noderestriction: restrict nodes TokenRequest permission

nodes should only be able to create TokenRequests if:
* token is bound to a pod
* binding has uid and name
* the pod exists
* the pod is running on that node

plugin/pkg/admission/noderestriction/BUILD

@@ -12,6 +12,7 @@ go_library(
     importpath = "k8s.io/kubernetes/plugin/pkg/admission/noderestriction",
     deps = [
         "//pkg/api/pod:go_default_library",
+        "//pkg/apis/authentication:go_default_library",
         "//pkg/apis/core:go_default_library",
         "//pkg/apis/policy:go_default_library",
         "//pkg/auth/nodeidentifier:go_default_library",
@@ -33,14 +34,18 @@ go_test(
     srcs = ["admission_test.go"],
     embed = [":go_default_library"],
     deps = [
+        "//pkg/apis/authentication:go_default_library",
         "//pkg/apis/core:go_default_library",
         "//pkg/apis/policy:go_default_library",
         "//pkg/auth/nodeidentifier:go_default_library",
         "//pkg/client/clientset_generated/internalclientset/fake:go_default_library",
         "//pkg/client/clientset_generated/internalclientset/typed/core/internalversion:go_default_library",
+        "//pkg/features:go_default_library",
         "//vendor/k8s.io/apimachinery/pkg/apis/meta/v1:go_default_library",
+        "//vendor/k8s.io/apimachinery/pkg/types:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/admission:go_default_library",
         "//vendor/k8s.io/apiserver/pkg/authentication/user:go_default_library",
+        "//vendor/k8s.io/apiserver/pkg/util/feature:go_default_library",
     ],
 )
 

plugin/pkg/admission/noderestriction/admission.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/apiserver/pkg/admission"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
 	podutil "k8s.io/kubernetes/pkg/api/pod"
+	authenticationapi "k8s.io/kubernetes/pkg/apis/authentication"
 	api "k8s.io/kubernetes/pkg/apis/core"
 	"k8s.io/kubernetes/pkg/apis/policy"
 	"k8s.io/kubernetes/pkg/auth/nodeidentifier"
@@ -53,6 +54,7 @@ func NewPlugin(nodeIdentifier nodeidentifier.NodeIdentifier) *nodePlugin {
 	return &nodePlugin{
 		Handler:        admission.NewHandler(admission.Create, admission.Update, admission.Delete),
 		nodeIdentifier: nodeIdentifier,
+		features:       utilfeature.DefaultFeatureGate,
 	}
 }
 
@@ -61,6 +63,8 @@ type nodePlugin struct {
 	*admission.Handler
 	nodeIdentifier nodeidentifier.NodeIdentifier
 	podsGetter     coreinternalversion.PodsGetter
+	// allows overriding for testing
+	features utilfeature.FeatureGate
 }
 
 var (
@@ -83,9 +87,10 @@ func (p *nodePlugin) ValidateInitialization() error {
 }
 
 var (
-	podResource  = api.Resource("pods")
-	nodeResource = api.Resource("nodes")
-	pvcResource  = api.Resource("persistentvolumeclaims")
+	podResource     = api.Resource("pods")
+	nodeResource    = api.Resource("nodes")
+	pvcResource     = api.Resource("persistentvolumeclaims")
+	svcacctResource = api.Resource("serviceaccounts")
 )
 
 func (c *nodePlugin) Admit(a admission.Attributes) error {
@@ -125,6 +130,12 @@ func (c *nodePlugin) Admit(a admission.Attributes) error {
 			return admission.NewForbidden(a, fmt.Errorf("may only update PVC status"))
 		}
 
+	case svcacctResource:
+		if c.features.Enabled(features.TokenRequest) {
+			return c.admitServiceAccount(nodeName, a)
+		}
+		return nil
+
 	default:
 		return nil
 	}
@@ -256,7 +267,7 @@ func (c *nodePlugin) admitPodEviction(nodeName string, a admission.Attributes) e
 func (c *nodePlugin) admitPVCStatus(nodeName string, a admission.Attributes) error {
 	switch a.GetOperation() {
 	case admission.Update:
-		if !utilfeature.DefaultFeatureGate.Enabled(features.ExpandPersistentVolumes) {
+		if !c.features.Enabled(features.ExpandPersistentVolumes) {
 			return admission.NewForbidden(a, fmt.Errorf("node %q may not update persistentvolumeclaim metadata", nodeName))
 		}
 
@@ -340,3 +351,44 @@ func (c *nodePlugin) admitNode(nodeName string, a admission.Attributes) error {
 
 	return nil
 }
+
+func (c *nodePlugin) admitServiceAccount(nodeName string, a admission.Attributes) error {
+	if a.GetOperation() != admission.Create {
+		return nil
+	}
+	if a.GetSubresource() != "token" {
+		return nil
+	}
+	tr, ok := a.GetObject().(*authenticationapi.TokenRequest)
+	if !ok {
+		return admission.NewForbidden(a, fmt.Errorf("unexpected type %T", a.GetObject()))
+	}
+
+	// TokenRequests from a node must have a pod binding. That pod must be
+	// scheduled on the node.
+	ref := tr.Spec.BoundObjectRef
+	if ref == nil ||
+		ref.APIVersion != "v1" ||
+		ref.Kind != "Pod" ||
+		ref.Name == "" {
+		return admission.NewForbidden(a, fmt.Errorf("node requested token not bound to a pod"))
+	}
+	if ref.UID == "" {
+		return admission.NewForbidden(a, fmt.Errorf("node requested token with a pod binding without a uid"))
+	}
+	pod, err := c.podsGetter.Pods(a.GetNamespace()).Get(ref.Name, v1.GetOptions{})
+	if errors.IsNotFound(err) {
+		return err
+	}
+	if err != nil {
+		return admission.NewForbidden(a, err)
+	}
+	if ref.UID != pod.UID {
+		return admission.NewForbidden(a, fmt.Errorf("the UID in the bound object reference (%s) does not match the UID in record (%s). The object might have been deleted and then recreated", ref.UID, pod.UID))
+	}
+	if pod.Spec.NodeName != nodeName {
+		return admission.NewForbidden(a, fmt.Errorf("node requested token bound to a pod scheduled on a different node"))
+	}
+
+	return nil
+}

plugin/pkg/admission/noderestriction/admission_test.go

@@ -21,18 +21,37 @@ import (
 	"testing"
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/types"
 	"k8s.io/apiserver/pkg/admission"
 	"k8s.io/apiserver/pkg/authentication/user"
+	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	authenticationapi "k8s.io/kubernetes/pkg/apis/authentication"
 	api "k8s.io/kubernetes/pkg/apis/core"
 	"k8s.io/kubernetes/pkg/apis/policy"
 	"k8s.io/kubernetes/pkg/auth/nodeidentifier"
 	"k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset/fake"
 	coreinternalversion "k8s.io/kubernetes/pkg/client/clientset_generated/internalclientset/typed/core/internalversion"
+	"k8s.io/kubernetes/pkg/features"
 )
 
+var (
+	trEnabledFeature  = utilfeature.NewFeatureGate()
+	trDisabledFeature = utilfeature.NewFeatureGate()
+)
+
+func init() {
+	if err := trEnabledFeature.Add(map[utilfeature.Feature]utilfeature.FeatureSpec{features.TokenRequest: {Default: true}}); err != nil {
+		panic(err)
+	}
+	if err := trDisabledFeature.Add(map[utilfeature.Feature]utilfeature.FeatureSpec{features.TokenRequest: {Default: false}}); err != nil {
+		panic(err)
+	}
+}
+
 func makeTestPod(namespace, name, node string, mirror bool) *api.Pod {
 	pod := &api.Pod{}
 	pod.Namespace = namespace
+	pod.UID = types.UID("pod-uid")
 	pod.Name = name
 	pod.Spec.NodeName = node
 	if mirror {
@@ -47,6 +66,23 @@ func makeTestPodEviction(name string) *policy.Eviction {
 	return eviction
 }
 
+func makeTokenRequest(podname string, poduid types.UID) *authenticationapi.TokenRequest {
+	tr := &authenticationapi.TokenRequest{
+		Spec: authenticationapi.TokenRequestSpec{
+			Audiences: []string{"foo"},
+		},
+	}
+	if podname != "" {
+		tr.Spec.BoundObjectRef = &authenticationapi.BoundObjectReference{
+			Kind:       "Pod",
+			APIVersion: "v1",
+			Name:       podname,
+			UID:        poduid,
+		}
+	}
+	return tr
+}
+
 func Test_nodePlugin_Admit(t *testing.T) {
 	var (
 		mynode = &user.DefaultInfo{Name: "system:node:mynode", Groups: []string{"system:nodes"}}
@@ -86,6 +122,9 @@ func Test_nodePlugin_Admit(t *testing.T) {
 		nodeResource = api.Resource("nodes").WithVersion("v1")
 		nodeKind     = api.Kind("Node").WithVersion("v1")
 
+		svcacctResource  = api.Resource("serviceaccounts").WithVersion("v1")
+		tokenrequestKind = api.Kind("TokenRequest").WithVersion("v1")
+
 		noExistingPods = fake.NewSimpleClientset().Core()
 		existingPods   = fake.NewSimpleClientset(mymirrorpod, othermirrorpod, unboundmirrorpod, mypod, otherpod, unboundpod).Core()
 	)
@@ -106,6 +145,7 @@ func Test_nodePlugin_Admit(t *testing.T) {
 		name       string
 		podsGetter coreinternalversion.PodsGetter
 		attributes admission.Attributes
+		features   utilfeature.FeatureGate
 		err        string
 	}{
 		// Mirror pods bound to us
@@ -653,6 +693,42 @@ func Test_nodePlugin_Admit(t *testing.T) {
 			err:        "cannot modify node",
 		},
 
+		// Service accounts
+		{
+			name:       "forbid create of unbound token",
+			podsGetter: noExistingPods,
+			features:   trEnabledFeature,
+			attributes: admission.NewAttributesRecord(makeTokenRequest("", ""), nil, tokenrequestKind, "ns", "mysa", svcacctResource, "token", admission.Create, mynode),
+			err:        "not bound to a pod",
+		},
+		{
+			name:       "forbid create of token bound to nonexistant pod",
+			podsGetter: noExistingPods,
+			features:   trEnabledFeature,
+			attributes: admission.NewAttributesRecord(makeTokenRequest("nopod", "someuid"), nil, tokenrequestKind, "ns", "mysa", svcacctResource, "token", admission.Create, mynode),
+			err:        "not found",
+		},
+		{
+			name:       "forbid create of token bound to pod without uid",
+			podsGetter: existingPods,
+			features:   trEnabledFeature,
+			attributes: admission.NewAttributesRecord(makeTokenRequest(mypod.Name, ""), nil, tokenrequestKind, "ns", "mysa", svcacctResource, "token", admission.Create, mynode),
+			err:        "pod binding without a uid",
+		},
+		{
+			name:       "forbid create of token bound to pod scheduled on another node",
+			podsGetter: existingPods,
+			features:   trEnabledFeature,
+			attributes: admission.NewAttributesRecord(makeTokenRequest(otherpod.Name, otherpod.UID), nil, tokenrequestKind, otherpod.Namespace, "mysa", svcacctResource, "token", admission.Create, mynode),
+			err:        "pod scheduled on a different node",
+		},
+		{
+			name:       "allow create of token bound to pod scheduled this node",
+			podsGetter: existingPods,
+			features:   trEnabledFeature,
+			attributes: admission.NewAttributesRecord(makeTokenRequest(mypod.Name, mypod.UID), nil, tokenrequestKind, mypod.Namespace, "mysa", svcacctResource, "token", admission.Create, mynode),
+		},
+
 		// Unrelated objects
 		{
 			name:       "allow create of unrelated object",
@@ -714,6 +790,9 @@ func Test_nodePlugin_Admit(t *testing.T) {
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			c := NewPlugin(nodeidentifier.NewDefaultNodeIdentifier())
+			if tt.features != nil {
+				c.features = tt.features
+			}
 			c.podsGetter = tt.podsGetter
 			err := c.Admit(tt.attributes)
 			if (err == nil) != (len(tt.err) == 0) {

test/integration/auth/node_test.go

@@ -448,6 +448,8 @@ func TestNodeAuthorizer(t *testing.T) {
 	defer utilfeaturetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.CSIPersistentVolume, true)()
 	expectForbidden(t, getVolumeAttachment(node1ClientExternal))
 	expectAllowed(t, getVolumeAttachment(node2ClientExternal))
+
+	//TODO(mikedanese): integration test node restriction of TokenRequest
 }
 
 // expect executes a function a set number of times until it either returns the