kubeadm: update embedded CA in kubeconfig files on renewal

cmd/kubeadm/app/phases/certs/renewal/BUILD

@@ -41,6 +41,7 @@ go_test(
     embed = [":go_default_library"],
     deps = [
         "//cmd/kubeadm/app/apis/kubeadm:go_default_library",
+        "//cmd/kubeadm/app/constants:go_default_library",
         "//cmd/kubeadm/app/util/certs:go_default_library",
         "//cmd/kubeadm/app/util/kubeconfig:go_default_library",
         "//cmd/kubeadm/app/util/pkiutil:go_default_library",

cmd/kubeadm/app/phases/certs/renewal/manager.go

@@ -154,7 +154,8 @@ func NewManager(cfg *kubeadmapi.ClusterConfiguration, kubernetesDir string) (*Ma
 	// create a CertificateRenewHandler for each kubeConfig file
 	for _, kubeConfig := range kubeConfigs {
 		// create a ReadWriter for certificates embedded in kubeConfig files
-		kubeConfigReadWriter := newKubeconfigReadWriter(kubernetesDir, kubeConfig.fileName)
+		kubeConfigReadWriter := newKubeconfigReadWriter(kubernetesDir, kubeConfig.fileName,
+			rm.cfg.CertificatesDir, kubeadmconstants.CACertAndKeyBaseName)
 
 		// adds the certificateRenewHandler.
 		// Certificates embedded kubeConfig files in are indexed by fileName, that is a well know constant defined

cmd/kubeadm/app/phases/certs/renewal/readwriter.go

@@ -28,6 +28,7 @@ import (
 	clientcmdapi "k8s.io/client-go/tools/clientcmd/api"
 	certutil "k8s.io/client-go/util/cert"
 	"k8s.io/client-go/util/keyutil"
+	certsphase "k8s.io/kubernetes/cmd/kubeadm/app/phases/certs"
 	pkiutil "k8s.io/kubernetes/cmd/kubeadm/app/util/pkiutil"
 )
 
@@ -104,14 +105,19 @@ type kubeConfigReadWriter struct {
 	kubeConfigFileName string
 	kubeConfigFilePath string
 	kubeConfig         *clientcmdapi.Config
+	baseName           string
+	certificateDir     string
+	caCert             *x509.Certificate
 }
 
 // newKubeconfigReadWriter return a new kubeConfigReadWriter
-func newKubeconfigReadWriter(kubernetesDir string, kubeConfigFileName string) *kubeConfigReadWriter {
+func newKubeconfigReadWriter(kubernetesDir string, kubeConfigFileName string, certificateDir, baseName string) *kubeConfigReadWriter {
 	return &kubeConfigReadWriter{
 		kubernetesDir:      kubernetesDir,
 		kubeConfigFileName: kubeConfigFileName,
 		kubeConfigFilePath: filepath.Join(kubernetesDir, kubeConfigFileName),
+		certificateDir:     certificateDir,
+		baseName:           baseName,
 	}
 }
 
@@ -130,6 +136,16 @@ func (rw *kubeConfigReadWriter) Read() (*x509.Certificate, error) {
 		return nil, errors.Wrapf(err, "failed to load kubeConfig file %s", rw.kubeConfigFilePath)
 	}
 
+	// The CA cert is required for updating kubeconfig files.
+	// For local CA renewal, the local CA on disk could have changed, thus a reload is needed.
+	// For CSR renewal we assume the same CA on disk is mounted for usage with KCM's
+	// '--cluster-signing-cert-file' flag.
+	caCert, _, err := certsphase.LoadCertificateAuthority(rw.certificateDir, rw.baseName)
+	if err != nil {
+		return nil, err
+	}
+	rw.caCert = caCert
+
 	// get current context
 	if _, ok := kubeConfig.Contexts[kubeConfig.CurrentContext]; !ok {
 		return nil, errors.Errorf("invalid kubeConfig file %s: missing context %s", rw.kubeConfigFilePath, kubeConfig.CurrentContext)
@@ -143,7 +159,7 @@ func (rw *kubeConfigReadWriter) Read() (*x509.Certificate, error) {
 
 	cluster := kubeConfig.Clusters[clusterName]
 	if len(cluster.CertificateAuthorityData) == 0 {
-		return nil, errors.Errorf("kubeConfig file %s does not have and embedded server certificate", rw.kubeConfigFilePath)
+		return nil, errors.Errorf("kubeConfig file %s does not have an embedded server certificate", rw.kubeConfigFilePath)
 	}
 
 	// get auth info for current context and ensure a client certificate is embedded in it
@@ -154,7 +170,7 @@ func (rw *kubeConfigReadWriter) Read() (*x509.Certificate, error) {
 
 	authInfo := kubeConfig.AuthInfos[authInfoName]
 	if len(authInfo.ClientCertificateData) == 0 {
-		return nil, errors.Errorf("kubeConfig file %s does not have and embedded client certificate", rw.kubeConfigFilePath)
+		return nil, errors.Errorf("kubeConfig file %s does not have an embedded client certificate", rw.kubeConfigFilePath)
 	}
 
 	// parse the client certificate, retrive the cert config and then renew it
@@ -174,7 +190,7 @@ func (rw *kubeConfigReadWriter) Read() (*x509.Certificate, error) {
 func (rw *kubeConfigReadWriter) Write(newCert *x509.Certificate, newKey crypto.Signer) error {
 	// check if Read was called before Write
 	if rw.kubeConfig == nil {
-		return errors.Errorf("failed to Write kubeConfig file with renewd certs. It is necessary to call Read before Write")
+		return errors.Errorf("failed to Write kubeConfig file with renewed certs. It is necessary to call Read before Write")
 	}
 
 	// encodes the new key
@@ -183,6 +199,12 @@ func (rw *kubeConfigReadWriter) Write(newCert *x509.Certificate, newKey crypto.S
 		return errors.Wrapf(err, "failed to marshal private key to PEM")
 	}
 
+	// Update the embedded CA in the kubeconfig file.
+	// This assumes that the user has kept the current context to the desired one.
+	clusterName := rw.kubeConfig.Contexts[rw.kubeConfig.CurrentContext].Cluster
+	cluster := rw.kubeConfig.Clusters[clusterName]
+	cluster.CertificateAuthorityData = pkiutil.EncodeCertPEM(rw.caCert)
+
 	// get auth info for current context and ensure a client certificate is embedded in it
 	authInfoName := rw.kubeConfig.Contexts[rw.kubeConfig.CurrentContext].AuthInfo
 

cmd/kubeadm/app/phases/certs/renewal/readwriter_test.go

@@ -27,6 +27,7 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 	certutil "k8s.io/client-go/util/cert"
 	"k8s.io/client-go/util/keyutil"
+	kubeadmconstants "k8s.io/kubernetes/cmd/kubeadm/app/constants"
 	kubeconfigutil "k8s.io/kubernetes/cmd/kubeadm/app/util/kubeconfig"
 	pkiutil "k8s.io/kubernetes/cmd/kubeadm/app/util/pkiutil"
 	testutil "k8s.io/kubernetes/cmd/kubeadm/test"
@@ -79,15 +80,27 @@ func TestPKICertificateReadWriter(t *testing.T) {
 }
 
 func TestKubeconfigReadWriter(t *testing.T) {
-	// creates a tmp folder
-	dir := testutil.SetupTempDir(t)
-	defer os.RemoveAll(dir)
+	// creates tmp folders
+	dirKubernetes := testutil.SetupTempDir(t)
+	defer os.RemoveAll(dirKubernetes)
+	dirPKI := testutil.SetupTempDir(t)
+	defer os.RemoveAll(dirPKI)
+
+	// write the CA cert and key to the temporary PKI dir
+	caName := kubeadmconstants.CACertAndKeyBaseName
+	if err := pkiutil.WriteCertAndKey(
+		dirPKI,
+		caName,
+		testCACert,
+		testCAKey); err != nil {
+		t.Fatalf("couldn't write out certificate %s to %s", caName, dirPKI)
+	}
 
 	// creates a certificate and then embeds it into a kubeconfig file
-	cert := writeTestKubeconfig(t, dir, "test", testCACert, testCAKey)
+	cert := writeTestKubeconfig(t, dirKubernetes, "test", testCACert, testCAKey)
 
 	// Creates a KubeconfigReadWriter
-	kubeconfigReadWriter := newKubeconfigReadWriter(dir, "test")
+	kubeconfigReadWriter := newKubeconfigReadWriter(dirKubernetes, "test", dirPKI, caName)
 
 	// Reads the certificate embedded in a kubeconfig
 	readCert, err := kubeconfigReadWriter.Read()