// Copyright (c) Tailscale Inc & AUTHORS // SPDX-License-Identifier: BSD-3-Clause // The derper binary is a simple DERP server. package main // import "tailscale.com/cmd/derper" import ( "context" "crypto/tls" "encoding/json" "errors" "expvar" "flag" "fmt" "io" "log" "math" "net" "net/http" "net/netip" "os" "path/filepath" "regexp" "strings" "time" "go4.org/mem" "golang.org/x/time/rate" "tailscale.com/atomicfile" "tailscale.com/derp" "tailscale.com/derp/derphttp" "tailscale.com/metrics" "tailscale.com/net/stun" "tailscale.com/tsweb" "tailscale.com/types/key" "tailscale.com/util/cmpx" ) var ( dev = flag.Bool("dev", false, "run in localhost development mode (overrides -a)") addr = flag.String("a", ":443", "server HTTP/HTTPS listen address, in form \":port\", \"ip:port\", or for IPv6 \"[ip]:port\". If the IP is omitted, it defaults to all interfaces. Serves HTTPS if the port is 443 and/or -certmode is manual, otherwise HTTP.") httpPort = flag.Int("http-port", 80, "The port on which to serve HTTP. Set to -1 to disable. The listener is bound to the same IP (if any) as specified in the -a flag.") stunPort = flag.Int("stun-port", 3478, "The UDP port on which to serve STUN. The listener is bound to the same IP (if any) as specified in the -a flag.") configPath = flag.String("c", "", "config file path") certMode = flag.String("certmode", "letsencrypt", "mode for getting a cert. possible options: manual, letsencrypt") certDir = flag.String("certdir", tsweb.DefaultCertDir("derper-certs"), "directory to store LetsEncrypt certs, if addr's port is :443") hostname = flag.String("hostname", "derp.tailscale.com", "LetsEncrypt host name, if addr's port is :443") runSTUN = flag.Bool("stun", true, "whether to run a STUN server. It will bind to the same IP (if any) as the --addr flag value.") runDERP = flag.Bool("derp", true, "whether to run a DERP server. The only reason to set this false is if you're decommissioning a server but want to keep its bootstrap DNS functionality still running.") meshPSKFile = flag.String("mesh-psk-file", defaultMeshPSKFile(), "if non-empty, path to file containing the mesh pre-shared key file. It should contain some hex string; whitespace is trimmed.") meshWith = flag.String("mesh-with", "", "optional comma-separated list of hostnames to mesh with; the server's own hostname can be in the list") bootstrapDNS = flag.String("bootstrap-dns-names", "", "optional comma-separated list of hostnames to make available at /bootstrap-dns") unpublishedDNS = flag.String("unpublished-bootstrap-dns-names", "", "optional comma-separated list of hostnames to make available at /bootstrap-dns and not publish in the list") verifyClients = flag.Bool("verify-clients", false, "verify clients to this DERP server through a local tailscaled instance.") acceptConnLimit = flag.Float64("accept-connection-limit", math.Inf(+1), "rate limit for accepting new connection") acceptConnBurst = flag.Int("accept-connection-burst", math.MaxInt, "burst limit for accepting new connection") ) var ( stats = new(metrics.Set) stunDisposition = &metrics.LabelMap{Label: "disposition"} stunAddrFamily = &metrics.LabelMap{Label: "family"} tlsRequestVersion = &metrics.LabelMap{Label: "version"} tlsActiveVersion = &metrics.LabelMap{Label: "version"} stunReadError = stunDisposition.Get("read_error") stunNotSTUN = stunDisposition.Get("not_stun") stunWriteError = stunDisposition.Get("write_error") stunSuccess = stunDisposition.Get("success") stunIPv4 = stunAddrFamily.Get("ipv4") stunIPv6 = stunAddrFamily.Get("ipv6") ) func init() { stats.Set("counter_requests", stunDisposition) stats.Set("counter_addrfamily", stunAddrFamily) expvar.Publish("stun", stats) expvar.Publish("derper_tls_request_version", tlsRequestVersion) expvar.Publish("gauge_derper_tls_active_version", tlsActiveVersion) } type config struct { PrivateKey key.NodePrivate } func loadConfig() config { if *dev { return config{PrivateKey: key.NewNode()} } if *configPath == "" { if os.Getuid() == 0 { *configPath = "/var/lib/derper/derper.key" } else { log.Fatalf("derper: -c not specified") } log.Printf("no config path specified; using %s", *configPath) } b, err := os.ReadFile(*configPath) switch { case errors.Is(err, os.ErrNotExist): return writeNewConfig() case err != nil: log.Fatal(err) panic("unreachable") default: var cfg config if err := json.Unmarshal(b, &cfg); err != nil { log.Fatalf("derper: config: %v", err) } return cfg } } func writeNewConfig() config { k := key.NewNode() if err := os.MkdirAll(filepath.Dir(*configPath), 0777); err != nil { log.Fatal(err) } cfg := config{ PrivateKey: k, } b, err := json.MarshalIndent(cfg, "", "\t") if err != nil { log.Fatal(err) } if err := atomicfile.WriteFile(*configPath, b, 0600); err != nil { log.Fatal(err) } return cfg } func main() { flag.Parse() if *dev { *addr = ":3340" // above the keys DERP log.Printf("Running in dev mode.") tsweb.DevMode = true } listenHost, _, err := net.SplitHostPort(*addr) if err != nil { log.Fatalf("invalid server address: %v", err) } cfg := loadConfig() serveTLS := tsweb.IsProd443(*addr) || *certMode == "manual" s := derp.NewServer(cfg.PrivateKey, log.Printf) s.SetVerifyClient(*verifyClients) if *meshPSKFile != "" { b, err := os.ReadFile(*meshPSKFile) if err != nil { log.Fatal(err) } key := strings.TrimSpace(string(b)) if matched, _ := regexp.MatchString(`(?i)^[0-9a-f]{64,}$`, key); !matched { log.Fatalf("key in %s must contain 64+ hex digits", *meshPSKFile) } s.SetMeshKey(key) log.Printf("DERP mesh key configured") } if err := startMesh(s); err != nil { log.Fatalf("startMesh: %v", err) } expvar.Publish("derp", s.ExpVar()) mux := http.NewServeMux() if *runDERP { derpHandler := derphttp.Handler(s) derpHandler = addWebSocketSupport(s, derpHandler) mux.Handle("/derp", derpHandler) } else { mux.Handle("/derp", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { http.Error(w, "derp server disabled", http.StatusNotFound) })) } mux.HandleFunc("/derp/probe", probeHandler) go refreshBootstrapDNSLoop() mux.HandleFunc("/bootstrap-dns", handleBootstrapDNS) mux.Handle("/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { w.Header().Set("Content-Type", "text/html; charset=utf-8") w.WriteHeader(200) io.WriteString(w, `

DERP

This is a Tailscale DERP server.

`) if !*runDERP { io.WriteString(w, `

Status: disabled

`) } if tsweb.AllowDebugAccess(r) { io.WriteString(w, "

Debug info at /debug/.

\n") } })) mux.Handle("/robots.txt", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { io.WriteString(w, "User-agent: *\nDisallow: /\n") })) mux.Handle("/generate_204", http.HandlerFunc(serveNoContent)) debug := tsweb.Debugger(mux) debug.KV("TLS hostname", *hostname) debug.KV("Mesh key", s.HasMeshKey()) debug.Handle("check", "Consistency check", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { err := s.ConsistencyCheck() if err != nil { http.Error(w, err.Error(), 500) } else { io.WriteString(w, "derp.Server ConsistencyCheck okay") } })) debug.Handle("traffic", "Traffic check", http.HandlerFunc(s.ServeDebugTraffic)) if *runSTUN { go serveSTUN(listenHost, *stunPort) } quietLogger := log.New(logFilter{}, "", 0) httpsrv := &http.Server{ Addr: *addr, Handler: mux, ErrorLog: quietLogger, // Set read/write timeout. For derper, this basically // only affects TLS setup, as read/write deadlines are // cleared on Hijack, which the DERP server does. But // without this, we slowly accumulate stuck TLS // handshake goroutines forever. This also affects // /debug/ traffic, but 30 seconds is plenty for // Prometheus/etc scraping. ReadTimeout: 30 * time.Second, WriteTimeout: 30 * time.Second, } if serveTLS { log.Printf("derper: serving on %s with TLS", *addr) var certManager certProvider certManager, err = certProviderByCertMode(*certMode, *certDir, *hostname) if err != nil { log.Fatalf("derper: can not start cert provider: %v", err) } httpsrv.TLSConfig = certManager.TLSConfig() getCert := httpsrv.TLSConfig.GetCertificate httpsrv.TLSConfig.GetCertificate = func(hi *tls.ClientHelloInfo) (*tls.Certificate, error) { cert, err := getCert(hi) if err != nil { return nil, err } cert.Certificate = append(cert.Certificate, s.MetaCert()) return cert, nil } // Disable TLS 1.0 and 1.1, which are obsolete and have security issues. httpsrv.TLSConfig.MinVersion = tls.VersionTLS12 httpsrv.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { if r.TLS != nil { label := "unknown" switch r.TLS.Version { case tls.VersionTLS10: label = "1.0" case tls.VersionTLS11: label = "1.1" case tls.VersionTLS12: label = "1.2" case tls.VersionTLS13: label = "1.3" } tlsRequestVersion.Add(label, 1) tlsActiveVersion.Add(label, 1) defer tlsActiveVersion.Add(label, -1) } // Set HTTP headers to appease automated security scanners. // // Security automation gets cranky when HTTPS sites don't // set HSTS, and when they don't specify a content // security policy for XSS mitigation. // // DERP's HTTP interface is only ever used for debug // access (for which trivial safe policies work just // fine), and by DERP clients which don't obey any of // these browser-centric headers anyway. w.Header().Set("Strict-Transport-Security", "max-age=63072000; includeSubDomains") w.Header().Set("Content-Security-Policy", "default-src 'none'; frame-ancestors 'none'; form-action 'none'; base-uri 'self'; block-all-mixed-content; plugin-types 'none'") mux.ServeHTTP(w, r) }) if *httpPort > -1 { go func() { port80mux := http.NewServeMux() port80mux.HandleFunc("/generate_204", serveNoContent) port80mux.Handle("/", certManager.HTTPHandler(tsweb.Port80Handler{Main: mux})) port80srv := &http.Server{ Addr: net.JoinHostPort(listenHost, fmt.Sprintf("%d", *httpPort)), Handler: port80mux, ErrorLog: quietLogger, ReadTimeout: 30 * time.Second, // Crank up WriteTimeout a bit more than usually // necessary just so we can do long CPU profiles // and not hit net/http/pprof's "profile // duration exceeds server's WriteTimeout". WriteTimeout: 5 * time.Minute, } err := port80srv.ListenAndServe() if err != nil { if err != http.ErrServerClosed { log.Fatal(err) } } }() } err = rateLimitedListenAndServeTLS(httpsrv) } else { log.Printf("derper: serving on %s", *addr) err = httpsrv.ListenAndServe() } if err != nil && err != http.ErrServerClosed { log.Fatalf("derper: %v", err) } } const ( noContentChallengeHeader = "X-Tailscale-Challenge" noContentResponseHeader = "X-Tailscale-Response" ) // For captive portal detection func serveNoContent(w http.ResponseWriter, r *http.Request) { if challenge := r.Header.Get(noContentChallengeHeader); challenge != "" { badChar := strings.IndexFunc(challenge, func(r rune) bool { return !isChallengeChar(r) }) != -1 if len(challenge) <= 64 && !badChar { w.Header().Set(noContentResponseHeader, "response "+challenge) } } w.WriteHeader(http.StatusNoContent) } func isChallengeChar(c rune) bool { // Semi-randomly chosen as a limited set of valid characters return ('a' <= c && c <= 'z') || ('A' <= c && c <= 'Z') || ('0' <= c && c <= '9') || c == '.' || c == '-' || c == '_' } // probeHandler is the endpoint that js/wasm clients hit to measure // DERP latency, since they can't do UDP STUN queries. func probeHandler(w http.ResponseWriter, r *http.Request) { switch r.Method { case "HEAD", "GET": w.Header().Set("Access-Control-Allow-Origin", "*") default: http.Error(w, "bogus probe method", http.StatusMethodNotAllowed) } } func serveSTUN(host string, port int) { pc, err := net.ListenPacket("udp", net.JoinHostPort(host, fmt.Sprint(port))) if err != nil { log.Fatalf("failed to open STUN listener: %v", err) } log.Printf("running STUN server on %v", pc.LocalAddr()) serverSTUNListener(context.Background(), pc.(*net.UDPConn)) } func serverSTUNListener(ctx context.Context, pc *net.UDPConn) { var buf [64 << 10]byte var ( n int ua *net.UDPAddr err error ) for { n, ua, err = pc.ReadFromUDP(buf[:]) if err != nil { if ctx.Err() != nil { return } log.Printf("STUN ReadFrom: %v", err) time.Sleep(time.Second) stunReadError.Add(1) continue } pkt := buf[:n] if !stun.Is(pkt) { stunNotSTUN.Add(1) continue } txid, err := stun.ParseBindingRequest(pkt) if err != nil { stunNotSTUN.Add(1) continue } if ua.IP.To4() != nil { stunIPv4.Add(1) } else { stunIPv6.Add(1) } addr, _ := netip.AddrFromSlice(ua.IP) res := stun.Response(txid, netip.AddrPortFrom(addr, uint16(ua.Port))) _, err = pc.WriteTo(res, ua) if err != nil { stunWriteError.Add(1) } else { stunSuccess.Add(1) } } } var validProdHostname = regexp.MustCompile(`^derp([^.]*)\.tailscale\.com\.?$`) func prodAutocertHostPolicy(_ context.Context, host string) error { if validProdHostname.MatchString(host) { return nil } return errors.New("invalid hostname") } func defaultMeshPSKFile() string { try := []string{ "/home/derp/keys/derp-mesh.key", filepath.Join(os.Getenv("HOME"), "keys", "derp-mesh.key"), } for _, p := range try { if _, err := os.Stat(p); err == nil { return p } } return "" } func rateLimitedListenAndServeTLS(srv *http.Server) error { ln, err := net.Listen("tcp", cmpx.Or(srv.Addr, ":https")) if err != nil { return err } rln := newRateLimitedListener(ln, rate.Limit(*acceptConnLimit), *acceptConnBurst) expvar.Publish("tls_listener", rln.ExpVar()) defer rln.Close() return srv.ServeTLS(rln, "", "") } type rateLimitedListener struct { // These are at the start of the struct to ensure 64-bit alignment // on 32-bit architecture regardless of what other fields may exist // in this package. numAccepts expvar.Int // does not include number of rejects numRejects expvar.Int net.Listener lim *rate.Limiter } func newRateLimitedListener(ln net.Listener, limit rate.Limit, burst int) *rateLimitedListener { return &rateLimitedListener{Listener: ln, lim: rate.NewLimiter(limit, burst)} } func (l *rateLimitedListener) ExpVar() expvar.Var { m := new(metrics.Set) m.Set("counter_accepted_connections", &l.numAccepts) m.Set("counter_rejected_connections", &l.numRejects) return m } var errLimitedConn = errors.New("cannot accept connection; rate limited") func (l *rateLimitedListener) Accept() (net.Conn, error) { // Even under a rate limited situation, we accept the connection immediately // and close it, rather than being slow at accepting new connections. // This provides two benefits: 1) it signals to the client that something // is going on on the server, and 2) it prevents new connections from // piling up and occupying resources in the OS kernel. // The client will retry as needing (with backoffs in place). cn, err := l.Listener.Accept() if err != nil { return nil, err } if !l.lim.Allow() { l.numRejects.Add(1) cn.Close() return nil, errLimitedConn } l.numAccepts.Add(1) return cn, nil } // logFilter is used to filter out useless error logs that are logged to // the net/http.Server.ErrorLog logger. type logFilter struct{} func (logFilter) Write(p []byte) (int, error) { b := mem.B(p) if mem.HasSuffix(b, mem.S(": EOF\n")) || mem.HasSuffix(b, mem.S(": i/o timeout\n")) || mem.HasSuffix(b, mem.S(": read: connection reset by peer\n")) || mem.HasSuffix(b, mem.S(": remote error: tls: bad certificate\n")) || mem.HasSuffix(b, mem.S(": tls: first record does not look like a TLS handshake\n")) { // Skip this log message, but say that we processed it return len(p), nil } log.Printf("%s", p) return len(p), nil }