helper/bwrap: ordered filesystem args

The argument builder was written based on the incorrect assumption that bwrap arguments are unordered. The argument builder is replaced in this commit to correct that mistake.

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

internal/app/config.go

@@ -1,11 +1,18 @@
 package app
 
 import (
+	"encoding/gob"
+	"os"
+
 	"git.ophivana.moe/cat/fortify/dbus"
 	"git.ophivana.moe/cat/fortify/helper/bwrap"
 	"git.ophivana.moe/cat/fortify/internal/state"
 )
 
+func init() {
+	gob.Register(new(bwrap.PermConfig[*bwrap.TmpfsConfig]))
+}
+
 // Config is used to seal an *App
 type Config struct {
 	// D-Bus application ID
@@ -55,7 +62,7 @@ type SandboxConfig struct {
 	// sandbox host filesystem access
 	Filesystem []*FilesystemConfig `json:"filesystem"`
 	// tmpfs mount points to mount last
-	Tmpfs []bwrap.TmpfsConfig `json:"tmpfs"`
+	Tmpfs []string `json:"tmpfs"`
 }
 
 type FilesystemConfig struct {
@@ -71,61 +78,39 @@ type FilesystemConfig struct {
 	Must bool `json:"require,omitempty"`
 }
 
+// Bwrap returns the address of the corresponding bwrap.Config to s.
+// Note that remaining tmpfs entries must be queued by the caller prior to launch.
 func (s *SandboxConfig) Bwrap() *bwrap.Config {
 	if s == nil {
 		return nil
 	}
 
-	nobody := 65534
-	conf := &bwrap.Config{
+	conf := (&bwrap.Config{
 		Net:           s.Net,
 		UserNS:        s.UserNS,
-		UID:           &nobody,
-		GID:           &nobody,
 		Hostname:      s.Hostname,
 		Clearenv:      true,
 		SetEnv:        s.Env,
-		Procfs:        []string{"/proc"},
-		DevTmpfs:      []string{"/dev"},
-		Mqueue:        []string{"/dev/mqueue"},
 		NewSession:    !s.NoNewSession,
 		DieWithParent: true,
 		AsInit:        true,
-	}
+
+		// initialise map
+		Chmod: make(map[string]os.FileMode),
+	}).
+		SetUID(65534).SetGID(65534).
+		Procfs("/proc").DevTmpfs("/dev").Mqueue("/dev/mqueue")
 
 	for _, c := range s.Filesystem {
 		if c == nil {
 			continue
 		}
-		p := [2]string{c.Src, c.Dst}
+		src := c.Src
+		dest := c.Dst
 		if c.Dst == "" {
-			p[1] = c.Src
+			dest = c.Src
 		}
-
-		switch {
-		case c.Device:
-			if c.Must {
-				conf.DevBind = append(conf.DevBind, p)
-			} else {
-				conf.DevBindTry = append(conf.DevBindTry, p)
-			}
-		case c.Write:
-			if c.Must {
-				conf.Bind = append(conf.Bind, p)
-			} else {
-				conf.BindTry = append(conf.BindTry, p)
-			}
-		default:
-			if c.Must {
-				conf.ROBind = append(conf.ROBind, p)
-			} else {
-				conf.ROBindTry = append(conf.ROBindTry, p)
-			}
-		}
-	}
-
-	for _, tmpfs := range s.Tmpfs {
-		conf.Tmpfs = append(conf.Tmpfs, bwrap.PermConfig[bwrap.TmpfsConfig]{Path: tmpfs, Last: true})
+		conf.Bind(src, dest, !c.Must, c.Write, c.Device)
 	}
 
 	return conf
@@ -164,9 +149,7 @@ func Template() *Config {
 					{Src: "/data/user/0", Dst: "/data/data", Write: true, Must: true},
 					{Src: "/var/tmp", Write: true},
 				},
-				Tmpfs: []bwrap.TmpfsConfig{
-					{Size: 8 * 1024, Dir: "/var/run/nscd"},
-				},
+				Tmpfs: []string{"/var/run/nscd"},
 			},
 			SystemBus: &dbus.Config{
 				See:       nil,

internal/app/seal.go

@@ -9,7 +9,6 @@ import (
 	"strconv"
 
 	"git.ophivana.moe/cat/fortify/dbus"
-	"git.ophivana.moe/cat/fortify/helper/bwrap"
 	"git.ophivana.moe/cat/fortify/internal"
 	"git.ophivana.moe/cat/fortify/internal/state"
 	"git.ophivana.moe/cat/fortify/internal/verbose"
@@ -163,7 +162,7 @@ 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) {
-			conf.Tmpfs = append(conf.Tmpfs, bwrap.TmpfsConfig{Size: 8 * 1024, Dir: nscd})
+			conf.Tmpfs = append(conf.Tmpfs, nscd)
 		}
 		// bind GPU stuff
 		if config.Confinement.Enablements.Has(state.EnableX) || config.Confinement.Enablements.Has(state.EnableWayland) {
@@ -172,6 +171,7 @@ func (a *app) Seal(config *Config) error {
 		config.Confinement.Sandbox = conf
 	}
 	seal.sys.bwrap = config.Confinement.Sandbox.Bwrap()
+	seal.sys.tmpfs = config.Confinement.Sandbox.Tmpfs
 	if seal.sys.bwrap.SetEnv == nil {
 		seal.sys.bwrap.SetEnv = make(map[string]string)
 	}

internal/app/share.dbus.go

@@ -65,12 +65,12 @@ func (seal *appSeal) shareDBus(config [2]*dbus.Config) error {
 	// share proxy sockets
 	sessionInner := path.Join(seal.sys.runtime, "bus")
 	seal.sys.setEnv(dbusSessionBusAddress, "unix:path="+sessionInner)
-	seal.sys.bind(sessionBus[1], sessionInner, true)
+	seal.sys.bwrap.Bind(sessionBus[1], sessionInner)
 	seal.sys.updatePerm(sessionBus[1], acl.Read, acl.Write)
 	if seal.sys.dbusSystem {
 		systemInner := "/run/dbus/system_bus_socket"
 		seal.sys.setEnv(dbusSystemBusAddress, "unix:path="+systemInner)
-		seal.sys.bind(systemBus[1], systemInner, true)
+		seal.sys.bwrap.Bind(systemBus[1], systemInner)
 		seal.sys.updatePerm(systemBus[1], acl.Read, acl.Write)
 	}
 

internal/app/share.display.go

@@ -41,7 +41,7 @@ func (seal *appSeal) shareDisplay() error {
 			w := path.Join(seal.sys.runtime, "wayland-0")
 			seal.sys.link(wp, wpi)
 			seal.sys.setEnv(waylandDisplay, w)
-			seal.sys.bind(wpi, w, true)
+			seal.sys.bwrap.Bind(wpi, w)
 
 			// ensure Wayland socket ACL (e.g. `/run/user/%d/wayland-%d`)
 			seal.sys.updatePermTag(state.EnableWayland, wp, acl.Read, acl.Write, acl.Execute)
@@ -59,7 +59,7 @@ func (seal *appSeal) shareDisplay() error {
 		} else {
 			seal.sys.changeHosts(seal.sys.Username)
 			seal.sys.setEnv(display, d)
-			seal.sys.bind("/tmp/.X11-unix", "/tmp/.X11-unix", true)
+			seal.sys.bwrap.Bind("/tmp/.X11-unix", "/tmp/.X11-unix")
 		}
 	}
 

internal/app/share.pulse.go

@@ -65,7 +65,7 @@ func (seal *appSeal) sharePulse() error {
 	psi := path.Join(seal.shareLocal, "pulse")
 	p := path.Join(seal.sys.runtime, "pulse", "native")
 	seal.sys.link(ps, psi)
-	seal.sys.bind(psi, p, true)
+	seal.sys.bwrap.Bind(psi, p)
 	seal.sys.setEnv(pulseServer, "unix:"+p)
 
 	// publish current user's pulse cookie for target user

internal/app/share.runtime.go

@@ -4,7 +4,6 @@ import (
 	"path"
 
 	"git.ophivana.moe/cat/fortify/acl"
-	"git.ophivana.moe/cat/fortify/helper/bwrap"
 	"git.ophivana.moe/cat/fortify/internal/state"
 )
 
@@ -17,20 +16,13 @@ const (
 // shareRuntime queues actions for sharing/ensuring the runtime and share directories
 func (seal *appSeal) shareRuntime() {
 	// mount tmpfs on inner runtime (e.g. `/run/user/%d`)
-	seal.sys.bwrap.Tmpfs = append(seal.sys.bwrap.Tmpfs,
-		bwrap.PermConfig[bwrap.TmpfsConfig]{
-			Path: bwrap.TmpfsConfig{
-				Size: 1 * 1024 * 1024,
-				Dir:  "/run/user",
-			},
-		},
-		bwrap.PermConfig[bwrap.TmpfsConfig]{
-			Path: bwrap.TmpfsConfig{
-				Size: 8 * 1024 * 1024,
-				Dir:  seal.sys.runtime,
-			},
-		},
-	)
+	seal.sys.bwrap.Tmpfs("/run/user", 1*1024*1024)
+	seal.sys.bwrap.Tmpfs(seal.sys.runtime, 8*1024*1024)
+
+	// point to inner runtime path `/run/user/%d`
+	seal.sys.setEnv(xdgRuntimeDir, seal.sys.runtime)
+	seal.sys.setEnv(xdgSessionClass, "user")
+	seal.sys.setEnv(xdgSessionType, "tty")
 
 	// ensure RunDir (e.g. `/run/user/%d/fortify`)
 	seal.sys.ensure(seal.RunDirPath, 0700)
@@ -53,22 +45,3 @@ func (seal *appSeal) shareRuntime() {
 	seal.sys.ensureEphemeral(seal.shareLocal, 0700)
 	seal.sys.updatePerm(seal.shareLocal, acl.Execute)
 }
-
-func (seal *appSeal) shareRuntimeChild() string {
-	// ensure child runtime parent directory (e.g. `/tmp/fortify.%d/runtime`)
-	targetRuntimeParent := path.Join(seal.SharePath, "runtime")
-	seal.sys.ensure(targetRuntimeParent, 0700)
-	seal.sys.updatePermTag(state.EnableLength, targetRuntimeParent, acl.Execute)
-
-	// ensure child runtime directory (e.g. `/tmp/fortify.%d/runtime/%d`)
-	targetRuntime := path.Join(targetRuntimeParent, seal.sys.Uid)
-	seal.sys.ensure(targetRuntime, 0700)
-	seal.sys.updatePermTag(state.EnableLength, targetRuntime, acl.Read, acl.Write, acl.Execute)
-
-	// point to ensured runtime path
-	seal.sys.setEnv(xdgRuntimeDir, targetRuntime)
-	seal.sys.setEnv(xdgSessionClass, "user")
-	seal.sys.setEnv(xdgSessionType, "tty")
-
-	return targetRuntime
-}

internal/app/share.system.go

@@ -3,6 +3,9 @@ package app
 import (
 	"os"
 	"path"
+
+	"git.ophivana.moe/cat/fortify/acl"
+	"git.ophivana.moe/cat/fortify/internal/state"
 )
 
 const (
@@ -38,6 +41,24 @@ func (seal *appSeal) shareSystem() {
 	seal.sys.writeFile(groupPath, []byte("fortify:x:65534:\n"))
 
 	// bind /etc/passwd and /etc/group
-	seal.sys.bind(passwdPath, "/etc/passwd", true)
-	seal.sys.bind(groupPath, "/etc/group", true)
+	seal.sys.bwrap.Bind(passwdPath, "/etc/passwd")
+	seal.sys.bwrap.Bind(groupPath, "/etc/group")
+}
+
+func (seal *appSeal) shareTmpdirChild() string {
+	// ensure child tmpdir parent directory (e.g. `/tmp/fortify.%d/tmpdir`)
+	targetTmpdirParent := path.Join(seal.SharePath, "tmpdir")
+	seal.sys.ensure(targetTmpdirParent, 0700)
+	seal.sys.updatePermTag(state.EnableLength, targetTmpdirParent, acl.Execute)
+
+	// ensure child tmpdir (e.g. `/tmp/fortify.%d/tmpdir/%d`)
+	targetTmpdir := path.Join(targetTmpdirParent, seal.sys.Uid)
+	seal.sys.ensure(targetTmpdir, 01700)
+	seal.sys.updatePermTag(state.EnableLength, targetTmpdir, acl.Read, acl.Write, acl.Execute)
+	seal.sys.bwrap.Bind(targetTmpdir, "/tmp", false, true)
+
+	// mount tmpfs on inner shared directory (e.g. `/tmp/fortify.%d`)
+	seal.sys.bwrap.Tmpfs(seal.SharePath, 1*1024*1024)
+
+	return targetTmpdir
 }

internal/app/start.go

@@ -70,7 +70,7 @@ func (a *app) Start() error {
 	a.cmd.Stderr = os.Stderr
 	a.cmd.Dir = a.seal.RunDirPath
 
-	if wls, err := shim.ServeConfig(confSockPath, &shim.Payload{
+	if wls, err := shim.ServeConfig(confSockPath, a.seal.sys.uid, &shim.Payload{
 		Argv:  a.seal.command,
 		Exec:  shimExec,
 		Bwrap: a.seal.sys.bwrap,

internal/app/system.go

@@ -59,6 +59,7 @@ type appSeal struct {
 // appSealTx contains the system-level component of the app seal
 type appSealTx struct {
 	bwrap *bwrap.Config
+	tmpfs []string
 
 	// reference to D-Bus proxy instance, nil if disabled
 	dbus *dbus.Proxy
@@ -110,15 +111,6 @@ func (tx *appSealTx) setEnv(k, v string) {
 	tx.bwrap.SetEnv[k] = v
 }
 
-// bind mounts a directory within the sandbox
-func (tx *appSealTx) bind(src, dest string, ro bool) {
-	if !ro {
-		tx.bwrap.Bind = append(tx.bwrap.Bind, [2]string{src, dest})
-	} else {
-		tx.bwrap.ROBind = append(tx.bwrap.ROBind, [2]string{src, dest})
-	}
-}
-
 // ensure appends a directory ensure action
 func (tx *appSealTx) ensure(path string, perm os.FileMode) {
 	tx.mkdir = append(tx.mkdir, appEnsureEntry{path, perm, false})
@@ -183,14 +175,14 @@ func (tx *appSealTx) changeHosts(username string) {
 func (tx *appSealTx) writeFile(dst string, data []byte) {
 	tx.files = append(tx.files, [2]string{dst, string(data)})
 	tx.updatePerm(dst, acl.Read)
-	tx.bind(dst, dst, true)
+	tx.bwrap.Bind(dst, dst)
 }
 
 // copyFile appends a tmpfiles action
 func (tx *appSealTx) copyFile(dst, src string) {
 	tx.tmpfiles = append(tx.tmpfiles, [2]string{dst, src})
 	tx.updatePerm(dst, acl.Read)
-	tx.bind(dst, dst, true)
+	tx.bwrap.Bind(dst, dst)
 }
 
 // link appends a hardlink action
@@ -324,6 +316,12 @@ func (tx *appSealTx) commit() error {
 
 	// disarm partial commit rollback
 	txp = nil
+
+	// queue tmpfs at the end of tx.bwrap.Filesystem
+	for _, dest := range tx.tmpfs {
+		tx.bwrap.Tmpfs(dest, 8*1024)
+	}
+
 	return nil
 }
 
@@ -416,10 +414,10 @@ func (seal *appSeal) shareAll(bus [2]*dbus.Config) error {
 	}
 	seal.shared = true
 
+	targetTmpdir := seal.shareTmpdirChild()
+	verbose.Printf("child tmpdir %q configured\n", targetTmpdir)
 	seal.shareRuntime()
 	seal.shareSystem()
-	targetRuntime := seal.shareRuntimeChild()
-	verbose.Printf("child runtime data dir '%s' configured\n", targetRuntime)
 	if err := seal.shareDisplay(); err != nil {
 		return err
 	}

internal/shim/parent.go

@@ -8,12 +8,13 @@ import (
 	"os"
 	"syscall"
 
+	"git.ophivana.moe/cat/fortify/acl"
 	"git.ophivana.moe/cat/fortify/internal/verbose"
 )
 
 // called in the parent process
 
-func ServeConfig(socket string, payload *Payload, wl string, done chan struct{}) (*net.UnixConn, error) {
+func ServeConfig(socket string, uid int, payload *Payload, wl string, done chan struct{}) (*net.UnixConn, error) {
 	var ws *net.UnixConn
 	if payload.WL {
 		if f, err := net.DialUnix("unix", nil, &net.UnixAddr{Name: wl, Net: "unix"}); err != nil {
@@ -28,7 +29,7 @@ func ServeConfig(socket string, payload *Payload, wl string, done chan struct{})
 		return nil, err
 	} else {
 		verbose.Println("configuring shim on socket", socket)
-		if err = os.Chmod(socket, 0777); err != nil {
+		if err = acl.UpdatePerm(socket, uid, acl.Read, acl.Write, acl.Execute); err != nil {
 			fmt.Println("fortify: cannot change permissions of shim setup socket:", err)
 		}
 
@@ -39,6 +40,7 @@ func ServeConfig(socket string, payload *Payload, wl string, done chan struct{})
 			} else {
 				if err = gob.NewEncoder(conn).Encode(*payload); err != nil {
 					fmt.Println("fortify: cannot stream shim payload:", err)
+					_ = os.Remove(socket)
 					return
 				}