Implement redirect logic in UDP proxy

client/iface/wgproxy/udp/proxy.go

@@ -18,16 +18,18 @@ import (
 type WGUDPProxy struct {
 	localWGListenPort int
 
-	remoteConn net.Conn
-	localConn  net.Conn
-	ctx        context.Context
-	cancel     context.CancelFunc
-	closeMu    sync.Mutex
-	closed     bool
+	remoteConn   net.Conn
+	localConn    net.Conn
+	srcFakerConn *SrcFaker
+	sendPkg      func(data []byte) (int, error)
+	ctx          context.Context
+	cancel       context.CancelFunc
+	closeMu      sync.Mutex
+	closed       bool
 
-	pausedMu  sync.Mutex
-	paused    bool
-	isStarted bool
+	paused     bool
+	pausedCond *sync.Cond
+	isStarted  bool
 }
 
 // NewWGUDPProxy instantiate a UDP based WireGuard proxy. This is not a thread safe implementation
@@ -35,6 +37,7 @@ func NewWGUDPProxy(wgPort int) *WGUDPProxy {
 	log.Debugf("Initializing new user space proxy with port %d", wgPort)
 	p := &WGUDPProxy{
 		localWGListenPort: wgPort,
+		pausedCond:        sync.NewCond(&sync.Mutex{}),
 	}
 	return p
 }
@@ -54,6 +57,7 @@ func (p *WGUDPProxy) AddTurnConn(ctx context.Context, endpoint *net.UDPAddr, rem
 
 	p.ctx, p.cancel = context.WithCancel(ctx)
 	p.localConn = localConn
+	p.sendPkg = p.localConn.Write
 	p.remoteConn = remoteConn
 
 	return err
@@ -73,15 +77,17 @@ func (p *WGUDPProxy) Work() {
 		return
 	}
 
-	p.pausedMu.Lock()
+	p.pausedCond.L.Lock()
 	p.paused = false
-	p.pausedMu.Unlock()
+	p.sendPkg = p.localConn.Write
 
 	if !p.isStarted {
 		p.isStarted = true
 		go p.proxyToRemote(p.ctx)
 		go p.proxyToLocal(p.ctx)
 	}
+	p.pausedCond.L.Unlock()
+	p.pausedCond.Signal()
 }
 
 // Pause pauses the proxy from receiving data from the remote peer
@@ -90,13 +96,33 @@ func (p *WGUDPProxy) Pause() {
 		return
 	}
 
-	p.pausedMu.Lock()
+	p.pausedCond.L.Lock()
 	p.paused = true
-	p.pausedMu.Unlock()
+	p.pausedCond.L.Unlock()
 }
 
-func (p *WGUDPProxy) RedirectTo(endpoint *net.UDPAddr) {
-	// todo implement me
+// RedirectAs start to use the fake sourced raw socket as package sender
+func (p *WGUDPProxy) RedirectAs(endpoint *net.UDPAddr) {
+	p.pausedCond.L.Lock()
+	defer func() {
+		p.pausedCond.L.Unlock()
+		p.pausedCond.Signal()
+	}()
+
+	p.paused = false
+	if p.srcFakerConn != nil {
+		if err := p.srcFakerConn.Close(); err != nil {
+			log.Errorf("failed to close src faker conn: %s", err)
+		}
+		p.srcFakerConn = nil
+	}
+	srcFakerConn, err := NewSrcFaker(p.localWGListenPort, endpoint)
+	if err != nil {
+		log.Errorf("failed to create src faker conn: %s", err)
+		return
+	}
+	p.srcFakerConn = srcFakerConn
+	p.sendPkg = p.srcFakerConn.SendPkg
 }
 
 // CloseConn close the localConn
@@ -108,6 +134,8 @@ func (p *WGUDPProxy) CloseConn() error {
 }
 
 func (p *WGUDPProxy) close() error {
+	var result *multierror.Error
+
 	p.closeMu.Lock()
 	defer p.closeMu.Unlock()
 
@@ -115,11 +143,14 @@ func (p *WGUDPProxy) close() error {
 	if p.closed {
 		return nil
 	}
-	p.closed = true
 
 	p.cancel()
 
-	var result *multierror.Error
+	p.pausedCond.L.Lock()
+	p.paused = false
+	p.pausedCond.L.Unlock()
+	p.pausedCond.Signal()
+
 	if err := p.remoteConn.Close(); err != nil && !errors.Is(err, net.ErrClosed) {
 		result = multierror.Append(result, fmt.Errorf("remote conn: %s", err))
 	}
@@ -127,6 +158,11 @@ func (p *WGUDPProxy) close() error {
 	if err := p.localConn.Close(); err != nil {
 		result = multierror.Append(result, fmt.Errorf("local conn: %s", err))
 	}
+
+	if err := p.srcFakerConn.Close(); err != nil {
+		result = multierror.Append(result, fmt.Errorf("src faker raw conn: %s", err))
+	}
+
 	return cerrors.FormatErrorOrNil(result)
 }
 
@@ -179,14 +215,20 @@ func (p *WGUDPProxy) proxyToLocal(ctx context.Context) {
 			return
 		}
 
-		p.pausedMu.Lock()
-		if p.paused {
-			p.pausedMu.Unlock()
-			continue
+		for {
+			p.pausedCond.L.Lock()
+			if p.paused {
+				p.pausedCond.Wait()
+				if !p.paused {
+					break
+				}
+				p.pausedCond.L.Unlock()
+				continue
+			}
+			break
 		}
-
-		_, err = p.localConn.Write(buf[:n])
-		p.pausedMu.Unlock()
+		_, err = p.sendPkg(buf[:n])
+		p.pausedCond.L.Unlock()
 
 		if err != nil {
 			if ctx.Err() != nil {

client/iface/wgproxy/udp/rawsocket.go

@@ -0,0 +1,139 @@
+package udp
+
+import (
+	"fmt"
+	"net"
+	"os"
+	"syscall"
+
+	"github.com/google/gopacket"
+	"github.com/google/gopacket/layers"
+	log "github.com/sirupsen/logrus"
+
+	nbnet "github.com/netbirdio/netbird/util/net"
+)
+
+var (
+	serializeOpts = gopacket.SerializeOptions{
+		ComputeChecksums: true,
+		FixLengths:       true,
+	}
+
+	localHostNetIPAddr = &net.IPAddr{
+		IP: net.ParseIP("127.0.0.1"),
+	}
+)
+
+type SrcFaker struct {
+	srcAddr *net.UDPAddr
+
+	rawSocket   net.PacketConn
+	ipH         gopacket.SerializableLayer
+	udpH        gopacket.SerializableLayer
+	layerBuffer gopacket.SerializeBuffer
+}
+
+func NewSrcFaker(dstPort int, srcAddr *net.UDPAddr) (*SrcFaker, error) {
+	rawSocket, err := prepareSenderRawSocket()
+	if err != nil {
+		return nil, err
+	}
+
+	ipH, udpH, err := prepareHeaders(dstPort, srcAddr)
+	if err != nil {
+		return nil, err
+	}
+
+	f := &SrcFaker{
+		srcAddr:     srcAddr,
+		rawSocket:   rawSocket,
+		ipH:         ipH,
+		udpH:        udpH,
+		layerBuffer: gopacket.NewSerializeBuffer(),
+	}
+
+	return f, nil
+}
+
+func (f *SrcFaker) Close() error {
+	return f.rawSocket.Close()
+}
+
+func (f *SrcFaker) SendPkg(data []byte) (int, error) {
+	defer func() {
+		if err := f.layerBuffer.Clear(); err != nil {
+			log.Errorf("failed to clear layer buffer: %s", err)
+		}
+	}()
+
+	payload := gopacket.Payload(data)
+
+	err := gopacket.SerializeLayers(f.layerBuffer, serializeOpts, f.ipH, f.udpH, payload)
+	if err != nil {
+		return 0, fmt.Errorf("serialize layers: %w", err)
+	}
+	n, err := f.rawSocket.WriteTo(f.layerBuffer.Bytes(), localHostNetIPAddr)
+	if err != nil {
+		return 0, fmt.Errorf("write to raw conn: %w", err)
+	}
+	return n, nil
+}
+
+func prepareHeaders(dstPort int, srcAddr *net.UDPAddr) (gopacket.SerializableLayer, gopacket.SerializableLayer, error) {
+	ipH := &layers.IPv4{
+		DstIP:    net.ParseIP("127.0.0.1"),
+		SrcIP:    srcAddr.IP,
+		Version:  4,
+		TTL:      64,
+		Protocol: layers.IPProtocolUDP,
+	}
+	udpH := &layers.UDP{
+		SrcPort: layers.UDPPort(srcAddr.Port),
+		DstPort: layers.UDPPort(dstPort), // dst is the localhost WireGuard port
+	}
+
+	err := udpH.SetNetworkLayerForChecksum(ipH)
+	if err != nil {
+		return nil, nil, fmt.Errorf("set network layer for checksum: %w", err)
+	}
+
+	return ipH, udpH, nil
+}
+
+func prepareSenderRawSocket() (net.PacketConn, error) {
+	// Create a raw socket.
+	fd, err := syscall.Socket(syscall.AF_INET, syscall.SOCK_RAW, syscall.IPPROTO_RAW)
+	if err != nil {
+		return nil, fmt.Errorf("creating raw socket failed: %w", err)
+	}
+
+	// Set the IP_HDRINCL option on the socket to tell the kernel that headers are included in the packet.
+	err = syscall.SetsockoptInt(fd, syscall.IPPROTO_IP, syscall.IP_HDRINCL, 1)
+	if err != nil {
+		return nil, fmt.Errorf("setting IP_HDRINCL failed: %w", err)
+	}
+
+	// Bind the socket to the "lo" interface.
+	err = syscall.SetsockoptString(fd, syscall.SOL_SOCKET, syscall.SO_BINDTODEVICE, "lo")
+	if err != nil {
+		return nil, fmt.Errorf("binding to lo interface failed: %w", err)
+	}
+
+	// Set the fwmark on the socket.
+	err = nbnet.SetSocketOpt(fd)
+	if err != nil {
+		return nil, fmt.Errorf("setting fwmark failed: %w", err)
+	}
+
+	// Convert the file descriptor to a PacketConn.
+	file := os.NewFile(uintptr(fd), fmt.Sprintf("fd %d", fd))
+	if file == nil {
+		return nil, fmt.Errorf("converting fd to file failed")
+	}
+	packetConn, err := net.FilePacketConn(file)
+	if err != nil {
+		return nil, fmt.Errorf("converting file to packet conn failed: %w", err)
+	}
+
+	return packetConn, nil
+}