Add L3 routing support

transport/wireguard/device_stack.go

@@ -8,10 +8,12 @@ import (
 	"net/netip"
 	"os"
 
+	"github.com/sagernet/sing-tun"
+	"github.com/sagernet/sing/common/buf"
 	E "github.com/sagernet/sing/common/exceptions"
 	M "github.com/sagernet/sing/common/metadata"
 	N "github.com/sagernet/sing/common/network"
-	"github.com/sagernet/wireguard-go/tun"
+	wgTun "github.com/sagernet/wireguard-go/tun"
 
 	"gvisor.dev/gvisor/pkg/bufferv2"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -25,33 +27,38 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/transport/udp"
 )
 
-var _ Device = (*StackDevice)(nil)
+var _ NatDevice = (*StackDevice)(nil)
 
 const defaultNIC tcpip.NICID = 1
 
 type StackDevice struct {
-	stack      *stack.Stack
-	mtu        uint32
-	events     chan tun.Event
-	outbound   chan *stack.PacketBuffer
-	done       chan struct{}
-	dispatcher stack.NetworkDispatcher
-	addr4      tcpip.Address
-	addr6      tcpip.Address
+	stack          *stack.Stack
+	mtu            uint32
+	events         chan wgTun.Event
+	outbound       chan *stack.PacketBuffer
+	packetOutbound chan *buf.Buffer
+	done           chan struct{}
+	dispatcher     stack.NetworkDispatcher
+	addr4          tcpip.Address
+	addr6          tcpip.Address
+	mapping        *tun.NatMapping
+	writer         *tun.NatWriter
 }
 
-func NewStackDevice(localAddresses []netip.Prefix, mtu uint32) (*StackDevice, error) {
+func NewStackDevice(localAddresses []netip.Prefix, mtu uint32, ipRewrite bool) (*StackDevice, error) {
 	ipStack := stack.New(stack.Options{
 		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
 		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol, udp.NewProtocol, icmp.NewProtocol4, icmp.NewProtocol6},
 		HandleLocal:        true,
 	})
 	tunDevice := &StackDevice{
-		stack:    ipStack,
-		mtu:      mtu,
-		events:   make(chan tun.Event, 1),
-		outbound: make(chan *stack.PacketBuffer, 256),
-		done:     make(chan struct{}),
+		stack:          ipStack,
+		mtu:            mtu,
+		events:         make(chan wgTun.Event, 1),
+		outbound:       make(chan *stack.PacketBuffer, 256),
+		packetOutbound: make(chan *buf.Buffer, 256),
+		done:           make(chan struct{}),
+		mapping:        tun.NewNatMapping(ipRewrite),
 	}
 	err := ipStack.CreateNIC(defaultNIC, (*wireEndpoint)(tunDevice))
 	if err != nil {
@@ -77,6 +84,9 @@ func NewStackDevice(localAddresses []netip.Prefix, mtu uint32) (*StackDevice, er
 			return nil, E.New("parse local address ", protoAddr.AddressWithPrefix, ": ", err.String())
 		}
 	}
+	if ipRewrite {
+		tunDevice.writer = tun.NewNatWriter(tunDevice.Inet4Address(), tunDevice.Inet6Address())
+	}
 	sOpt := tcpip.TCPSACKEnabled(true)
 	ipStack.SetTransportProtocolOption(tcp.ProtocolNumber, &sOpt)
 	cOpt := tcpip.CongestionControlOption("cubic")
@@ -144,8 +154,16 @@ func (w *StackDevice) ListenPacket(ctx context.Context, destination M.Socksaddr)
 	return udpConn, nil
 }
 
+func (w *StackDevice) Inet4Address() netip.Addr {
+	return M.AddrFromIP(net.IP(w.addr4))
+}
+
+func (w *StackDevice) Inet6Address() netip.Addr {
+	return M.AddrFromIP(net.IP(w.addr6))
+}
+
 func (w *StackDevice) Start() error {
-	w.events <- tun.EventUp
+	w.events <- wgTun.EventUp
 	return nil
 }
 
@@ -165,6 +183,10 @@ func (w *StackDevice) Read(p []byte, offset int) (n int, err error) {
 			n += copy(p[n:], slice)
 		}
 		return
+	case packet := <-w.packetOutbound:
+		defer packet.Release()
+		n = copy(p[offset:], packet.Bytes())
+		return
 	case <-w.done:
 		return 0, os.ErrClosed
 	}
@@ -175,6 +197,10 @@ func (w *StackDevice) Write(p []byte, offset int) (n int, err error) {
 	if len(p) == 0 {
 		return
 	}
+	handled, err := w.mapping.WritePacket(p)
+	if handled {
+		return len(p), err
+	}
 	var networkProtocol tcpip.NetworkProtocolNumber
 	switch header.IPVersion(p) {
 	case header.IPv4Version:
@@ -203,7 +229,7 @@ func (w *StackDevice) Name() (string, error) {
 	return "sing-box", nil
 }
 
-func (w *StackDevice) Events() chan tun.Event {
+func (w *StackDevice) Events() chan wgTun.Event {
 	return w.events
 }
 
@@ -222,6 +248,44 @@ func (w *StackDevice) Close() error {
 	return nil
 }
 
+func (w *StackDevice) CreateDestination(session tun.RouteSession, conn tun.RouteContext) tun.DirectDestination {
+	w.mapping.CreateSession(session, conn)
+	return &stackNatDestination{
+		device:  w,
+		session: session,
+	}
+}
+
+type stackNatDestination struct {
+	device  *StackDevice
+	session tun.RouteSession
+}
+
+func (d *stackNatDestination) WritePacket(buffer *buf.Buffer) error {
+	if d.device.writer != nil {
+		d.device.writer.RewritePacket(buffer.Bytes())
+	}
+	d.device.packetOutbound <- buffer
+	return nil
+}
+
+func (d *stackNatDestination) WritePacketBuffer(buffer *stack.PacketBuffer) error {
+	if d.device.writer != nil {
+		d.device.writer.RewritePacketBuffer(buffer)
+	}
+	d.device.outbound <- buffer
+	return nil
+}
+
+func (d *stackNatDestination) Close() error {
+	d.device.mapping.DeleteSession(d.session)
+	return nil
+}
+
+func (d *stackNatDestination) Timeout() bool {
+	return false
+}
+
 var _ stack.LinkEndpoint = (*wireEndpoint)(nil)
 
 type wireEndpoint StackDevice