
 	conn.AddObj(syn1)
 	conn.AddObj(syn2)
 	conn.AddObj(syn3)
-
 	if err := conn.Flush(); err != nil {
 		t.Fatalf(err.Error())
 	}
@@ -1437,7 +1436,6 @@ func TestSynProxyObject(t *testing.T) {
 	if err != nil {
 		t.Errorf("c.GetObjects(table) failed: %v", err)
 	}
-
 	if got, want := len(objs), 3; got != want {
 		t.Fatalf("received %d objects, expected %d", got, want)
 	}
@@ -1481,6 +1479,74 @@ func TestSynProxyObject(t *testing.T) {
 	}
 }
 
+func TestCtExpect(t *testing.T) {
+	conn, newNS := nftest.OpenSystemConn(t, *enableSysTests)
+	defer nftest.CleanupSystemConn(t, newNS)
+	conn.FlushRuleset()
+	defer conn.FlushRuleset()
+
+	table := conn.AddTable(&nftables.Table{
+		Family: nftables.TableFamilyIPv4,
+		Name:   "filter",
+	})
+
+	cte := &nftables.NamedObj{
+		Table: table,
+		Name:  "expect",
+		Type:  nftables.ObjTypeCtExpect,
+		Obj: &expr.CtExpect{
+			L3Proto: unix.NFPROTO_IPV4,
+			L4Proto: unix.IPPROTO_TCP,
+			DPort:   53,
+			Timeout: 20,
+			Size:    100,
+		},
+	}
+
+	conn.AddObj(cte)
+	if err := conn.Flush(); err != nil {
+		t.Fatalf(err.Error())
+	}
+
+	objs, err := conn.GetNamedObjects(table)
+	if err != nil {
+		t.Errorf("c.GetObjects(table) failed: %v", err)
+	}
+
+	if got, want := len(objs), 1; got != want {
+		t.Fatalf("received %d objects, expected %d", got, want)
+	}
+
+	obj := objs[0].(*nftables.NamedObj)
+	if got, want := obj.Name, cte.Name; got != want {
+		t.Errorf("object names are not equal: got %s, want %s", got, want)
+	}
+	if got, want := obj.Type, cte.Type; got != want {
+		t.Errorf("object types are not equal: got %v, want %v", got, want)
+	}
+	if got, want := obj.Table.Name, cte.Table.Name; got != want {
+		t.Errorf("object tables are not equal: got %s, want %s", got, want)
+	}
+
+	ce1 := obj.Obj.(*expr.CtExpect)
+	ce2 := cte.Obj.(*expr.CtExpect)
+	if got, want := ce1.L3Proto, ce2.L3Proto; got != want {
+		t.Errorf("object l3proto not equal: got %d, want %d", got, want)
+	}
+	if got, want := ce1.L4Proto, ce2.L4Proto; got != want {
+		t.Errorf("object l4proto not equal: got %d, want %d", got, want)
+	}
+	if got, want := ce1.DPort, ce2.DPort; got != want {
+		t.Errorf("object dport not equal: got %d, want %d", got, want)
+	}
+	if got, want := ce1.Size, ce2.Size; got != want {
+		t.Errorf("object Size not equal: got %d, want %d", got, want)
+	}
+	if got, want := ce1.Timeout, ce2.Timeout; got != want {
+		t.Errorf("object timeout not equal: got %d, want %d", got, want)
+	}
+}
+
 func TestCtHelper(t *testing.T) {
 	conn, newNS := nftest.OpenSystemConn(t, *enableSysTests)
 	defer nftest.CleanupSystemConn(t, newNS)

obj.go

@@ -55,8 +55,8 @@ var objByObjTypeMagic = map[ObjType]string{
 	ObjTypeTunnel:    "tunnel",    // not implemented in expr
 	ObjTypeCtTimeout: "cttimeout", // not implemented in expr
 	ObjTypeSecMark:   "secmark",   // not implemented in expr
-	ObjTypeCtExpect:  "ctexpect",  // not implemented in expr
-	ObjTypeSynProxy:  "synproxy",  // not implemented in expr
+	ObjTypeCtExpect:  "ctexpect",
+	ObjTypeSynProxy:  "synproxy",
 }
 
 // Obj represents a netfilter stateful object. See also