Fix kubeadm init regression

Don't create admin rolebindings when --kubeconfig is set to a
non-default value.

Fixes: https://github.com/kubernetes/kubeadm/issues/2992

Signed-off-by: Mario Valderrama <mario.valderrama@ionos.com>

cmd/kubeadm/app/cmd/init.go

@@ -518,7 +518,10 @@ func (d *initData) Client() (clientset.Interface, error) {
 				return nil, err
 			}
 		} else { // Use a real client
-			if !d.adminKubeConfigBootstrapped {
+			isDefaultKubeConfigPath := d.KubeConfigPath() == kubeadmconstants.GetAdminKubeConfigPath()
+			// Only bootstrap the admin.conf if it's used by the user (i.e. --kubeconfig has its default value)
+			// and if the bootstrapping was not already done
+			if !d.adminKubeConfigBootstrapped && isDefaultKubeConfigPath {
 				// Call EnsureAdminClusterRoleBinding() to obtain a working client from admin.conf.
 				d.client, err = kubeconfigphase.EnsureAdminClusterRoleBinding(kubeadmconstants.KubernetesDir, nil)
 				if err != nil {
@@ -526,8 +529,7 @@ func (d *initData) Client() (clientset.Interface, error) {
 				}
 				d.adminKubeConfigBootstrapped = true
 			} else {
-				// In case adminKubeConfigBootstrapped is already set just return a client from the default
-				// kubeconfig location.
+				// Alternatively, just load the config pointed at the --kubeconfig path
 				d.client, err = kubeconfigutil.ClientSetFromFile(d.KubeConfigPath())
 				if err != nil {
 					return nil, err

cmd/kubeadm/app/cmd/init_test.go

@@ -17,7 +17,10 @@ limitations under the License.
 package cmd
 
 import (
+	"context"
 	"fmt"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"testing"
@@ -54,6 +57,20 @@ kind: ClusterConfiguration
 controlPlaneEndpoint: "3.4.5.6"
 `, kubeadmapiv1.SchemeGroupVersion.String(), expectedCRISocket)
 
+const testKubeconfigDataFormat = `---
+apiVersion: v1
+clusters:
+- name: foo-cluster
+  cluster:
+    server: %s
+contexts:
+- name: foo-context
+  context:
+    cluster: foo-cluster
+current-context: foo-context
+kind: Config
+`
+
 func TestNewInitData(t *testing.T) {
 	// create temp directory
 	tmpDir, err := os.MkdirTemp("", "kubeadm-init-test")
@@ -349,3 +366,38 @@ func expectedInitIgnorePreflightErrors(expectedItems ...string) func(t *testing.
 		}
 	}
 }
+
+func TestInitDataClientWithNonDefaultKubeconfig(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodHead {
+			w.WriteHeader(http.StatusMethodNotAllowed)
+		}
+	}))
+	defer ts.Close()
+
+	kubeconfigPath := filepath.Join(t.TempDir(), "custom.conf")
+	if err := os.WriteFile(kubeconfigPath, []byte(fmt.Sprintf(testKubeconfigDataFormat, ts.URL)), 0o600); err != nil {
+		t.Fatalf("os.WriteFile returned unexpected error: %v", err)
+	}
+
+	// initialize an external init option and inject it to the init cmd
+	initOptions := newInitOptions()
+	initOptions.skipCRIDetect = true // avoid CRI detection in unit tests
+	initOptions.kubeconfigPath = kubeconfigPath
+	cmd := newCmdInit(nil, initOptions)
+
+	data, err := newInitData(cmd, nil, initOptions, nil)
+	if err != nil {
+		t.Fatalf("newInitData returned unexpected error: %v", err)
+	}
+
+	client, err := data.Client()
+	if err != nil {
+		t.Fatalf("data.Client returned unexpected error: %v", err)
+	}
+
+	result := client.Discovery().RESTClient().Verb("HEAD").Do(context.Background())
+	if err := result.Error(); err != nil {
+		t.Fatalf("REST client request returned unexpected error: %v", err)
+	}
+}