Use fake address instead of wireguard address

client/internal/dns/service_listener.go

@@ -26,6 +26,7 @@ type serviceViaListener struct {
 	dnsMux            *dns.ServeMux
 	customAddr        *netip.AddrPort
 	server            *dns.Server
+	fakeIP            string
 	listenIP          string
 	listenPort        int
 	listenerIsRunning bool
@@ -67,8 +68,9 @@ func (s *serviceViaListener) Listen() error {
 	s.server.Addr = fmt.Sprintf("%s:%d", s.listenIP, s.listenPort)
 
 	if s.shouldApplyPortFwd() {
+		s.fakeIP = getLastIPFromNetwork(s.wgInterface.Address().Network, 1)
 		s.ebpfService = ebpf.GetEbpfManagerInstance()
-		err = s.ebpfService.LoadDNSFwd(s.listenIP, s.listenPort)
+		err = s.ebpfService.LoadDNSFwd(s.fakeIP, s.listenIP, s.listenPort)
 		if err != nil {
 			log.Warnf("failed to load DNS port fwd, custom port may not support well: %s", err)
 			s.ebpfService = nil
@@ -132,8 +134,15 @@ func (s *serviceViaListener) RuntimePort() int {
 }
 
 func (s *serviceViaListener) RuntimeIP() string {
+	s.listenerFlagLock.Lock()
+	defer s.listenerFlagLock.Unlock()
+
+	if s.ebpfService != nil {
+		return s.fakeIP
+	} else {
 		return s.listenIP
 	}
+}
 
 func (s *serviceViaListener) setListenerStatus(running bool) {
 	s.listenerIsRunning = running

client/internal/ebpf/dns_fwd_linux.go

@@ -10,12 +10,13 @@ import (
 )
 
 const (
-	mapKeyDNSIP   uint32 = 0
-	mapKeyDNSPort uint32 = 1
+	mapKeyFakeIP  uint32 = 0
+	mapKeyDNSIP   uint32 = 1
+	mapKeyDNSPort uint32 = 2
 )
 
-func (tf *GeneralManager) LoadDNSFwd(ip string, dnsPort int) error {
-	log.Debugf("load ebpf DNS forwarder: address: %s:%d", ip, dnsPort)
+func (tf *GeneralManager) LoadDNSFwd(fakeIp, dnsIp string, dnsPort int) error {
+	log.Debugf("load ebpf DNS forwarder: address: %s:%d", dnsIp, dnsPort)
 	tf.lock.Lock()
 	defer tf.lock.Unlock()
 
@@ -24,7 +25,12 @@ func (tf *GeneralManager) LoadDNSFwd(ip string, dnsPort int) error {
 		return err
 	}
 
-	err = tf.bpfObjs.NbMapDnsIp.Put(mapKeyDNSIP, ip2int(ip))
+	err = tf.bpfObjs.NbMapDnsIp.Put(mapKeyFakeIP, ip2int(fakeIp))
+	if err != nil {
+		return err
+	}
+
+	err = tf.bpfObjs.NbMapDnsIp.Put(mapKeyDNSIP, ip2int(dnsIp))
 	if err != nil {
 		return err
 	}

client/internal/ebpf/manager.go

@@ -1,7 +1,7 @@
 package ebpf
 
 type Manager interface {
-	LoadDNSFwd(ip string, dnsPort int) error
+	LoadDNSFwd(fakeIP, dnsIP string, dnsPort int) error
 	FreeDNSFwd() error
 	LoadWgProxy(proxyPort, wgPort int) error
 	FreeWGProxy() error

client/internal/ebpf/manager_linux.go

@@ -74,6 +74,7 @@ func (tf *GeneralManager) loadXdp() error {
 		Program:   tf.bpfObjs.NbXdpProg,
 		Interface: iFace.Index,
 	})
+
 	return err
 }
 

client/internal/ebpf/src/dns_fwd.c

@@ -1,5 +1,7 @@
-const __u32 map_key_dns_ip = 0;
-const __u32 map_key_dns_port = 1;
+
+const __u32 map_key_fake_ip = 0;
+const __u32 map_key_dns_ip = 1;
+const __u32 map_key_dns_port = 2;
 
 struct bpf_map_def SEC("maps") nb_map_dns_ip = {
 	.type = BPF_MAP_TYPE_ARRAY,
@@ -15,6 +17,7 @@ struct bpf_map_def SEC("maps") nb_map_dns_port = {
 	.max_entries = 10,
 };
 
+__be32 fake_ip = 0;
 __be32 dns_ip = 0;
 __be16 dns_port = 0;
 
@@ -22,8 +25,16 @@ __be16 dns_port = 0;
 __be16 GENERAL_DNS_PORT = 13568;
 
 bool read_settings() {
-    __u16 *port_value;
+    __u32 *fake_ip_value;
     __u32 *ip_value;
+    __u16 *port_value;
+
+    // read fake ip
+    fake_ip_value = bpf_map_lookup_elem(&nb_map_dns_ip, &map_key_fake_ip);
+    if(!fake_ip_value) {
+        return false;
+    }
+    fake_ip = htonl(*fake_ip_value);
 
     // read dns ip
     ip_value = bpf_map_lookup_elem(&nb_map_dns_ip, &map_key_dns_ip);
@@ -46,17 +57,17 @@ int xdp_dns_fwd(struct iphdr  *ip, struct udphdr *udp) {
         if(!read_settings()){
             return XDP_PASS;
         }
-        bpf_printk("dns port: %d", ntohs(dns_port));
-        bpf_printk("dns ip: %d", ntohl(dns_ip));
     }
 
-    if (udp->dest == GENERAL_DNS_PORT && ip->daddr == dns_ip) {
+    if (udp->dest == GENERAL_DNS_PORT && ip->daddr == fake_ip) {
         udp->dest = dns_port;
+        ip->daddr = dns_ip;
         return XDP_PASS;
     }
 
     if (udp->source == dns_port && ip->saddr == dns_ip) {
         udp->source = GENERAL_DNS_PORT;
+        ip->saddr = fake_ip;
         return XDP_PASS;
     }
 

client/internal/ebpf/wg_proxy_linux.go

@@ -2,7 +2,9 @@
 
 package ebpf
 
-import log "github.com/sirupsen/logrus"
+import (
+	log "github.com/sirupsen/logrus"
+)
 
 const (
 	mapKeyProxyPort uint32 = 0
@@ -35,6 +37,7 @@ func (tf *GeneralManager) LoadWgProxy(proxyPort, wgPort int) error {
 		return err
 	}
 	return nil
+
 }
 
 func (tf *GeneralManager) FreeWGProxy() error {