internal: wrap calls to os standard library functions

This change helps tests stub out and simulate OS behaviour during the sealing process. This also removes dependency on XDG_RUNTIME_DIR as the internal.System implementation provided to App provides a compat directory inside the tmpdir-based share when XDG_RUNTIME_DIR is unavailable.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>

config.go

@@ -4,7 +4,6 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
-	"os"
 
 	"git.ophivana.moe/security/fortify/dbus"
 	"git.ophivana.moe/security/fortify/internal"

internal/app/app.go

@@ -3,6 +3,8 @@ package app
 import (
 	"os/exec"
 	"sync"
+
+	"git.ophivana.moe/security/fortify/internal"
 )
 
 type App interface {
@@ -22,6 +24,8 @@ type App interface {
 type app struct {
 	// application unique identifier
 	id *ID
+	// operating system interface
+	os internal.System
 	// underlying user switcher process
 	cmd *exec.Cmd
 	// shim setup abort reason and completion
@@ -61,8 +65,9 @@ func (a *app) WaitErr() error {
 	return a.waitErr
 }
 
-func New() (App, error) {
+func New(os internal.System) (App, error) {
 	a := new(app)
 	a.id = new(ID)
+	a.os = os
 	return a, newAppID(a.id)
 }

internal/app/launch.machinectl.go

@@ -1,7 +1,6 @@
 package app
 
 import (
-	"os/exec"
 	"strings"
 
 	"git.ophivana.moe/security/fortify/internal/fmsg"
@@ -31,7 +30,7 @@ func (a *app) commandBuilderMachineCtl(shimEnv string) (args []string) {
 	args = append(args, "--", ".host")
 
 	// /bin/sh -c
-	if sh, err := exec.LookPath("sh"); err != nil {
+	if sh, err := a.os.LookPath("sh"); err != nil {
 		// hardcode /bin/sh path since it exists more often than not
 		args = append(args, "/bin/sh", "-c")
 	} else {

internal/app/launch.sudo.go

@@ -1,8 +1,6 @@
 package app
 
 import (
-	"os"
-
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
 
@@ -17,7 +15,7 @@ func (a *app) commandBuilderSudo(shimEnv string) (args []string) {
 	args = append(args, "-Hiu", a.seal.sys.user.Username)
 
 	// -A?
-	if _, ok := os.LookupEnv(sudoAskPass); ok {
+	if _, ok := a.os.LookupEnv(sudoAskPass); ok {
 		fmsg.VPrintln(sudoAskPass, "set, adding askpass flag")
 		args = append(args, "-A")
 	}

internal/app/seal.go

@@ -2,8 +2,7 @@ package app
 
 import (
 	"errors"
-	"os"
-	"os/exec"
+	"io/fs"
 	"os/user"
 	"path"
 	"strconv"
@@ -67,8 +66,7 @@ type appSeal struct {
 	// seal system-level component
 	sys *appSealSys
 
-	// used in various sealing operations
-	internal.SystemConstants
+	internal.Paths
 
 	// protected by upstream mutex
 }
@@ -91,7 +89,7 @@ func (a *app) Seal(config *Config) error {
 	seal := new(appSeal)
 
 	// fetch system constants
-	seal.SystemConstants = internal.GetSC()
+	seal.Paths = a.os.Paths()
 
 	// pass through config values
 	seal.id = a.id.String()
@@ -102,7 +100,7 @@ func (a *app) Seal(config *Config) error {
 	switch config.Method {
 	case method[LaunchMethodSudo]:
 		seal.launchOption = LaunchMethodSudo
-		if sudoPath, err := exec.LookPath("sudo"); err != nil {
+		if sudoPath, err := a.os.LookPath("sudo"); err != nil {
 			return fmsg.WrapError(ErrSudo,
 				"sudo not found")
 		} else {
@@ -115,7 +113,7 @@ func (a *app) Seal(config *Config) error {
 				"system has not been booted with systemd as init system")
 		}
 
-		if machineCtlPath, err := exec.LookPath("machinectl"); err != nil {
+		if machineCtlPath, err := a.os.LookPath("machinectl"); err != nil {
 			return fmsg.WrapError(ErrMachineCtl,
 				"machinectl not found")
 		} else {
@@ -130,14 +128,14 @@ func (a *app) Seal(config *Config) error {
 	seal.sys = new(appSealSys)
 
 	// look up fortify executable path
-	if p, err := os.Executable(); err != nil {
+	if p, err := a.os.Executable(); err != nil {
 		return fmsg.WrapErrorSuffix(err, "cannot look up fortify executable path:")
 	} else {
 		seal.sys.executable = p
 	}
 
 	// look up user from system
-	if u, err := user.Lookup(config.User); err != nil {
+	if u, err := a.os.Lookup(config.User); err != nil {
 		if errors.As(err, new(user.UnknownUserError)) {
 			return fmsg.WrapError(ErrUser, "unknown user", config.User)
 		} else {
@@ -160,7 +158,7 @@ func (a *app) Seal(config *Config) error {
 			NoNewSession: true,
 		}
 		// bind entries in /
-		if d, err := os.ReadDir("/"); err != nil {
+		if d, err := a.os.ReadDir("/"); err != nil {
 			return err
 		} else {
 			b := make([]*FilesystemConfig, 0, len(d))
@@ -180,7 +178,7 @@ func (a *app) Seal(config *Config) error {
 			conf.Filesystem = append(conf.Filesystem, b...)
 		}
 		// bind entries in /run
-		if d, err := os.ReadDir("/run"); err != nil {
+		if d, err := a.os.ReadDir("/run"); err != nil {
 			return err
 		} else {
 			b := make([]*FilesystemConfig, 0, len(d))
@@ -198,7 +196,7 @@ func (a *app) Seal(config *Config) error {
 		}
 		// hide nscd from sandbox if present
 		nscd := "/var/run/nscd"
-		if _, err := os.Stat(nscd); !errors.Is(err, os.ErrNotExist) {
+		if _, err := a.os.Stat(nscd); !errors.Is(err, fs.ErrNotExist) {
 			conf.Override = append(conf.Override, nscd)
 		}
 		// bind GPU stuff
@@ -222,7 +220,7 @@ func (a *app) Seal(config *Config) error {
 	// 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.user.Uid)
+	seal.store = state.NewSimple(seal.RunDirPath, seal.sys.user.Uid)
 
 	// parse string UID
 	if u, err := strconv.Atoi(seal.sys.user.Uid); err != nil {
@@ -236,7 +234,7 @@ func (a *app) Seal(config *Config) error {
 	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 {
+	if err := seal.shareAll([2]*dbus.Config{config.Confinement.SessionBus, config.Confinement.SystemBus}, a.os); err != nil {
 		return err
 	}
 

internal/app/share.display.go

@@ -2,10 +2,10 @@ package app
 
 import (
 	"errors"
-	"os"
 	"path"
 
 	"git.ophivana.moe/security/fortify/acl"
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
@@ -23,7 +23,7 @@ var (
 	ErrXDisplay = errors.New(display + " unset")
 )
 
-func (seal *appSeal) shareDisplay() error {
+func (seal *appSeal) shareDisplay(os internal.System) error {
 	// pass $TERM to launcher
 	if t, ok := os.LookupEnv(term); ok {
 		seal.sys.bwrap.SetEnv[term] = t

internal/app/share.pulse.go

@@ -4,9 +4,9 @@ import (
 	"errors"
 	"fmt"
 	"io/fs"
-	"os"
 	"path"
 
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
@@ -25,7 +25,7 @@ var (
 	ErrPulseMode   = errors.New("unexpected pulse socket mode")
 )
 
-func (seal *appSeal) sharePulse() error {
+func (seal *appSeal) sharePulse(os internal.System) error {
 	if !seal.et.Has(system.EPulse) {
 		return nil
 	}
@@ -65,7 +65,7 @@ func (seal *appSeal) sharePulse() error {
 	seal.sys.bwrap.SetEnv[pulseServer] = "unix:" + p
 
 	// publish current user's pulse cookie for target user
-	if src, err := discoverPulseCookie(); err != nil {
+	if src, err := discoverPulseCookie(os); err != nil {
 		return err
 	} else {
 		dst := path.Join(seal.share, "pulse-cookie")
@@ -78,7 +78,7 @@ func (seal *appSeal) sharePulse() error {
 }
 
 // discoverPulseCookie attempts various standard methods to discover the current user's PulseAudio authentication cookie
-func discoverPulseCookie() (string, error) {
+func discoverPulseCookie(os internal.System) (string, error) {
 	if p, ok := os.LookupEnv(pulseCookie); ok {
 		return p, nil
 	}

internal/app/share.runtime.go

@@ -29,6 +29,7 @@ func (seal *appSeal) shareRuntime() {
 	seal.sys.UpdatePermType(system.User, seal.RunDirPath, acl.Execute)
 
 	// ensure runtime directory ACL (e.g. `/run/user/%d`)
+	seal.sys.Ensure(seal.RuntimePath, 0700) // ensure this dir in case XDG_RUNTIME_DIR is unset
 	seal.sys.UpdatePermType(system.User, seal.RuntimePath, acl.Execute)
 
 	// ensure process-specific share local to XDG_RUNTIME_DIR (e.g. `/run/user/%d/fortify/%s`)

internal/app/share.system.go

@@ -1,10 +1,10 @@
 package app
 
 import (
-	"os"
 	"path"
 
 	"git.ophivana.moe/security/fortify/acl"
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -38,7 +38,7 @@ func (seal *appSeal) shareSystem() {
 	seal.sys.bwrap.Tmpfs(seal.SharePath, 1*1024*1024)
 }
 
-func (seal *appSeal) sharePasswd() {
+func (seal *appSeal) sharePasswd(os internal.System) {
 	// look up shell
 	sh := "/bin/sh"
 	if s, ok := os.LookupEnv(shell); ok {

internal/app/system.go

@@ -5,6 +5,7 @@ import (
 
 	"git.ophivana.moe/security/fortify/dbus"
 	"git.ophivana.moe/security/fortify/helper/bwrap"
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -27,7 +28,7 @@ type appSealSys struct {
 }
 
 // shareAll calls all share methods in sequence
-func (seal *appSeal) shareAll(bus [2]*dbus.Config) error {
+func (seal *appSeal) shareAll(bus [2]*dbus.Config, os internal.System) error {
 	if seal.shared {
 		panic("seal shared twice")
 	}
@@ -35,11 +36,11 @@ func (seal *appSeal) shareAll(bus [2]*dbus.Config) error {
 
 	seal.shareSystem()
 	seal.shareRuntime()
-	seal.sharePasswd()
-	if err := seal.shareDisplay(); err != nil {
+	seal.sharePasswd(os)
+	if err := seal.shareDisplay(os); err != nil {
 		return err
 	}
-	if err := seal.sharePulse(); err != nil {
+	if err := seal.sharePulse(os); err != nil {
 		return err
 	}
 

internal/environ.go

@@ -1,58 +0,0 @@
-package internal
-
-import (
-	"os"
-	"path"
-	"strconv"
-	"sync"
-
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-)
-
-// state that remain constant for the lifetime of the process
-// fetched and cached here
-
-const (
-	xdgRuntimeDir = "XDG_RUNTIME_DIR"
-)
-
-// SystemConstants contains state from the operating system
-type SystemConstants struct {
-	// path to shared directory e.g. /tmp/fortify.%d
-	SharePath string `json:"share_path"`
-	// XDG_RUNTIME_DIR value e.g. /run/user/%d
-	RuntimePath string `json:"runtime_path"`
-	// application runtime directory e.g. /run/user/%d/fortify
-	RunDirPath string `json:"run_dir_path"`
-}
-
-var (
-	scVal  SystemConstants
-	scOnce sync.Once
-)
-
-func copySC() {
-	sc := SystemConstants{
-		SharePath: path.Join(os.TempDir(), "fortify."+strconv.Itoa(os.Geteuid())),
-	}
-
-	fmsg.VPrintf("process share directory at %q", sc.SharePath)
-
-	// runtimePath, runDirPath
-	if r, ok := os.LookupEnv(xdgRuntimeDir); !ok {
-		fmsg.Println("variable", xdgRuntimeDir, "unset")
-		os.Exit(1)
-	} else {
-		sc.RuntimePath = r
-		sc.RunDirPath = path.Join(sc.RuntimePath, "fortify")
-		fmsg.VPrintf("XDG runtime directory at %q", sc.RunDirPath)
-	}
-
-	scVal = sc
-}
-
-// GetSC returns a populated SystemConstants value
-func GetSC() SystemConstants {
-	scOnce.Do(copySC)
-	return scVal
-}

internal/system.go

@@ -0,0 +1,120 @@
+package internal
+
+import (
+	"io/fs"
+	"os"
+	"os/exec"
+	"os/user"
+	"path"
+	"strconv"
+	"sync"
+
+	"git.ophivana.moe/security/fortify/internal/fmsg"
+)
+
+// System provides safe access to operating system resources.
+type System interface {
+	// Geteuid provides [os.Geteuid].
+	Geteuid() int
+	// LookupEnv provides [os.LookupEnv].
+	LookupEnv(key string) (string, bool)
+	// TempDir provides [os.TempDir].
+	TempDir() string
+	// LookPath provides [exec.LookPath].
+	LookPath(file string) (string, error)
+	// Executable provides [os.Executable].
+	Executable() (string, error)
+	// Lookup provides [user.Lookup].
+	Lookup(username string) (*user.User, error)
+	// ReadDir provides [os.ReadDir].
+	ReadDir(name string) ([]os.DirEntry, error)
+	// Stat provides [os.Stat].
+	Stat(name string) (fs.FileInfo, error)
+	// Open provides [os.Open]
+	Open(name string) (fs.File, error)
+	// Exit provides [os.Exit].
+	Exit(code int)
+
+	// Paths returns a populated [Paths] struct.
+	Paths() Paths
+}
+
+// Paths contains environment dependent paths used by fortify.
+type Paths struct {
+	// path to shared directory e.g. /tmp/fortify.%d
+	SharePath string `json:"share_path"`
+	// XDG_RUNTIME_DIR value e.g. /run/user/%d
+	RuntimePath string `json:"runtime_path"`
+	// application runtime directory e.g. /run/user/%d/fortify
+	RunDirPath string `json:"run_dir_path"`
+}
+
+// CopyPaths is a generic implementation of [System.Paths].
+func CopyPaths(os System, v *Paths) {
+	v.SharePath = path.Join(os.TempDir(), "fortify."+strconv.Itoa(os.Geteuid()))
+
+	fmsg.VPrintf("process share directory at %q", v.SharePath)
+
+	if r, ok := os.LookupEnv(xdgRuntimeDir); !ok {
+		// fall back to path in share since fortify has no hard XDG dependency
+		v.RunDirPath = path.Join(v.SharePath, "run")
+		v.RuntimePath = path.Join(v.RunDirPath, "compat")
+	} else {
+		v.RuntimePath = r
+		v.RunDirPath = path.Join(v.RuntimePath, "fortify")
+	}
+
+	fmsg.VPrintf("runtime directory at %q", v.RunDirPath)
+}
+
+// Std implements System using the standard library.
+type Std struct {
+	paths     Paths
+	pathsOnce sync.Once
+}
+
+func (s *Std) Geteuid() int {
+	return os.Geteuid()
+}
+
+func (s *Std) LookupEnv(key string) (string, bool) {
+	return os.LookupEnv(key)
+}
+
+func (s *Std) TempDir() string {
+	return os.TempDir()
+}
+
+func (s *Std) LookPath(file string) (string, error) {
+	return exec.LookPath(file)
+}
+
+func (s *Std) Executable() (string, error) {
+	return os.Executable()
+}
+
+func (s *Std) Lookup(username string) (*user.User, error) {
+	return user.Lookup(username)
+}
+
+func (s *Std) ReadDir(name string) ([]os.DirEntry, error) {
+	return os.ReadDir(name)
+}
+
+func (s *Std) Stat(name string) (fs.FileInfo, error) {
+	return os.Stat(name)
+}
+
+func (s *Std) Open(name string) (fs.File, error) {
+	return os.Open(name)
+}
+func (s *Std) Exit(code int) {
+	os.Exit(code)
+}
+
+const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+func (s *Std) Paths() Paths {
+	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
+	return s.paths
+}

license.go

@@ -4,7 +4,6 @@ import (
 	_ "embed"
 	"flag"
 	"fmt"
-	"os"
 )
 
 var (

main.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"flag"
-	"os"
 	"syscall"
 
 	"git.ophivana.moe/security/fortify/internal"
@@ -20,6 +19,8 @@ func init() {
 	flag.BoolVar(&flagVerbose, "v", false, "Verbose output")
 }
 
+var os = new(internal.Std)
+
 func main() {
 	// linux/sched/coredump.h
 	if _, _, errno := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_DUMPABLE, 0, 0); errno != 0 {
@@ -38,9 +39,9 @@ func main() {
 	shim.Try()
 
 	// root check
-	if os.Getuid() == 0 {
-		fmsg.Println("this program must not run as root")
-		os.Exit(1)
+	if os.Geteuid() == 0 {
+		fmsg.Fatal("this program must not run as root")
+		panic("unreachable")
 	}
 
 	// version/license/template command early exit
@@ -53,7 +54,7 @@ func main() {
 
 	// invoke app
 	r := 1
-	a, err := app.New()
+	a, err := app.New(os)
 	if err != nil {
 		fmsg.Fatalf("cannot create app: %s\n", err)
 	} else if err = a.Seal(loadConfig()); err != nil {

state.go

@@ -3,10 +3,8 @@ package main
 import (
 	"flag"
 	"fmt"
-	"os"
 	"text/tabwriter"
 
-	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 	"git.ophivana.moe/security/fortify/internal/state"
 )
@@ -23,7 +21,7 @@ func init() {
 func tryState() {
 	if stateActionEarly {
 		var w *tabwriter.Writer
-		state.MustPrintLauncherStateSimpleGlobal(&w, internal.GetSC().RunDirPath)
+		state.MustPrintLauncherStateSimpleGlobal(&w, os.Paths().RunDirPath)
 		if w != nil {
 			if err := w.Flush(); err != nil {
 				fmsg.Println("cannot format output:", err)

version.go

@@ -3,7 +3,6 @@ package main
 import (
 	"flag"
 	"fmt"
-	"os"
 )
 
 var (