Feat fake dns address (#902)

Works only with userspace implementation:
1. Configure host to solve DNS requests via a fake DSN server address in the Netbird network.
2. Add to firewall catch rule for these DNS requests.
3. Resolve these DNS requests and respond by writing directly to wireguard device.

client/firewall/uspfilter/rule.go

@@ -20,6 +20,8 @@ type Rule struct {
 	dPort      uint16
 	drop       bool
 	comment    string
+
+	udpHook func([]byte) bool
 }
 
 // GetRuleID returns the rule id

client/firewall/uspfilter/uspfilter.go

@@ -18,7 +18,7 @@ const layerTypeAll = 0
 
 // IFaceMapper defines subset methods of interface required for manager
 type IFaceMapper interface {
-	SetFiltering(iface.PacketFilter) error
+	SetFilter(iface.PacketFilter) error
 }
 
 // Manager userspace firewall manager
@@ -64,7 +64,7 @@ func Create(iface IFaceMapper) (*Manager, error) {
 		},
 	}
 
-	if err := iface.SetFiltering(m); err != nil {
+	if err := iface.SetFilter(m); err != nil {
 		return nil, err
 	}
 	return m, nil
@@ -273,6 +273,12 @@ func (m *Manager) dropFilter(packetData []byte, rules []Rule, isIncomingPacket b
 				return rule.drop
 			}
 		case layers.LayerTypeUDP:
+			// if rule has UDP hook (and if we are here we match this rule)
+			// we ignore rule.drop and call this hook
+			if rule.udpHook != nil {
+				return rule.udpHook(packetData)
+			}
+
 			if rule.sPort == 0 && rule.dPort == 0 {
 				return rule.drop
 			}
@@ -296,3 +302,58 @@ func (m *Manager) dropFilter(packetData []byte, rules []Rule, isIncomingPacket b
 func (m *Manager) SetNetwork(network *net.IPNet) {
 	m.wgNetwork = network
 }
+
+// AddUDPPacketHook calls hook when UDP packet from given direction matched
+//
+// Hook function returns flag which indicates should be the matched package dropped or not
+func (m *Manager) AddUDPPacketHook(
+	in bool, ip net.IP, dPort uint16, hook func([]byte) bool,
+) string {
+	r := Rule{
+		id:         uuid.New().String(),
+		ip:         ip,
+		protoLayer: layers.LayerTypeUDP,
+		dPort:      dPort,
+		ipLayer:    layers.LayerTypeIPv6,
+		direction:  fw.RuleDirectionOUT,
+		comment:    fmt.Sprintf("UDP Hook direction: %v, ip:%v, dport:%d", in, ip, dPort),
+		udpHook:    hook,
+	}
+
+	if ip.To4() != nil {
+		r.ipLayer = layers.LayerTypeIPv4
+	}
+
+	m.mutex.Lock()
+	var toUpdate []Rule
+	if in {
+		r.direction = fw.RuleDirectionIN
+		m.incomingRules = append([]Rule{r}, m.incomingRules...)
+		toUpdate = m.incomingRules
+	} else {
+		m.outgoingRules = append([]Rule{r}, m.outgoingRules...)
+		toUpdate = m.outgoingRules
+	}
+
+	for i := range toUpdate {
+		m.rulesIndex[toUpdate[i].id] = i
+	}
+	m.mutex.Unlock()
+
+	return r.id
+}
+
+// RemovePacketHook removes packet hook by given ID
+func (m *Manager) RemovePacketHook(hookID string) error {
+	for _, r := range m.incomingRules {
+		if r.id == hookID {
+			return m.DeleteRule(&r)
+		}
+	}
+	for _, r := range m.outgoingRules {
+		if r.id == hookID {
+			return m.DeleteRule(&r)
+		}
+	}
+	return fmt.Errorf("hook with given id not found")
+}

client/firewall/uspfilter/uspfilter_test.go

@@ -15,19 +15,19 @@ import (
 )
 
 type IFaceMock struct {
-	SetFilteringFunc func(iface.PacketFilter) error
+	SetFilterFunc func(iface.PacketFilter) error
 }
 
-func (i *IFaceMock) SetFiltering(iface iface.PacketFilter) error {
-	if i.SetFilteringFunc == nil {
+func (i *IFaceMock) SetFilter(iface iface.PacketFilter) error {
+	if i.SetFilterFunc == nil {
 		return fmt.Errorf("not implemented")
 	}
-	return i.SetFilteringFunc(iface)
+	return i.SetFilterFunc(iface)
 }
 
 func TestManagerCreate(t *testing.T) {
 	ifaceMock := &IFaceMock{
-		SetFilteringFunc: func(iface.PacketFilter) error { return nil },
+		SetFilterFunc: func(iface.PacketFilter) error { return nil },
 	}
 
 	m, err := Create(ifaceMock)
@@ -42,10 +42,10 @@ func TestManagerCreate(t *testing.T) {
 }
 
 func TestManagerAddFiltering(t *testing.T) {
-	isSetFilteringCalled := false
+	isSetFilterCalled := false
 	ifaceMock := &IFaceMock{
-		SetFilteringFunc: func(iface.PacketFilter) error {
-			isSetFilteringCalled = true
+		SetFilterFunc: func(iface.PacketFilter) error {
+			isSetFilterCalled = true
 			return nil
 		},
 	}
@@ -74,15 +74,15 @@ func TestManagerAddFiltering(t *testing.T) {
 		return
 	}
 
-	if !isSetFilteringCalled {
-		t.Error("SetFiltering was not called")
+	if !isSetFilterCalled {
+		t.Error("SetFilter was not called")
 		return
 	}
 }
 
 func TestManagerDeleteRule(t *testing.T) {
 	ifaceMock := &IFaceMock{
-		SetFilteringFunc: func(iface.PacketFilter) error { return nil },
+		SetFilterFunc: func(iface.PacketFilter) error { return nil },
 	}
 
 	m, err := Create(ifaceMock)
@@ -138,9 +138,97 @@ func TestManagerDeleteRule(t *testing.T) {
 	}
 }
 
+func TestAddUDPPacketHook(t *testing.T) {
+	tests := []struct {
+		name       string
+		in         bool
+		expDir     fw.RuleDirection
+		ip         net.IP
+		dPort      uint16
+		hook       func([]byte) bool
+		expectedID string
+	}{
+		{
+			name:   "Test Outgoing UDP Packet Hook",
+			in:     false,
+			expDir: fw.RuleDirectionOUT,
+			ip:     net.IPv4(10, 168, 0, 1),
+			dPort:  8000,
+			hook:   func([]byte) bool { return true },
+		},
+		{
+			name:   "Test Incoming UDP Packet Hook",
+			in:     true,
+			expDir: fw.RuleDirectionIN,
+			ip:     net.IPv6loopback,
+			dPort:  9000,
+			hook:   func([]byte) bool { return false },
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			manager := &Manager{
+				incomingRules: []Rule{},
+				outgoingRules: []Rule{},
+				rulesIndex:    make(map[string]int),
+			}
+
+			manager.AddUDPPacketHook(tt.in, tt.ip, tt.dPort, tt.hook)
+
+			var addedRule Rule
+			if tt.in {
+				if len(manager.incomingRules) != 1 {
+					t.Errorf("expected 1 incoming rule, got %d", len(manager.incomingRules))
+					return
+				}
+				addedRule = manager.incomingRules[0]
+			} else {
+				if len(manager.outgoingRules) != 1 {
+					t.Errorf("expected 1 outgoing rule, got %d", len(manager.outgoingRules))
+					return
+				}
+				addedRule = manager.outgoingRules[0]
+			}
+
+			if !tt.ip.Equal(addedRule.ip) {
+				t.Errorf("expected ip %s, got %s", tt.ip, addedRule.ip)
+				return
+			}
+			if tt.dPort != addedRule.dPort {
+				t.Errorf("expected dPort %d, got %d", tt.dPort, addedRule.dPort)
+				return
+			}
+			if layers.LayerTypeUDP != addedRule.protoLayer {
+				t.Errorf("expected protoLayer %s, got %s", layers.LayerTypeUDP, addedRule.protoLayer)
+				return
+			}
+			if tt.expDir != addedRule.direction {
+				t.Errorf("expected direction %d, got %d", tt.expDir, addedRule.direction)
+				return
+			}
+			if addedRule.udpHook == nil {
+				t.Errorf("expected udpHook to be set")
+				return
+			}
+
+			// Ensure rulesIndex is correctly updated
+			index, ok := manager.rulesIndex[addedRule.id]
+			if !ok {
+				t.Errorf("expected rule to be in rulesIndex")
+				return
+			}
+			if index != 0 {
+				t.Errorf("expected rule index to be 0, got %d", index)
+				return
+			}
+		})
+	}
+}
+
 func TestManagerReset(t *testing.T) {
 	ifaceMock := &IFaceMock{
-		SetFilteringFunc: func(iface.PacketFilter) error { return nil },
+		SetFilterFunc: func(iface.PacketFilter) error { return nil },
 	}
 
 	m, err := Create(ifaceMock)
@@ -175,7 +263,7 @@ func TestManagerReset(t *testing.T) {
 
 func TestNotMatchByIP(t *testing.T) {
 	ifaceMock := &IFaceMock{
-		SetFilteringFunc: func(iface.PacketFilter) error { return nil },
+		SetFilterFunc: func(iface.PacketFilter) error { return nil },
 	}
 
 	m, err := Create(ifaceMock)
@@ -239,12 +327,56 @@ func TestNotMatchByIP(t *testing.T) {
 	}
 }
 
+// TestRemovePacketHook tests the functionality of the RemovePacketHook method
+func TestRemovePacketHook(t *testing.T) {
+	// creating mock iface
+	iface := &IFaceMock{
+		SetFilterFunc: func(iface.PacketFilter) error { return nil },
+	}
+
+	// creating manager instance
+	manager, err := Create(iface)
+	if err != nil {
+		t.Fatalf("Failed to create Manager: %s", err)
+	}
+
+	// Add a UDP packet hook
+	hookFunc := func(data []byte) bool { return true }
+	hookID := manager.AddUDPPacketHook(false, net.IPv4(192, 168, 0, 1), 8080, hookFunc)
+
+	// Assert the hook is added by finding it in the manager's outgoing rules
+	found := false
+	for _, rule := range manager.outgoingRules {
+		if rule.id == hookID {
+			found = true
+			break
+		}
+	}
+
+	if !found {
+		t.Fatalf("The hook was not added properly.")
+	}
+
+	// Now remove the packet hook
+	err = manager.RemovePacketHook(hookID)
+	if err != nil {
+		t.Fatalf("Failed to remove hook: %s", err)
+	}
+
+	// Assert the hook is removed by checking it in the manager's outgoing rules
+	for _, rule := range manager.outgoingRules {
+		if rule.id == hookID {
+			t.Fatalf("The hook was not removed properly.")
+		}
+	}
+}
+
 func TestUSPFilterCreatePerformance(t *testing.T) {
 	for _, testMax := range []int{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000} {
 		t.Run(fmt.Sprintf("Testing %d rules", testMax), func(t *testing.T) {
 			// just check on the local interface
 			ifaceMock := &IFaceMock{
-				SetFilteringFunc: func(iface.PacketFilter) error { return nil },
+				SetFilterFunc: func(iface.PacketFilter) error { return nil },
 			}
 			manager, err := Create(ifaceMock)
 			require.NoError(t, err)