cmd: shim and init into separate binaries

This change also fixes a deadlock when shim fails to connect and complete the setup.

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

internal/app/app.go

@@ -3,8 +3,8 @@ package app
 import (
 	"sync"
 
-	"git.ophivana.moe/security/fortify/internal"
-	"git.ophivana.moe/security/fortify/internal/shim"
+	"git.ophivana.moe/security/fortify/cmd/fshim/ipc/shim"
+	"git.ophivana.moe/security/fortify/internal/linux"
 )
 
 type App interface {
@@ -25,7 +25,7 @@ type app struct {
 	// application unique identifier
 	id *ID
 	// operating system interface
-	os internal.System
+	os linux.System
 	// shim process manager
 	shim *shim.Shim
 	// child process related information
@@ -63,7 +63,7 @@ func (a *app) WaitErr() error {
 	return a.waitErr
 }
 
-func New(os internal.System) (App, error) {
+func New(os linux.System) (App, error) {
 	a := new(app)
 	a.id = new(ID)
 	a.os = os

internal/app/app_nixos_test.go

@@ -9,8 +9,8 @@ import (
 	"git.ophivana.moe/security/fortify/acl"
 	"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/app"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -579,8 +579,12 @@ func (s *stubNixOS) Exit(code int) {
 	panic("called exit on stub with code " + strconv.Itoa(code))
 }
 
-func (s *stubNixOS) Paths() internal.Paths {
-	return internal.Paths{
+func (s *stubNixOS) FshimPath() string {
+	return "/nix/store/00000000000000000000000000000000-fortify-0.0.10/bin/.fshim"
+}
+
+func (s *stubNixOS) Paths() linux.Paths {
+	return linux.Paths{
 		SharePath:   "/tmp/fortify.1971",
 		RuntimePath: "/run/user/1971",
 		RunDirPath:  "/run/user/1971/fortify",

internal/app/app_test.go

@@ -7,14 +7,14 @@ import (
 	"time"
 
 	"git.ophivana.moe/security/fortify/helper/bwrap"
-	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/app"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
 type sealTestCase struct {
 	name      string
-	os        internal.System
+	os        linux.System
 	config    *app.Config
 	id        app.ID
 	wantSys   *system.I

internal/app/export_test.go

@@ -2,11 +2,11 @@ package app
 
 import (
 	"git.ophivana.moe/security/fortify/helper/bwrap"
-	"git.ophivana.moe/security/fortify/internal"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
-func NewWithID(id ID, os internal.System) App {
+func NewWithID(id ID, os linux.System) App {
 	a := new(app)
 	a.id = &id
 	a.os = os

internal/app/launch.machinectl.go

@@ -47,8 +47,8 @@ func (a *app) commandBuilderMachineCtl(shimEnv string) (args []string) {
 	}
 	innerCommand.WriteString("; ")
 
-	// launch fortify as shim
-	innerCommand.WriteString("exec " + a.seal.sys.executable + " shim")
+	// launch fortify shim
+	innerCommand.WriteString("exec " + a.os.FshimPath())
 
 	// append inner command
 	args = append(args, innerCommand.String())

internal/app/launch.sudo.go

@@ -24,7 +24,7 @@ func (a *app) commandBuilderSudo(shimEnv string) (args []string) {
 	args = append(args, shimEnv)
 
 	// -- $@
-	args = append(args, "--", a.seal.sys.executable, "shim")
+	args = append(args, "--", a.os.FshimPath())
 
 	return
 }

internal/app/seal.go

@@ -7,10 +7,10 @@ import (
 	"path"
 	"strconv"
 
+	shim "git.ophivana.moe/security/fortify/cmd/fshim/ipc"
 	"git.ophivana.moe/security/fortify/dbus"
-	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
-	"git.ophivana.moe/security/fortify/internal/shim"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"git.ophivana.moe/security/fortify/internal/state"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
@@ -66,7 +66,7 @@ type appSeal struct {
 	// seal system-level component
 	sys *appSealSys
 
-	internal.Paths
+	linux.Paths
 
 	// protected by upstream mutex
 }
@@ -127,13 +127,6 @@ func (a *app) Seal(config *Config) error {
 	// create seal system component
 	seal.sys = new(appSealSys)
 
-	// look up fortify executable path
-	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 := a.os.Lookup(config.User); err != nil {
 		if errors.As(err, new(user.UnknownUserError)) {

internal/app/share.display.go

@@ -5,8 +5,8 @@ import (
 	"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/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -23,7 +23,7 @@ var (
 	ErrXDisplay = errors.New(display + " unset")
 )
 
-func (seal *appSeal) shareDisplay(os internal.System) error {
+func (seal *appSeal) shareDisplay(os linux.System) error {
 	// pass $TERM to launcher
 	if t, ok := os.LookupEnv(term); ok {
 		seal.sys.bwrap.SetEnv[term] = t

internal/app/share.pulse.go

@@ -6,8 +6,8 @@ import (
 	"io/fs"
 	"path"
 
-	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -25,7 +25,7 @@ var (
 	ErrPulseMode   = errors.New("unexpected pulse socket mode")
 )
 
-func (seal *appSeal) sharePulse(os internal.System) error {
+func (seal *appSeal) sharePulse(os linux.System) error {
 	if !seal.et.Has(system.EPulse) {
 		return nil
 	}
@@ -78,7 +78,7 @@ func (seal *appSeal) sharePulse(os internal.System) error {
 }
 
 // discoverPulseCookie attempts various standard methods to discover the current user's PulseAudio authentication cookie
-func discoverPulseCookie(os internal.System) (string, error) {
+func discoverPulseCookie(os linux.System) (string, error) {
 	if p, ok := os.LookupEnv(pulseCookie); ok {
 		return p, nil
 	}

internal/app/share.system.go

@@ -4,7 +4,7 @@ import (
 	"path"
 
 	"git.ophivana.moe/security/fortify/acl"
-	"git.ophivana.moe/security/fortify/internal"
+	"git.ophivana.moe/security/fortify/internal/linux"
 	"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(os internal.System) {
+func (seal *appSeal) sharePasswd(os linux.System) {
 	// look up shell
 	sh := "/bin/sh"
 	if s, ok := os.LookupEnv(shell); ok {

internal/app/start.go

@@ -8,9 +8,10 @@ import (
 	"path/filepath"
 	"strings"
 
+	shim0 "git.ophivana.moe/security/fortify/cmd/fshim/ipc"
+	"git.ophivana.moe/security/fortify/cmd/fshim/ipc/shim"
 	"git.ophivana.moe/security/fortify/helper"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
-	"git.ophivana.moe/security/fortify/internal/shim"
 	"git.ophivana.moe/security/fortify/internal/state"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
@@ -22,9 +23,9 @@ func (a *app) Start() error {
 	defer a.lock.Unlock()
 
 	// resolve exec paths
-	shimExec := [3]string{a.seal.sys.executable, helper.BubblewrapName}
+	shimExec := [2]string{helper.BubblewrapName}
 	if len(a.seal.command) > 0 {
-		shimExec[2] = a.seal.command[0]
+		shimExec[1] = a.seal.command[0]
 	}
 	for i, n := range shimExec {
 		if len(n) == 0 {
@@ -53,7 +54,7 @@ func (a *app) Start() error {
 
 	// construct shim manager
 	a.shim = shim.New(a.seal.toolPath, uint32(a.seal.sys.UID()), path.Join(a.seal.share, "shim"), a.seal.wl,
-		&shim.Payload{
+		&shim0.Payload{
 			Argv:  a.seal.command,
 			Exec:  shimExec,
 			Bwrap: a.seal.sys.bwrap,

internal/app/system.go

@@ -5,7 +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/linux"
 	"git.ophivana.moe/security/fortify/internal/system"
 )
 
@@ -17,8 +17,6 @@ type appSealSys struct {
 
 	// default formatted XDG_RUNTIME_DIR of User
 	runtime string
-	// sealed path to fortify executable, used by shim
-	executable string
 	// target user sealed from config
 	user *user.User
 
@@ -30,7 +28,7 @@ type appSealSys struct {
 }
 
 // shareAll calls all share methods in sequence
-func (seal *appSeal) shareAll(bus [2]*dbus.Config, os internal.System) error {
+func (seal *appSeal) shareAll(bus [2]*dbus.Config, os linux.System) error {
 	if seal.shared {
 		panic("seal shared twice")
 	}

internal/comp.go

@@ -0,0 +1,12 @@
+package internal
+
+const compPoison = "INVALIDINVALIDINVALIDINVALIDINVALID"
+
+var (
+	Version = compPoison
+)
+
+// Check validates string value set at compile time.
+func Check(s string) (string, bool) {
+	return s, s != compPoison && s != ""
+}

internal/init/main.go

@@ -1,174 +0,0 @@
-package init0
-
-import (
-	"encoding/gob"
-	"errors"
-	"flag"
-	"os"
-	"os/exec"
-	"os/signal"
-	"path"
-	"strconv"
-	"syscall"
-	"time"
-
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-)
-
-const (
-	// time to wait for linger processes after death initial process
-	residualProcessTimeout = 5 * time.Second
-)
-
-// everything beyond this point runs within pid namespace
-// proceed with caution!
-
-func doInit(fd uintptr) {
-	fmsg.SetPrefix("init")
-
-	// re-exec
-	if len(os.Args) > 0 && os.Args[0] != "fortify" && path.IsAbs(os.Args[0]) {
-		if err := syscall.Exec(os.Args[0], []string{"fortify", "init"}, os.Environ()); err != nil {
-			fmsg.Println("cannot re-exec self:", err)
-			// continue anyway
-		}
-	}
-
-	var payload Payload
-	p := os.NewFile(fd, "config-stream")
-	if p == nil {
-		fmsg.Fatal("invalid config descriptor")
-	}
-	if err := gob.NewDecoder(p).Decode(&payload); err != nil {
-		fmsg.Fatal("cannot decode init payload:", err)
-	} else {
-		// sharing stdout with parent
-		// USE WITH CAUTION
-		fmsg.SetVerbose(payload.Verbose)
-
-		// child does not need to see this
-		if err = os.Unsetenv(EnvInit); err != nil {
-			fmsg.Println("cannot unset", EnvInit+":", err)
-			// not fatal
-		} else {
-			fmsg.VPrintln("received configuration")
-		}
-	}
-
-	// close config fd
-	if err := p.Close(); err != nil {
-		fmsg.Println("cannot close config fd:", err)
-		// not fatal
-	}
-
-	// die with parent
-	if _, _, errno := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGKILL), 0); errno != 0 {
-		fmsg.Fatal("prctl(PR_SET_PDEATHSIG, SIGKILL):", errno.Error())
-	}
-
-	cmd := exec.Command(payload.Argv0)
-	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-	cmd.Args = payload.Argv
-	cmd.Env = os.Environ()
-
-	// pass wayland fd
-	if payload.WL != -1 {
-		if f := os.NewFile(uintptr(payload.WL), "wayland"); f != nil {
-			cmd.Env = append(cmd.Env, "WAYLAND_SOCKET="+strconv.Itoa(3+len(cmd.ExtraFiles)))
-			cmd.ExtraFiles = append(cmd.ExtraFiles, f)
-		}
-	}
-
-	if err := cmd.Start(); err != nil {
-		fmsg.Fatalf("cannot start %q: %v", payload.Argv0, err)
-	}
-
-	sig := make(chan os.Signal, 2)
-	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
-
-	type winfo struct {
-		wpid    int
-		wstatus syscall.WaitStatus
-	}
-	info := make(chan winfo, 1)
-	done := make(chan struct{})
-
-	go func() {
-		var (
-			err     error
-			wpid    = -2
-			wstatus syscall.WaitStatus
-		)
-
-		// keep going until no child process is left
-		for wpid != -1 {
-			if err != nil {
-				break
-			}
-
-			if wpid != -2 {
-				info <- winfo{wpid, wstatus}
-			}
-
-			err = syscall.EINTR
-			for errors.Is(err, syscall.EINTR) {
-				wpid, err = syscall.Wait4(-1, &wstatus, 0, nil)
-			}
-		}
-		if !errors.Is(err, syscall.ECHILD) {
-			fmsg.Println("unexpected wait4 response:", err)
-		}
-
-		close(done)
-	}()
-
-	timeout := make(chan struct{})
-
-	r := 2
-	for {
-		select {
-		case s := <-sig:
-			fmsg.VPrintln("received", s.String())
-			fmsg.Exit(0)
-		case w := <-info:
-			if w.wpid == cmd.Process.Pid {
-				switch {
-				case w.wstatus.Exited():
-					r = w.wstatus.ExitStatus()
-				case w.wstatus.Signaled():
-					r = 128 + int(w.wstatus.Signal())
-				default:
-					r = 255
-				}
-
-				go func() {
-					time.Sleep(residualProcessTimeout)
-					close(timeout)
-				}()
-			}
-		case <-done:
-			fmsg.Exit(r)
-		case <-timeout:
-			fmsg.Println("timeout exceeded waiting for lingering processes")
-			fmsg.Exit(r)
-		}
-	}
-}
-
-// Try runs init and stops execution if FORTIFY_INIT is set.
-func Try() {
-	if os.Getpid() != 1 {
-		return
-	}
-
-	if args := flag.Args(); len(args) == 1 && args[0] == "init" {
-		if s, ok := os.LookupEnv(EnvInit); ok {
-			if fd, err := strconv.Atoi(s); err != nil {
-				fmsg.Fatalf("cannot parse %q: %v", s, err)
-			} else {
-				doInit(uintptr(fd))
-			}
-			panic("unreachable")
-		}
-	}
-}

internal/init/payload.go

@@ -1,15 +0,0 @@
-package init0
-
-const EnvInit = "FORTIFY_INIT"
-
-type Payload struct {
-	// target full exec path
-	Argv0 string
-	// child full argv
-	Argv []string
-	// wayland fd, -1 to disable
-	WL int
-
-	// verbosity pass through
-	Verbose bool
-}

internal/linux/interface.go

@@ -1,14 +1,10 @@
-package internal
+package linux
 
 import (
-	"errors"
 	"io/fs"
-	"os"
-	"os/exec"
 	"os/user"
 	"path"
 	"strconv"
-	"sync"
 
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
@@ -36,6 +32,8 @@ type System interface {
 	// Exit provides [os.Exit].
 	Exit(code int)
 
+	// FshimPath returns an absolute path to the fshim binary.
+	FshimPath() string
 	// Paths returns a populated [Paths] struct.
 	Paths() Paths
 	// SdBooted implements https://www.freedesktop.org/software/systemd/man/sd_booted.html
@@ -69,58 +67,3 @@ func CopyPaths(os System, v *Paths) {
 
 	fmsg.VPrintf("runtime directory at %q", v.RunDirPath)
 }
-
-// Std implements System using the standard library.
-type Std struct {
-	paths     Paths
-	pathsOnce sync.Once
-
-	sdBooted     bool
-	sdBootedOnce 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)                              { fmsg.Exit(code) }
-
-const xdgRuntimeDir = "XDG_RUNTIME_DIR"
-
-func (s *Std) Paths() Paths {
-	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
-	return s.paths
-}
-
-func (s *Std) SdBooted() bool {
-	s.sdBootedOnce.Do(func() { s.sdBooted = copySdBooted() })
-	return s.sdBooted
-}
-
-const systemdCheckPath = "/run/systemd/system"
-
-func copySdBooted() bool {
-	if v, err := sdBooted(); err != nil {
-		fmsg.Println("cannot read systemd marker:", err)
-		return false
-	} else {
-		return v
-	}
-}
-
-func sdBooted() (bool, error) {
-	_, err := os.Stat(systemdCheckPath)
-	if err != nil {
-		if errors.Is(err, fs.ErrNotExist) {
-			err = nil
-		}
-		return false, err
-	}
-
-	return true, nil
-}

internal/linux/std.go

@@ -0,0 +1,83 @@
+package linux
+
+import (
+	"errors"
+	"io/fs"
+	"os"
+	"os/exec"
+	"os/user"
+	"sync"
+
+	"git.ophivana.moe/security/fortify/internal"
+	"git.ophivana.moe/security/fortify/internal/fmsg"
+)
+
+// Std implements System using the standard library.
+type Std struct {
+	paths     Paths
+	pathsOnce sync.Once
+
+	sdBooted     bool
+	sdBootedOnce sync.Once
+
+	fshim     string
+	fshimOnce 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)                              { fmsg.Exit(code) }
+
+const xdgRuntimeDir = "XDG_RUNTIME_DIR"
+
+func (s *Std) FshimPath() string {
+	s.fshimOnce.Do(func() {
+		p, ok := internal.Path(internal.Fshim)
+		if !ok {
+			fmsg.Fatal("invalid fshim path, this copy of fortify is not compiled correctly")
+		}
+		s.fshim = p
+	})
+
+	return s.fshim
+}
+
+func (s *Std) Paths() Paths {
+	s.pathsOnce.Do(func() { CopyPaths(s, &s.paths) })
+	return s.paths
+}
+
+func (s *Std) SdBooted() bool {
+	s.sdBootedOnce.Do(func() { s.sdBooted = copySdBooted() })
+	return s.sdBooted
+}
+
+const systemdCheckPath = "/run/systemd/system"
+
+func copySdBooted() bool {
+	if v, err := sdBooted(); err != nil {
+		fmsg.Println("cannot read systemd marker:", err)
+		return false
+	} else {
+		return v
+	}
+}
+
+func sdBooted() (bool, error) {
+	_, err := os.Stat(systemdCheckPath)
+	if err != nil {
+		if errors.Is(err, fs.ErrNotExist) {
+			err = nil
+		}
+		return false, err
+	}
+
+	return true, nil
+}

internal/path.go

@@ -0,0 +1,14 @@
+package internal
+
+import "path"
+
+var (
+	Fmain = compPoison
+	Fsu   = compPoison
+	Fshim = compPoison
+	Finit = compPoison
+)
+
+func Path(p string) (string, bool) {
+	return p, p != compPoison && p != "" && path.IsAbs(p)
+}

internal/prctl.go

@@ -0,0 +1,20 @@
+package internal
+
+import "syscall"
+
+func PR_SET_DUMPABLE__SUID_DUMP_DISABLE() error {
+	// linux/sched/coredump.h
+	if _, _, errno := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_DUMPABLE, 0, 0); errno != 0 {
+		return errno
+	}
+
+	return nil
+}
+
+func PR_SET_PDEATHSIG__SIGKILL() error {
+	if _, _, errno := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, syscall.PR_SET_PDEATHSIG, uintptr(syscall.SIGKILL), 0); errno != 0 {
+		return errno
+	}
+
+	return nil
+}

internal/shim/main.go

@@ -1,179 +0,0 @@
-package shim
-
-import (
-	"encoding/gob"
-	"errors"
-	"flag"
-	"net"
-	"os"
-	"path"
-	"strconv"
-	"syscall"
-
-	"git.ophivana.moe/security/fortify/helper"
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-	init0 "git.ophivana.moe/security/fortify/internal/init"
-)
-
-// everything beyond this point runs as target user
-// proceed with caution!
-
-func doShim(socket string) {
-	fmsg.SetPrefix("shim")
-
-	// re-exec
-	if len(os.Args) > 0 && os.Args[0] != "fortify" && path.IsAbs(os.Args[0]) {
-		if err := syscall.Exec(os.Args[0], []string{"fortify", "shim"}, os.Environ()); err != nil {
-			fmsg.Println("cannot re-exec self:", err)
-			// continue anyway
-		}
-	}
-
-	// dial setup socket
-	var conn *net.UnixConn
-	if c, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: socket, Net: "unix"}); err != nil {
-		fmsg.Fatal("cannot dial setup socket:", err)
-		panic("unreachable")
-	} else {
-		conn = c
-	}
-
-	// decode payload gob stream
-	var payload Payload
-	if err := gob.NewDecoder(conn).Decode(&payload); err != nil {
-		fmsg.Fatal("cannot decode shim payload:", err)
-	} else {
-		// sharing stdout with parent
-		// USE WITH CAUTION
-		fmsg.SetVerbose(payload.Verbose)
-	}
-
-	if payload.Bwrap == nil {
-		fmsg.Fatal("bwrap config not supplied")
-	}
-
-	// receive wayland fd over socket
-	wfd := -1
-	if payload.WL {
-		if fd, err := receiveWLfd(conn); err != nil {
-			fmsg.Fatal("cannot receive wayland fd:", err)
-		} else {
-			wfd = fd
-		}
-	}
-
-	// close setup socket
-	if err := conn.Close(); err != nil {
-		fmsg.Println("cannot close setup socket:", err)
-		// not fatal
-	}
-
-	var ic init0.Payload
-
-	// resolve argv0
-	ic.Argv = payload.Argv
-	if len(ic.Argv) > 0 {
-		// looked up from $PATH by parent
-		ic.Argv0 = payload.Exec[2]
-	} else {
-		// no argv, look up shell instead
-		var ok bool
-		if ic.Argv0, ok = os.LookupEnv("SHELL"); !ok {
-			fmsg.Fatal("no command was specified and $SHELL was unset")
-		}
-
-		ic.Argv = []string{ic.Argv0}
-	}
-
-	conf := payload.Bwrap
-
-	var extraFiles []*os.File
-
-	// pass wayland fd
-	if wfd != -1 {
-		if f := os.NewFile(uintptr(wfd), "wayland"); f != nil {
-			ic.WL = 3 + len(extraFiles)
-			extraFiles = append(extraFiles, f)
-		}
-	} else {
-		ic.WL = -1
-	}
-
-	// share config pipe
-	if r, w, err := os.Pipe(); err != nil {
-		fmsg.Fatal("cannot pipe:", err)
-	} else {
-		conf.SetEnv[init0.EnvInit] = strconv.Itoa(3 + len(extraFiles))
-		extraFiles = append(extraFiles, r)
-
-		fmsg.VPrintln("transmitting config to init")
-		go func() {
-			// stream config to pipe
-			if err = gob.NewEncoder(w).Encode(&ic); err != nil {
-				fmsg.Fatal("cannot transmit init config:", err)
-			}
-		}()
-	}
-
-	helper.BubblewrapName = payload.Exec[1] // resolved bwrap path by parent
-	if b, err := helper.NewBwrap(conf, nil, payload.Exec[0], func(int, int) []string { return []string{"init"} }); err != nil {
-		fmsg.Fatal("malformed sandbox config:", err)
-	} else {
-		cmd := b.Unwrap()
-		cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-		cmd.ExtraFiles = extraFiles
-
-		if fmsg.Verbose() {
-			fmsg.VPrintln("bwrap args:", conf.Args())
-		}
-
-		// run and pass through exit code
-		if err = b.Start(); err != nil {
-			fmsg.Fatal("cannot start target process:", err)
-		} else if err = b.Wait(); err != nil {
-			fmsg.VPrintln("wait:", err)
-		}
-		if b.Unwrap().ProcessState != nil {
-			fmsg.Exit(b.Unwrap().ProcessState.ExitCode())
-		} else {
-			fmsg.Exit(127)
-		}
-	}
-}
-
-func receiveWLfd(conn *net.UnixConn) (int, error) {
-	oob := make([]byte, syscall.CmsgSpace(4)) // single fd
-
-	if _, oobn, _, _, err := conn.ReadMsgUnix(nil, oob); err != nil {
-		return -1, err
-	} else if len(oob) != oobn {
-		return -1, errors.New("invalid message length")
-	}
-
-	var msg syscall.SocketControlMessage
-	if messages, err := syscall.ParseSocketControlMessage(oob); err != nil {
-		return -1, err
-	} else if len(messages) != 1 {
-		return -1, errors.New("unexpected message count")
-	} else {
-		msg = messages[0]
-	}
-
-	if fds, err := syscall.ParseUnixRights(&msg); err != nil {
-		return -1, err
-	} else if len(fds) != 1 {
-		return -1, errors.New("unexpected fd count")
-	} else {
-		return fds[0], nil
-	}
-}
-
-// Try runs shim and stops execution if FORTIFY_SHIM is set.
-func Try() {
-	if args := flag.Args(); len(args) == 1 && args[0] == "shim" {
-		if s, ok := os.LookupEnv(EnvShim); ok {
-			doShim(s)
-			panic("unreachable")
-		}
-	}
-}

internal/shim/parent.go

@@ -1,200 +0,0 @@
-package shim
-
-import (
-	"errors"
-	"net"
-	"os"
-	"os/exec"
-	"sync"
-	"sync/atomic"
-	"syscall"
-	"time"
-
-	"git.ophivana.moe/security/fortify/acl"
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-)
-
-// used by the parent process
-
-type Shim struct {
-	// user switcher process
-	cmd *exec.Cmd
-	// uid of shim target user
-	uid uint32
-	// whether to check shim pid
-	checkPid bool
-	// user switcher executable path
-	executable string
-	// path to setup socket
-	socket string
-	// shim setup abort reason and completion
-	abort     chan error
-	abortErr  atomic.Pointer[error]
-	abortOnce sync.Once
-	// wayland mediation, nil if disabled
-	wl *Wayland
-	// shim setup payload
-	payload *Payload
-}
-
-func New(executable string, uid uint32, socket string, wl *Wayland, payload *Payload, checkPid bool) *Shim {
-	return &Shim{uid: uid, executable: executable, socket: socket, wl: wl, payload: payload, checkPid: checkPid}
-}
-
-func (s *Shim) String() string {
-	if s.cmd == nil {
-		return "(unused shim manager)"
-	}
-	return s.cmd.String()
-}
-
-func (s *Shim) Unwrap() *exec.Cmd {
-	return s.cmd
-}
-
-func (s *Shim) Abort(err error) {
-	s.abortOnce.Do(func() {
-		s.abortErr.Store(&err)
-		// s.abort is buffered so this will never block
-		s.abort <- err
-	})
-}
-
-func (s *Shim) AbortWait(err error) {
-	s.Abort(err)
-	<-s.abort
-}
-
-type CommandBuilder func(shimEnv string) (args []string)
-
-func (s *Shim) Start(f CommandBuilder) (*time.Time, error) {
-	var (
-		cf     chan *net.UnixConn
-		accept func()
-	)
-
-	// listen on setup socket
-	if c, a, err := s.serve(); err != nil {
-		return nil, fmsg.WrapErrorSuffix(err,
-			"cannot listen on shim setup socket:")
-	} else {
-		// accepts a connection after each call to accept
-		// connections are sent to the channel cf
-		cf, accept = c, a
-	}
-
-	// start user switcher process and save time
-	s.cmd = exec.Command(s.executable, f(EnvShim+"="+s.socket)...)
-	s.cmd.Env = []string{}
-	s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
-	s.cmd.Dir = "/"
-	fmsg.VPrintln("starting shim via user switcher:", s.cmd)
-	fmsg.Withhold() // withhold messages to stderr
-	if err := s.cmd.Start(); err != nil {
-		return nil, fmsg.WrapErrorSuffix(err,
-			"cannot start user switcher:")
-	}
-	startTime := time.Now().UTC()
-
-	// kill shim if something goes wrong and an error is returned
-	killShim := func() {
-		if err := s.cmd.Process.Signal(os.Interrupt); err != nil {
-			fmsg.Println("cannot terminate shim on faulted setup:", err)
-		}
-	}
-	defer func() { killShim() }()
-
-	accept()
-	conn := <-cf
-	if conn == nil {
-		return &startTime, fmsg.WrapErrorSuffix(*s.abortErr.Load(), "cannot accept call on setup socket:")
-	}
-
-	// authenticate against called provided uid and shim pid
-	if cred, err := peerCred(conn); err != nil {
-		return &startTime, fmsg.WrapErrorSuffix(*s.abortErr.Load(), "cannot retrieve shim credentials:")
-	} else if cred.Uid != s.uid {
-		fmsg.Printf("process %d owned by user %d tried to connect, expecting %d",
-			cred.Pid, cred.Uid, s.uid)
-		err = errors.New("compromised fortify build")
-		s.Abort(err)
-		return &startTime, err
-	} else if s.checkPid && cred.Pid != int32(s.cmd.Process.Pid) {
-		fmsg.Printf("process %d tried to connect to shim setup socket, expecting shim %d",
-			cred.Pid, s.cmd.Process.Pid)
-		err = errors.New("compromised target user")
-		s.Abort(err)
-		return &startTime, err
-	}
-
-	// serve payload and wayland fd if enabled
-	// this also closes the connection
-	err := s.payload.serve(conn, s.wl)
-	if err == nil {
-		killShim = func() {}
-	}
-	s.Abort(err) // aborting with nil indicates success
-	return &startTime, err
-}
-
-func (s *Shim) serve() (chan *net.UnixConn, func(), error) {
-	if s.abort != nil {
-		panic("attempted to serve shim setup twice")
-	}
-	s.abort = make(chan error, 1)
-
-	cf := make(chan *net.UnixConn)
-	accept := make(chan struct{}, 1)
-
-	if l, err := net.ListenUnix("unix", &net.UnixAddr{Name: s.socket, Net: "unix"}); err != nil {
-		return nil, nil, err
-	} else {
-		l.SetUnlinkOnClose(true)
-
-		fmsg.VPrintf("listening on shim setup socket %q", s.socket)
-		if err = acl.UpdatePerm(s.socket, int(s.uid), acl.Read, acl.Write, acl.Execute); err != nil {
-			fmsg.Println("cannot append ACL entry to shim setup socket:", err)
-			s.Abort(err) // ensures setup socket cleanup
-		}
-
-		go func() {
-			for {
-				select {
-				case err = <-s.abort:
-					if err != nil {
-						fmsg.VPrintln("aborting shim setup, reason:", err)
-					}
-					if err = l.Close(); err != nil {
-						fmsg.Println("cannot close setup socket:", err)
-					}
-					close(s.abort)
-					close(cf)
-					return
-				case <-accept:
-					if conn, err0 := l.AcceptUnix(); err0 != nil {
-						s.Abort(err0) // does not block, breaks loop
-						cf <- nil     // receiver sees nil value and loads err0 stored during abort
-					} else {
-						cf <- conn
-					}
-				}
-			}
-		}()
-	}
-
-	return cf, func() { accept <- struct{}{} }, nil
-}
-
-// peerCred fetches peer credentials of conn
-func peerCred(conn *net.UnixConn) (ucred *syscall.Ucred, err error) {
-	var raw syscall.RawConn
-	if raw, err = conn.SyscallConn(); err != nil {
-		return
-	}
-
-	err0 := raw.Control(func(fd uintptr) {
-		ucred, err = syscall.GetsockoptUcred(int(fd), syscall.SOL_SOCKET, syscall.SO_PEERCRED)
-	})
-	err = errors.Join(err, err0)
-	return
-}

internal/shim/payload.go

@@ -1,42 +0,0 @@
-package shim
-
-import (
-	"encoding/gob"
-	"errors"
-	"net"
-
-	"git.ophivana.moe/security/fortify/helper/bwrap"
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-)
-
-const EnvShim = "FORTIFY_SHIM"
-
-type Payload struct {
-	// child full argv
-	Argv []string
-	// fortify, bwrap, target full exec path
-	Exec [3]string
-	// bwrap config
-	Bwrap *bwrap.Config
-	// whether to pass wayland fd
-	WL bool
-
-	// verbosity pass through
-	Verbose bool
-}
-
-func (p *Payload) serve(conn *net.UnixConn, wl *Wayland) error {
-	if err := gob.NewEncoder(conn).Encode(*p); err != nil {
-		return fmsg.WrapErrorSuffix(err,
-			"cannot stream shim payload:")
-	}
-
-	if wl != nil {
-		if err := wl.WriteUnix(conn); err != nil {
-			return errors.Join(err, conn.Close())
-		}
-	}
-
-	return fmsg.WrapErrorSuffix(conn.Close(),
-		"cannot close setup connection:")
-}

internal/shim/wayland.go

@@ -1,75 +0,0 @@
-package shim
-
-import (
-	"fmt"
-	"net"
-	"sync"
-	"syscall"
-
-	"git.ophivana.moe/security/fortify/internal/fmsg"
-)
-
-// Wayland implements wayland mediation.
-type Wayland struct {
-	// wayland socket path
-	Path string
-
-	// wayland connection
-	conn *net.UnixConn
-
-	connErr error
-	sync.Once
-	// wait for wayland client to exit
-	done chan struct{}
-}
-
-func (wl *Wayland) WriteUnix(conn *net.UnixConn) error {
-	// connect to host wayland socket
-	if f, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: wl.Path, Net: "unix"}); err != nil {
-		return fmsg.WrapErrorSuffix(err,
-			fmt.Sprintf("cannot connect to wayland at %q:", wl.Path))
-	} else {
-		fmsg.VPrintf("connected to wayland at %q", wl.Path)
-		wl.conn = f
-	}
-
-	// set up for passing wayland socket
-	if rc, err := wl.conn.SyscallConn(); err != nil {
-		return fmsg.WrapErrorSuffix(err, "cannot obtain raw wayland connection:")
-	} else {
-		ec := make(chan error)
-		go func() {
-			// pass wayland connection fd
-			if err = rc.Control(func(fd uintptr) {
-				if _, _, err = conn.WriteMsgUnix(nil, syscall.UnixRights(int(fd)), nil); err != nil {
-					ec <- fmsg.WrapErrorSuffix(err, "cannot pass wayland connection to shim:")
-					return
-				}
-				ec <- nil
-
-				// block until shim exits
-				<-wl.done
-				fmsg.VPrintln("releasing wayland connection")
-			}); err != nil {
-				ec <- fmsg.WrapErrorSuffix(err, "cannot obtain wayland connection fd:")
-				return
-			}
-		}()
-		return <-ec
-	}
-}
-
-func (wl *Wayland) Close() error {
-	wl.Do(func() {
-		close(wl.done)
-		wl.connErr = wl.conn.Close()
-	})
-
-	return wl.connErr
-}
-
-func NewWayland() *Wayland {
-	wl := new(Wayland)
-	wl.done = make(chan struct{})
-	return wl
-}