services/mgmt/device/impl/helper_manager.go

// Copyright 2015 The Vanadium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package impl

import (
	"fmt"
	"os"
	"os/user"

	"v.io/v23/rpc"
	"v.io/v23/security"
	"v.io/v23/verror"
	"v.io/x/lib/vlog"
)

type suidHelperState string

var suidHelper suidHelperState

func init() {
	u, err := user.Current()
	if err != nil {
		vlog.Panicf("devicemanager has no current user: %v", err)
	}
	suidHelper = suidHelperState(u.Username)
}

// isSetuid is defined like this so we can override its
// implementation for tests.
var isSetuid = func(fileStat os.FileInfo) bool {
	vlog.VI(2).Infof("running the original isSetuid")
	return fileStat.Mode()&os.ModeSetuid == os.ModeSetuid
}

// suidhelperEnabled determines if the suidhelper must exist and be
// setuid to run an application as system user un. If false, the
// setuidhelper must be invoked with the --dryrun flag to skip making
// system calls that will fail or provide apps with a trivial
// priviledge escalation.
func (dn suidHelperState) suidhelperEnabled(un, helperPath string) (bool, error) {
	helperStat, err := os.Stat(helperPath)
	if err != nil {
		return false, verror.New(ErrOperationFailed, nil, fmt.Sprintf("Stat(%v) failed: %v. helper is required.", helperPath, err))
	}
	haveHelper := isSetuid(helperStat)

	switch {
	case haveHelper && string(dn) != un:
		return true, nil
	case haveHelper && string(dn) == un:
		return false, verror.New(verror.ErrNoAccess, nil, fmt.Sprintf("suidhelperEnabled failed: %q == %q", string(dn), un))
	default:
		return false, nil
	}
	// Keep the compiler happy.
	return false, nil
}

// usernameForPrincipal returns the system name that the
// devicemanager will use to invoke apps.
// TODO(rjkroege): This code assumes a desktop target and will need
// to be reconsidered for embedded contexts.
func (i suidHelperState) usernameForPrincipal(call rpc.ServerCall, uat BlessingSystemAssociationStore) string {
	identityNames, _ := security.RemoteBlessingNames(call.Context())
	systemName, present := uat.SystemAccountForBlessings(identityNames)

	if present {
		return systemName
	} else {
		return string(i)
	}
}