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tailscale/appc/appc.go

329 lines
7.8 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
// Package appc implements App Connectors.
package appc
import (
"expvar"
"log"
"net"
"net/netip"
"sync"
"time"
"golang.org/x/net/dns/dnsmessage"
"tailscale.com/metrics"
"tailscale.com/tailcfg"
"tailscale.com/types/appctype"
"tailscale.com/types/ipproto"
"tailscale.com/types/nettype"
"tailscale.com/util/clientmetric"
"tailscale.com/util/mak"
)
var tsMBox = dnsmessage.MustNewName("support.tailscale.com.")
// target describes the predicates which route some inbound
// traffic to the app connector to a specific handler.
type target struct {
Dest netip.Prefix
Matching tailcfg.ProtoPortRange
}
// Server implements an App Connector.
type Server struct {
mu sync.RWMutex // mu guards following fields
connectors map[appctype.ConfigID]connector
}
type appcMetrics struct {
dnsResponses expvar.Int
dnsFailures expvar.Int
tcpConns expvar.Int
sniConns expvar.Int
unhandledConns expvar.Int
}
var getMetrics = sync.OnceValue[*appcMetrics](func() *appcMetrics {
m := appcMetrics{}
stats := new(metrics.Set)
stats.Set("tls_sessions", &m.sniConns)
clientmetric.NewCounterFunc("sniproxy_tls_sessions", m.sniConns.Value)
stats.Set("tcp_sessions", &m.tcpConns)
clientmetric.NewCounterFunc("sniproxy_tcp_sessions", m.tcpConns.Value)
stats.Set("dns_responses", &m.dnsResponses)
clientmetric.NewCounterFunc("sniproxy_dns_responses", m.dnsResponses.Value)
stats.Set("dns_failed", &m.dnsFailures)
clientmetric.NewCounterFunc("sniproxy_dns_failed", m.dnsFailures.Value)
expvar.Publish("sniproxy", stats)
return &m
})
// Configure applies the provided configuration to the app connector.
func (s *Server) Configure(cfg *appctype.AppConnectorConfig) {
s.mu.Lock()
defer s.mu.Unlock()
s.connectors = makeConnectorsFromConfig(cfg)
}
// HandleTCPFlow implements tsnet.FallbackTCPHandler.
func (s *Server) HandleTCPFlow(src, dst netip.AddrPort) (handler func(net.Conn), intercept bool) {
m := getMetrics()
s.mu.RLock()
defer s.mu.RUnlock()
for _, c := range s.connectors {
if handler, intercept := c.handleTCPFlow(src, dst, m); intercept {
return handler, intercept
}
}
return nil, false
}
// HandleDNS handles a DNS request to the app connector.
func (s *Server) HandleDNS(c nettype.ConnPacketConn) {
defer c.Close()
c.SetReadDeadline(time.Now().Add(5 * time.Second))
m := getMetrics()
buf := make([]byte, 1500)
n, err := c.Read(buf)
if err != nil {
log.Printf("HandleDNS: read failed: %v\n ", err)
m.dnsFailures.Add(1)
return
}
addrPortStr := c.LocalAddr().String()
host, _, err := net.SplitHostPort(addrPortStr)
if err != nil {
log.Printf("HandleDNS: bogus addrPort %q", addrPortStr)
m.dnsFailures.Add(1)
return
}
localAddr, err := netip.ParseAddr(host)
if err != nil {
log.Printf("HandleDNS: bogus local address %q", host)
m.dnsFailures.Add(1)
return
}
var msg dnsmessage.Message
err = msg.Unpack(buf[:n])
if err != nil {
log.Printf("HandleDNS: dnsmessage unpack failed: %v\n ", err)
m.dnsFailures.Add(1)
return
}
s.mu.RLock()
defer s.mu.RUnlock()
for _, connector := range s.connectors {
resp, err := connector.handleDNS(&msg, localAddr)
if err != nil {
log.Printf("HandleDNS: connector handling failed: %v\n", err)
m.dnsFailures.Add(1)
return
}
if len(resp) > 0 {
// This connector handled the DNS request
_, err = c.Write(resp)
if err != nil {
log.Printf("HandleDNS: write failed: %v\n", err)
m.dnsFailures.Add(1)
return
}
m.dnsResponses.Add(1)
return
}
}
}
// connector describes a logical collection of
// services which need to be proxied.
type connector struct {
Handlers map[target]handler
}
// handleTCPFlow implements tsnet.FallbackTCPHandler.
func (c *connector) handleTCPFlow(src, dst netip.AddrPort, m *appcMetrics) (handler func(net.Conn), intercept bool) {
for t, h := range c.Handlers {
if t.Matching.Proto != 0 && t.Matching.Proto != int(ipproto.TCP) {
continue
}
if !t.Dest.Contains(dst.Addr()) {
continue
}
if !t.Matching.Ports.Contains(dst.Port()) {
continue
}
switch h.(type) {
case *tcpSNIHandler:
m.sniConns.Add(1)
case *tcpRoundRobinHandler:
m.tcpConns.Add(1)
default:
log.Printf("handleTCPFlow: unhandled handler type %T", h)
}
return h.Handle, true
}
m.unhandledConns.Add(1)
return nil, false
}
// handleDNS returns the DNS response to the given query. If this
// connector is unable to handle the request, nil is returned.
func (c *connector) handleDNS(req *dnsmessage.Message, localAddr netip.Addr) (response []byte, err error) {
for t, h := range c.Handlers {
if t.Dest.Contains(localAddr) {
return makeDNSResponse(req, h.ReachableOn())
}
}
// Did not match, signal 'not handled' to caller
return nil, nil
}
func makeDNSResponse(req *dnsmessage.Message, reachableIPs []netip.Addr) (response []byte, err error) {
buf := make([]byte, 1500)
resp := dnsmessage.NewBuilder(buf,
dnsmessage.Header{
ID: req.Header.ID,
Response: true,
Authoritative: true,
})
resp.EnableCompression()
if len(req.Questions) == 0 {
buf, _ = resp.Finish()
return buf, nil
}
q := req.Questions[0]
err = resp.StartQuestions()
if err != nil {
return
}
resp.Question(q)
err = resp.StartAnswers()
if err != nil {
return
}
switch q.Type {
case dnsmessage.TypeAAAA:
for _, ip := range reachableIPs {
if ip.Is6() {
err = resp.AAAAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.AAAAResource{AAAA: ip.As16()},
)
}
}
case dnsmessage.TypeA:
for _, ip := range reachableIPs {
if ip.Is4() {
err = resp.AResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.AResource{A: ip.As4()},
)
}
}
case dnsmessage.TypeSOA:
err = resp.SOAResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.SOAResource{NS: q.Name, MBox: tsMBox, Serial: 2023030600,
Refresh: 120, Retry: 120, Expire: 120, MinTTL: 60},
)
case dnsmessage.TypeNS:
err = resp.NSResource(
dnsmessage.ResourceHeader{Name: q.Name, Class: q.Class, TTL: 120},
dnsmessage.NSResource{NS: tsMBox},
)
}
if err != nil {
return nil, err
}
return resp.Finish()
}
type handler interface {
// Handle handles the given socket.
Handle(c net.Conn)
// ReachableOn returns the IP addresses this handler is reachable on.
ReachableOn() []netip.Addr
}
func installDNATHandler(d *appctype.DNATConfig, out *connector) {
// These handlers don't actually do DNAT, they just
// proxy the data over the connection.
var dialer net.Dialer
dialer.Timeout = 5 * time.Second
h := tcpRoundRobinHandler{
To: d.To,
DialContext: dialer.DialContext,
ReachableIPs: d.Addrs,
}
for _, addr := range d.Addrs {
for _, protoPort := range d.IP {
t := target{
Dest: netip.PrefixFrom(addr, addr.BitLen()),
Matching: protoPort,
}
mak.Set(&out.Handlers, t, handler(&h))
}
}
}
func installSNIHandler(c *appctype.SNIProxyConfig, out *connector) {
var dialer net.Dialer
dialer.Timeout = 5 * time.Second
h := tcpSNIHandler{
Allowlist: c.AllowedDomains,
DialContext: dialer.DialContext,
ReachableIPs: c.Addrs,
}
for _, addr := range c.Addrs {
for _, protoPort := range c.IP {
t := target{
Dest: netip.PrefixFrom(addr, addr.BitLen()),
Matching: protoPort,
}
mak.Set(&out.Handlers, t, handler(&h))
}
}
}
func makeConnectorsFromConfig(cfg *appctype.AppConnectorConfig) map[appctype.ConfigID]connector {
var connectors map[appctype.ConfigID]connector
for cID, d := range cfg.DNAT {
c := connectors[cID]
installDNATHandler(&d, &c)
mak.Set(&connectors, cID, c)
}
for cID, d := range cfg.SNIProxy {
c := connectors[cID]
installSNIHandler(&d, &c)
mak.Set(&connectors, cID, c)
}
return connectors
}