node_authorizer.go

/*
Copyright 2017 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package node

import (
	"context"
	"fmt"

	"k8s.io/klog/v2"

	rbacv1 "k8s.io/api/rbac/v1"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/apiserver/pkg/authentication/user"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	utilfeature "k8s.io/apiserver/pkg/util/feature"
	"k8s.io/component-base/featuregate"
	coordapi "k8s.io/kubernetes/pkg/apis/coordination"
	api "k8s.io/kubernetes/pkg/apis/core"
	storageapi "k8s.io/kubernetes/pkg/apis/storage"
	"k8s.io/kubernetes/pkg/auth/nodeidentifier"
	"k8s.io/kubernetes/pkg/features"
	"k8s.io/kubernetes/plugin/pkg/auth/authorizer/rbac"
	"k8s.io/kubernetes/third_party/forked/gonum/graph"
	"k8s.io/kubernetes/third_party/forked/gonum/graph/traverse"
)

// NodeAuthorizer authorizes requests from kubelets, with the following logic:
// 1. If a request is not from a node (NodeIdentity() returns isNode=false), reject
// 2. If a specific node cannot be identified (NodeIdentity() returns nodeName=""), reject
// 3. If a request is for a secret, configmap, persistent volume or persistent volume claim, reject unless the verb is get, and the requested object is related to the requesting node:
//    node <- configmap
//    node <- pod
//    node <- pod <- secret
//    node <- pod <- configmap
//    node <- pod <- pvc
//    node <- pod <- pvc <- pv
//    node <- pod <- pvc <- pv <- secret
// 4. For other resources, authorize all nodes uniformly using statically defined rules
type NodeAuthorizer struct {
	graph      *Graph
	identifier nodeidentifier.NodeIdentifier
	nodeRules  []rbacv1.PolicyRule

	// allows overriding for testing
	features featuregate.FeatureGate
}

var _ = authorizer.Authorizer(&NodeAuthorizer{})
var _ = authorizer.RuleResolver(&NodeAuthorizer{})

// NewAuthorizer returns a new node authorizer
func NewAuthorizer(graph *Graph, identifier nodeidentifier.NodeIdentifier, rules []rbacv1.PolicyRule) *NodeAuthorizer {
	return &NodeAuthorizer{
		graph:      graph,
		identifier: identifier,
		nodeRules:  rules,
		features:   utilfeature.DefaultFeatureGate,
	}
}

var (
	configMapResource = api.Resource("configmaps")
	secretResource    = api.Resource("secrets")
	pvcResource       = api.Resource("persistentvolumeclaims")
	pvResource        = api.Resource("persistentvolumes")
	vaResource        = storageapi.Resource("volumeattachments")
	svcAcctResource   = api.Resource("serviceaccounts")
	leaseResource     = coordapi.Resource("leases")
	csiNodeResource   = storageapi.Resource("csinodes")
)

func (r *NodeAuthorizer) RulesFor(user user.Info, namespace string) ([]authorizer.ResourceRuleInfo, []authorizer.NonResourceRuleInfo, bool, error) {
	if _, isNode := r.identifier.NodeIdentity(user); isNode {
		// indicate nodes do not have fully enumerated permissions
		return nil, nil, true, fmt.Errorf("node authorizer does not support user rule resolution")
	}
	return nil, nil, false, nil
}

func (r *NodeAuthorizer) Authorize(ctx context.Context, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	nodeName, isNode := r.identifier.NodeIdentity(attrs.GetUser())
	if !isNode {
		// reject requests from non-nodes
		return authorizer.DecisionNoOpinion, "", nil
	}
	if len(nodeName) == 0 {
		// reject requests from unidentifiable nodes
		klog.V(2).Infof("NODE DENY: unknown node for user %q", attrs.GetUser().GetName())
		return authorizer.DecisionNoOpinion, fmt.Sprintf("unknown node for user %q", attrs.GetUser().GetName()), nil
	}

	// subdivide access to specific resources
	if attrs.IsResourceRequest() {
		requestResource := schema.GroupResource{Group: attrs.GetAPIGroup(), Resource: attrs.GetResource()}
		switch requestResource {
		case secretResource:
			return r.authorizeReadNamespacedObject(nodeName, secretVertexType, attrs)
		case configMapResource:
			return r.authorizeReadNamespacedObject(nodeName, configMapVertexType, attrs)
		case pvcResource:
			if r.features.Enabled(features.ExpandPersistentVolumes) {
				if attrs.GetSubresource() == "status" {
					return r.authorizeStatusUpdate(nodeName, pvcVertexType, attrs)
				}
			}
			return r.authorizeGet(nodeName, pvcVertexType, attrs)
		case pvResource:
			return r.authorizeGet(nodeName, pvVertexType, attrs)
		case vaResource:
			return r.authorizeGet(nodeName, vaVertexType, attrs)
		case svcAcctResource:
			return r.authorizeCreateToken(nodeName, serviceAccountVertexType, attrs)
		case leaseResource:
			return r.authorizeLease(nodeName, attrs)
		case csiNodeResource:
			if r.features.Enabled(features.CSINodeInfo) {
				return r.authorizeCSINode(nodeName, attrs)
			}
			return authorizer.DecisionNoOpinion, fmt.Sprintf("disabled by feature gates %s", features.CSINodeInfo), nil
		}

	}

	// Access to other resources is not subdivided, so just evaluate against the statically defined node rules
	if rbac.RulesAllow(attrs, r.nodeRules...) {
		return authorizer.DecisionAllow, "", nil
	}
	return authorizer.DecisionNoOpinion, "", nil
}

// authorizeStatusUpdate authorizes get/update/patch requests to status subresources of the specified type if they are related to the specified node
func (r *NodeAuthorizer) authorizeStatusUpdate(nodeName string, startingType vertexType, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	switch attrs.GetVerb() {
	case "update", "patch":
		// ok
	default:
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only get/update/patch this type", nil
	}

	if attrs.GetSubresource() != "status" {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only update status subresource", nil
	}

	return r.authorize(nodeName, startingType, attrs)
}

// authorizeGet authorizes "get" requests to objects of the specified type if they are related to the specified node
func (r *NodeAuthorizer) authorizeGet(nodeName string, startingType vertexType, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	if attrs.GetVerb() != "get" {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only get individual resources of this type", nil
	}
	if len(attrs.GetSubresource()) > 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "cannot get subresource", nil
	}
	return r.authorize(nodeName, startingType, attrs)
}

// authorizeReadNamespacedObject authorizes "get", "list" and "watch" requests to single objects of a
// specified types if they are related to the specified node.
func (r *NodeAuthorizer) authorizeReadNamespacedObject(nodeName string, startingType vertexType, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	switch attrs.GetVerb() {
	case "get", "list", "watch":
		//ok
	default:
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only read resources of this type", nil
	}

	if len(attrs.GetSubresource()) > 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "cannot read subresource", nil
	}
	if len(attrs.GetNamespace()) == 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only read namespaced object of this type", nil
	}
	return r.authorize(nodeName, startingType, attrs)
}

func (r *NodeAuthorizer) authorize(nodeName string, startingType vertexType, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	if len(attrs.GetName()) == 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "No Object name found", nil
	}

	ok, err := r.hasPathFrom(nodeName, startingType, attrs.GetNamespace(), attrs.GetName())
	if err != nil {
		klog.V(2).InfoS("NODE DENY", "err", err)
		return authorizer.DecisionNoOpinion, fmt.Sprintf("no relationship found between node '%s' and this object", nodeName), nil
	}
	if !ok {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, fmt.Sprintf("no relationship found between node '%s' and this object", nodeName), nil
	}
	return authorizer.DecisionAllow, "", nil
}

// authorizeCreateToken authorizes "create" requests to serviceaccounts 'token'
// subresource of pods running on a node
func (r *NodeAuthorizer) authorizeCreateToken(nodeName string, startingType vertexType, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	if attrs.GetVerb() != "create" || len(attrs.GetName()) == 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only create tokens for individual service accounts", nil
	}

	if attrs.GetSubresource() != "token" {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only create token subresource of serviceaccount", nil
	}

	ok, err := r.hasPathFrom(nodeName, startingType, attrs.GetNamespace(), attrs.GetName())
	if err != nil {
		klog.V(2).Infof("NODE DENY: %v", err)
		return authorizer.DecisionNoOpinion, fmt.Sprintf("no relationship found between node '%s' and this object", nodeName), nil
	}
	if !ok {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, fmt.Sprintf("no relationship found between node '%s' and this object", nodeName), nil
	}
	return authorizer.DecisionAllow, "", nil
}

// authorizeLease authorizes node requests to coordination.k8s.io/leases.
func (r *NodeAuthorizer) authorizeLease(nodeName string, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	// allowed verbs: get, create, update, patch, delete
	verb := attrs.GetVerb()
	switch verb {
	case "get", "create", "update", "patch", "delete":
		//ok
	default:
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only get, create, update, patch, or delete a node lease", nil
	}

	// the request must be against the system namespace reserved for node leases
	if attrs.GetNamespace() != api.NamespaceNodeLease {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, fmt.Sprintf("can only access leases in the %q system namespace", api.NamespaceNodeLease), nil
	}

	// the request must come from a node with the same name as the lease
	// note we skip this check for create, since the authorizer doesn't know the name on create
	// the noderestriction admission plugin is capable of performing this check at create time
	if verb != "create" && attrs.GetName() != nodeName {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only access node lease with the same name as the requesting node", nil
	}

	return authorizer.DecisionAllow, "", nil
}

// authorizeCSINode authorizes node requests to CSINode storage.k8s.io/csinodes
func (r *NodeAuthorizer) authorizeCSINode(nodeName string, attrs authorizer.Attributes) (authorizer.Decision, string, error) {
	// allowed verbs: get, create, update, patch, delete
	verb := attrs.GetVerb()
	switch verb {
	case "get", "create", "update", "patch", "delete":
		//ok
	default:
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only get, create, update, patch, or delete a CSINode", nil
	}

	if len(attrs.GetSubresource()) > 0 {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "cannot authorize CSINode subresources", nil
	}

	// the request must come from a node with the same name as the CSINode
	// note we skip this check for create, since the authorizer doesn't know the name on create
	// the noderestriction admission plugin is capable of performing this check at create time
	if verb != "create" && attrs.GetName() != nodeName {
		klog.V(2).Infof("NODE DENY: '%s' %#v", nodeName, attrs)
		return authorizer.DecisionNoOpinion, "can only access CSINode with the same name as the requesting node", nil
	}

	return authorizer.DecisionAllow, "", nil
}

// hasPathFrom returns true if there is a directed path from the specified type/namespace/name to the specified Node
func (r *NodeAuthorizer) hasPathFrom(nodeName string, startingType vertexType, startingNamespace, startingName string) (bool, error) {
	r.graph.lock.RLock()
	defer r.graph.lock.RUnlock()

	nodeVertex, exists := r.graph.getVertex_rlocked(nodeVertexType, "", nodeName)
	if !exists {
		return false, fmt.Errorf("unknown node '%s' cannot get %s %s/%s", nodeName, vertexTypes[startingType], startingNamespace, startingName)
	}

	startingVertex, exists := r.graph.getVertex_rlocked(startingType, startingNamespace, startingName)
	if !exists {
		return false, fmt.Errorf("node '%s' cannot get unknown %s %s/%s", nodeName, vertexTypes[startingType], startingNamespace, startingName)
	}

	// Fast check to see if we know of a destination edge
	if r.graph.destinationEdgeIndex[startingVertex.ID()].has(nodeVertex.ID()) {
		return true, nil
	}

	found := false
	traversal := &traverse.VisitingDepthFirst{
		EdgeFilter: func(edge graph.Edge) bool {
			if destinationEdge, ok := edge.(*destinationEdge); ok {
				if destinationEdge.DestinationID() != nodeVertex.ID() {
					// Don't follow edges leading to other nodes
					return false
				}
				// We found an edge leading to the node we want
				found = true
			}
			// Visit this edge
			return true
		},
	}
	traversal.Walk(r.graph.graph, startingVertex, func(n graph.Node) bool {
		if n.ID() == nodeVertex.ID() {
			// We found the node we want
			found = true
		}
		// Stop visiting if we've found the node we want
		return found
	})
	if !found {
		return false, fmt.Errorf("node '%s' cannot get %s %s/%s, no relationship to this object was found in the node authorizer graph", nodeName, vertexTypes[startingType], startingNamespace, startingName)
	}
	return true, nil
}