cmd/k8s-operator: remove auth key once proxy has logged in (#13612)

The operator creates a non-reusable auth key for each of
the cluster proxies that it creates and puts in the tailscaled
configfile mounted to the proxies.
The proxies are always tagged, and their state is persisted
in a Kubernetes Secret, so their node keys are expected to never
be regenerated, so that they don't need to re-auth.

Some tailnet configurations however have seen issues where the auth
keys being left in the tailscaled configfile cause the proxies
to end up in unauthorized state after a restart at a later point
in time.
Currently, we have not found a way to reproduce this issue,
however this commit removes the auth key from the config once
the proxy can be assumed to have logged in.

If an existing, logged-in proxy is upgraded to this version,
its redundant auth key will be removed from the conffile.

If an existing, logged-in proxy is downgraded from this version
to a previous version, it will work as before without re-issuing key
as the previous code did not enforce that a key must be present.

Updates tailscale/tailscale#13451

Signed-off-by: Irbe Krumina <irbe@tailscale.com>

cmd/k8s-operator/operator_test.go

@@ -1487,6 +1487,72 @@ func Test_clusterDomainFromResolverConf(t *testing.T) {
 		})
 	}
 }
+func Test_authKeyRemoval(t *testing.T) {
+	fc := fake.NewFakeClient()
+	ft := &fakeTSClient{}
+	zl, err := zap.NewDevelopment()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// 1. A new Service that should be exposed via Tailscale gets created, a Secret with a config that contains auth
+	// key is generated.
+	clock := tstest.NewClock(tstest.ClockOpts{})
+	sr := &ServiceReconciler{
+		Client: fc,
+		ssr: &tailscaleSTSReconciler{
+			Client:            fc,
+			tsClient:          ft,
+			defaultTags:       []string{"tag:k8s"},
+			operatorNamespace: "operator-ns",
+			proxyImage:        "tailscale/tailscale",
+		},
+		logger: zl.Sugar(),
+		clock:  clock,
+	}
+
+	mustCreate(t, fc, &corev1.Service{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:      "test",
+			Namespace: "default",
+			UID:       types.UID("1234-UID"),
+		},
+		Spec: corev1.ServiceSpec{
+			ClusterIP:         "10.20.30.40",
+			Type:              corev1.ServiceTypeLoadBalancer,
+			LoadBalancerClass: ptr.To("tailscale"),
+		},
+	})
+
+	expectReconciled(t, sr, "default", "test")
+
+	fullName, shortName := findGenName(t, fc, "default", "test", "svc")
+	opts := configOpts{
+		stsName:         shortName,
+		secretName:      fullName,
+		namespace:       "default",
+		parentType:      "svc",
+		hostname:        "default-test",
+		clusterTargetIP: "10.20.30.40",
+		app:             kubetypes.AppIngressProxy,
+	}
+
+	expectEqual(t, fc, expectedSecret(t, fc, opts), nil)
+	expectEqual(t, fc, expectedHeadlessService(shortName, "svc"), nil)
+	expectEqual(t, fc, expectedSTS(t, fc, opts), removeHashAnnotation)
+
+	// 2. Apply update to the Secret that imitates the proxy setting device_id.
+	s := expectedSecret(t, fc, opts)
+	mustUpdate(t, fc, s.Namespace, s.Name, func(s *corev1.Secret) {
+		mak.Set(&s.Data, "device_id", []byte("dkkdi4CNTRL"))
+	})
+
+	// 3. Config should no longer contain auth key
+	expectReconciled(t, sr, "default", "test")
+	opts.shouldRemoveAuthKey = true
+	opts.secretExtraData = map[string][]byte{"device_id": []byte("dkkdi4CNTRL")}
+	expectEqual(t, fc, expectedSecret(t, fc, opts), nil)
+}
 
 func Test_externalNameService(t *testing.T) {
 	fc := fake.NewFakeClient()

cmd/k8s-operator/sts.go

@@ -821,11 +821,25 @@ func tailscaledConfig(stsC *tailscaleSTSConfig, newAuthkey string, oldSecret *co
 
 	if newAuthkey != "" {
 		conf.AuthKey = &newAuthkey
-	} else if oldSecret != nil {
-		var err error
+	} else if shouldRetainAuthKey(oldSecret) {
+		key, err := authKeyFromSecret(oldSecret)
+		if err != nil {
+			return nil, fmt.Errorf("error retrieving auth key from Secret: %w", err)
+		}
+		conf.AuthKey = key
+	}
+	capVerConfigs := make(map[tailcfg.CapabilityVersion]ipn.ConfigVAlpha)
+	capVerConfigs[95] = *conf
+	// legacy config should not contain NoStatefulFiltering field.
+	conf.NoStatefulFiltering.Clear()
+	capVerConfigs[94] = *conf
+	return capVerConfigs, nil
+}
+
+func authKeyFromSecret(s *corev1.Secret) (key *string, err error) {
 	latest := tailcfg.CapabilityVersion(-1)
 	latestStr := ""
-		for k, data := range oldSecret.Data {
+	for k, data := range s.Data {
 		// write to StringData, read from Data as StringData is write-only
 		if len(data) == 0 {
 			continue
@@ -843,18 +857,18 @@ func tailscaledConfig(stsC *tailscaleSTSConfig, newAuthkey string, oldSecret *co
 	// users have some mechanisms to delete them. Auth key is
 	// normally not needed after the initial login.
 	if latestStr != "" {
-			conf.AuthKey, err = readAuthKey(oldSecret, latestStr)
-			if err != nil {
-				return nil, err
+		return readAuthKey(s, latestStr)
 	}
+	return key, nil
 }
+
+// shouldRetainAuthKey returns true if the state stored in a proxy's state Secret suggests that auth key should be
+// retained (because the proxy has not yet successfully authenticated).
+func shouldRetainAuthKey(s *corev1.Secret) bool {
+	if s == nil {
+		return false // nothing to retain here
 	}
-	capVerConfigs := make(map[tailcfg.CapabilityVersion]ipn.ConfigVAlpha)
-	capVerConfigs[95] = *conf
-	// legacy config should not contain NoStatefulFiltering field.
-	conf.NoStatefulFiltering.Clear()
-	capVerConfigs[94] = *conf
-	return capVerConfigs, nil
+	return len(s.Data["device_id"]) == 0 // proxy has not authed yet
 }
 
 func shouldAcceptRoutes(pc *tsapi.ProxyClass) bool {

cmd/k8s-operator/testutils_test.go

@@ -53,6 +53,8 @@ type configOpts struct {
 	shouldEnableForwardingClusterTrafficViaIngress bool
 	proxyClass                                     string // configuration from the named ProxyClass should be applied to proxy resources
 	app                                            string
+	shouldRemoveAuthKey                            bool
+	secretExtraData                                map[string][]byte
 }
 
 func expectedSTS(t *testing.T, cl client.Client, opts configOpts) *appsv1.StatefulSet {
@@ -365,6 +367,9 @@ func expectedSecret(t *testing.T, cl client.Client, opts configOpts) *corev1.Sec
 			conf.AcceptRoutes = "true"
 		}
 	}
+	if opts.shouldRemoveAuthKey {
+		conf.AuthKey = nil
+	}
 	var routes []netip.Prefix
 	if opts.subnetRoutes != "" || opts.isExitNode {
 		r := opts.subnetRoutes
@@ -405,6 +410,9 @@ func expectedSecret(t *testing.T, cl client.Client, opts configOpts) *corev1.Sec
 		labels["tailscale.com/parent-resource-ns"] = "" // Connector is cluster scoped
 	}
 	s.Labels = labels
+	for key, val := range opts.secretExtraData {
+		mak.Set(&s.Data, key, val)
+	}
 	return s
 }