tun/netstack: implement ICMP ping

Provide a PacketConn interface for netstack's ICMP endpoint; netstack
currently only provides EchoRequest/EchoResponse ICMP support, so this
code exposes only an interface for doing ping.

Signed-off-by: Thomas Ptacek <thomas@sockpuppet.org>
[Jason: rework structure, match std go interfaces, add example code]
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

tun/netstack/tun.go

@@ -14,8 +14,10 @@ import (
 	"io"
 	"net"
 	"os"
+	"regexp"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"golang.zx2c4.com/go118/netip"
@@ -29,8 +31,10 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/network/ipv4"
 	"gvisor.dev/gvisor/pkg/tcpip/network/ipv6"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
+	"gvisor.dev/gvisor/pkg/tcpip/transport/icmp"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/tcp"
 	"gvisor.dev/gvisor/pkg/tcpip/transport/udp"
+	"gvisor.dev/gvisor/pkg/waiter"
 )
 
 type netTun struct {
@@ -101,7 +105,7 @@ func (e *endpoint) AddHeader(tcpip.LinkAddress, tcpip.LinkAddress, tcpip.Network
 func CreateNetTUN(localAddresses, dnsServers []netip.Addr, mtu int) (tun.Device, *Net, error) {
 	opts := stack.Options{
 		NetworkProtocols:   []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
-		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol, udp.NewProtocol},
+		TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol, udp.NewProtocol, icmp.NewProtocol6, icmp.NewProtocol4},
 		HandleLocal:        true,
 	}
 	dev := &netTun{
@@ -270,6 +274,10 @@ func (net *Net) DialUDPAddrPort(laddr, raddr netip.AddrPort) (*gonet.UDPConn, er
 	return gonet.DialUDP(net.stack, lfa, rfa, pn)
 }
 
+func (net *Net) ListenUDPAddrPort(laddr netip.AddrPort) (*gonet.UDPConn, error) {
+	return net.DialUDPAddrPort(laddr, netip.AddrPort{})
+}
+
 func (net *Net) DialUDP(laddr, raddr *net.UDPAddr) (*gonet.UDPConn, error) {
 	var la, ra netip.AddrPort
 	if laddr != nil {
@@ -281,6 +289,233 @@ func (net *Net) DialUDP(laddr, raddr *net.UDPAddr) (*gonet.UDPConn, error) {
 	return net.DialUDPAddrPort(la, ra)
 }
 
+func (net *Net) ListenUDP(laddr *net.UDPAddr) (*gonet.UDPConn, error) {
+	return net.DialUDP(laddr, nil)
+}
+
+type PingConn struct {
+	laddr           PingAddr
+	raddr           PingAddr
+	wq              waiter.Queue
+	ep              tcpip.Endpoint
+	mu              sync.RWMutex
+	deadline        time.Time
+	deadlineBreaker chan struct{}
+}
+
+type PingAddr struct{ addr netip.Addr }
+
+func (ia PingAddr) String() string {
+	return ia.addr.String()
+}
+
+func (ia PingAddr) Network() string {
+	if ia.addr.Is4() {
+		return "ping4"
+	} else if ia.addr.Is6() {
+		return "ping6"
+	}
+	return "ping"
+}
+
+func (ia PingAddr) Addr() netip.Addr {
+	return ia.addr
+}
+
+func PingAddrFromAddr(addr netip.Addr) *PingAddr {
+	return &PingAddr{addr}
+}
+
+func (net *Net) DialPingAddr(laddr, raddr netip.Addr) (*PingConn, error) {
+	if !laddr.IsValid() && !raddr.IsValid() {
+		return nil, errors.New("ping dial: invalid address")
+	}
+	v6 := laddr.Is6() || raddr.Is6()
+	bind := laddr.IsValid()
+	if !bind {
+		if v6 {
+			laddr = netip.IPv6Unspecified()
+		} else {
+			laddr = netip.IPv4Unspecified()
+		}
+	}
+
+	tn := icmp.ProtocolNumber4
+	pn := ipv4.ProtocolNumber
+	if v6 {
+		tn = icmp.ProtocolNumber6
+		pn = ipv6.ProtocolNumber
+	}
+
+	pc := &PingConn{
+		laddr:           PingAddr{laddr},
+		deadlineBreaker: make(chan struct{}, 1),
+	}
+
+	ep, tcpipErr := net.stack.NewEndpoint(tn, pn, &pc.wq)
+	if tcpipErr != nil {
+		return nil, fmt.Errorf("ping socket: endpoint: %s", tcpipErr)
+	}
+	pc.ep = ep
+
+	if bind {
+		fa, _ := convertToFullAddr(netip.AddrPortFrom(laddr, 0))
+		if tcpipErr = pc.ep.Bind(fa); tcpipErr != nil {
+			return nil, fmt.Errorf("ping bind: %s", tcpipErr)
+		}
+	}
+
+	if raddr.IsValid() {
+		pc.raddr = PingAddr{raddr}
+		fa, _ := convertToFullAddr(netip.AddrPortFrom(raddr, 0))
+		if tcpipErr = pc.ep.Connect(fa); tcpipErr != nil {
+			return nil, fmt.Errorf("ping connect: %s", tcpipErr)
+		}
+	}
+
+	return pc, nil
+}
+
+func (net *Net) ListenPingAddr(laddr netip.Addr) (*PingConn, error) {
+	return net.DialPingAddr(laddr, netip.Addr{})
+}
+
+func (net *Net) DialPing(laddr, raddr *PingAddr) (*PingConn, error) {
+	var la, ra netip.Addr
+	if laddr != nil {
+		la = laddr.addr
+	}
+	if raddr != nil {
+		ra = raddr.addr
+	}
+	return net.DialPingAddr(la, ra)
+}
+
+func (net *Net) ListenPing(laddr *PingAddr) (*PingConn, error) {
+	var la netip.Addr
+	if laddr != nil {
+		la = laddr.addr
+	}
+	return net.ListenPingAddr(la)
+}
+
+func (pc *PingConn) LocalAddr() net.Addr {
+	return pc.laddr
+}
+
+func (pc *PingConn) RemoteAddr() net.Addr {
+	return pc.raddr
+}
+
+func (pc *PingConn) Close() error {
+	close(pc.deadlineBreaker)
+	pc.ep.Close()
+	return nil
+}
+
+func (pc *PingConn) SetWriteDeadline(t time.Time) error {
+	return errors.New("not implemented")
+}
+
+func (pc *PingConn) WriteTo(p []byte, addr net.Addr) (n int, err error) {
+	var na netip.Addr
+	switch v := addr.(type) {
+	case *PingAddr:
+		na = v.addr
+	case *net.IPAddr:
+		na = netip.AddrFromSlice(v.IP)
+	default:
+		return 0, fmt.Errorf("ping write: wrong net.Addr type")
+	}
+	if !((na.Is4() && pc.laddr.addr.Is4()) || (na.Is6() && pc.laddr.addr.Is6())) {
+		return 0, fmt.Errorf("ping write: mismatched protocols")
+	}
+
+	buf := buffer.NewViewFromBytes(p)
+	rdr := buf.Reader()
+	rfa, _ := convertToFullAddr(netip.AddrPortFrom(na, 0))
+	// won't block, no deadlines
+	n64, tcpipErr := pc.ep.Write(&rdr, tcpip.WriteOptions{
+		To: &rfa,
+	})
+	if tcpipErr != nil {
+		return int(n64), fmt.Errorf("ping write: %s", tcpipErr)
+	}
+
+	return int(n64), nil
+}
+
+func (pc *PingConn) Write(p []byte) (n int, err error) {
+	return pc.WriteTo(p, &pc.raddr)
+}
+
+func (pc *PingConn) ReadFrom(p []byte) (n int, addr net.Addr, err error) {
+	e, notifyCh := waiter.NewChannelEntry(nil)
+	pc.wq.EventRegister(&e, waiter.EventIn)
+	defer pc.wq.EventUnregister(&e)
+
+	ready := false
+
+	for !ready {
+		pc.mu.RLock()
+		deadlineBreaker := pc.deadlineBreaker
+		deadline := pc.deadline
+		pc.mu.RUnlock()
+
+		if deadline.IsZero() {
+			select {
+			case <-deadlineBreaker:
+			case <-notifyCh:
+				ready = true
+			}
+		} else {
+			t := time.NewTimer(deadline.Sub(time.Now()))
+			defer t.Stop()
+
+			select {
+			case <-t.C:
+				return 0, nil, os.ErrDeadlineExceeded
+
+			case <-deadlineBreaker:
+			case <-notifyCh:
+				ready = true
+			}
+		}
+	}
+
+	w := tcpip.SliceWriter(p)
+
+	res, tcpipErr := pc.ep.Read(&w, tcpip.ReadOptions{
+		NeedRemoteAddr: true,
+	})
+	if tcpipErr != nil {
+		return 0, nil, fmt.Errorf("ping read: %s", tcpipErr)
+	}
+
+	addr = &PingAddr{netip.AddrFromSlice([]byte(res.RemoteAddr.Addr))}
+	return res.Count, addr, nil
+}
+
+func (pc *PingConn) Read(p []byte) (n int, err error) {
+	n, _, err = pc.ReadFrom(p)
+	return
+}
+
+func (pc *PingConn) SetDeadline(t time.Time) error {
+	// pc.SetWriteDeadline is unimplemented
+
+	return pc.SetReadDeadline(t)
+}
+
+func (pc *PingConn) SetReadDeadline(t time.Time) error {
+	pc.mu.Lock()
+	defer pc.mu.Unlock()
+	close(pc.deadlineBreaker)
+	pc.deadlineBreaker = make(chan struct{}, 1)
+	pc.deadline = t
+	return nil
+}
+
 var (
 	errNoSuchHost                   = errors.New("no such host")
 	errLameReferral                 = errors.New("lame referral")
@@ -755,33 +990,38 @@ func partialDeadline(now, deadline time.Time, addrsRemaining int) (time.Time, er
 	return now.Add(timeout), nil
 }
 
+var protoSplitter = regexp.MustCompile(`^(tcp|udp|ping)(4|6)?$`)
+
 func (tnet *Net) DialContext(ctx context.Context, network, address string) (net.Conn, error) {
 	if ctx == nil {
 		panic("nil context")
 	}
-	var acceptV4, acceptV6, useUDP bool
-	if len(network) == 3 {
+	var acceptV4, acceptV6 bool
+	matches := protoSplitter.FindStringSubmatch(network)
+	if matches == nil {
+		return nil, &net.OpError{Op: "dial", Err: net.UnknownNetworkError(network)}
+	} else if len(matches[2]) == 0 {
 		acceptV4 = true
 		acceptV6 = true
-	} else if len(network) == 4 {
-		acceptV4 = network[3] == '4'
-		acceptV6 = network[3] == '6'
+	} else {
+		acceptV4 = matches[2][0] == '4'
+		acceptV6 = !acceptV4
 	}
-	if !acceptV4 && !acceptV6 {
-		return nil, &net.OpError{Op: "dial", Err: net.UnknownNetworkError(network)}
-	}
-	if network[:3] == "udp" {
-		useUDP = true
-	} else if network[:3] != "tcp" {
-		return nil, &net.OpError{Op: "dial", Err: net.UnknownNetworkError(network)}
-	}
-	host, sport, err := net.SplitHostPort(address)
-	if err != nil {
-		return nil, &net.OpError{Op: "dial", Err: err}
-	}
-	port, err := strconv.Atoi(sport)
-	if err != nil || port < 0 || port > 65535 {
-		return nil, &net.OpError{Op: "dial", Err: errNumericPort}
+	var host string
+	var port int
+	if matches[1] == "ping" {
+		host = address
+	} else {
+		var sport string
+		var err error
+		host, sport, err = net.SplitHostPort(address)
+		if err != nil {
+			return nil, &net.OpError{Op: "dial", Err: err}
+		}
+		port, err = strconv.Atoi(sport)
+		if err != nil || port < 0 || port > 65535 {
+			return nil, &net.OpError{Op: "dial", Err: errNumericPort}
+		}
 	}
 	allAddr, err := tnet.LookupContextHost(ctx, host)
 	if err != nil {
@@ -829,10 +1069,13 @@ func (tnet *Net) DialContext(ctx context.Context, network, address string) (net.
 		}
 
 		var c net.Conn
-		if useUDP {
-			c, err = tnet.DialUDPAddrPort(netip.AddrPort{}, addr)
-		} else {
+		switch matches[1] {
+		case "tcp":
 			c, err = tnet.DialContextTCPAddrPort(dialCtx, addr)
+		case "udp":
+			c, err = tnet.DialUDPAddrPort(netip.AddrPort{}, addr)
+		case "ping":
+			c, err = tnet.DialPingAddr(netip.Addr{}, addr.Addr())
 		}
 		if err == nil {
 			return c, nil