fortify/internal/app/seal.go

package app

import (
	"errors"
	"os"
	"os/exec"
	"os/user"
	"strconv"

	"git.ophivana.moe/cat/fortify/dbus"
	"git.ophivana.moe/cat/fortify/internal"
	"git.ophivana.moe/cat/fortify/internal/state"
	"git.ophivana.moe/cat/fortify/internal/verbose"
)

const (
	LaunchMethodSudo uint8 = iota
	LaunchMethodMachineCtl
)

var (
	ErrConfig = errors.New("no configuration to seal")
	ErrUser   = errors.New("unknown user")
	ErrLaunch = errors.New("invalid launch method")

	ErrSudo       = errors.New("sudo not available")
	ErrSystemd    = errors.New("systemd not available")
	ErrMachineCtl = errors.New("machinectl not available")
)

type (
	SealConfigError     BaseError
	LauncherLookupError BaseError
	SecurityError       BaseError
)

// Seal seals the app launch context
func (a *app) Seal(config *Config) error {
	a.lock.Lock()
	defer a.lock.Unlock()

	if a.seal != nil {
		panic("app sealed twice")
	}

	if config == nil {
		return (*SealConfigError)(wrapError(ErrConfig, "attempted to seal app with nil config"))
	}

	// create seal
	seal := new(appSeal)

	// generate application ID
	if id, err := newAppID(); err != nil {
		return (*SecurityError)(wrapError(err, "cannot generate application ID:", err))
	} else {
		seal.id = id
	}

	// fetch system constants
	seal.SystemConstants = internal.GetSC()

	// pass through config values
	seal.fid = config.ID
	seal.command = config.Command

	// parses launch method text and looks up tool path
	switch config.Method {
	case "sudo":
		seal.launchOption = LaunchMethodSudo
		if sudoPath, err := exec.LookPath("sudo"); err != nil {
			return (*LauncherLookupError)(wrapError(ErrSudo, "sudo not found"))
		} else {
			seal.toolPath = sudoPath
		}
	case "systemd":
		seal.launchOption = LaunchMethodMachineCtl
		if !internal.SdBootedV {
			return (*LauncherLookupError)(wrapError(ErrSystemd,
				"system has not been booted with systemd as init system"))
		}

		if machineCtlPath, err := exec.LookPath("machinectl"); err != nil {
			return (*LauncherLookupError)(wrapError(ErrMachineCtl, "machinectl not found"))
		} else {
			seal.toolPath = machineCtlPath
		}
	default:
		return (*SealConfigError)(wrapError(ErrLaunch, "invalid launch method"))
	}

	// create seal system component
	seal.sys = new(appSealTx)

	// look up fortify executable path
	if p, err := os.Executable(); err != nil {
		return (*LauncherLookupError)(wrapError(err, "cannot look up fortify executable path:", err))
	} else {
		seal.sys.executable = p
	}

	// look up user from system
	if u, err := user.Lookup(config.User); err != nil {
		if errors.As(err, new(user.UnknownUserError)) {
			return (*SealConfigError)(wrapError(ErrUser, "unknown user", config.User))
		} else {
			// unreachable
			panic(err)
		}
	} else {
		seal.sys.User = u
	}

	// open process state store
	// the simple store only starts holding an open file after first action
	// store activity begins after Start is called and must end before Wait
	seal.store = state.NewSimple(seal.SystemConstants.RunDirPath, seal.sys.Uid)

	// parse string UID
	if u, err := strconv.Atoi(seal.sys.Uid); err != nil {
		// unreachable unless kernel bug
		panic("uid parse")
	} else {
		seal.sys.uid = u
	}

	// pass through enablements
	seal.et = config.Confinement.Enablements

	// this method calls all share methods in sequence
	if err := seal.shareAll([2]*dbus.Config{config.Confinement.SessionBus, config.Confinement.SystemBus}); err != nil {
		return err
	}

	// verbose log seal information
	verbose.Println("created application seal as user",
		seal.sys.Username, "("+seal.sys.Uid+"),",
		"method:", config.Method+",",
		"launcher:", seal.toolPath+",",
		"command:", config.Command)

	// seal app and release lock
	a.seal = seal
	return nil
}