[client] Redirect dns forwarder port 5353 to new listening port 22054 (#4707)

- Port dnat changes from #4015 (nftables/iptables/userspace)
  - For userspace: rewrite the original port to the target port
  - Remember original destination port in conntrack
  - Rewrite the source port back to the original port for replies
- Redirect incoming port 5353 to 22054 (tcp/udp)
- Revert port changes based on the network map received from management
- Adjust tracer to show NAT stages

Author: lixmal

client/firewall/iptables/manager_linux.go

@@ -260,6 +260,22 @@ func (m *Manager) UpdateSet(set firewall.Set, prefixes []netip.Prefix) error {
 	return m.router.UpdateSet(set, prefixes)
 }
 
+// AddInboundDNAT adds an inbound DNAT rule redirecting traffic from NetBird peers to local services.
+func (m *Manager) AddInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	return m.router.AddInboundDNAT(localAddr, protocol, sourcePort, targetPort)
+}
+
+// RemoveInboundDNAT removes an inbound DNAT rule.
+func (m *Manager) RemoveInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	return m.router.RemoveInboundDNAT(localAddr, protocol, sourcePort, targetPort)
+}
+
 func getConntrackEstablished() []string {
 	return []string{"-m", "conntrack", "--ctstate", "RELATED,ESTABLISHED", "-j", "ACCEPT"}
 }

client/firewall/iptables/router_linux.go

@@ -880,6 +880,54 @@ func (r *router) UpdateSet(set firewall.Set, prefixes []netip.Prefix) error {
 	return nberrors.FormatErrorOrNil(merr)
 }
 
+// AddInboundDNAT adds an inbound DNAT rule redirecting traffic from NetBird peers to local services.
+func (r *router) AddInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	ruleID := fmt.Sprintf("inbound-dnat-%s-%s-%d-%d", localAddr.String(), protocol, sourcePort, targetPort)
+
+	if _, exists := r.rules[ruleID]; exists {
+		return nil
+	}
+
+	dnatRule := []string{
+		"-i", r.wgIface.Name(),
+		"-p", strings.ToLower(string(protocol)),
+		"--dport", strconv.Itoa(int(sourcePort)),
+		"-d", localAddr.String(),
+		"-m", "addrtype", "--dst-type", "LOCAL",
+		"-j", "DNAT",
+		"--to-destination", ":" + strconv.Itoa(int(targetPort)),
+	}
+
+	ruleInfo := ruleInfo{
+		table: tableNat,
+		chain: chainRTRDR,
+		rule:  dnatRule,
+	}
+
+	if err := r.iptablesClient.Append(ruleInfo.table, ruleInfo.chain, ruleInfo.rule...); err != nil {
+		return fmt.Errorf("add inbound DNAT rule: %w", err)
+	}
+	r.rules[ruleID] = ruleInfo.rule
+
+	r.updateState()
+	return nil
+}
+
+// RemoveInboundDNAT removes an inbound DNAT rule.
+func (r *router) RemoveInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	ruleID := fmt.Sprintf("inbound-dnat-%s-%s-%d-%d", localAddr.String(), protocol, sourcePort, targetPort)
+
+	if dnatRule, exists := r.rules[ruleID]; exists {
+		if err := r.iptablesClient.Delete(tableNat, chainRTRDR, dnatRule...); err != nil {
+			return fmt.Errorf("delete inbound DNAT rule: %w", err)
+		}
+		delete(r.rules, ruleID)
+	}
+
+	r.updateState()
+	return nil
+}
+
 func applyPort(flag string, port *firewall.Port) []string {
 	if port == nil {
 		return nil

client/firewall/manager/firewall.go

@@ -151,14 +151,20 @@ type Manager interface {
 
 	DisableRouting() error
 
-	// AddDNATRule adds a DNAT rule
+	// AddDNATRule adds outbound DNAT rule for forwarding external traffic to the NetBird network.
 	AddDNATRule(ForwardRule) (Rule, error)
 
-	// DeleteDNATRule deletes a DNAT rule
+	// DeleteDNATRule deletes the outbound DNAT rule.
 	DeleteDNATRule(Rule) error
 
 	// UpdateSet updates the set with the given prefixes
 	UpdateSet(hash Set, prefixes []netip.Prefix) error
+
+	// AddInboundDNAT adds an inbound DNAT rule redirecting traffic from NetBird peers to local services
+	AddInboundDNAT(localAddr netip.Addr, protocol Protocol, sourcePort, targetPort uint16) error
+
+	// RemoveInboundDNAT removes inbound DNAT rule
+	RemoveInboundDNAT(localAddr netip.Addr, protocol Protocol, sourcePort, targetPort uint16) error
 }
 
 func GenKey(format string, pair RouterPair) string {

client/firewall/nftables/manager_linux.go

@@ -376,6 +376,22 @@ func (m *Manager) UpdateSet(set firewall.Set, prefixes []netip.Prefix) error {
 	return m.router.UpdateSet(set, prefixes)
 }
 
+// AddInboundDNAT adds an inbound DNAT rule redirecting traffic from NetBird peers to local services.
+func (m *Manager) AddInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	return m.router.AddInboundDNAT(localAddr, protocol, sourcePort, targetPort)
+}
+
+// RemoveInboundDNAT removes an inbound DNAT rule.
+func (m *Manager) RemoveInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	return m.router.RemoveInboundDNAT(localAddr, protocol, sourcePort, targetPort)
+}
+
 func (m *Manager) createWorkTable() (*nftables.Table, error) {
 	tables, err := m.rConn.ListTablesOfFamily(nftables.TableFamilyIPv4)
 	if err != nil {

client/firewall/nftables/router_linux.go

@@ -1350,6 +1350,103 @@ func (r *router) UpdateSet(set firewall.Set, prefixes []netip.Prefix) error {
 	return nil
 }
 
+// AddInboundDNAT adds an inbound DNAT rule redirecting traffic from NetBird peers to local services.
+func (r *router) AddInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	ruleID := fmt.Sprintf("inbound-dnat-%s-%s-%d-%d", localAddr.String(), protocol, sourcePort, targetPort)
+
+	if _, exists := r.rules[ruleID]; exists {
+		return nil
+	}
+
+	protoNum, err := protoToInt(protocol)
+	if err != nil {
+		return fmt.Errorf("convert protocol to number: %w", err)
+	}
+
+	exprs := []expr.Any{
+		&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     ifname(r.wgIface.Name()),
+		},
+		&expr.Meta{Key: expr.MetaKeyL4PROTO, Register: 2},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 2,
+			Data:     []byte{protoNum},
+		},
+		&expr.Payload{
+			DestRegister: 3,
+			Base:         expr.PayloadBaseTransportHeader,
+			Offset:       2,
+			Len:          2,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 3,
+			Data:     binaryutil.BigEndian.PutUint16(sourcePort),
+		},
+	}
+
+	exprs = append(exprs, applyPrefix(netip.PrefixFrom(localAddr, 32), false)...)
+
+	exprs = append(exprs,
+		&expr.Immediate{
+			Register: 1,
+			Data:     localAddr.AsSlice(),
+		},
+		&expr.Immediate{
+			Register: 2,
+			Data:     binaryutil.BigEndian.PutUint16(targetPort),
+		},
+		&expr.NAT{
+			Type:        expr.NATTypeDestNAT,
+			Family:      uint32(nftables.TableFamilyIPv4),
+			RegAddrMin:  1,
+			RegProtoMin: 2,
+			RegProtoMax: 0,
+		},
+	)
+
+	dnatRule := &nftables.Rule{
+		Table:    r.workTable,
+		Chain:    r.chains[chainNameRoutingRdr],
+		Exprs:    exprs,
+		UserData: []byte(ruleID),
+	}
+	r.conn.AddRule(dnatRule)
+
+	if err := r.conn.Flush(); err != nil {
+		return fmt.Errorf("add inbound DNAT rule: %w", err)
+	}
+
+	r.rules[ruleID] = dnatRule
+
+	return nil
+}
+
+// RemoveInboundDNAT removes an inbound DNAT rule.
+func (r *router) RemoveInboundDNAT(localAddr netip.Addr, protocol firewall.Protocol, sourcePort, targetPort uint16) error {
+	if err := r.refreshRulesMap(); err != nil {
+		return fmt.Errorf(refreshRulesMapError, err)
+	}
+
+	ruleID := fmt.Sprintf("inbound-dnat-%s-%s-%d-%d", localAddr.String(), protocol, sourcePort, targetPort)
+
+	if rule, exists := r.rules[ruleID]; exists {
+		if err := r.conn.DelRule(rule); err != nil {
+			return fmt.Errorf("delete inbound DNAT rule %s: %w", ruleID, err)
+		}
+		if err := r.conn.Flush(); err != nil {
+			return fmt.Errorf("flush delete inbound DNAT rule: %w", err)
+		}
+		delete(r.rules, ruleID)
+	}
+
+	return nil
+}
+
 // applyNetwork generates nftables expressions for networks (CIDR) or sets
 func (r *router) applyNetwork(
 	network firewall.Network,

client/firewall/uspfilter/conntrack/common.go

@@ -22,6 +22,8 @@ type BaseConnTrack struct {
 	PacketsRx atomic.Uint64
 	BytesTx   atomic.Uint64
 	BytesRx   atomic.Uint64
+
+	DNATOrigPort atomic.Uint32
 }
 
 // these small methods will be inlined by the compiler

client/firewall/uspfilter/conntrack/tcp.go

@@ -157,7 +157,7 @@ func NewTCPTracker(timeout time.Duration, logger *nblog.Logger, flowLogger nftyp
 	return tracker
 }
 
-func (t *TCPTracker) updateIfExists(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, direction nftypes.Direction, size int) (ConnKey, bool) {
+func (t *TCPTracker) updateIfExists(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, direction nftypes.Direction, size int) (ConnKey, uint16, bool) {
 	key := ConnKey{
 		SrcIP:   srcIP,
 		DstIP:   dstIP,
@@ -171,28 +171,30 @@ func (t *TCPTracker) updateIfExists(srcIP, dstIP netip.Addr, srcPort, dstPort ui
 
 	if exists {
 		t.updateState(key, conn, flags, direction, size)
-		return key, true
+		return key, uint16(conn.DNATOrigPort.Load()), true
 	}
 
-	return key, false
+	return key, 0, false
 }
 
-// TrackOutbound records an outbound TCP connection
-func (t *TCPTracker) TrackOutbound(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, size int) {
-	if _, exists := t.updateIfExists(dstIP, srcIP, dstPort, srcPort, flags, nftypes.Egress, size); !exists {
-		// if (inverted direction) conn is not tracked, track this direction
-		t.track(srcIP, dstIP, srcPort, dstPort, flags, nftypes.Egress, nil, size)
+// TrackOutbound records an outbound TCP connection and returns the original port if DNAT reversal is needed
+func (t *TCPTracker) TrackOutbound(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, size int) uint16 {
+	if _, origPort, exists := t.updateIfExists(dstIP, srcIP, dstPort, srcPort, flags, nftypes.Egress, size); exists {
+		return origPort
 	}
+	// if (inverted direction) conn is not tracked, track this direction
+	t.track(srcIP, dstIP, srcPort, dstPort, flags, nftypes.Egress, nil, size, 0)
+	return 0
 }
 
 // TrackInbound processes an inbound TCP packet and updates connection state
-func (t *TCPTracker) TrackInbound(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, ruleID []byte, size int) {
-	t.track(srcIP, dstIP, srcPort, dstPort, flags, nftypes.Ingress, ruleID, size)
+func (t *TCPTracker) TrackInbound(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, ruleID []byte, size int, dnatOrigPort uint16) {
+	t.track(srcIP, dstIP, srcPort, dstPort, flags, nftypes.Ingress, ruleID, size, dnatOrigPort)
 }
 
 // track is the common implementation for tracking both inbound and outbound connections
-func (t *TCPTracker) track(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, direction nftypes.Direction, ruleID []byte, size int) {
-	key, exists := t.updateIfExists(srcIP, dstIP, srcPort, dstPort, flags, direction, size)
+func (t *TCPTracker) track(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, flags uint8, direction nftypes.Direction, ruleID []byte, size int, origPort uint16) {
+	key, _, exists := t.updateIfExists(srcIP, dstIP, srcPort, dstPort, flags, direction, size)
 	if exists || flags&TCPSyn == 0 {
 		return
 	}
@@ -210,8 +212,13 @@ func (t *TCPTracker) track(srcIP, dstIP netip.Addr, srcPort, dstPort uint16, fla
 
 	conn.tombstone.Store(false)
 	conn.state.Store(int32(TCPStateNew))
+	conn.DNATOrigPort.Store(uint32(origPort))
 
-	t.logger.Trace2("New %s TCP connection: %s", direction, key)
+	if origPort != 0 {
+		t.logger.Trace4("New %s TCP connection: %s (port DNAT %d -> %d)", direction, key, origPort, dstPort)
+	} else {
+		t.logger.Trace2("New %s TCP connection: %s", direction, key)
+	}
 	t.updateState(key, conn, flags, direction, size)
 
 	t.mutex.Lock()
@@ -449,6 +456,21 @@ func (t *TCPTracker) cleanup() {
 	}
 }
 
+// GetConnection safely retrieves a connection state
+func (t *TCPTracker) GetConnection(srcIP netip.Addr, srcPort uint16, dstIP netip.Addr, dstPort uint16) (*TCPConnTrack, bool) {
+	t.mutex.RLock()
+	defer t.mutex.RUnlock()
+
+	key := ConnKey{
+		SrcIP:   srcIP,
+		DstIP:   dstIP,
+		SrcPort: srcPort,
+		DstPort: dstPort,
+	}
+	conn, exists := t.connections[key]
+	return conn, exists
+}
+
 // Close stops the cleanup routine and releases resources
 func (t *TCPTracker) Close() {
 	t.tickerCancel()

client/firewall/uspfilter/conntrack/tcp_test.go

@@ -603,7 +603,7 @@ func TestTCPInboundInitiatedConnection(t *testing.T) {
 	serverPort := uint16(80)
 
 	// 1. Client sends SYN (we receive it as inbound)
-	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPSyn, nil, 100)
+	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPSyn, nil, 100, 0)
 
 	key := ConnKey{
 		SrcIP:   clientIP,
@@ -623,12 +623,12 @@ func TestTCPInboundInitiatedConnection(t *testing.T) {
 	tracker.TrackOutbound(serverIP, clientIP, serverPort, clientPort, TCPSyn|TCPAck, 100)
 
 	// 3. Client sends ACK to complete handshake
-	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPAck, nil, 100)
+	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPAck, nil, 100, 0)
 	require.Equal(t, TCPStateEstablished, conn.GetState(), "Connection should be ESTABLISHED after handshake completion")
 
 	// 4. Test data transfer
 	// Client sends data
-	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPPush|TCPAck, nil, 1000)
+	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPPush|TCPAck, nil, 1000, 0)
 
 	// Server sends ACK for data
 	tracker.TrackOutbound(serverIP, clientIP, serverPort, clientPort, TCPAck, 100)
@@ -637,7 +637,7 @@ func TestTCPInboundInitiatedConnection(t *testing.T) {
 	tracker.TrackOutbound(serverIP, clientIP, serverPort, clientPort, TCPPush|TCPAck, 1500)
 
 	// Client sends ACK for data
-	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPAck, nil, 100)
+	tracker.TrackInbound(clientIP, serverIP, clientPort, serverPort, TCPAck, nil, 100, 0)
 
 	// Verify state and counters
 	require.Equal(t, TCPStateEstablished, conn.GetState())