[client] Add reverse dns zone (#3217)

client/internal/dns.go

@@ -0,0 +1,111 @@
+package internal
+
+import (
+	"fmt"
+	"net"
+	"slices"
+	"strings"
+
+	"github.com/miekg/dns"
+	log "github.com/sirupsen/logrus"
+
+	nbdns "github.com/netbirdio/netbird/dns"
+)
+
+func createPTRRecord(aRecord nbdns.SimpleRecord, ipNet *net.IPNet) (nbdns.SimpleRecord, bool) {
+	ip := net.ParseIP(aRecord.RData)
+	if ip == nil || ip.To4() == nil {
+		return nbdns.SimpleRecord{}, false
+	}
+
+	if !ipNet.Contains(ip) {
+		return nbdns.SimpleRecord{}, false
+	}
+
+	ipOctets := strings.Split(ip.String(), ".")
+	slices.Reverse(ipOctets)
+	rdnsName := dns.Fqdn(strings.Join(ipOctets, ".") + ".in-addr.arpa")
+
+	return nbdns.SimpleRecord{
+		Name:  rdnsName,
+		Type:  int(dns.TypePTR),
+		Class: aRecord.Class,
+		TTL:   aRecord.TTL,
+		RData: dns.Fqdn(aRecord.Name),
+	}, true
+}
+
+// generateReverseZoneName creates the reverse DNS zone name for a given network
+func generateReverseZoneName(ipNet *net.IPNet) (string, error) {
+	networkIP := ipNet.IP.Mask(ipNet.Mask)
+	maskOnes, _ := ipNet.Mask.Size()
+
+	// round up to nearest byte
+	octetsToUse := (maskOnes + 7) / 8
+
+	octets := strings.Split(networkIP.String(), ".")
+	if octetsToUse > len(octets) {
+		return "", fmt.Errorf("invalid network mask size for reverse DNS: %d", maskOnes)
+	}
+
+	reverseOctets := make([]string, octetsToUse)
+	for i := 0; i < octetsToUse; i++ {
+		reverseOctets[octetsToUse-1-i] = octets[i]
+	}
+
+	return dns.Fqdn(strings.Join(reverseOctets, ".") + ".in-addr.arpa"), nil
+}
+
+// zoneExists checks if a zone with the given name already exists in the configuration
+func zoneExists(config *nbdns.Config, zoneName string) bool {
+	for _, zone := range config.CustomZones {
+		if zone.Domain == zoneName {
+			log.Debugf("reverse DNS zone %s already exists", zoneName)
+			return true
+		}
+	}
+	return false
+}
+
+// collectPTRRecords gathers all PTR records for the given network from A records
+func collectPTRRecords(config *nbdns.Config, ipNet *net.IPNet) []nbdns.SimpleRecord {
+	var records []nbdns.SimpleRecord
+
+	for _, zone := range config.CustomZones {
+		for _, record := range zone.Records {
+			if record.Type != int(dns.TypeA) {
+				continue
+			}
+
+			if ptrRecord, ok := createPTRRecord(record, ipNet); ok {
+				records = append(records, ptrRecord)
+			}
+		}
+	}
+
+	return records
+}
+
+// addReverseZone adds a reverse DNS zone to the configuration for the given network
+func addReverseZone(config *nbdns.Config, ipNet *net.IPNet) {
+	zoneName, err := generateReverseZoneName(ipNet)
+	if err != nil {
+		log.Warn(err)
+		return
+	}
+
+	if zoneExists(config, zoneName) {
+		log.Debugf("reverse DNS zone %s already exists", zoneName)
+		return
+	}
+
+	records := collectPTRRecords(config, ipNet)
+
+	reverseZone := nbdns.CustomZone{
+		Domain:  zoneName,
+		Records: records,
+	}
+
+	config.CustomZones = append(config.CustomZones, reverseZone)
+	log.Debugf("added reverse DNS zone: %s with %d records", zoneName, len(records))
+}

client/internal/dns/host.go

@@ -9,6 +9,11 @@ import (
 	nbdns "github.com/netbirdio/netbird/dns"
 )
 
+const (
+	ipv4ReverseZone = ".in-addr.arpa"
+	ipv6ReverseZone = ".ip6.arpa"
+)
+
 type hostManager interface {
 	applyDNSConfig(config HostDNSConfig, stateManager *statemanager.Manager) error
 	restoreHostDNS() error
@@ -94,9 +99,10 @@ func dnsConfigToHostDNSConfig(dnsConfig nbdns.Config, ip string, port int) HostD
 	}
 
 	for _, customZone := range dnsConfig.CustomZones {
+		matchOnly := strings.HasSuffix(customZone.Domain, ipv4ReverseZone) || strings.HasSuffix(customZone.Domain, ipv6ReverseZone)
 		config.Domains = append(config.Domains, DomainConfig{
 			Domain:    strings.TrimSuffix(customZone.Domain, "."),
-			MatchOnly: false,
+			MatchOnly: matchOnly,
 		})
 	}
 

client/internal/dns/server.go

@@ -395,12 +395,12 @@ func (s *DefaultServer) applyConfiguration(update nbdns.Config) error {
 
 	localMuxUpdates, localRecordsByDomain, err := s.buildLocalHandlerUpdate(update.CustomZones)
 	if err != nil {
-		return fmt.Errorf("not applying dns update, error: %v", err)
+		return fmt.Errorf("local handler updater: %w", err)
 	}
 
 	upstreamMuxUpdates, err := s.buildUpstreamHandlerUpdate(update.NameServerGroups)
 	if err != nil {
-		return fmt.Errorf("not applying dns update, error: %v", err)
+		return fmt.Errorf("upstream handler updater: %w", err)
 	}
 	muxUpdates := append(localMuxUpdates, upstreamMuxUpdates...) //nolint:gocritic
 
@@ -447,7 +447,8 @@ func (s *DefaultServer) buildLocalHandlerUpdate(
 
 	for _, customZone := range customZones {
 		if len(customZone.Records) == 0 {
-			return nil, nil, fmt.Errorf("received an empty list of records")
+			log.Warnf("received a custom zone with empty records, skipping domain: %s", customZone.Domain)
+			continue
 		}
 
 		muxUpdates = append(muxUpdates, handlerWrapper{
@@ -460,7 +461,8 @@ func (s *DefaultServer) buildLocalHandlerUpdate(
 		for _, record := range customZone.Records {
 			var class uint16 = dns.ClassINET
 			if record.Class != nbdns.DefaultClass {
-				return nil, nil, fmt.Errorf("received an invalid class type: %s", record.Class)
+				log.Warnf("received an invalid class type: %s", record.Class)
+				continue
 			}
 
 			key := buildRecordKey(record.Name, class, uint16(record.Type))

client/internal/dns/server_test.go

@@ -266,7 +266,7 @@ func TestUpdateDNSServer(t *testing.T) {
 			shouldFail: true,
 		},
 		{
-			name:            "Invalid Custom Zone Records list Should Fail",
+			name:            "Invalid Custom Zone Records list Should Skip",
 			initLocalMap:    make(registrationMap),
 			initUpstreamMap: make(registeredHandlerMap),
 			initSerial:      0,
@@ -285,7 +285,11 @@ func TestUpdateDNSServer(t *testing.T) {
 					},
 				},
 			},
-			shouldFail: true,
+			expectedUpstreamMap: registeredHandlerMap{generateDummyHandler(".", nameServers).id(): handlerWrapper{
+				domain:   ".",
+				handler:  dummyHandler,
+				priority: PriorityDefault,
+			}},
 		},
 		{
 			name:         "Empty Config Should Succeed and Clean Maps",

client/internal/engine.go

@@ -953,7 +953,7 @@ func (e *Engine) updateNetworkMap(networkMap *mgmProto.NetworkMap) error {
 		protoDNSConfig = &mgmProto.DNSConfig{}
 	}
 
-	if err := e.dnsServer.UpdateDNSServer(serial, toDNSConfig(protoDNSConfig)); err != nil {
+	if err := e.dnsServer.UpdateDNSServer(serial, toDNSConfig(protoDNSConfig, e.wgInterface.Address().Network)); err != nil {
 		log.Errorf("failed to update dns server, err: %v", err)
 	}
 
@@ -1022,7 +1022,7 @@ func toRouteDomains(myPubKey string, protoRoutes []*mgmProto.Route) []string {
 	return dnsRoutes
 }
 
-func toDNSConfig(protoDNSConfig *mgmProto.DNSConfig) nbdns.Config {
+func toDNSConfig(protoDNSConfig *mgmProto.DNSConfig, network *net.IPNet) nbdns.Config {
 	dnsUpdate := nbdns.Config{
 		ServiceEnable:    protoDNSConfig.GetServiceEnable(),
 		CustomZones:      make([]nbdns.CustomZone, 0),
@@ -1062,6 +1062,11 @@ func toDNSConfig(protoDNSConfig *mgmProto.DNSConfig) nbdns.Config {
 		}
 		dnsUpdate.NameServerGroups = append(dnsUpdate.NameServerGroups, dnsNSGroup)
 	}
+
+	if len(dnsUpdate.CustomZones) > 0 {
+		addReverseZone(&dnsUpdate, network)
+	}
+
 	return dnsUpdate
 }
 
@@ -1368,7 +1373,7 @@ func (e *Engine) readInitialSettings() ([]*route.Route, *nbdns.Config, error) {
 		return nil, nil, err
 	}
 	routes := toRoutes(netMap.GetRoutes())
-	dnsCfg := toDNSConfig(netMap.GetDNSConfig())
+	dnsCfg := toDNSConfig(netMap.GetDNSConfig(), e.wgInterface.Address().Network)
 	return routes, &dnsCfg, nil
 }
 

client/internal/engine_test.go

@@ -361,6 +361,15 @@ func TestEngine_UpdateNetworkMap(t *testing.T) {
 		RemovePeerFunc: func(peerKey string) error {
 			return nil
 		},
+		AddressFunc: func() iface.WGAddress {
+			return iface.WGAddress{
+				IP: net.ParseIP("10.20.0.1"),
+				Network: &net.IPNet{
+					IP:   net.ParseIP("10.20.0.0"),
+					Mask: net.IPv4Mask(255, 255, 255, 0),
+				},
+			}
+		},
 	}
 	engine.wgInterface = wgIface
 	engine.routeManager = routemanager.NewManager(routemanager.ManagerConfig{
@@ -803,6 +812,9 @@ func TestEngine_UpdateNetworkMapWithDNSUpdate(t *testing.T) {
 								},
 							},
 						},
+						{
+							Domain: "0.66.100.in-addr.arpa.",
+						},
 					},
 					NameServerGroups: []*mgmtProto.NameServerGroup{
 						{
@@ -832,6 +844,9 @@ func TestEngine_UpdateNetworkMapWithDNSUpdate(t *testing.T) {
 						},
 					},
 				},
+				{
+					Domain: "0.66.100.in-addr.arpa.",
+				},
 			},
 			expectedNSGroupsLen: 1,
 			expectedNSGroups: []*nbdns.NameServerGroup{