WIP: use first ULA address as DHCPv6 source address

5 files changed, 65 insertions, 13 deletions

diff --git a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
index 32e3572a..1d900db0 100644
--- a/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/tunnel/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -384,8 +384,20 @@ public final class GoBackend implements Backend {
     private void Dhcp(VpnService service) throws Exception{
         obtainDhcpLease = false;
 
+        // Heuristics: Use first ULA address as client address
+        com.wireguard.android.backend.gen.InetAddress source = null;
+
+        for (final InetNetwork net : currentConfig.getInterface().getAddresses()) {
+            InetAddress addr = net.getAddress();
+            if (addr instanceof Inet6Address) {
+                if (Resolver.isULA((Inet6Address)addr)) {
+                    source = com.wireguard.android.backend.gen.InetAddress.newBuilder().setAddress(ByteString.copyFrom(addr.getAddress())).build();
+                }
+            }
+        }
+
         LibwgGrpc.LibwgBlockingStub stub = LibwgGrpc.newBlockingStub(channel);
-        DhcpRequest request = DhcpRequest.newBuilder().build();
+        DhcpRequest request = DhcpRequest.newBuilder().setSource(source).build();
         DhcpResponse resp = stub.dhcp(request);
         Log.i(TAG, "Dhcp: " + resp.getError().getMessage());
 
diff --git a/tunnel/src/main/java/com/wireguard/util/Resolver.java b/tunnel/src/main/java/com/wireguard/util/Resolver.java
index f401b584..301e03e0 100644
--- a/tunnel/src/main/java/com/wireguard/util/Resolver.java
+++ b/tunnel/src/main/java/com/wireguard/util/Resolver.java
@@ -36,7 +36,7 @@ public class Resolver {
         }
     }
 
-    static boolean isULA(Inet6Address addr) {
+    public static boolean isULA(Inet6Address addr) {
         byte[] raw = addr.getAddress();
         return ((raw[0] & 0xfe) == 0xfc);
     }
diff --git a/tunnel/src/main/proto/libwg.proto b/tunnel/src/main/proto/libwg.proto
index 349166ca..4fa4468b 100644
--- a/tunnel/src/main/proto/libwg.proto
+++ b/tunnel/src/main/proto/libwg.proto
@@ -115,6 +115,8 @@ message Lease {
 }
 
 message DhcpRequest {
+        InetAddress relay = 1;
+        InetAddress source = 2;
 }
 
 message DhcpResponse { 
diff --git a/tunnel/tools/libwg-go/dhcp.go b/tunnel/tools/libwg-go/dhcp.go
index 83a8c865..f6f25739 100644
--- a/tunnel/tools/libwg-go/dhcp.go
+++ b/tunnel/tools/libwg-go/dhcp.go
@@ -85,7 +85,7 @@ func isRelayMessageType(t dhcpv6.MessageType, tt ...dhcpv6.MessageType) nclient6
 // func New() *dhcp {
 // }
 
-func RunDhcp(ctx context.Context) ([]*gen.Lease, error) {
+func RunDhcp(ctx context.Context, laddr, raddr netip.Addr) ([]*gen.Lease, error) {
         d := &dhcp{}
         
         d.linkAddr = net.ParseIP("fe80::101")
@@ -95,25 +95,17 @@ func RunDhcp(ctx context.Context) ([]*gen.Lease, error) {
 	d.fqdn = hostName + ".m7n.se"
         d.hwAddr = []byte{41, 42, 43, 44, 45, 46}
 
-        laddr, err := netip.ParseAddr("fd1c:a56b:a0d7:1260::101")
-        if err != nil {
-                return nil, err
-        }
 
         src := net.UDPAddr{IP: laddr.AsSlice(),
                 Port: 0,        // Use non-restrict UDP source port
         }
 
-        raddr, err := netip.ParseAddr("fd1c:a56b:a0d7:1260::1")
-        if err != nil {
-                return nil, err
-        }
 
         d.serverAddr = net.UDPAddr{IP: raddr.AsSlice(),
                 Port: 547,
         }
 
-        err = d.Start(&src)
+        err := d.Start(&src)
         if err != nil {
                 return nil, err
         }
diff --git a/tunnel/tools/libwg-go/service.go b/tunnel/tools/libwg-go/service.go
index 2c688e26..38601f14 100644
--- a/tunnel/tools/libwg-go/service.go
+++ b/tunnel/tools/libwg-go/service.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"net/netip"
 //	"net/url"
 	"os"
 
@@ -256,7 +257,52 @@ func (e *LibwgServiceImpl) IpcSet(ctx context.Context, req *gen.IpcSetRequest) (
 }
 
 func (e *LibwgServiceImpl) Dhcp(ctx context.Context, req *gen.DhcpRequest) (*gen.DhcpResponse, error) {
-	leases, err := RunDhcp(ctx)
+	var relayAddr netip.Addr
+	var sourceAddr netip.Addr
+
+	source := req.GetSource()
+	if source != nil {
+		sourceAddr, _ = netip.AddrFromSlice(source.GetAddress())
+	}
+
+	if !sourceAddr.IsValid() || !sourceAddr.Is6() {
+		r := &gen.DhcpResponse{
+			Error: &gen.Error{
+				Message: fmt.Sprintf("DHCPv6 source address missing"),
+			},
+		}
+		return r, nil
+	}
+
+	relay := req.GetRelay()
+	if relay != nil {
+		relayAddr, _ = netip.AddrFromSlice(relay.GetAddress())
+	} else {
+		// Construct relay address from source prefix
+		relayRaw := source.GetAddress()[:8]
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 0)
+		relayRaw = append(relayRaw, 1)
+		relayAddr, _ = netip.AddrFromSlice(relayRaw)
+	}
+
+	if !relayAddr.IsValid() || !relayAddr.Is6() {
+		r := &gen.DhcpResponse{
+			Error: &gen.Error{
+				Message: fmt.Sprintf("DHCPv6 relay address calculation failed"),
+			},
+		}
+		return r, nil
+	}
+
+	e.logger.Verbosef("RunDhcp %v %v", sourceAddr, relayAddr)
+
+	leases, err := RunDhcp(ctx, sourceAddr, relayAddr)
 	if err != nil {
 		r := &gen.DhcpResponse{
 			Error: &gen.Error{