// Copyright (c) Tailscale Inc & AUTHORS // SPDX-License-Identifier: BSD-3-Clause package ipnserver import ( "context" "encoding/json" "errors" "fmt" "io" "net" "net/http" "os/user" "strconv" "strings" "sync" "sync/atomic" "time" "unicode" "tailscale.com/envknob" "tailscale.com/ipn" "tailscale.com/ipn/ipnauth" "tailscale.com/ipn/ipnlocal" "tailscale.com/ipn/localapi" "tailscale.com/net/netmon" "tailscale.com/types/logger" "tailscale.com/types/logid" "tailscale.com/util/mak" "tailscale.com/util/set" "tailscale.com/util/systemd" ) // Server is an IPN backend and its set of 0 or more active localhost // TCP or unix socket connections talking to that backend. type Server struct { lb atomic.Pointer[ipnlocal.LocalBackend] logf logger.Logf netMon *netmon.Monitor // must be non-nil backendLogID logid.PublicID // resetOnZero is whether to call bs.Reset on transition from // 1->0 active HTTP requests. That is, this is whether the backend is // being run in "client mode" that requires an active GUI // connection (such as on Windows by default). Even if this // is true, the ForceDaemon pref can override this. resetOnZero bool startBackendOnce sync.Once runCalled atomic.Bool // mu guards the fields that follow. // lock order: mu, then LocalBackend.mu mu sync.Mutex lastUserID ipn.WindowsUserID // tracks last userid; on change, Reset state for paranoia activeReqs map[*http.Request]*ipnauth.ConnIdentity backendWaiter waiterSet // of LocalBackend waiters zeroReqWaiter waiterSet // of blockUntilZeroConnections waiters } func (s *Server) mustBackend() *ipnlocal.LocalBackend { lb := s.lb.Load() if lb == nil { panic("unexpected: call to mustBackend in path where SetLocalBackend should've been called") } return lb } // waiterSet is a set of callers waiting on something. Each item (map value) in // the set is a func that wakes up that waiter's context. The waiter is responsible // for removing itself from the set when woken up. The (*waiterSet).add method // returns a cleanup method which does that removal. The caller than defers that // cleanup. // // TODO(bradfitz): this is a generally useful pattern. Move elsewhere? type waiterSet set.HandleSet[context.CancelFunc] // add registers a new waiter in the set. // It aquires mu to add the waiter, and does so again when cleanup is called to remove it. // ready is closed when the waiter is ready (or ctx is done). func (s *waiterSet) add(mu *sync.Mutex, ctx context.Context) (ready <-chan struct{}, cleanup func()) { ctx, cancel := context.WithCancel(ctx) hs := (*set.HandleSet[context.CancelFunc])(s) // change method set mu.Lock() h := hs.Add(cancel) mu.Unlock() return ctx.Done(), func() { mu.Lock() delete(*hs, h) mu.Unlock() cancel() } } // wakeAll wakes up all waiters in the set. func (w waiterSet) wakeAll() { for _, cancel := range w { cancel() // they'll remove themselves } } func (s *Server) awaitBackend(ctx context.Context) (_ *ipnlocal.LocalBackend, ok bool) { lb := s.lb.Load() if lb != nil { return lb, true } ready, cleanup := s.backendWaiter.add(&s.mu, ctx) defer cleanup() // Try again, now that we've registered, in case there was a // race. lb = s.lb.Load() if lb != nil { return lb, true } <-ready lb = s.lb.Load() return lb, lb != nil } // serveServerStatus serves the /server-status endpoint which reports whether // the LocalBackend is up yet. // This is primarily for the Windows GUI, because wintun can take awhile to // come up. See https://github.com/tailscale/tailscale/issues/6522. func (s *Server) serveServerStatus(w http.ResponseWriter, r *http.Request) { ctx := r.Context() w.Header().Set("Content-Type", "application/json") var res struct { Error string `json:"error,omitempty"` } lb := s.lb.Load() if lb == nil { w.WriteHeader(http.StatusServiceUnavailable) if wait, _ := strconv.ParseBool(r.FormValue("wait")); wait { w.(http.Flusher).Flush() lb, _ = s.awaitBackend(ctx) } } if lb == nil { res.Error = "backend not ready" } json.NewEncoder(w).Encode(res) } func (s *Server) serveHTTP(w http.ResponseWriter, r *http.Request) { ctx := r.Context() if r.Method == "CONNECT" { if envknob.GOOS() == "windows" { // For the GUI client when using an exit node. See docs on handleProxyConnectConn. s.handleProxyConnectConn(w, r) } else { http.Error(w, "bad method for platform", http.StatusMethodNotAllowed) } return } // Check for this method before the awaitBackend call, as it reports whether // the backend is available. if r.Method == "GET" && r.URL.Path == "/server-status" { s.serveServerStatus(w, r) return } lb, ok := s.awaitBackend(ctx) if !ok { // Almost certainly because the context was canceled so the response // here doesn't really matter. The client is gone. http.Error(w, "no backend", http.StatusServiceUnavailable) return } var ci *ipnauth.ConnIdentity switch v := r.Context().Value(connIdentityContextKey{}).(type) { case *ipnauth.ConnIdentity: ci = v case error: http.Error(w, v.Error(), http.StatusUnauthorized) return case nil: http.Error(w, "internal error: no connIdentityContextKey", http.StatusInternalServerError) return } onDone, err := s.addActiveHTTPRequest(r, ci) if err != nil { if ou, ok := err.(inUseOtherUserError); ok && localapi.InUseOtherUserIPNStream(w, r, ou.Unwrap()) { w.(http.Flusher).Flush() s.blockWhileIdentityInUse(ctx, ci) return } http.Error(w, err.Error(), http.StatusUnauthorized) return } defer onDone() if strings.HasPrefix(r.URL.Path, "/localapi/") { lah := localapi.NewHandler(lb, s.logf, s.netMon, s.backendLogID) lah.PermitRead, lah.PermitWrite = s.localAPIPermissions(ci) lah.PermitCert = s.connCanFetchCerts(ci) lah.CallerIsLocalAdmin = s.connIsLocalAdmin(ci) lah.ServeHTTP(w, r) return } if r.URL.Path != "/" { http.NotFound(w, r) return } if envknob.GOOS() == "windows" { // TODO(bradfitz): remove this once we moved to named pipes for LocalAPI // on Windows. This could then move to all platforms instead at // 100.100.100.100 or something (quad100 handler in LocalAPI) s.ServeHTMLStatus(w, r) return } io.WriteString(w, "Tailscale

Tailscale

This is the local Tailscale daemon.\n") } // inUseOtherUserError is the error type for when the server is in use // by a different local user. type inUseOtherUserError struct{ error } func (e inUseOtherUserError) Unwrap() error { return e.error } // checkConnIdentityLocked checks whether the provided identity is // allowed to connect to the server. // // The returned error, when non-nil, will be of type inUseOtherUserError. // // s.mu must be held. func (s *Server) checkConnIdentityLocked(ci *ipnauth.ConnIdentity) error { // If clients are already connected, verify they're the same user. // This mostly matters on Windows at the moment. if len(s.activeReqs) > 0 { var active *ipnauth.ConnIdentity for _, active = range s.activeReqs { break } if active != nil { chkTok, err := ci.WindowsToken() if err == nil { defer chkTok.Close() } else if !errors.Is(err, ipnauth.ErrNotImplemented) { return err } activeTok, err := active.WindowsToken() if err == nil { defer activeTok.Close() } else if !errors.Is(err, ipnauth.ErrNotImplemented) { return err } if chkTok != nil && !chkTok.EqualUIDs(activeTok) { var b strings.Builder b.WriteString("Tailscale already in use") if username, err := activeTok.Username(); err == nil { fmt.Fprintf(&b, " by %s", username) } fmt.Fprintf(&b, ", pid %d", active.Pid()) return inUseOtherUserError{errors.New(b.String())} } } } if err := s.mustBackend().CheckIPNConnectionAllowed(ci); err != nil { return inUseOtherUserError{err} } return nil } // blockWhileIdentityInUse blocks while ci can't connect to the server because // the server is in use by a different user. // // This is primarily used for the Windows GUI, to block until one user's done // controlling the tailscaled process. func (s *Server) blockWhileIdentityInUse(ctx context.Context, ci *ipnauth.ConnIdentity) error { inUse := func() bool { s.mu.Lock() defer s.mu.Unlock() _, ok := s.checkConnIdentityLocked(ci).(inUseOtherUserError) return ok } for inUse() { // Check whenever the connection count drops down to zero. ready, cleanup := s.zeroReqWaiter.add(&s.mu, ctx) <-ready cleanup() if err := ctx.Err(); err != nil { return err } } return nil } // localAPIPermissions returns the permissions for the given identity accessing // the Tailscale local daemon API. // // s.mu must not be held. func (s *Server) localAPIPermissions(ci *ipnauth.ConnIdentity) (read, write bool) { switch envknob.GOOS() { case "windows": s.mu.Lock() defer s.mu.Unlock() if s.checkConnIdentityLocked(ci) == nil { return true, true } return false, false case "js": return true, true } if ci.IsUnixSock() { return true, !ci.IsReadonlyConn(s.mustBackend().OperatorUserID(), logger.Discard) } return false, false } // userIDFromString maps from either a numeric user id in string form // ("998") or username ("caddy") to its string userid ("998"). // It returns the empty string on error. func userIDFromString(v string) string { if v == "" || isAllDigit(v) { return v } u, err := user.Lookup(v) if err != nil { return "" } return u.Uid } func isAllDigit(s string) bool { for i := 0; i < len(s); i++ { if b := s[i]; b < '0' || b > '9' { return false } } return true } // connCanFetchCerts reports whether ci is allowed to fetch HTTPS // certs from this server when it wouldn't otherwise be able to. // // That is, this reports whether ci should grant additional // capabilities over what the conn would otherwise be able to do. // // For now this only returns true on Unix machines when // TS_PERMIT_CERT_UID is set the to the userid of the peer // connection. It's intended to give your non-root webserver access // (www-data, caddy, nginx, etc) to certs. func (s *Server) connCanFetchCerts(ci *ipnauth.ConnIdentity) bool { if ci.IsUnixSock() && ci.Creds() != nil { connUID, ok := ci.Creds().UserID() if ok && connUID == userIDFromString(envknob.String("TS_PERMIT_CERT_UID")) { return true } } return false } // connIsLocalAdmin reports whether ci has administrative access to the local // machine, for whatever that means with respect to the current OS. // // This returns true only on Windows machines when the client user is a // member of the built-in Administrators group (but not necessarily elevated). // This is useful because, on Windows, tailscaled itself always runs with // elevated rights: we want to avoid privilege escalation for certain mutative operations. func (s *Server) connIsLocalAdmin(ci *ipnauth.ConnIdentity) bool { tok, err := ci.WindowsToken() if err != nil { if !errors.Is(err, ipnauth.ErrNotImplemented) { s.logf("ipnauth.ConnIdentity.WindowsToken() error: %v", err) } return false } defer tok.Close() isAdmin, err := tok.IsAdministrator() if err != nil { s.logf("ipnauth.WindowsToken.IsAdministrator() error: %v", err) return false } return isAdmin } // addActiveHTTPRequest adds c to the server's list of active HTTP requests. // // If the returned error may be of type inUseOtherUserError. // // onDone must be called when the HTTP request is done. func (s *Server) addActiveHTTPRequest(req *http.Request, ci *ipnauth.ConnIdentity) (onDone func(), err error) { if ci == nil { return nil, errors.New("internal error: nil connIdentity") } lb := s.mustBackend() // If the connected user changes, reset the backend server state to make // sure node keys don't leak between users. var doReset bool defer func() { if doReset { s.logf("identity changed; resetting server") lb.ResetForClientDisconnect() } }() s.mu.Lock() defer s.mu.Unlock() if err := s.checkConnIdentityLocked(ci); err != nil { return nil, err } mak.Set(&s.activeReqs, req, ci) if len(s.activeReqs) == 1 { token, err := ci.WindowsToken() if err != nil { if !errors.Is(err, ipnauth.ErrNotImplemented) { s.logf("error obtaining access token: %v", err) } } else { // Tell the LocalBackend about the identity we're now running as. uid, err := lb.SetCurrentUser(token) if err != nil { token.Close() return nil, err } if s.lastUserID != uid { if s.lastUserID != "" { doReset = true } s.lastUserID = uid } } } onDone = func() { s.mu.Lock() delete(s.activeReqs, req) remain := len(s.activeReqs) s.mu.Unlock() if remain == 0 && s.resetOnZero { if lb.InServerMode() { s.logf("client disconnected; staying alive in server mode") } else { s.logf("client disconnected; stopping server") lb.ResetForClientDisconnect() } } // Wake up callers waiting for the server to be idle: if remain == 0 { s.mu.Lock() s.zeroReqWaiter.wakeAll() s.mu.Unlock() } } return onDone, nil } // New returns a new Server. // // To start it, use the Server.Run method. // // At some point, either before or after Run, the Server's SetLocalBackend // method must also be called before Server can do anything useful. func New(logf logger.Logf, logID logid.PublicID, netMon *netmon.Monitor) *Server { if netMon == nil { panic("nil netMon") } return &Server{ backendLogID: logID, logf: logf, netMon: netMon, resetOnZero: envknob.GOOS() == "windows", } } // SetLocalBackend sets the server's LocalBackend. // // If b.Run has already been called, then lb.Start will be called. // Otherwise Start will be called once Run is called. func (s *Server) SetLocalBackend(lb *ipnlocal.LocalBackend) { if lb == nil { panic("nil LocalBackend") } if !s.lb.CompareAndSwap(nil, lb) { panic("already set") } s.startBackendIfNeeded() s.mu.Lock() s.backendWaiter.wakeAll() s.mu.Unlock() // TODO(bradfitz): send status update to GUI long poller waiter. See // https://github.com/tailscale/tailscale/issues/6522 } func (b *Server) startBackendIfNeeded() { if !b.runCalled.Load() { return } lb := b.lb.Load() if lb == nil { return } if lb.Prefs().Valid() { b.startBackendOnce.Do(func() { lb.Start(ipn.Options{}) }) } } // connIdentityContextKey is the http.Request.Context's context.Value key for either an // *ipnauth.ConnIdentity or an error. type connIdentityContextKey struct{} // Run runs the server, accepting connections from ln forever. // // If the context is done, the listener is closed. It is also the base context // of all HTTP requests. // // If the Server's LocalBackend has already been set, Run starts it. // Otherwise, the next call to SetLocalBackend will start it. func (s *Server) Run(ctx context.Context, ln net.Listener) error { s.runCalled.Store(true) defer func() { if lb := s.lb.Load(); lb != nil { lb.Shutdown() } }() runDone := make(chan struct{}) defer close(runDone) // When the context is closed or when we return, whichever is first, close our listener // and all open connections. go func() { select { case <-ctx.Done(): case <-runDone: } ln.Close() }() s.startBackendIfNeeded() systemd.Ready() hs := &http.Server{ Handler: http.HandlerFunc(s.serveHTTP), BaseContext: func(_ net.Listener) context.Context { return ctx }, ConnContext: func(ctx context.Context, c net.Conn) context.Context { ci, err := ipnauth.GetConnIdentity(s.logf, c) if err != nil { return context.WithValue(ctx, connIdentityContextKey{}, err) } return context.WithValue(ctx, connIdentityContextKey{}, ci) }, // Localhost connections are cheap; so only do // keep-alives for a short period of time, as these // active connections lock the server into only serving // that user. If the user has this page open, we don't // want another switching user to be locked out for // minutes. 5 seconds is enough to let browser hit // favicon.ico and such. IdleTimeout: 5 * time.Second, ErrorLog: logger.StdLogger(logger.WithPrefix(s.logf, "ipnserver: ")), } if err := hs.Serve(ln); err != nil { if err := ctx.Err(); err != nil { return err } return err } return nil } // ServeHTMLStatus serves an HTML status page at http://localhost:41112/ for // Windows and via $DEBUG_LISTENER/debug/ipn when tailscaled's --debug flag // is used to run a debug server. func (s *Server) ServeHTMLStatus(w http.ResponseWriter, r *http.Request) { lb := s.lb.Load() if lb == nil { http.Error(w, "no LocalBackend", http.StatusServiceUnavailable) return } // As this is only meant for debug, verify there's no DNS name being used to // access this. if !strings.HasPrefix(r.Host, "localhost:") && strings.IndexFunc(r.Host, unicode.IsLetter) != -1 { http.Error(w, "invalid host", http.StatusForbidden) return } w.Header().Set("Content-Security-Policy", `default-src 'none'; frame-ancestors 'none'; script-src 'none'; script-src-elem 'none'; script-src-attr 'none'`) w.Header().Set("X-Frame-Options", "DENY") w.Header().Set("X-Content-Type-Options", "nosniff") w.Header().Set("Content-Type", "text/html; charset=utf-8") st := lb.Status() // TODO(bradfitz): add LogID and opts to st? st.WriteHTML(w) }