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>

cmd/finit/ipc/payload.go

@@ -1,6 +1,6 @@
 package init0
 
-const EnvInit = "FORTIFY_INIT"
+const Env = "FORTIFY_INIT"
 
 type Payload struct {
 	// target full exec path

cmd/finit/main.go

@@ -1,9 +1,8 @@
-package init0
+package main
 
 import (
 	"encoding/gob"
 	"errors"
-	"flag"
 	"os"
 	"os/exec"
 	"os/signal"
@@ -12,58 +11,80 @@ import (
 	"syscall"
 	"time"
 
+	init0 "git.ophivana.moe/security/fortify/cmd/finit/ipc"
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
 
 const (
-	// time to wait for linger processes after death initial process
+	// time to wait for linger processes after death of initial process
 	residualProcessTimeout = 5 * time.Second
 )
 
 // everything beyond this point runs within pid namespace
 // proceed with caution!
 
-func doInit(fd uintptr) {
+func main() {
+	// sharing stdout with shim
+	// USE WITH CAUTION
 	fmsg.SetPrefix("init")
 
+	// setting this prevents ptrace
+	if err := internal.PR_SET_DUMPABLE__SUID_DUMP_DISABLE(); err != nil {
+		fmsg.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
+		panic("unreachable")
+	}
+
+	if os.Getpid() != 1 {
+		fmsg.Fatal("this process must run as pid 1")
+		panic("unreachable")
+	}
+
 	// re-exec
-	if len(os.Args) > 0 && os.Args[0] != "fortify" && path.IsAbs(os.Args[0]) {
+	if len(os.Args) > 0 && (os.Args[0] != "finit" || len(os.Args) != 1) && path.IsAbs(os.Args[0]) {
-		if err := syscall.Exec(os.Args[0], []string{"fortify", "init"}, os.Environ()); err != nil {
+		if err := syscall.Exec(os.Args[0], []string{"finit"}, os.Environ()); err != nil {
 			fmsg.Println("cannot re-exec self:", err)
 			// continue anyway
 		}
 	}
 
-	var payload Payload
+	// setup pipe fd from environment
-	p := os.NewFile(fd, "config-stream")
+	var setup *os.File
-	if p == nil {
+	if s, ok := os.LookupEnv(init0.Env); !ok {
-		fmsg.Fatal("invalid config descriptor")
+		fmsg.Fatal("FORTIFY_INIT not set")
-	}
+		panic("unreachable")
-	if err := gob.NewDecoder(p).Decode(&payload); err != nil {
+	} else {
-		fmsg.Fatal("cannot decode init payload:", err)
+		if fd, err := strconv.Atoi(s); err != nil {
+			fmsg.Fatalf("cannot parse %q: %v", s, err)
+			panic("unreachable")
+		} else {
+			setup = os.NewFile(uintptr(fd), "setup")
+			if setup == nil {
+				fmsg.Fatal("invalid config descriptor")
+				panic("unreachable")
+			}
+		}
+	}
+
+	var payload init0.Payload
+	if err := gob.NewDecoder(setup).Decode(&payload); err != nil {
+		fmsg.Fatal("cannot decode init setup payload:", err)
+		panic("unreachable")
 	} 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 {
+		if err = os.Unsetenv(init0.Env); err != nil {
-			fmsg.Println("cannot unset", EnvInit+":", err)
+			fmsg.Printf("cannot unset %s: %v", init0.Env, 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 {
+	if err := internal.PR_SET_PDEATHSIG__SIGKILL(); err != nil {
-		fmsg.Fatal("prctl(PR_SET_PDEATHSIG, SIGKILL):", errno.Error())
+		fmsg.Fatalf("prctl(PR_SET_PDEATHSIG, SIGKILL): %v", err)
 	}
 
 	cmd := exec.Command(payload.Argv0)
@@ -82,6 +103,13 @@ func doInit(fd uintptr) {
 	if err := cmd.Start(); err != nil {
 		fmsg.Fatalf("cannot start %q: %v", payload.Argv0, err)
 	}
+	fmsg.Withhold()
+
+	// close setup pipe as setup is now complete
+	if err := setup.Close(); err != nil {
+		fmsg.Println("cannot close setup pipe:", err)
+		// not fatal
+	}
 
 	sig := make(chan os.Signal, 2)
 	signal.Notify(sig, syscall.SIGINT, syscall.SIGTERM)
@@ -122,6 +150,7 @@ func doInit(fd uintptr) {
 		close(done)
 	}()
 
+	// closed after residualProcessTimeout has elapsed after initial process death
 	timeout := make(chan struct{})
 
 	r := 2
@@ -129,9 +158,13 @@ func doInit(fd uintptr) {
 		select {
 		case s := <-sig:
 			fmsg.VPrintln("received", s.String())
+			fmsg.Resume() // output could still be withheld at this point, so resume is called
 			fmsg.Exit(0)
 		case w := <-info:
 			if w.wpid == cmd.Process.Pid {
+				// initial process exited, output is most likely available again
+				fmsg.Resume()
+
 				switch {
 				case w.wstatus.Exited():
 					r = w.wstatus.ExitStatus()
@@ -154,21 +187,3 @@ func doInit(fd uintptr) {
 		}
 	}
 }
-
-// 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")
-		}
-	}
-}

cmd/fshim/ipc/payload.go

@@ -1,4 +1,4 @@
-package shim
+package shim0
 
 import (
 	"encoding/gob"
@@ -9,13 +9,13 @@ import (
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
 
-const EnvShim = "FORTIFY_SHIM"
+const Env = "FORTIFY_SHIM"
 
 type Payload struct {
 	// child full argv
 	Argv []string
-	// fortify, bwrap, target full exec path
+	// bwrap, target full exec path
-	Exec [3]string
+	Exec [2]string
 	// bwrap config
 	Bwrap *bwrap.Config
 	// whether to pass wayland fd
@@ -25,7 +25,7 @@ type Payload struct {
 	Verbose bool
 }
 
-func (p *Payload) serve(conn *net.UnixConn, wl *Wayland) error {
+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:")

cmd/fshim/ipc/shim/shim.go

@@ -11,9 +11,12 @@ import (
 	"time"
 
 	"git.ophivana.moe/security/fortify/acl"
+	shim0 "git.ophivana.moe/security/fortify/cmd/fshim/ipc"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
 )
 
+const shimSetupTimeout = 5 * time.Second
+
 // used by the parent process
 
 type Shim struct {
@@ -32,12 +35,12 @@ type Shim struct {
 	abortErr  atomic.Pointer[error]
 	abortOnce sync.Once
 	// wayland mediation, nil if disabled
-	wl *Wayland
+	wl *shim0.Wayland
 	// shim setup payload
-	payload *Payload
+	payload *shim0.Payload
 }
 
-func New(executable string, uid uint32, socket string, wl *Wayland, payload *Payload, checkPid bool) *Shim {
+func New(executable string, uid uint32, socket string, wl *shim0.Wayland, payload *shim0.Payload, checkPid bool) *Shim {
 	return &Shim{uid: uid, executable: executable, socket: socket, wl: wl, payload: payload, checkPid: checkPid}
 }
 
@@ -84,7 +87,7 @@ func (s *Shim) Start(f CommandBuilder) (*time.Time, error) {
 	}
 
 	// start user switcher process and save time
-	s.cmd = exec.Command(s.executable, f(EnvShim+"="+s.socket)...)
+	s.cmd = exec.Command(s.executable, f(shim0.Env+"="+s.socket)...)
 	s.cmd.Env = []string{}
 	s.cmd.Stdin, s.cmd.Stdout, s.cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
 	s.cmd.Dir = "/"
@@ -105,9 +108,18 @@ func (s *Shim) Start(f CommandBuilder) (*time.Time, error) {
 	defer func() { killShim() }()
 
 	accept()
-	conn := <-cf
+	var conn *net.UnixConn
-	if conn == nil {
+	select {
+	case c := <-cf:
+		if c == nil {
 			return &startTime, fmsg.WrapErrorSuffix(*s.abortErr.Load(), "cannot accept call on setup socket:")
+		} else {
+			conn = c
+		}
+	case <-time.After(shimSetupTimeout):
+		err := errors.New("timed out waiting for shim")
+		s.AbortWait(err)
+		return &startTime, err
 	}
 
 	// authenticate against called provided uid and shim pid
@@ -129,7 +141,7 @@ func (s *Shim) Start(f CommandBuilder) (*time.Time, error) {
 
 	// serve payload and wayland fd if enabled
 	// this also closes the connection
-	err := s.payload.serve(conn, s.wl)
+	err := s.payload.Serve(conn, s.wl)
 	if err == nil {
 		killShim = func() {}
 	}
@@ -158,6 +170,7 @@ func (s *Shim) serve() (chan *net.UnixConn, func(), error) {
 		}
 
 		go func() {
+			cfWg := new(sync.WaitGroup)
 			for {
 				select {
 				case err = <-s.abort:
@@ -168,15 +181,24 @@ func (s *Shim) serve() (chan *net.UnixConn, func(), error) {
 						fmsg.Println("cannot close setup socket:", err)
 					}
 					close(s.abort)
+					go func() {
+						cfWg.Wait()
 						close(cf)
+					}()
 					return
 				case <-accept:
+					cfWg.Add(1)
+					go func() {
+						defer cfWg.Done()
 						if conn, err0 := l.AcceptUnix(); err0 != nil {
-						s.Abort(err0) // does not block, breaks loop
+							// breaks loop
-						cf <- nil     // receiver sees nil value and loads err0 stored during abort
+							s.Abort(err0)
+							// receiver sees nil value and loads err0 stored during abort
+							cf <- nil
 						} else {
 							cf <- conn
 						}
+					}()
 				}
 			}
 		}()

cmd/fshim/ipc/wayland.go

@@ -1,4 +1,4 @@
-package shim
+package shim0
 
 import (
 	"fmt"

cmd/fshim/main.go

@@ -1,37 +1,63 @@
-package shim
+package main
 
 import (
 	"encoding/gob"
 	"errors"
-	"flag"
 	"net"
 	"os"
 	"path"
 	"strconv"
 	"syscall"
 
+	init0 "git.ophivana.moe/security/fortify/cmd/finit/ipc"
+	shim "git.ophivana.moe/security/fortify/cmd/fshim/ipc"
 	"git.ophivana.moe/security/fortify/helper"
+	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
-	init0 "git.ophivana.moe/security/fortify/internal/init"
 )
 
-// everything beyond this point runs as target user
+// everything beyond this point runs as unconstrained target user
 // proceed with caution!
 
-func doShim(socket string) {
+func main() {
+	// sharing stdout with fortify
+	// USE WITH CAUTION
 	fmsg.SetPrefix("shim")
 
+	// setting this prevents ptrace
+	if err := internal.PR_SET_DUMPABLE__SUID_DUMP_DISABLE(); err != nil {
+		fmsg.Fatalf("cannot set SUID_DUMP_DISABLE: %s", err)
+		panic("unreachable")
+	}
+
 	// re-exec
-	if len(os.Args) > 0 && os.Args[0] != "fortify" && path.IsAbs(os.Args[0]) {
+	if len(os.Args) > 0 && (os.Args[0] != "fshim" || len(os.Args) != 1) && path.IsAbs(os.Args[0]) {
-		if err := syscall.Exec(os.Args[0], []string{"fortify", "shim"}, os.Environ()); err != nil {
+		if err := syscall.Exec(os.Args[0], []string{"fshim"}, os.Environ()); err != nil {
 			fmsg.Println("cannot re-exec self:", err)
 			// continue anyway
 		}
 	}
 
+	// lookup socket path from environment
+	var socketPath string
+	if s, ok := os.LookupEnv(shim.Env); !ok {
+		fmsg.Fatal("FORTIFY_SHIM not set")
+		panic("unreachable")
+	} else {
+		socketPath = s
+	}
+
+	// check path to finit
+	var finitPath string
+	if p, ok := internal.Path(internal.Finit); !ok {
+		fmsg.Fatal("invalid finit path, this copy of fshim is not compiled correctly")
+	} else {
+		finitPath = p
+	}
+
 	// dial setup socket
 	var conn *net.UnixConn
-	if c, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: socket, Net: "unix"}); err != nil {
+	if c, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: socketPath, Net: "unix"}); err != nil {
 		fmsg.Fatal("cannot dial setup socket:", err)
 		panic("unreachable")
 	} else {
@@ -39,12 +65,10 @@ func doShim(socket string) {
 	}
 
 	// decode payload gob stream
-	var payload Payload
+	var payload shim.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)
 	}
 
@@ -74,7 +98,7 @@ func doShim(socket string) {
 	ic.Argv = payload.Argv
 	if len(ic.Argv) > 0 {
 		// looked up from $PATH by parent
-		ic.Argv0 = payload.Exec[2]
+		ic.Argv0 = payload.Exec[1]
 	} else {
 		// no argv, look up shell instead
 		var ok bool
@@ -103,7 +127,7 @@ func doShim(socket string) {
 	if r, w, err := os.Pipe(); err != nil {
 		fmsg.Fatal("cannot pipe:", err)
 	} else {
-		conf.SetEnv[init0.EnvInit] = strconv.Itoa(3 + len(extraFiles))
+		conf.SetEnv[init0.Env] = strconv.Itoa(3 + len(extraFiles))
 		extraFiles = append(extraFiles, r)
 
 		fmsg.VPrintln("transmitting config to init")
@@ -115,8 +139,9 @@ func doShim(socket string) {
 		}()
 	}
 
-	helper.BubblewrapName = payload.Exec[1] // resolved bwrap path by parent
+	helper.BubblewrapName = payload.Exec[0] // resolved bwrap path by parent
-	if b, err := helper.NewBwrap(conf, nil, payload.Exec[0], func(int, int) []string { return []string{"init"} }); err != nil {
+	if b, err := helper.NewBwrap(conf, nil, finitPath,
+		func(int, int) []string { return make([]string, 0) }); err != nil {
 		fmsg.Fatal("malformed sandbox config:", err)
 	} else {
 		cmd := b.Unwrap()
@@ -167,13 +192,3 @@ func receiveWLfd(conn *net.UnixConn) (int, error) {
 		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")
-		}
-	}
-}

cmd/fsu/main.go

@@ -8,19 +8,16 @@ import (
 	"strconv"
 	"strings"
 	"syscall"
+
+	"git.ophivana.moe/security/fortify/internal"
 )
 
 const (
 	fsuConfFile = "/etc/fsurc"
 	envShim     = "FORTIFY_SHIM"
 	envAID      = "FORTIFY_APP_ID"
-
-	fpPoison = "INVALIDINVALIDINVALIDINVALIDINVALID"
 )
 
-// FortifyPath is the path to fortify, set at compile time.
-var FortifyPath = fpPoison
-
 func main() {
 	log.SetFlags(0)
 	log.SetPrefix("fsu: ")
@@ -35,9 +32,11 @@ func main() {
 		log.Fatal("this program must not be started by root")
 	}
 
-	// validate compiled in fortify path
+	var fmain string
-	if FortifyPath == fpPoison || !path.IsAbs(FortifyPath) {
+	if p, ok := internal.Path(internal.Fmain); !ok {
 		log.Fatal("invalid fortify path, this copy of fsu is not compiled correctly")
+	} else {
+		fmain = p
 	}
 
 	pexe := path.Join("/proc", strconv.Itoa(os.Getppid()), "exe")
@@ -45,7 +44,7 @@ func main() {
 		log.Fatalf("cannot read parent executable path: %v", err)
 	} else if strings.HasSuffix(p, " (deleted)") {
 		log.Fatal("fortify executable has been deleted")
-	} else if p != FortifyPath {
+	} else if p != fmain {
 		log.Fatal("this program must be started by fortify")
 	}
 
@@ -86,7 +85,7 @@ func main() {
 	if err := syscall.Setresuid(uid, uid, uid); err != nil {
 		log.Fatalf("cannot set uid: %v", err)
 	}
-	if err := syscall.Exec(FortifyPath, []string{"fortify", "shim"}, []string{envShim + "=" + shimSetupPath}); err != nil {
+	if err := syscall.Exec(fmain, []string{"fortify", "shim"}, []string{envShim + "=" + shimSetupPath}); err != nil {
 		log.Fatalf("cannot start shim: %v", err)
 	}
 

internal/app/app.go

@@ -3,8 +3,8 @@ package app
 import (
 	"sync"
 
-	"git.ophivana.moe/security/fortify/internal"
+	"git.ophivana.moe/security/fortify/cmd/fshim/ipc/shim"
-	"git.ophivana.moe/security/fortify/internal/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 {
+func (s *stubNixOS) FshimPath() string {
-	return internal.Paths{
+	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
+	// launch fortify shim
-	innerCommand.WriteString("exec " + a.seal.sys.executable + " 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/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
+}

main.go

@@ -4,11 +4,9 @@ import (
 	"flag"
 	"syscall"
 
-	"git.ophivana.moe/security/fortify/internal"
 	"git.ophivana.moe/security/fortify/internal/app"
 	"git.ophivana.moe/security/fortify/internal/fmsg"
-	init0 "git.ophivana.moe/security/fortify/internal/init"
+	"git.ophivana.moe/security/fortify/internal/linux"
-	"git.ophivana.moe/security/fortify/internal/shim"
 )
 
 var (
@@ -19,12 +17,12 @@ func init() {
 	flag.BoolVar(&flagVerbose, "v", false, "Verbose output")
 }
 
-var os = new(internal.Std)
+var os = new(linux.Std)
 
 func main() {
 	// linux/sched/coredump.h
 	if _, _, errno := syscall.RawSyscall(syscall.SYS_PRCTL, syscall.PR_SET_DUMPABLE, 0, 0); errno != 0 {
-		fmsg.Printf("fortify: cannot set SUID_DUMP_DISABLE: %s", errno.Error())
+		fmsg.Printf("cannot set SUID_DUMP_DISABLE: %s", errno.Error())
 	}
 
 	flag.Parse()
@@ -34,10 +32,6 @@ func main() {
 		fmsg.VPrintln("system booted with systemd as init system")
 	}
 
-	// shim/init early exit
-	init0.Try()
-	shim.Try()
-
 	// root check
 	if os.Geteuid() == 0 {
 		fmsg.Fatal("this program must not run as root")

package.nix

@@ -15,14 +15,27 @@ buildGoModule rec {
   src = ./.;
   vendorHash = null;
 
-  ldflags = [
+  ldflags =
+    lib.attrsets.foldlAttrs
+      (
+        ldflags: name: value:
+        ldflags
+        ++ [
+          "-X"
+          "git.ophivana.moe/security/fortify/internal.${name}=${value}"
+        ]
+      )
+      [
         "-s"
         "-w"
-    "-X"
+      ]
-    "main.Version=v${version}"
+      {
-    "-X"
+        Version = "v${version}";
-    "main.FortifyPath=${placeholder "out"}/bin/.fortify-wrapped"
+        Fmain = "${placeholder "out"}/bin/.fortify-wrapped";
-  ];
+        Fsu = "/run/wrappers/bin/fsu";
+        Fshim = "${placeholder "out"}/bin/.fshim";
+        Finit = "${placeholder "out"}/bin/.finit";
+      };
 
   buildInputs = [
     acl
@@ -40,5 +53,7 @@ buildGoModule rec {
     }
 
     mv $out/bin/fsu $out/bin/.fsu
+    mv $out/bin/fshim $out/bin/.fshim
+    mv $out/bin/finit $out/bin/.finit
   '';
 }

version.go

@@ -3,11 +3,11 @@ package main
 import (
 	"flag"
 	"fmt"
+
+	"git.ophivana.moe/security/fortify/internal"
 )
 
 var (
-	Version = "impure"
-
 	printVersion bool
 )
 
@@ -17,7 +17,11 @@ func init() {
 
 func tryVersion() {
 	if printVersion {
-		fmt.Println(Version)
+		if v, ok := internal.Check(internal.Version); ok {
+			fmt.Println(v)
+		} else {
+			fmt.Println("impure")
+		}
 		os.Exit(0)
 	}
 }