Rewrite check for admin

x-pack/elastic-agent/pkg/agent/cmd/install.go

@@ -46,8 +46,11 @@ would like the Agent to operate.
 }
 
 func installCmd(streams *cli.IOStreams, cmd *cobra.Command, flags *globalFlags, args []string) error {
-	var err error
-	if !install.HasRoot() {
+	isAdmin, err := install.HasRoot()
+	if err != nil {
+		return fmt.Errorf("unable to perform install command while checking for administrator rights, %v", err)
+	}
+	if !isAdmin {
 		return fmt.Errorf("unable to perform install command, not executed with %s permissions", install.PermissionUser)
 	}
 	status, reason := install.Status()

x-pack/elastic-agent/pkg/agent/cmd/uninstall.go

@@ -37,8 +37,12 @@ Unless -f is used this command will ask confirmation before performing removal.
 }
 
 func uninstallCmd(streams *cli.IOStreams, cmd *cobra.Command, flags *globalFlags, args []string) error {
-	if !install.HasRoot() {
-		return fmt.Errorf("unable to perform uninstall command, not executed with %s permissions", install.PermissionUser)
+	isAdmin, err := install.HasRoot()
+	if err != nil {
+		return fmt.Errorf("unable to perform perform command while checking for administrator rights, %v", err)
+	}
+	if !isAdmin {
+		return fmt.Errorf("unable to perform perform command, not executed with %s permissions", install.PermissionUser)
 	}
 	status, reason := install.Status()
 	if status == install.NotInstalled {

x-pack/elastic-agent/pkg/agent/install/root_windows.go

@@ -7,7 +7,8 @@
 package install
 
 import (
-	"os"
+	"github.com/pkg/errors"
+	"golang.org/x/sys/windows"
 )
 
 const (
@@ -16,12 +17,26 @@ const (
 )
 
 // HasRoot returns true if the user has Administrator/SYSTEM permissions.
-func HasRoot() bool {
-	// only valid rights can open the physical drive
-	f, err := os.Open("\\\\.\\PHYSICALDRIVE0")
+func HasRoot() (bool, error) {
+	var sid *windows.SID
+	// See https://docs.microsoft.com/en-us/windows/desktop/api/securitybaseapi/nf-securitybaseapi-checktokenmembership for more on the api
+	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 false
+		return false, errors.Errorf("sid error: %s", err)
 	}
-	defer f.Close()
-	return true
+
+	token := windows.Token(0)
+
+	member, err := token.IsMember(sid)
+	if err != nil {
+		return false, errors.Errorf("token membership error: %s", err)
+	}
+
+	return member, nil
 }

x-pack/elastic-agent/pkg/agent/install/root_windows_test.go

@@ -0,0 +1,20 @@
+// Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+// or more contributor license agreements. Licensed under the Elastic License;
+// you may not use this file except in compliance with the Elastic License.
+
+// +build windows
+
+package install
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestHasRoot(t *testing.T) {
+	t.Run("check if user is admin", func(t *testing.T) {
+		result, err := HasRoot()
+		assert.NoError(t, err)
+		assert.True(t, result)
+	})
+}