add agentcsrapproving controller to auto approve agent csr

cmd/controller-manager/app/controllermanager.go

@@ -51,6 +51,7 @@ import (
 	"github.com/karmada-io/karmada/pkg/clusterdiscovery/clusterapi"
 	"github.com/karmada-io/karmada/pkg/controllers/applicationfailover"
 	"github.com/karmada-io/karmada/pkg/controllers/binding"
+	"github.com/karmada-io/karmada/pkg/controllers/certificate/approver"
 	"github.com/karmada-io/karmada/pkg/controllers/cluster"
 	controllerscontext "github.com/karmada-io/karmada/pkg/controllers/context"
 	"github.com/karmada-io/karmada/pkg/controllers/cronfederatedhpa"
@@ -209,7 +210,7 @@ func Run(ctx context.Context, opts *options.Options) error {
 var controllers = make(controllerscontext.Initializers)
 
 // controllersDisabledByDefault is the set of controllers which is disabled by default
-var controllersDisabledByDefault = sets.New("hpaScaleTargetMarker", "deploymentReplicasSyncer")
+var controllersDisabledByDefault = sets.New("hpaScaleTargetMarker", "deploymentReplicasSyncer", "agentcsrapproving")
 
 func init() {
 	controllers["cluster"] = startClusterController
@@ -236,6 +237,7 @@ func init() {
 	controllers["endpointsliceDispatch"] = startEndpointSliceDispatchController
 	controllers["remedy"] = startRemedyController
 	controllers["workloadRebalancer"] = startWorkloadRebalancerController
+	controllers["agentcsrapproving"] = startAgentCSRApprovingController
 }
 
 func startClusterController(ctx controllerscontext.Context) (enabled bool, err error) {
@@ -723,6 +725,15 @@ func startWorkloadRebalancerController(ctx controllerscontext.Context) (enabled
 	return true, nil
 }
 
+func startAgentCSRApprovingController(ctx controllerscontext.Context) (enabled bool, err error) {
+	agentCSRApprover := approver.AgentCSRApprovingController{Client: ctx.KubeClientSet}
+	err = agentCSRApprover.SetupWithManager(ctx.Mgr)
+	if err != nil {
+		return false, err
+	}
+	return true, nil
+}
+
 // setupControllers initialize controllers and setup one by one.
 func setupControllers(mgr controllerruntime.Manager, opts *options.Options, stopChan <-chan struct{}) {
 	restConfig := mgr.GetConfig()

pkg/controllers/certificate/approver/agent_csr_approving.go

@@ -0,0 +1,293 @@
+/*
+Copyright 2024 The Karmada 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 approver
+
+import (
+	"context"
+	"crypto/x509"
+	"fmt"
+	"reflect"
+	"strings"
+
+	authorizationv1 "k8s.io/api/authorization/v1"
+	certificatesv1 "k8s.io/api/certificates/v1"
+	corev1 "k8s.io/api/core/v1"
+	apierrors "k8s.io/apimachinery/pkg/api/errors"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"k8s.io/apimachinery/pkg/util/sets"
+	"k8s.io/client-go/kubernetes"
+	"k8s.io/klog/v2"
+	controllerruntime "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/builder"
+	"sigs.k8s.io/controller-runtime/pkg/event"
+	"sigs.k8s.io/controller-runtime/pkg/predicate"
+
+	"github.com/karmada-io/karmada/pkg/util/certificate"
+)
+
+const (
+	csrApprovingController = "agent-csr-approving-controller"
+	agentCSRGroup          = "system:karmada:agents"
+	agentCSRUserPrefix     = "system:karmada:agent:"
+)
+
+// AgentCSRApprovingController is used to automatically approve the agent's CSR.
+type AgentCSRApprovingController struct {
+	Client kubernetes.Interface
+}
+
+// Reconcile performs a full reconciliation for the object referred to by the Request.
+// The Controller will requeue the Request to be processed again if an error is non-nil or
+// Result.Requeue is true, otherwise upon completion it will remove the work from the queue.
+func (a *AgentCSRApprovingController) Reconcile(ctx context.Context, req controllerruntime.Request) (controllerruntime.Result, error) {
+	klog.V(4).Infof("Reconciling for CertificateSigningRequest %s", req.Name)
+
+	// 1. get latest CertificateSigningRequest
+	var csr *certificatesv1.CertificateSigningRequest
+	var err error
+	if csr, err = a.Client.CertificatesV1().CertificateSigningRequests().Get(ctx, req.Name, metav1.GetOptions{}); err != nil {
+		if apierrors.IsNotFound(err) {
+			klog.Infof("no need to reconcile CertificateSigningRequest %s for it not found", req.Name)
+			return controllerruntime.Result{}, nil
+		}
+		return controllerruntime.Result{}, err
+	}
+
+	if csr.DeletionTimestamp != nil {
+		klog.Infof("no need to reconcile CertificateSigningRequest %s for it has been deleted", csr.Name)
+		return controllerruntime.Result{}, nil
+	}
+
+	// 2. auto approve csr if it is an agent csr and passes authentication.
+	err = a.handleCertificateSigningRequest(ctx, csr)
+	if err != nil {
+		return controllerruntime.Result{}, err
+	}
+
+	return controllerruntime.Result{}, nil
+}
+
+func (a *AgentCSRApprovingController) handleCertificateSigningRequest(ctx context.Context, csr *certificatesv1.CertificateSigningRequest) error {
+	if len(csr.Status.Certificate) != 0 {
+		return nil
+	}
+	if approved, denied := certificate.GetCertApprovalCondition(&csr.Status); approved || denied {
+		return nil
+	}
+	x509cr, err := certificate.ParseCSR(csr.Spec.Request)
+	if err != nil {
+		return fmt.Errorf("unable to parse csr %q: %v", csr.Name, err)
+	}
+	var tried []string
+
+	for _, r := range agentCSRRecognizers() {
+		if !r.recognize(csr, x509cr) {
+			continue
+		}
+
+		tried = append(tried, r.permission.Subresource)
+
+		approved, err := a.authorize(ctx, csr, r.permission)
+		if err != nil {
+			return err
+		}
+		if approved {
+			appendApprovalCondition(csr, r.successMessage)
+			_, err = a.Client.CertificatesV1().CertificateSigningRequests().UpdateApproval(ctx, csr.Name, csr, metav1.UpdateOptions{})
+			if err != nil {
+				return fmt.Errorf("error updating approval for csr %s: %v", csr.Name, err)
+			}
+			return nil
+		}
+	}
+
+	if len(tried) != 0 {
+		klog.Warningf("recognized csr %q as %v but subject access review was not approved", csr.Name, tried)
+	}
+
+	return nil
+}
+
+func (a *AgentCSRApprovingController) authorize(ctx context.Context, csr *certificatesv1.CertificateSigningRequest, rattrs authorizationv1.ResourceAttributes) (bool, error) {
+	extra := make(map[string]authorizationv1.ExtraValue)
+	for k, v := range csr.Spec.Extra {
+		extra[k] = authorizationv1.ExtraValue(v)
+	}
+
+	sar := &authorizationv1.SubjectAccessReview{
+		Spec: authorizationv1.SubjectAccessReviewSpec{
+			User:               csr.Spec.Username,
+			UID:                csr.Spec.UID,
+			Groups:             csr.Spec.Groups,
+			Extra:              extra,
+			ResourceAttributes: &rattrs,
+		},
+	}
+	sar, err := a.Client.AuthorizationV1().SubjectAccessReviews().Create(ctx, sar, metav1.CreateOptions{})
+	if err != nil {
+		return false, err
+	}
+	return sar.Status.Allowed, nil
+}
+
+func isIssuedByKubeAPIServerClientSigner(csr *certificatesv1.CertificateSigningRequest) bool {
+	return csr.Spec.SignerName == certificatesv1.KubeAPIServerClientSignerName
+}
+
+// csrRecognizer used to identify whether the CSRs is the target CSRs and to perform authentication.
+type csrRecognizer struct {
+	// recognize identifies whether the CSRs is the target CSRs
+	recognize func(csr *certificatesv1.CertificateSigningRequest, x509cr *x509.CertificateRequest) bool
+	// permission used to indicate the permissions required for auto csr approving.
+	permission authorizationv1.ResourceAttributes
+	// successMessage contains a human-readable message with details if auto csr approving is successful.
+	successMessage string
+}
+
+// agentCSRRecognizers used to identify whether the CSRs is the agent CSRs and to perform authentication.
+func agentCSRRecognizers() []csrRecognizer {
+	recognizers := []csrRecognizer{
+		{
+			recognize:      isSelfAgentCSR,
+			permission:     authorizationv1.ResourceAttributes{Group: "certificates.k8s.io", Resource: "certificatesigningrequests", Verb: "create", Subresource: "selfclusteragent", Version: "*"},
+			successMessage: "Auto approving self karmada agent certificate after SubjectAccessReview.",
+		},
+		{
+			recognize:      isAgentCSR,
+			permission:     authorizationv1.ResourceAttributes{Group: "certificates.k8s.io", Resource: "certificatesigningrequests", Verb: "create", Subresource: "clusteragent", Version: "*"},
+			successMessage: "Auto approving karmada agent certificate after SubjectAccessReview.",
+		},
+	}
+	return recognizers
+}
+
+func appendApprovalCondition(csr *certificatesv1.CertificateSigningRequest, message string) {
+	csr.Status.Conditions = append(csr.Status.Conditions, certificatesv1.CertificateSigningRequestCondition{
+		Type:    certificatesv1.CertificateApproved,
+		Status:  corev1.ConditionTrue,
+		Reason:  "AutoApproved",
+		Message: message,
+	})
+}
+
+// isAgentCSR determines if the provided csr is an agent csr.
+// Agent csr is created for karmada-agent by bootstrap token during the cluster registering process.
+// The 'signer' field must be set to "kubernetes.io/kube-apiserver-client".
+// The 'Organization' field in the CertificateRequest must be "system:agents".
+// The 'CommonName' must be prefixed with "system:agent:".
+func isAgentCSR(csr *certificatesv1.CertificateSigningRequest, x509cr *x509.CertificateRequest) bool {
+	if csr.Spec.SignerName != certificatesv1.KubeAPIServerClientSignerName {
+		return false
+	}
+
+	return ValidateAgentCSR(x509cr, usagesToSet(csr.Spec.Usages)) == nil
+}
+
+// isSelfAgentCSR determines if the provided csr is a self-agent csr.
+// Self-agent csr is created by karmada-agent to enable certificate rotation feature.
+// In contrast to the agent CSR, for a self-agent CSR, the username of the user who creates the `CertificateSigningRequest` must be identical to the 'CommonName' specified in the CertificateRequest.
+func isSelfAgentCSR(csr *certificatesv1.CertificateSigningRequest, x509cr *x509.CertificateRequest) bool {
+	if csr.Spec.Username != x509cr.Subject.CommonName {
+		return false
+	}
+	return isAgentCSR(csr, x509cr)
+}
+
+var (
+	errOrganizationNotSystemAgents = fmt.Errorf("subject organization is not system:karmada:agents")
+	errCommonNameNotSystemAgent    = fmt.Errorf("subject common name does not begin with system:karmada:agent: prefix")
+	errDNSSANNotAllowed            = fmt.Errorf("DNS subjectAltNames are not allowed")
+	errEmailSANNotAllowed          = fmt.Errorf("email subjectAltNames are not allowed")
+	errIPSANNotAllowed             = fmt.Errorf("IP subjectAltNames are not allowed")
+	errURISANNotAllowed            = fmt.Errorf("URI subjectAltNames are not allowed")
+)
+
+// ValidateAgentCSR used to determine if the CSR is a valid agent's CSR.
+func ValidateAgentCSR(req *x509.CertificateRequest, usages sets.Set[string]) error {
+	if !reflect.DeepEqual([]string{agentCSRGroup}, req.Subject.Organization) {
+		return errOrganizationNotSystemAgents
+	}
+
+	if len(req.DNSNames) > 0 {
+		return errDNSSANNotAllowed
+	}
+
+	if len(req.EmailAddresses) > 0 {
+		return errEmailSANNotAllowed
+	}
+
+	if len(req.IPAddresses) > 0 {
+		return errIPSANNotAllowed
+	}
+
+	if len(req.URIs) > 0 {
+		return errURISANNotAllowed
+	}
+
+	if !strings.HasPrefix(req.Subject.CommonName, agentCSRUserPrefix) {
+		return errCommonNameNotSystemAgent
+	}
+
+	if !agentRequiredUsages.Equal(usages) && !agentRequiredUsagesNoKeyEncipherment.Equal(usages) {
+		return fmt.Errorf("usages did not match %v", sets.List(agentRequiredUsages))
+	}
+
+	return nil
+}
+
+var (
+	agentRequiredUsagesNoKeyEncipherment = sets.New[string](
+		string(certificatesv1.UsageDigitalSignature),
+		string(certificatesv1.UsageClientAuth),
+	)
+	agentRequiredUsages = sets.New[string](
+		string(certificatesv1.UsageDigitalSignature),
+		string(certificatesv1.UsageKeyEncipherment),
+		string(certificatesv1.UsageClientAuth),
+	)
+)
+
+func usagesToSet(usages []certificatesv1.KeyUsage) sets.Set[string] {
+	result := sets.New[string]()
+	for _, usage := range usages {
+		result.Insert(string(usage))
+	}
+	return result
+}
+
+// SetupWithManager creates a controller and registers to controller manager.
+func (a *AgentCSRApprovingController) SetupWithManager(mgr controllerruntime.Manager) error {
+	var predicateFunc = predicate.Funcs{
+		CreateFunc: func(e event.CreateEvent) bool {
+			csr := e.Object.(*certificatesv1.CertificateSigningRequest)
+			// agent certificate is signed by "kubernetes.io/kube-apiserver-Client" signer
+			return isIssuedByKubeAPIServerClientSigner(csr)
+		},
+		UpdateFunc: func(e event.UpdateEvent) bool {
+			newCSR := e.ObjectNew.(*certificatesv1.CertificateSigningRequest)
+			// agent certificate is signed by "kubernetes.io/kube-apiserver-Client" signer
+			return isIssuedByKubeAPIServerClientSigner(newCSR)
+		},
+		DeleteFunc:  func(event.DeleteEvent) bool { return false },
+		GenericFunc: func(event.GenericEvent) bool { return false },
+	}
+
+	return controllerruntime.NewControllerManagedBy(mgr).
+		Named(csrApprovingController).
+		For(&certificatesv1.CertificateSigningRequest{}, builder.WithPredicates(predicateFunc)).
+		Complete(a)
+}

pkg/util/certificate/csr.go

@@ -0,0 +1,53 @@
+/*
+Copyright 2024 The Karmada 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 certificate
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+
+	certificatesv1 "k8s.io/api/certificates/v1"
+)
+
+const certificateRequest = "CERTIFICATE REQUEST"
+
+// ParseCSR extracts the CSR from the bytes and decodes it.
+func ParseCSR(pemBytes []byte) (*x509.CertificateRequest, error) {
+	block, _ := pem.Decode(pemBytes)
+	if block == nil || block.Type != certificateRequest {
+		return nil, fmt.Errorf("PEM block type must be CERTIFICATE REQUEST")
+	}
+	csr, err := x509.ParseCertificateRequest(block.Bytes)
+	if err != nil {
+		return nil, err
+	}
+	return csr, nil
+}
+
+// GetCertApprovalCondition return true if the status conditions of csr is Approved or Denied.
+func GetCertApprovalCondition(status *certificatesv1.CertificateSigningRequestStatus) (approved bool, denied bool) {
+	for _, c := range status.Conditions {
+		if c.Type == certificatesv1.CertificateApproved {
+			approved = true
+		}
+		if c.Type == certificatesv1.CertificateDenied {
+			denied = true
+		}
+	}
+	return
+}