client/web: add some security checks for full client

Require that requests to servers in manage mode are made to the
Tailscale IP (either ipv4 or ipv6) or quad-100. Also set various
security headers on those responses.  These might be too restrictive,
but we can relax them as needed.

Allow requests to /ok (even in manage mode) with no checks. This will be
used for the connectivity check from a login client to see if the
management client is reachable.

Updates tailscale/corp#14335

Signed-off-by: Will Norris <will@tailscale.com>

client/web/web.go

@@ -29,12 +29,17 @@
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/licenses"
 	"tailscale.com/net/netutil"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/util/httpm"
 	"tailscale.com/version/distro"
 )
 
+// ListenPort is the static port used for the web client when run inside tailscaled.
+// (5252 are the numbers above the letters "TSTS" on a qwerty keyboard.)
+const ListenPort = 5252
+
 // Server is the backend server for a Tailscale web client.
 type Server struct {
 	mode ServerMode
@@ -202,6 +207,24 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Server) serve(w http.ResponseWriter, r *http.Request) {
+	if s.mode == ManageServerMode {
+		// In manage mode, requests must be sent directly to the bare Tailscale IP address.
+		// If a request comes in on any other hostname, redirect.
+		if s.requireTailscaleIP(w, r) {
+			return // user was redirected
+		}
+
+		// serve HTTP 204 on /ok requests as connectivity check
+		if r.Method == httpm.GET && r.URL.Path == "/ok" {
+			w.WriteHeader(http.StatusNoContent)
+			return
+		}
+
+		w.Header().Set("X-Frame-Options", "DENY")
+		w.Header().Set("Content-Security-Policy", "default-src 'self'")
+		w.Header().Set("Cross-Origin-Resource-Policy", "same-origin")
+	}
+
 	if strings.HasPrefix(r.URL.Path, "/api/") {
 		switch {
 		case r.URL.Path == "/api/auth" && r.Method == httpm.GET:
@@ -228,6 +251,45 @@ func (s *Server) serve(w http.ResponseWriter, r *http.Request) {
 	s.assetsHandler.ServeHTTP(w, r)
 }
 
+// requireTailscaleIP redirects an incoming request if the HTTP request was not made to a bare Tailscale IP address.
+// The request will be redirected to the Tailscale IP, port 5252, with the original request path.
+// This allows any custom hostname to be used to access the device, but protects against DNS rebinding attacks.
+// Returns true if the request has been fully handled, either be returning a redirect or an HTTP error.
+func (s *Server) requireTailscaleIP(w http.ResponseWriter, r *http.Request) (handled bool) {
+	const (
+		ipv4ServiceHost = tsaddr.TailscaleServiceIPString
+		ipv6ServiceHost = "[" + tsaddr.TailscaleServiceIPv6String + "]"
+	)
+	// allow requests on quad-100 (or ipv6 equivalent)
+	if r.URL.Host == ipv4ServiceHost || r.URL.Host == ipv6ServiceHost {
+		return false
+	}
+
+	st, err := s.lc.StatusWithoutPeers(r.Context())
+	if err != nil {
+		s.logf("error getting status: %v", err)
+		http.Error(w, "internal error", http.StatusInternalServerError)
+		return true
+	}
+
+	var ipv4 string // store the first IPv4 address we see for redirect later
+	for _, ip := range st.Self.TailscaleIPs {
+		if ip.Is4() {
+			if r.Host == fmt.Sprintf("%s:%d", ip, ListenPort) {
+				return false
+			}
+			ipv4 = ip.String()
+		}
+		if ip.Is6() && r.Host == fmt.Sprintf("[%s]:%d", ip, ListenPort) {
+			return false
+		}
+	}
+	newURL := *r.URL
+	newURL.Host = fmt.Sprintf("%s:%d", ipv4, ListenPort)
+	http.Redirect(w, r, newURL.String(), http.StatusMovedPermanently)
+	return true
+}
+
 // authorizeRequest reports whether the request from the web client
 // is authorized to be completed.
 // It reports true if the request is authorized, and false otherwise.

client/web/web_test.go

@@ -10,6 +10,7 @@
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"net/netip"
 	"net/url"
 	"strings"
 	"testing"
@@ -410,7 +411,11 @@ func() *ipnstate.PeerStatus { return self },
 
 func TestServeAuth(t *testing.T) {
 	user := &tailcfg.UserProfile{ID: tailcfg.UserID(1)}
-	self := &ipnstate.PeerStatus{ID: "self", UserID: user.ID}
+	self := &ipnstate.PeerStatus{
+		ID:           "self",
+		UserID:       user.ID,
+		TailscaleIPs: []netip.Addr{netip.MustParseAddr("100.1.2.3")},
+	}
 	remoteNode := &apitype.WhoIsResponse{Node: &tailcfg.Node{ID: 1}, UserProfile: user}
 	remoteIP := "100.100.100.101"
 
@@ -605,7 +610,7 @@ func() *ipnstate.PeerStatus { return self },
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			r := httptest.NewRequest("GET", tt.path, nil)
+			r := httptest.NewRequest("GET", "http://100.1.2.3:5252"+tt.path, nil)
 			r.RemoteAddr = remoteIP
 			r.AddCookie(&http.Cookie{Name: sessionCookieName, Value: tt.cookie})
 			w := httptest.NewRecorder()
@@ -663,6 +668,92 @@ func() *ipnstate.PeerStatus { return self },
 	}
 }
 
+func TestRequireTailscaleIP(t *testing.T) {
+	self := &ipnstate.PeerStatus{
+		TailscaleIPs: []netip.Addr{
+			netip.MustParseAddr("100.1.2.3"),
+			netip.MustParseAddr("fd7a:115c::1234"),
+		},
+	}
+
+	lal := memnet.Listen("local-tailscaled.sock:80")
+	defer lal.Close()
+	localapi := mockLocalAPI(t, nil, func() *ipnstate.PeerStatus { return self })
+	defer localapi.Close()
+	go localapi.Serve(lal)
+
+	s := &Server{
+		mode:    ManageServerMode,
+		lc:      &tailscale.LocalClient{Dial: lal.Dial},
+		timeNow: time.Now,
+		logf:    t.Logf,
+	}
+
+	tests := []struct {
+		name         string
+		target       string
+		wantHandled  bool
+		wantLocation string
+	}{
+		{
+			name:         "localhost",
+			target:       "http://localhost/",
+			wantHandled:  true,
+			wantLocation: "http://100.1.2.3:5252/",
+		},
+		{
+			name:         "ipv4-no-port",
+			target:       "http://100.1.2.3/",
+			wantHandled:  true,
+			wantLocation: "http://100.1.2.3:5252/",
+		},
+		{
+			name:        "ipv4-correct-port",
+			target:      "http://100.1.2.3:5252/",
+			wantHandled: false,
+		},
+		{
+			name:         "ipv6-no-port",
+			target:       "http://[fd7a:115c::1234]/",
+			wantHandled:  true,
+			wantLocation: "http://100.1.2.3:5252/",
+		},
+		{
+			name:        "ipv6-correct-port",
+			target:      "http://[fd7a:115c::1234]:5252/",
+			wantHandled: false,
+		},
+		{
+			name:        "quad-100",
+			target:      "http://100.100.100.100/",
+			wantHandled: false,
+		},
+		{
+			name:        "ipv6-service-addr",
+			target:      "http://[fd7a:115c:a1e0::53]/",
+			wantHandled: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.target, func(t *testing.T) {
+			s.logf = t.Logf
+			r := httptest.NewRequest(httpm.GET, tt.target, nil)
+			w := httptest.NewRecorder()
+			handled := s.requireTailscaleIP(w, r)
+
+			if handled != tt.wantHandled {
+				t.Errorf("request(%q) was handled; want=%v, got=%v", tt.target, tt.wantHandled, handled)
+			}
+
+			location := w.Header().Get("Location")
+			if location != tt.wantLocation {
+				t.Errorf("request(%q) wrong location; want=%q, got=%q", tt.target, tt.wantLocation, location)
+			}
+		})
+	}
+}
+
 var (
 	testControlURL      = "http://localhost:8080"
 	testAuthPath        = "/a/12345"

ipn/ipnlocal/local.go

@@ -3132,7 +3132,7 @@ func (b *LocalBackend) TCPHandlerForDst(src, dst netip.AddrPort) (handler func(c
 		return b.handleSSHConn, opts
 	}
 	// TODO(will,sonia): allow customizing web client port ?
-	if dst.Port() == 5252 && b.ShouldRunWebClient() {
+	if dst.Port() == webClientPort && b.ShouldRunWebClient() {
 		return b.handleWebClientConn, opts
 	}
 	if port, ok := b.GetPeerAPIPort(dst.Addr()); ok && dst.Port() == port {
@@ -4474,7 +4474,7 @@ func (b *LocalBackend) setTCPPortsInterceptedFromNetmapAndPrefsLocked(prefs ipn.
 		handlePorts = append(handlePorts, 22)
 	}
 	if b.ShouldRunWebClient() {
-		handlePorts = append(handlePorts, 5252)
+		handlePorts = append(handlePorts, webClientPort)
 	}
 
 	b.reloadServeConfigLocked(prefs)

ipn/ipnlocal/web_client.go

@@ -16,6 +16,8 @@
 	"tailscale.com/net/netutil"
 )
 
+const webClientPort = web.ListenPort
+
 // webClient holds state for the web interface for managing
 // this tailscale instance. The web interface is not used by
 // default, but initialized by calling LocalBackend.WebOrInit.

ipn/ipnlocal/web_client_stub.go

@@ -12,6 +12,8 @@
 	"tailscale.com/client/tailscale"
 )
 
+const webClientPort = 5252
+
 type webClient struct{}
 
 func (b *LocalBackend) SetWebLocalClient(lc *tailscale.LocalClient) {}