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tailscale/wgengine/netstack/netstack.go

1211 lines
39 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package netstack wires up gVisor's netstack into Tailscale.
package netstack
import (
"context"
"errors"
"fmt"
"io"
"log"
"net"
"net/netip"
"os"
"os/exec"
"runtime"
"strconv"
"strings"
"sync"
"sync/atomic"
"time"
"gvisor.dev/gvisor/pkg/bufferv2"
"gvisor.dev/gvisor/pkg/refs"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/adapters/gonet"
"gvisor.dev/gvisor/pkg/tcpip/header"
"gvisor.dev/gvisor/pkg/tcpip/link/channel"
"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"
"tailscale.com/envknob"
"tailscale.com/ipn/ipnlocal"
"tailscale.com/net/dns"
"tailscale.com/net/netaddr"
"tailscale.com/net/packet"
"tailscale.com/net/tsaddr"
"tailscale.com/net/tsdial"
"tailscale.com/net/tstun"
"tailscale.com/syncs"
"tailscale.com/types/ipproto"
"tailscale.com/types/logger"
"tailscale.com/types/netmap"
"tailscale.com/version/distro"
"tailscale.com/wgengine"
"tailscale.com/wgengine/filter"
"tailscale.com/wgengine/magicsock"
)
const debugPackets = false
var debugNetstack = envknob.RegisterBool("TS_DEBUG_NETSTACK")
var (
magicDNSIP = tsaddr.TailscaleServiceIP()
magicDNSIPv6 = tsaddr.TailscaleServiceIPv6()
)
func init() {
var debugNetstackLeakMode = envknob.String("TS_DEBUG_NETSTACK_LEAK_MODE")
// Note: netstacks refsvfs2 package that will eventually replace refs
// consumes the refs.LeakMode setting, but enables some checks when set to
// UninitializedLeakChecking which is what empty string becomes. This mode
// is largely un-useful, so it is explicitly disabled here, and more useful
// modes can be set via the envknob. See #4309 for more references.
if debugNetstackLeakMode == "" {
debugNetstackLeakMode = "disabled"
}
var lm refs.LeakMode
lm.Set(debugNetstackLeakMode)
refs.SetLeakMode(lm)
}
// Impl contains the state for the netstack implementation,
// and implements wgengine.FakeImpl to act as a userspace network
// stack when Tailscale is running in fake mode.
type Impl struct {
// ForwardTCPIn, if non-nil, handles forwarding an inbound TCP
// connection.
// TODO(bradfitz): provide mechanism for tsnet to reject a
// port other than accepting it and closing it.
ForwardTCPIn func(c net.Conn, port uint16)
// ProcessLocalIPs is whether netstack should handle incoming
// traffic directed at the Node.Addresses (local IPs).
// It can only be set before calling Start.
ProcessLocalIPs bool
// ProcessSubnets is whether netstack should handle incoming
// traffic destined to non-local IPs (i.e. whether it should
// be a subnet router).
// It can only be set before calling Start.
ProcessSubnets bool
ipstack *stack.Stack
linkEP *channel.Endpoint
tundev *tstun.Wrapper
e wgengine.Engine
mc *magicsock.Conn
logf logger.Logf
dialer *tsdial.Dialer
ctx context.Context // alive until Close
ctxCancel context.CancelFunc // called on Close
lb *ipnlocal.LocalBackend // or nil
dns *dns.Manager
peerapiPort4Atomic uint32 // uint16 port number for IPv4 peerapi
peerapiPort6Atomic uint32 // uint16 port number for IPv6 peerapi
// atomicIsLocalIPFunc holds a func that reports whether an IP
// is a local (non-subnet) Tailscale IP address of this
// machine. It's always a non-nil func. It's changed on netmap
// updates.
atomicIsLocalIPFunc syncs.AtomicValue[func(netip.Addr) bool]
mu sync.Mutex
// connsOpenBySubnetIP keeps track of number of connections open
// for each subnet IP temporarily registered on netstack for active
// TCP connections, so they can be unregistered when connections are
// closed.
connsOpenBySubnetIP map[netip.Addr]int
}
const nicID = 1
const mtu = tstun.DefaultMTU
// maxUDPPacketSize is the maximum size of a UDP packet we copy in startPacketCopy
// when relaying UDP packets. We don't use the 'mtu' const in anticipation of
// one day making the MTU more dynamic.
const maxUDPPacketSize = 1500
// Create creates and populates a new Impl.
func Create(logf logger.Logf, tundev *tstun.Wrapper, e wgengine.Engine, mc *magicsock.Conn, dialer *tsdial.Dialer, dns *dns.Manager) (*Impl, error) {
if mc == nil {
return nil, errors.New("nil magicsock.Conn")
}
if tundev == nil {
return nil, errors.New("nil tundev")
}
if logf == nil {
return nil, errors.New("nil logger")
}
if e == nil {
return nil, errors.New("nil Engine")
}
if dialer == nil {
return nil, errors.New("nil Dialer")
}
ipstack := stack.New(stack.Options{
NetworkProtocols: []stack.NetworkProtocolFactory{ipv4.NewProtocol, ipv6.NewProtocol},
TransportProtocols: []stack.TransportProtocolFactory{tcp.NewProtocol, udp.NewProtocol, icmp.NewProtocol4, icmp.NewProtocol6},
})
sackEnabledOpt := tcpip.TCPSACKEnabled(true) // TCP SACK is disabled by default
tcpipErr := ipstack.SetTransportProtocolOption(tcp.ProtocolNumber, &sackEnabledOpt)
if tcpipErr != nil {
return nil, fmt.Errorf("could not enable TCP SACK: %v", tcpipErr)
}
linkEP := channel.New(512, mtu, "")
if tcpipProblem := ipstack.CreateNIC(nicID, linkEP); tcpipProblem != nil {
return nil, fmt.Errorf("could not create netstack NIC: %v", tcpipProblem)
}
// By default the netstack NIC will only accept packets for the IPs
// registered to it. Since in some cases we dynamically register IPs
// based on the packets that arrive, the NIC needs to accept all
// incoming packets. The NIC won't receive anything it isn't meant to
// since WireGuard will only send us packets that are meant for us.
ipstack.SetPromiscuousMode(nicID, true)
// Add IPv4 and IPv6 default routes, so all incoming packets from the Tailscale side
// are handled by the one fake NIC we use.
ipv4Subnet, _ := tcpip.NewSubnet(tcpip.Address(strings.Repeat("\x00", 4)), tcpip.AddressMask(strings.Repeat("\x00", 4)))
ipv6Subnet, _ := tcpip.NewSubnet(tcpip.Address(strings.Repeat("\x00", 16)), tcpip.AddressMask(strings.Repeat("\x00", 16)))
ipstack.SetRouteTable([]tcpip.Route{
{
Destination: ipv4Subnet,
NIC: nicID,
},
{
Destination: ipv6Subnet,
NIC: nicID,
},
})
ns := &Impl{
logf: logf,
ipstack: ipstack,
linkEP: linkEP,
tundev: tundev,
e: e,
mc: mc,
dialer: dialer,
connsOpenBySubnetIP: make(map[netip.Addr]int),
dns: dns,
}
ns.ctx, ns.ctxCancel = context.WithCancel(context.Background())
ns.atomicIsLocalIPFunc.Store(tsaddr.NewContainsIPFunc(nil))
return ns, nil
}
func (ns *Impl) Close() error {
ns.ctxCancel()
ns.ipstack.Close()
return nil
}
// SetLocalBackend sets the LocalBackend; it should only be run before
// the Start method is called.
func (ns *Impl) SetLocalBackend(lb *ipnlocal.LocalBackend) {
ns.lb = lb
}
// wrapProtoHandler returns protocol handler h wrapped in a version
// that dynamically reconfigures ns's subnet addresses as needed for
// outbound traffic.
func (ns *Impl) wrapProtoHandler(h func(stack.TransportEndpointID, *stack.PacketBuffer) bool) func(stack.TransportEndpointID, *stack.PacketBuffer) bool {
return func(tei stack.TransportEndpointID, pb *stack.PacketBuffer) bool {
addr := tei.LocalAddress
ip, ok := netip.AddrFromSlice(net.IP(addr))
if !ok {
ns.logf("netstack: could not parse local address for incoming connection")
return false
}
ip = ip.Unmap()
if !ns.isLocalIP(ip) {
ns.addSubnetAddress(ip)
}
return h(tei, pb)
}
}
// Start sets up all the handlers so netstack can start working. Implements
// wgengine.FakeImpl.
func (ns *Impl) Start() error {
ns.e.AddNetworkMapCallback(ns.updateIPs)
// size = 0 means use default buffer size
const tcpReceiveBufferSize = 0
const maxInFlightConnectionAttempts = 16
tcpFwd := tcp.NewForwarder(ns.ipstack, tcpReceiveBufferSize, maxInFlightConnectionAttempts, ns.acceptTCP)
udpFwd := udp.NewForwarder(ns.ipstack, ns.acceptUDP)
ns.ipstack.SetTransportProtocolHandler(tcp.ProtocolNumber, ns.wrapProtoHandler(tcpFwd.HandlePacket))
ns.ipstack.SetTransportProtocolHandler(udp.ProtocolNumber, ns.wrapProtoHandler(udpFwd.HandlePacket))
go ns.inject()
ns.tundev.PostFilterIn = ns.injectInbound
ns.tundev.PreFilterFromTunToNetstack = ns.handleLocalPackets
return nil
}
func (ns *Impl) addSubnetAddress(ip netip.Addr) {
ns.mu.Lock()
ns.connsOpenBySubnetIP[ip]++
needAdd := ns.connsOpenBySubnetIP[ip] == 1
ns.mu.Unlock()
// Only register address into netstack for first concurrent connection.
if needAdd {
pa := tcpip.ProtocolAddress{
AddressWithPrefix: tcpip.AddressWithPrefix{
Address: tcpip.Address(ip.AsSlice()),
PrefixLen: int(ip.BitLen()),
},
}
if ip.Is4() {
pa.Protocol = ipv4.ProtocolNumber
} else if ip.Is6() {
pa.Protocol = ipv6.ProtocolNumber
}
ns.ipstack.AddProtocolAddress(nicID, pa, stack.AddressProperties{
PEB: stack.CanBePrimaryEndpoint, // zero value default
ConfigType: stack.AddressConfigStatic, // zero value default
})
}
}
func (ns *Impl) removeSubnetAddress(ip netip.Addr) {
ns.mu.Lock()
defer ns.mu.Unlock()
ns.connsOpenBySubnetIP[ip]--
// Only unregister address from netstack after last concurrent connection.
if ns.connsOpenBySubnetIP[ip] == 0 {
ns.ipstack.RemoveAddress(nicID, tcpip.Address(ip.AsSlice()))
delete(ns.connsOpenBySubnetIP, ip)
}
}
func ipPrefixToAddressWithPrefix(ipp netip.Prefix) tcpip.AddressWithPrefix {
return tcpip.AddressWithPrefix{
Address: tcpip.Address(ipp.Addr().AsSlice()),
PrefixLen: int(ipp.Bits()),
}
}
var v4broadcast = netaddr.IPv4(255, 255, 255, 255)
func (ns *Impl) updateIPs(nm *netmap.NetworkMap) {
ns.atomicIsLocalIPFunc.Store(tsaddr.NewContainsIPFunc(nm.Addresses))
oldIPs := make(map[tcpip.AddressWithPrefix]bool)
for _, protocolAddr := range ns.ipstack.AllAddresses()[nicID] {
ap := protocolAddr.AddressWithPrefix
ip := netaddrIPFromNetstackIP(ap.Address)
if ip == v4broadcast && ap.PrefixLen == 32 {
// Don't add 255.255.255.255/32 to oldIPs so we don't
// delete it later. We didn't install it, so it's not
// ours to delete.
continue
}
oldIPs[ap] = true
}
newIPs := make(map[tcpip.AddressWithPrefix]bool)
isAddr := map[netip.Prefix]bool{}
if nm.SelfNode != nil {
for _, ipp := range nm.SelfNode.Addresses {
isAddr[ipp] = true
newIPs[ipPrefixToAddressWithPrefix(ipp)] = true
}
for _, ipp := range nm.SelfNode.AllowedIPs {
if !isAddr[ipp] && ns.ProcessSubnets {
newIPs[ipPrefixToAddressWithPrefix(ipp)] = true
}
}
}
ipsToBeAdded := make(map[tcpip.AddressWithPrefix]bool)
for ipp := range newIPs {
if !oldIPs[ipp] {
ipsToBeAdded[ipp] = true
}
}
ipsToBeRemoved := make(map[tcpip.AddressWithPrefix]bool)
for ip := range oldIPs {
if !newIPs[ip] {
ipsToBeRemoved[ip] = true
}
}
ns.mu.Lock()
for ip := range ns.connsOpenBySubnetIP {
ipp := tcpip.Address(ip.AsSlice()).WithPrefix()
delete(ipsToBeRemoved, ipp)
}
ns.mu.Unlock()
for ipp := range ipsToBeRemoved {
err := ns.ipstack.RemoveAddress(nicID, ipp.Address)
if err != nil {
ns.logf("netstack: could not deregister IP %s: %v", ipp, err)
} else {
ns.logf("[v2] netstack: deregistered IP %s", ipp)
}
}
for ipp := range ipsToBeAdded {
pa := tcpip.ProtocolAddress{
AddressWithPrefix: ipp,
}
if ipp.Address.To4() == "" {
pa.Protocol = ipv6.ProtocolNumber
} else {
pa.Protocol = ipv4.ProtocolNumber
}
var err tcpip.Error
err = ns.ipstack.AddProtocolAddress(nicID, pa, stack.AddressProperties{
PEB: stack.CanBePrimaryEndpoint, // zero value default
ConfigType: stack.AddressConfigStatic, // zero value default
})
if err != nil {
ns.logf("netstack: could not register IP %s: %v", ipp, err)
} else {
ns.logf("[v2] netstack: registered IP %s", ipp)
}
}
}
// handleLocalPackets is hooked into the tun datapath for packets leaving
// the host and arriving at tailscaled. This method returns filter.DropSilently
// to intercept a packet for handling, for instance traffic to quad-100.
func (ns *Impl) handleLocalPackets(p *packet.Parsed, t *tstun.Wrapper) filter.Response {
// If it's not traffic to the service IP (i.e. magicDNS) we don't
// care; resume processing.
if dst := p.Dst.Addr(); dst != magicDNSIP && dst != magicDNSIPv6 {
return filter.Accept
}
// Of traffic to the service IP, we only care about UDP 53, and TCP
// on port 80 & 53.
switch p.IPProto {
case ipproto.TCP:
if port := p.Dst.Port(); port != 53 && port != 80 {
return filter.Accept
}
case ipproto.UDP:
if port := p.Dst.Port(); port != 53 {
return filter.Accept
}
}
var pn tcpip.NetworkProtocolNumber
switch p.IPVersion {
case 4:
pn = header.IPv4ProtocolNumber
case 6:
pn = header.IPv6ProtocolNumber
}
if debugPackets {
ns.logf("[v2] service packet in (from %v): % x", p.Src, p.Buffer())
}
packetBuf := stack.NewPacketBuffer(stack.PacketBufferOptions{
Payload: bufferv2.MakeWithData(append([]byte(nil), p.Buffer()...)),
})
ns.linkEP.InjectInbound(pn, packetBuf)
packetBuf.DecRef()
return filter.DropSilently
}
func (ns *Impl) DialContextTCP(ctx context.Context, ipp netip.AddrPort) (*gonet.TCPConn, error) {
remoteAddress := tcpip.FullAddress{
NIC: nicID,
Addr: tcpip.Address(ipp.Addr().AsSlice()),
Port: ipp.Port(),
}
var ipType tcpip.NetworkProtocolNumber
if ipp.Addr().Is4() {
ipType = ipv4.ProtocolNumber
} else {
ipType = ipv6.ProtocolNumber
}
return gonet.DialContextTCP(ctx, ns.ipstack, remoteAddress, ipType)
}
func (ns *Impl) DialContextUDP(ctx context.Context, ipp netip.AddrPort) (*gonet.UDPConn, error) {
remoteAddress := &tcpip.FullAddress{
NIC: nicID,
Addr: tcpip.Address(ipp.Addr().AsSlice()),
Port: ipp.Port(),
}
var ipType tcpip.NetworkProtocolNumber
if ipp.Addr().Is4() {
ipType = ipv4.ProtocolNumber
} else {
ipType = ipv6.ProtocolNumber
}
return gonet.DialUDP(ns.ipstack, nil, remoteAddress, ipType)
}
// The inject goroutine reads in packets that netstack generated, and delivers
// them to the correct path.
func (ns *Impl) inject() {
for {
pkt := ns.linkEP.ReadContext(ns.ctx)
if pkt == nil {
if ns.ctx.Err() != nil {
// Return without logging.
return
}
ns.logf("[v2] ReadContext-for-write = ok=false")
continue
}
if debugPackets {
ns.logf("[v2] packet Write out: % x", stack.PayloadSince(pkt.NetworkHeader()))
}
// In the normal case, netstack synthesizes the bytes for
// traffic which should transit back into WG and go to peers.
// However, some uses of netstack (presently, magic DNS)
// send traffic destined for the local device, hence must
// be injected 'inbound'.
sendToHost := false
// Determine if the packet is from a service IP, in which case it
// needs to go back into the machines network (inbound) instead of
// out.
// TODO(tom): Work out a way to avoid parsing packets to determine if
// its from the service IP. Maybe gvisor netstack magic. I
// went through the fields of PacketBuffer, and nop :/
// TODO(tom): Figure out if its safe to modify packet.Parsed to fill in
// the IP src/dest even if its missing the rest of the pkt.
// That way we dont have to do this twitchy-af byte-yeeting.
if b := pkt.NetworkHeader().Slice(); len(b) >= 20 { // min ipv4 header
switch b[0] >> 4 { // ip proto field
case 4:
if srcIP := netaddr.IPv4(b[12], b[13], b[14], b[15]); magicDNSIP == srcIP {
sendToHost = true
}
case 6:
if len(b) >= 40 { // min ipv6 header
if srcIP, ok := netip.AddrFromSlice(net.IP(b[8:24])); ok && magicDNSIPv6 == srcIP {
sendToHost = true
}
}
}
}
// pkt has a non-zero refcount, so injection methods takes
// ownership of one count and will decrement on completion.
if sendToHost {
if err := ns.tundev.InjectInboundPacketBuffer(pkt); err != nil {
log.Printf("netstack inject inbound: %v", err)
return
}
} else {
if err := ns.tundev.InjectOutboundPacketBuffer(pkt); err != nil {
log.Printf("netstack inject outbound: %v", err)
return
}
}
}
}
// isLocalIP reports whether ip is a Tailscale IP assigned to this
// node directly (but not a subnet-routed IP).
func (ns *Impl) isLocalIP(ip netip.Addr) bool {
return ns.atomicIsLocalIPFunc.Load()(ip)
}
func (ns *Impl) processSSH() bool {
return ns.lb != nil && ns.lb.ShouldRunSSH()
}
func (ns *Impl) peerAPIPortAtomic(ip netip.Addr) *uint32 {
if ip.Is4() {
return &ns.peerapiPort4Atomic
} else {
return &ns.peerapiPort6Atomic
}
}
var viaRange = tsaddr.TailscaleViaRange()
// shouldProcessInbound reports whether an inbound packet (a packet from a
// WireGuard peer) should be handled by netstack.
func (ns *Impl) shouldProcessInbound(p *packet.Parsed, t *tstun.Wrapper) bool {
// Handle incoming peerapi connections in netstack.
dstIP := p.Dst.Addr()
isLocal := ns.isLocalIP(dstIP)
// Handle TCP connection to the Tailscale IP(s) in some cases:
if ns.lb != nil && p.IPProto == ipproto.TCP && isLocal {
var peerAPIPort uint16
if p.TCPFlags&packet.TCPSynAck == packet.TCPSyn {
if port, ok := ns.lb.GetPeerAPIPort(dstIP); ok {
peerAPIPort = port
atomic.StoreUint32(ns.peerAPIPortAtomic(dstIP), uint32(port))
}
} else {
peerAPIPort = uint16(atomic.LoadUint32(ns.peerAPIPortAtomic(dstIP)))
}
dport := p.Dst.Port()
if dport == peerAPIPort {
return true
}
// Also handle SSH connections, webserver, etc, if enabled:
if ns.lb.ShouldInterceptTCPPort(dport) {
return true
}
}
if p.IPVersion == 6 && !isLocal && viaRange.Contains(dstIP) {
return ns.lb != nil && ns.lb.ShouldHandleViaIP(dstIP)
}
if !ns.ProcessLocalIPs && !ns.ProcessSubnets {
// Fast path for common case (e.g. Linux server in TUN mode) where
// netstack isn't used at all; don't even do an isLocalIP lookup.
return false
}
if ns.ProcessLocalIPs && isLocal {
return true
}
if ns.ProcessSubnets && !isLocal {
return true
}
return false
}
// setAmbientCapsRaw is non-nil on Linux for Synology, to run ping with
// CAP_NET_RAW from tailscaled's binary.
var setAmbientCapsRaw func(*exec.Cmd)
var userPingSem = syncs.NewSemaphore(20) // 20 child ping processes at once
var isSynology = runtime.GOOS == "linux" && distro.Get() == distro.Synology
// userPing tried to ping dstIP and if it succeeds, injects pingResPkt
// into the tundev.
//
// It's used in userspace/netstack mode when we don't have kernel
// support or raw socket access. As such, this does the dumbest thing
// that can work: runs the ping command. It's not super efficient, so
// it bounds the number of pings going on at once. The idea is that
// people only use ping occasionally to see if their internet's working
// so this doesn't need to be great.
//
// TODO(bradfitz): when we're running on Windows as the system user, use
// raw socket APIs instead of ping child processes.
func (ns *Impl) userPing(dstIP netip.Addr, pingResPkt []byte) {
if !userPingSem.TryAcquire() {
return
}
defer userPingSem.Release()
t0 := time.Now()
var err error
switch runtime.GOOS {
case "windows":
err = exec.Command("ping", "-n", "1", "-w", "3000", dstIP.String()).Run()
case "darwin":
// Note: 2000 ms is actually 1 second + 2,000
// milliseconds extra for 3 seconds total.
// See https://github.com/tailscale/tailscale/pull/3753 for details.
err = exec.Command("ping", "-c", "1", "-W", "2000", dstIP.String()).Run()
case "android":
ping := "/system/bin/ping"
if dstIP.Is6() {
ping = "/system/bin/ping6"
}
err = exec.Command(ping, "-c", "1", "-w", "3", dstIP.String()).Run()
default:
ping := "ping"
if isSynology {
ping = "/bin/ping"
}
cmd := exec.Command(ping, "-c", "1", "-W", "3", dstIP.String())
if isSynology && os.Getuid() != 0 {
// On DSM7 we run as non-root and need to pass
// CAP_NET_RAW if our binary has it.
setAmbientCapsRaw(cmd)
}
err = cmd.Run()
}
d := time.Since(t0)
if err != nil {
if d < time.Second/2 {
// If it failed quicker than the 3 second
// timeout we gave above (500 ms is a
// reasonable threshold), then assume the ping
// failed for problems finding/running
// ping. We don't want to log if the host is
// just down.
ns.logf("exec ping of %v failed in %v: %v", dstIP, d, err)
}
return
}
if debugNetstack() {
ns.logf("exec pinged %v in %v", dstIP, time.Since(t0))
}
if err := ns.tundev.InjectOutbound(pingResPkt); err != nil {
ns.logf("InjectOutbound ping response: %v", err)
}
}
// injectInbound is installed as a packet hook on the 'inbound' (from a
// WireGuard peer) path. Returning filter.Accept releases the packet to
// continue normally (typically being delivered to the host networking stack),
// whereas returning filter.DropSilently is done when netstack intercepts the
// packet and no further processing towards to host should be done.
func (ns *Impl) injectInbound(p *packet.Parsed, t *tstun.Wrapper) filter.Response {
if !ns.shouldProcessInbound(p, t) {
// Let the host network stack (if any) deal with it.
return filter.Accept
}
destIP := p.Dst.Addr()
// If this is an echo request and we're a subnet router, handle pings
// ourselves instead of forwarding the packet on.
pingIP, handlePing := ns.shouldHandlePing(p)
if handlePing {
var pong []byte // the reply to the ping, if our relayed ping works
if destIP.Is4() {
h := p.ICMP4Header()
h.ToResponse()
pong = packet.Generate(&h, p.Payload())
} else if destIP.Is6() {
h := p.ICMP6Header()
h.ToResponse()
pong = packet.Generate(&h, p.Payload())
}
go ns.userPing(pingIP, pong)
return filter.DropSilently
}
var pn tcpip.NetworkProtocolNumber
switch p.IPVersion {
case 4:
pn = header.IPv4ProtocolNumber
case 6:
pn = header.IPv6ProtocolNumber
}
if debugPackets {
ns.logf("[v2] packet in (from %v): % x", p.Src, p.Buffer())
}
packetBuf := stack.NewPacketBuffer(stack.PacketBufferOptions{
Payload: bufferv2.MakeWithData(append([]byte(nil), p.Buffer()...)),
})
ns.linkEP.InjectInbound(pn, packetBuf)
packetBuf.DecRef()
// We've now delivered this to netstack, so we're done.
// Instead of returning a filter.Accept here (which would also
// potentially deliver it to the host OS), and instead of
// filter.Drop (which would log about rejected traffic),
// instead return filter.DropSilently which just quietly stops
// processing it in the tstun TUN wrapper.
return filter.DropSilently
}
// shouldHandlePing returns whether or not netstack should handle an incoming
// ICMP echo request packet, and the IP address that should be pinged from this
// process. The IP address can be different from the destination in the packet
// if the destination is a 4via6 address.
func (ns *Impl) shouldHandlePing(p *packet.Parsed) (_ netip.Addr, ok bool) {
if !p.IsEchoRequest() {
return netip.Addr{}, false
}
destIP := p.Dst.Addr()
// We need to handle pings for all 4via6 addresses, even if this
// netstack instance normally isn't responsible for processing subnets.
//
// For example, on Linux, subnet router traffic could be handled via
// tun+iptables rules for most packets, but we still need to handle
// ICMP echo requests over 4via6 since the host networking stack
// doesn't know what to do with a 4via6 address.
//
// shouldProcessInbound returns 'true' to say that we should process
// all IPv6 packets with a destination address in the 'via' range, so
// check before we check the "ProcessSubnets" boolean below.
if viaRange.Contains(destIP) {
// The input echo request was to a 4via6 address, which we cannot
// simply ping as-is from this process. Translate the destination to an
// IPv4 address, so that our relayed ping (in userPing) is pinging the
// underlying destination IP.
//
// ICMPv4 and ICMPv6 are different protocols with different on-the-wire
// representations, so normally you can't send an ICMPv6 message over
// IPv4 and expect to get a useful result. However, in this specific
// case things are safe because the 'userPing' function doesn't make
// use of the input packet.
return tsaddr.UnmapVia(destIP), true
}
// If we get here, we don't do anything unless this netstack instance
// is responsible for processing subnet traffic.
if !ns.ProcessSubnets {
return netip.Addr{}, false
}
// For non-4via6 addresses, we don't handle pings if they're destined
// for a Tailscale IP.
if tsaddr.IsTailscaleIP(destIP) {
return netip.Addr{}, false
}
// This netstack instance is processing subnet traffic, so handle the
// ping ourselves.
return destIP, true
}
func netaddrIPFromNetstackIP(s tcpip.Address) netip.Addr {
switch len(s) {
case 4:
return netaddr.IPv4(s[0], s[1], s[2], s[3])
case 16:
var a [16]byte
copy(a[:], s)
return netip.AddrFrom16(a).Unmap()
}
return netip.Addr{}
}
func (ns *Impl) acceptTCP(r *tcp.ForwarderRequest) {
reqDetails := r.ID()
if debugNetstack() {
ns.logf("[v2] TCP ForwarderRequest: %s", stringifyTEI(reqDetails))
}
clientRemoteIP := netaddrIPFromNetstackIP(reqDetails.RemoteAddress)
if !clientRemoteIP.IsValid() {
ns.logf("invalid RemoteAddress in TCP ForwarderRequest: %s", stringifyTEI(reqDetails))
r.Complete(true) // sends a RST
return
}
clientRemotePort := reqDetails.RemotePort
clientRemoteAddrPort := netip.AddrPortFrom(clientRemoteIP, clientRemotePort)
dialIP := netaddrIPFromNetstackIP(reqDetails.LocalAddress)
isTailscaleIP := tsaddr.IsTailscaleIP(dialIP)
if viaRange.Contains(dialIP) {
isTailscaleIP = false
dialIP = tsaddr.UnmapVia(dialIP)
}
defer func() {
if !isTailscaleIP {
// if this is a subnet IP, we added this in before the TCP handshake
// so netstack is happy TCP-handshaking as a subnet IP
ns.removeSubnetAddress(dialIP)
}
}()
var wq waiter.Queue
// We can't actually create the endpoint or complete the inbound
// request until we're sure that the connection can be handled by this
// endpoint. This function sets up the TCP connection and should be
// called immediately before a connection is handled.
createConn := func(opts ...tcpip.SettableSocketOption) *gonet.TCPConn {
ep, err := r.CreateEndpoint(&wq)
if err != nil {
ns.logf("CreateEndpoint error for %s: %v", stringifyTEI(reqDetails), err)
r.Complete(true) // sends a RST
return nil
}
r.Complete(false)
for _, opt := range opts {
ep.SetSockOpt(opt)
}
// SetKeepAlive so that idle connections to peers that have forgotten about
// the connection or gone completely offline eventually time out.
// Applications might be setting this on a forwarded connection, but from
// userspace we can not see those, so the best we can do is to always
// perform them with conservative timing.
// TODO(tailscale/tailscale#4522): Netstack defaults match the Linux
// defaults, and results in a little over two hours before the socket would
// be closed due to keepalive. A shorter default might be better, or seeking
// a default from the host IP stack. This also might be a useful
// user-tunable, as in userspace mode this can have broad implications such
// as lingering connections to fork style daemons. On the other side of the
// fence, the long duration timers are low impact values for battery powered
// peers.
ep.SocketOptions().SetKeepAlive(true)
// The ForwarderRequest.CreateEndpoint above asynchronously
// starts the TCP handshake. Note that the gonet.TCPConn
// methods c.RemoteAddr() and c.LocalAddr() will return nil
// until the handshake actually completes. But we have the
// remote address in reqDetails instead, so we don't use
// gonet.TCPConn.RemoteAddr. The byte copies in both
// directions to/from the gonet.TCPConn in forwardTCP will
// block until the TCP handshake is complete.
return gonet.NewTCPConn(&wq, ep)
}
// DNS
if reqDetails.LocalPort == 53 && (dialIP == magicDNSIP || dialIP == magicDNSIPv6) {
c := createConn()
if c == nil {
return
}
go ns.dns.HandleTCPConn(c, netip.AddrPortFrom(clientRemoteIP, reqDetails.RemotePort))
return
}
if ns.lb != nil {
if reqDetails.LocalPort == 22 && ns.processSSH() && ns.isLocalIP(dialIP) {
// Use a higher keepalive idle time for SSH connections, as they are
// typically long lived and idle connections are more likely to be
// intentional. Ideally we would turn this off entirely, but we can't
// tell the difference between a long lived connection that is idle
// vs a connection that is dead because the peer has gone away.
// We pick 72h as that is typically sufficient for a long weekend.
idle := tcpip.KeepaliveIdleOption(72 * time.Hour)
c := createConn(&idle)
if c == nil {
return
}
if err := ns.lb.HandleSSHConn(c); err != nil {
ns.logf("ssh error: %v", err)
}
return
}
if port, ok := ns.lb.GetPeerAPIPort(dialIP); ok {
if reqDetails.LocalPort == port && ns.isLocalIP(dialIP) {
c := createConn()
if c == nil {
return
}
src := netip.AddrPortFrom(clientRemoteIP, reqDetails.RemotePort)
dst := netip.AddrPortFrom(dialIP, port)
ns.lb.ServePeerAPIConnection(src, dst, c)
return
}
}
if reqDetails.LocalPort == 80 && (dialIP == magicDNSIP || dialIP == magicDNSIPv6) {
c := createConn()
if c == nil {
return
}
ns.lb.HandleQuad100Port80Conn(c)
return
}
if ns.lb.ShouldInterceptTCPPort(reqDetails.LocalPort) && ns.isLocalIP(dialIP) {
getTCPConn := func() (_ net.Conn, ok bool) {
c := createConn()
return c, c != nil
}
sendRST := func() {
r.Complete(true)
}
ns.lb.HandleInterceptedTCPConn(reqDetails.LocalPort, clientRemoteAddrPort, getTCPConn, sendRST)
return
}
}
if ns.ForwardTCPIn != nil {
c := createConn()
if c == nil {
return
}
ns.ForwardTCPIn(c, reqDetails.LocalPort)
return
}
if isTailscaleIP {
dialIP = netaddr.IPv4(127, 0, 0, 1)
}
dialAddr := netip.AddrPortFrom(dialIP, uint16(reqDetails.LocalPort))
if !ns.forwardTCP(createConn, clientRemoteIP, &wq, dialAddr) {
r.Complete(true) // sends a RST
}
}
func (ns *Impl) forwardTCP(getClient func(...tcpip.SettableSocketOption) *gonet.TCPConn, clientRemoteIP netip.Addr, wq *waiter.Queue, dialAddr netip.AddrPort) (handled bool) {
dialAddrStr := dialAddr.String()
if debugNetstack() {
ns.logf("[v2] netstack: forwarding incoming connection to %s", dialAddrStr)
}
ctx, cancel := context.WithCancel(context.Background())
defer cancel()
waitEntry, notifyCh := waiter.NewChannelEntry(waiter.EventHUp) // TODO(bradfitz): right EventMask?
wq.EventRegister(&waitEntry)
defer wq.EventUnregister(&waitEntry)
done := make(chan bool)
// netstack doesn't close the notification channel automatically if there was no
// hup signal, so we close done after we're done to not leak the goroutine below.
defer close(done)
go func() {
select {
case <-notifyCh:
if debugNetstack() {
ns.logf("[v2] netstack: forwardTCP notifyCh fired; canceling context for %s", dialAddrStr)
}
case <-done:
}
cancel()
}()
// Attempt to dial the outbound connection before we accept the inbound one.
var stdDialer net.Dialer
server, err := stdDialer.DialContext(ctx, "tcp", dialAddrStr)
if err != nil {
ns.logf("netstack: could not connect to local server at %s: %v", dialAddr.String(), err)
return
}
defer server.Close()
// If we get here, either the getClient call below will succeed and
// return something we can Close, or it will fail and will properly
// respond to the client with a RST. Either way, the caller no longer
// needs to clean up the client connection.
handled = true
// We dialed the connection; we can complete the client's TCP handshake.
client := getClient()
if client == nil {
return
}
defer client.Close()
backendLocalAddr := server.LocalAddr().(*net.TCPAddr)
backendLocalIPPort := netaddr.Unmap(backendLocalAddr.AddrPort())
ns.e.RegisterIPPortIdentity(backendLocalIPPort, clientRemoteIP)
defer ns.e.UnregisterIPPortIdentity(backendLocalIPPort)
connClosed := make(chan error, 2)
go func() {
_, err := io.Copy(server, client)
connClosed <- err
}()
go func() {
_, err := io.Copy(client, server)
connClosed <- err
}()
err = <-connClosed
if err != nil {
ns.logf("proxy connection closed with error: %v", err)
}
ns.logf("[v2] netstack: forwarder connection to %s closed", dialAddrStr)
return
}
func (ns *Impl) acceptUDP(r *udp.ForwarderRequest) {
sess := r.ID()
if debugNetstack() {
ns.logf("[v2] UDP ForwarderRequest: %v", stringifyTEI(sess))
}
var wq waiter.Queue
ep, err := r.CreateEndpoint(&wq)
if err != nil {
ns.logf("acceptUDP: could not create endpoint: %v", err)
return
}
dstAddr, ok := ipPortOfNetstackAddr(sess.LocalAddress, sess.LocalPort)
if !ok {
ep.Close()
return
}
srcAddr, ok := ipPortOfNetstackAddr(sess.RemoteAddress, sess.RemotePort)
if !ok {
ep.Close()
return
}
// Handle magicDNS traffic (via UDP) here.
if dst := dstAddr.Addr(); dst == magicDNSIP || dst == magicDNSIPv6 {
if dstAddr.Port() != 53 {
ep.Close()
return // Only MagicDNS traffic runs on the service IPs for now.
}
c := gonet.NewUDPConn(ns.ipstack, &wq, ep)
go ns.handleMagicDNSUDP(srcAddr, c)
return
}
c := gonet.NewUDPConn(ns.ipstack, &wq, ep)
go ns.forwardUDP(c, &wq, srcAddr, dstAddr)
}
func (ns *Impl) handleMagicDNSUDP(srcAddr netip.AddrPort, c *gonet.UDPConn) {
// In practice, implementations are advised not to exceed 512 bytes
// due to fragmenting. Just to be sure, we bump all the way to the MTU.
const maxUDPReqSize = mtu
// Packets are being generated by the local host, so there should be
// very, very little latency. 150ms was chosen as something of an upper
// bound on resource usage, while hopefully still being long enough for
// a heavily loaded system.
const readDeadline = 150 * time.Millisecond
defer c.Close()
q := make([]byte, maxUDPReqSize)
// libresolv from glibc is quite adamant that transmitting multiple DNS
// requests down the same UDP socket is valid. To support this, we read
// in a loop (with a tight deadline so we don't chew too many resources).
//
// See: https://github.com/bminor/glibc/blob/f7fbb99652eceb1b6b55e4be931649df5946497c/resolv/res_send.c#L995
for {
c.SetReadDeadline(time.Now().Add(readDeadline))
n, _, err := c.ReadFrom(q)
if err != nil {
if oe, ok := err.(*net.OpError); !(ok && oe.Timeout()) {
ns.logf("dns udp read: %v", err) // log non-timeout errors
}
return
}
resp, err := ns.dns.Query(context.Background(), q[:n], srcAddr)
if err != nil {
ns.logf("dns udp query: %v", err)
return
}
c.Write(resp)
}
}
// forwardUDP proxies between client (with addr clientAddr) and dstAddr.
//
// dstAddr may be either a local Tailscale IP, in which we case we proxy to
// 127.0.0.1, or any other IP (from an advertised subnet), in which case we
// proxy to it directly.
func (ns *Impl) forwardUDP(client *gonet.UDPConn, wq *waiter.Queue, clientAddr, dstAddr netip.AddrPort) {
port, srcPort := dstAddr.Port(), clientAddr.Port()
if debugNetstack() {
ns.logf("[v2] netstack: forwarding incoming UDP connection on port %v", port)
}
var backendListenAddr *net.UDPAddr
var backendRemoteAddr *net.UDPAddr
isLocal := ns.isLocalIP(dstAddr.Addr())
if isLocal {
backendRemoteAddr = &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: int(port)}
backendListenAddr = &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: int(srcPort)}
} else {
if dstIP := dstAddr.Addr(); viaRange.Contains(dstIP) {
dstAddr = netip.AddrPortFrom(tsaddr.UnmapVia(dstIP), dstAddr.Port())
}
backendRemoteAddr = net.UDPAddrFromAddrPort(dstAddr)
if dstAddr.Addr().Is4() {
backendListenAddr = &net.UDPAddr{IP: net.ParseIP("0.0.0.0"), Port: int(srcPort)}
} else {
backendListenAddr = &net.UDPAddr{IP: net.ParseIP("::"), Port: int(srcPort)}
}
}
backendConn, err := net.ListenUDP("udp", backendListenAddr)
if err != nil {
ns.logf("netstack: could not bind local port %v: %v, trying again with random port", backendListenAddr.Port, err)
backendListenAddr.Port = 0
backendConn, err = net.ListenUDP("udp", backendListenAddr)
if err != nil {
ns.logf("netstack: could not create UDP socket, preventing forwarding to %v: %v", dstAddr, err)
return
}
}
backendLocalAddr := backendConn.LocalAddr().(*net.UDPAddr)
backendLocalIPPort := netip.AddrPortFrom(backendListenAddr.AddrPort().Addr().Unmap().WithZone(backendLocalAddr.Zone), backendLocalAddr.AddrPort().Port())
if !backendLocalIPPort.IsValid() {
ns.logf("could not get backend local IP:port from %v:%v", backendLocalAddr.IP, backendLocalAddr.Port)
}
if isLocal {
ns.e.RegisterIPPortIdentity(backendLocalIPPort, dstAddr.Addr())
}
ctx, cancel := context.WithCancel(context.Background())
idleTimeout := 2 * time.Minute
if port == 53 {
// Make DNS packet copies time out much sooner.
//
// TODO(bradfitz): make DNS queries over UDP forwarding even
// cheaper by adding an additional idleTimeout post-DNS-reply.
// For instance, after the DNS response goes back out, then only
// wait a few seconds (or zero, really)
idleTimeout = 30 * time.Second
}
timer := time.AfterFunc(idleTimeout, func() {
if isLocal {
ns.e.UnregisterIPPortIdentity(backendLocalIPPort)
}
ns.logf("netstack: UDP session between %s and %s timed out", backendListenAddr, backendRemoteAddr)
cancel()
client.Close()
backendConn.Close()
})
extend := func() {
timer.Reset(idleTimeout)
}
startPacketCopy(ctx, cancel, client, net.UDPAddrFromAddrPort(clientAddr), backendConn, ns.logf, extend)
startPacketCopy(ctx, cancel, backendConn, backendRemoteAddr, client, ns.logf, extend)
if isLocal {
// Wait for the copies to be done before decrementing the
// subnet address count to potentially remove the route.
<-ctx.Done()
ns.removeSubnetAddress(dstAddr.Addr())
}
}
func startPacketCopy(ctx context.Context, cancel context.CancelFunc, dst net.PacketConn, dstAddr net.Addr, src net.PacketConn, logf logger.Logf, extend func()) {
if debugNetstack() {
logf("[v2] netstack: startPacketCopy to %v (%T) from %T", dstAddr, dst, src)
}
go func() {
defer cancel() // tear down the other direction's copy
pkt := make([]byte, maxUDPPacketSize)
for {
select {
case <-ctx.Done():
return
default:
n, srcAddr, err := src.ReadFrom(pkt)
if err != nil {
if ctx.Err() == nil {
logf("read packet from %s failed: %v", srcAddr, err)
}
return
}
_, err = dst.WriteTo(pkt[:n], dstAddr)
if err != nil {
if ctx.Err() == nil {
logf("write packet to %s failed: %v", dstAddr, err)
}
return
}
if debugNetstack() {
logf("[v2] wrote UDP packet %s -> %s", srcAddr, dstAddr)
}
extend()
}
}
}()
}
func stringifyTEI(tei stack.TransportEndpointID) string {
localHostPort := net.JoinHostPort(tei.LocalAddress.String(), strconv.Itoa(int(tei.LocalPort)))
remoteHostPort := net.JoinHostPort(tei.RemoteAddress.String(), strconv.Itoa(int(tei.RemotePort)))
return fmt.Sprintf("%s -> %s", remoteHostPort, localHostPort)
}
func ipPortOfNetstackAddr(a tcpip.Address, port uint16) (ipp netip.AddrPort, ok bool) {
var a16 [16]byte
copy(a16[:], a)
switch len(a) {
case 4:
return netip.AddrPortFrom(
netip.AddrFrom4(*(*[4]byte)(a16[:4])).Unmap(),
port,
), true
case 16:
return netip.AddrPortFrom(netip.AddrFrom16(a16).Unmap(), port), true
default:
return ipp, false
}
}