Added check for Windows Permissions

cmd/kubelet/app/server.go

@@ -1,5 +1,5 @@
 /*
-Copyright 2015 The Kubernetes Authors.
+Copyright 2021 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.
@@ -25,7 +25,6 @@ import (
 	"math"
 	"net"
 	"net/http"
-	"os"
 	"path"
 	"path/filepath"
 	"strconv"
@@ -260,6 +259,9 @@ HTTP server: The kubelet can also listen for HTTP and respond to a simple API
 			// add the kubelet config controller to kubeletDeps
 			kubeletDeps.KubeletConfigController = kubeletConfigController
 
+			if err := checkPermissions(); err != nil {
+				klog.ErrorS(err, "kubelet running with insufficient permissions")
+			}
 			// set up signal context here in order to be reused by kubelet and docker shim
 			ctx := genericapiserver.SetupSignalContext()
 
@@ -430,15 +432,6 @@ func Run(ctx context.Context, s *options.KubeletServer, kubeDeps *kubelet.Depend
 	return nil
 }
 
-func checkPermissions() error {
-	if uid := os.Getuid(); uid != 0 {
-		return fmt.Errorf("kubelet needs to run as uid `0`. It is being run as %d", uid)
-	}
-	// TODO: Check if kubelet is running in the `initial` user namespace.
-	// http://man7.org/linux/man-pages/man7/user_namespaces.7.html
-	return nil
-}
-
 func setConfigz(cz *configz.Config, kc *kubeletconfiginternal.KubeletConfiguration) error {
 	scheme, _, err := kubeletscheme.NewSchemeAndCodecs()
 	if err != nil {
@@ -760,10 +753,6 @@ func run(ctx context.Context, s *options.KubeletServer, kubeDeps *kubelet.Depend
 		}
 	}
 
-	if err := checkPermissions(); err != nil {
-		klog.Error(err)
-	}
-
 	utilruntime.ReallyCrash = s.ReallyCrashForTesting
 
 	// TODO(vmarmol): Do this through container config.

cmd/kubelet/app/server_others.go

@@ -0,0 +1,33 @@
+// +build !windows
+
+/*
+Copyright 2021 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 app
+
+import (
+	"fmt"
+	"os"
+)
+
+func checkPermissions() error {
+	if uid := os.Getuid(); uid != 0 {
+		return fmt.Errorf("kubelet needs to run as uid `0`. It is being run as %d", uid)
+	}
+	// TODO: Check if kubelet is running in the `initial` user namespace.
+	// http://man7.org/linux/man-pages/man7/user_namespaces.7.html
+	return nil
+}

cmd/kubelet/app/server_windows.go

@@ -0,0 +1,85 @@
+// +build windows
+
+/*
+Copyright 2021 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 app
+
+import (
+	"fmt"
+	"os/user"
+
+	"golang.org/x/sys/windows"
+)
+
+func isAdmin() (bool, error) {
+	// Get current user
+	u, err := user.Current()
+	if err != nil {
+		return false, fmt.Errorf("Error retrieving current user: %s", err)
+	}
+	// Get IDs of group user is a member of
+	ids, err := u.GroupIds()
+	if err != nil {
+		return false, fmt.Errorf("Error retrieving group ids: %s", err)
+	}
+
+	// Check for existence of BUILTIN\ADMINISTRATORS group id
+	for i := range ids {
+		// BUILTIN\ADMINISTRATORS
+		if "S-1-5-32-544" == ids[i] {
+			return true, nil
+		}
+	}
+	return false, nil
+}
+
+func checkPermissions() error {
+	//https://github.com/golang/go/issues/28804#issuecomment-505326268
+	var sid *windows.SID
+	var userIsAdmin bool
+
+	// https://docs.microsoft.com/en-us/windows/desktop/api/securitybaseapi/nf-securitybaseapi-checktokenmembership
+	err := windows.AllocateAndInitializeSid(
+		&windows.SECURITY_NT_AUTHORITY,
+		2,
+		windows.SECURITY_BUILTIN_DOMAIN_RID,
+		windows.DOMAIN_ALIAS_RID_ADMINS,
+		0, 0, 0, 0, 0, 0,
+		&sid)
+	if err != nil {
+		return fmt.Errorf("Error while checking for elevated permissions: %s", err)
+	}
+
+	//We must free the sid to prevent security token leaks
+	defer windows.FreeSid(sid)
+	token := windows.Token(0)
+
+	userIsAdmin, err = isAdmin()
+	if err != nil {
+		return fmt.Errorf("Error while checking admin group membership: %s", err)
+	}
+
+	member, err := token.IsMember(sid)
+	if err != nil {
+		return fmt.Errorf("Error while checking for elevated permissions: %s", err)
+	}
+	if !member {
+		return fmt.Errorf("kubelet needs to run with administrator permissions. Run as admin is: %t, User in admin group: %t", member, userIsAdmin)
+	}
+
+	return nil
+}