app: store values with string representation

Improves code readability without changing memory layout.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/app/app.go

@@ -1,6 +1,7 @@
 package app
 
 import (
+	"fmt"
 	"sync"
 
 	"git.gensokyo.uk/security/fortify/fst"
@@ -10,14 +11,18 @@ import (
 
 func New(os sys.State) (fst.App, error) {
 	a := new(app)
-	a.id = new(fst.ID)
 	a.os = os
-	return a, fst.NewAppID(a.id)
+
+	id := new(fst.ID)
+	err := fst.NewAppID(id)
+	a.id = newID(id)
+
+	return a, err
 }
 
 type app struct {
 	// application unique identifier
-	id *fst.ID
+	id *stringPair[fst.ID]
 	// operating system interface
 	os sys.State
 	// shim process manager
@@ -28,13 +33,11 @@ type app struct {
 	lock sync.RWMutex
 }
 
-func (a *app) ID() fst.ID {
-	return *a.id
-}
+func (a *app) ID() fst.ID { return a.id.unwrap() }
 
 func (a *app) String() string {
 	if a == nil {
-		return "(invalid fortified app)"
+		return "(invalid app)"
 	}
 
 	a.lock.RLock()
@@ -45,8 +48,11 @@ func (a *app) String() string {
 	}
 
 	if a.seal != nil {
-		return "(sealed fortified app as uid " + a.seal.sys.user.us + ")"
+		if a.seal.sys.user.uid == nil {
+			return fmt.Sprintf("(sealed app %s with invalid uid)", a.id)
+		}
+		return fmt.Sprintf("(sealed app %s as uid %s)", a.id, a.seal.sys.user.uid)
 	}
 
-	return "(unsealed fortified app)"
+	return fmt.Sprintf("(unsealed app %s)", a.id)
 }

internal/app/export_test.go

@@ -9,7 +9,7 @@ import (
 
 func NewWithID(id fst.ID, os sys.State) fst.App {
 	a := new(app)
-	a.id = &id
+	a.id = newID(&id)
 	a.os = os
 	return a
 }

internal/app/seal.go

@@ -9,7 +9,6 @@ import (
 	"io/fs"
 	"path"
 	"regexp"
-	"strconv"
 
 	"git.gensokyo.uk/security/fortify/acl"
 	"git.gensokyo.uk/security/fortify/dbus"
@@ -110,14 +109,17 @@ func (a *app) Seal(config *fst.Config) error {
 	// create seal system component
 	seal.sys = new(appSealSys)
 
-	// mapped uid
+	{
+		// mapped uid defaults to 65534 to work around file ownership checks due to a bwrap limitation
+		mapuid := 65534
 		if config.Confinement.Sandbox != nil && config.Confinement.Sandbox.MapRealUID {
-		seal.sys.mappedID = a.os.Geteuid()
-	} else {
-		seal.sys.mappedID = 65534
+			// some programs fail to connect to dbus session running as a different uid, so a
+			// separate workaround is introduced to map priv-side caller uid in namespace
+			mapuid = a.os.Geteuid()
+		}
+		seal.sys.mapuid = newInt(mapuid)
+		seal.sys.runtime = path.Join("/run/user", seal.sys.mapuid.String())
 	}
-	seal.sys.mappedIDString = strconv.Itoa(seal.sys.mappedID)
-	seal.sys.runtime = path.Join("/run/user", seal.sys.mappedIDString)
 
 	// validate uid and set user info
 	if config.Confinement.AppID < 0 || config.Confinement.AppID > 9999 {
@@ -125,8 +127,7 @@ func (a *app) Seal(config *fst.Config) error {
 			fmt.Sprintf("aid %d out of range", config.Confinement.AppID))
 	}
 	seal.sys.user = appUser{
-		aid:      config.Confinement.AppID,
-		as:       strconv.Itoa(config.Confinement.AppID),
+		aid:      newInt(config.Confinement.AppID),
 		data:     config.Confinement.Outer,
 		home:     config.Confinement.Inner,
 		username: config.Confinement.Username,
@@ -147,11 +148,10 @@ func (a *app) Seal(config *fst.Config) error {
 	}
 
 	// invoke fsu for full uid
-	if u, err := a.os.Uid(seal.sys.user.aid); err != nil {
+	if u, err := a.os.Uid(seal.sys.user.aid.unwrap()); err != nil {
 		return err
 	} else {
-		seal.sys.user.uid = u
-		seal.sys.user.us = strconv.Itoa(u)
+		seal.sys.user.uid = newInt(u)
 	}
 
 	// resolve supplementary group ids from names
@@ -251,7 +251,7 @@ func (a *app) Seal(config *fst.Config) error {
 	seal.store = state.NewMulti(seal.RunDirPath)
 
 	// initialise system interface with os uid
-	seal.sys.I = system.New(seal.sys.user.uid)
+	seal.sys.I = system.New(seal.sys.user.uid.unwrap())
 	seal.sys.I.IsVerbose = fmsg.Load
 	seal.sys.I.Verbose = fmsg.Verbose
 	seal.sys.I.Verbosef = fmsg.Verbosef
@@ -267,7 +267,7 @@ func (a *app) Seal(config *fst.Config) error {
 
 	// verbose log seal information
 	fmsg.Verbosef("created application seal for uid %s (%s) groups: %v, command: %s",
-		seal.sys.user.us, seal.sys.user.username, config.Confinement.Groups, config.Command)
+		seal.sys.user.uid, seal.sys.user.username, config.Confinement.Groups, config.Command)
 
 	// seal app and release lock
 	a.seal = seal

internal/app/share.go

@@ -68,7 +68,7 @@ func (seal *appSeal) setupShares(bus [2]*dbus.Config, os sys.State) error {
 	seal.sys.UpdatePermType(system.User, targetTmpdirParent, acl.Execute)
 
 	// ensure child tmpdir (e.g. `/tmp/fortify.%d/tmpdir/%d`)
-	targetTmpdir := path.Join(targetTmpdirParent, seal.sys.user.as)
+	targetTmpdir := path.Join(targetTmpdirParent, seal.sys.user.aid.String())
 	seal.sys.Ensure(targetTmpdir, 01700)
 	seal.sys.UpdatePermType(system.User, targetTmpdir, acl.Read, acl.Write, acl.Execute)
 	seal.sys.bwrap.Bind(targetTmpdir, "/tmp", false, true)
@@ -126,9 +126,9 @@ func (seal *appSeal) setupShares(bus [2]*dbus.Config, os sys.State) error {
 
 	// generate /etc/passwd and /etc/group
 	seal.sys.bwrap.CopyBind("/etc/passwd",
-		[]byte(username+":x:"+seal.sys.mappedIDString+":"+seal.sys.mappedIDString+":Fortify:"+homeDir+":"+sh+"\n"))
+		[]byte(username+":x:"+seal.sys.mapuid.String()+":"+seal.sys.mapuid.String()+":Fortify:"+homeDir+":"+sh+"\n"))
 	seal.sys.bwrap.CopyBind("/etc/group",
-		[]byte("fortify:x:"+seal.sys.mappedIDString+":\n"))
+		[]byte("fortify:x:"+seal.sys.mapuid.String()+":\n"))
 
 	/*
 		Display servers
@@ -181,7 +181,7 @@ func (seal *appSeal) setupShares(bus [2]*dbus.Config, os sys.State) error {
 			return fmsg.WrapError(ErrXDisplay,
 				"DISPLAY is not set")
 		} else {
-			seal.sys.ChangeHosts("#" + seal.sys.user.us)
+			seal.sys.ChangeHosts("#" + seal.sys.user.uid.String())
 			seal.sys.bwrap.SetEnv[display] = d
 			seal.sys.bwrap.Bind("/tmp/.X11-unix", "/tmp/.X11-unix")
 		}

internal/app/start.go

@@ -57,7 +57,7 @@ func (a *app) Run(ctx context.Context, rs *fst.RunState) error {
 	a.shim = new(shim.Shim)
 	waitErr := make(chan error, 1)
 	if startTime, err := a.shim.Start(
-		a.seal.sys.user.as,
+		a.seal.sys.user.aid.String(),
 		a.seal.sys.user.supp,
 		a.seal.sys.sp,
 	); err != nil {
@@ -90,14 +90,14 @@ func (a *app) Run(ctx context.Context, rs *fst.RunState) error {
 
 		// shim accepted setup payload, create process state
 		sd := state.State{
-			ID:   *a.id,
+			ID:   a.id.unwrap(),
 			PID:  a.shim.Unwrap().Process.Pid,
 			Time: *startTime,
 		}
 
 		// register process state
 		var err0 = new(StateStoreError)
-		err0.Inner, err0.DoErr = a.seal.store.Do(a.seal.sys.user.aid, func(c state.Cursor) {
+		err0.Inner, err0.DoErr = a.seal.store.Do(a.seal.sys.user.aid.unwrap(), func(c state.Cursor) {
 			err0.InnerErr = c.Save(&sd, a.seal.ct)
 		})
 		a.seal.sys.saveState = true
@@ -147,11 +147,11 @@ func (a *app) Run(ctx context.Context, rs *fst.RunState) error {
 
 	// update store and revert app setup transaction
 	e := new(StateStoreError)
-	e.Inner, e.DoErr = a.seal.store.Do(a.seal.sys.user.aid, func(b state.Cursor) {
+	e.Inner, e.DoErr = a.seal.store.Do(a.seal.sys.user.aid.unwrap(), func(b state.Cursor) {
 		e.InnerErr = func() error {
 			// destroy defunct state entry
 			if cmd := a.shim.Unwrap(); cmd != nil && a.seal.sys.saveState {
-				if err := b.Destroy(*a.id); err != nil {
+				if err := b.Destroy(a.id.unwrap()); err != nil {
 					return err
 				}
 			}

internal/app/strings.go

@@ -0,0 +1,19 @@
+package app
+
+import (
+	"strconv"
+
+	"git.gensokyo.uk/security/fortify/fst"
+)
+
+func newInt(v int) *stringPair[int]        { return &stringPair[int]{v, strconv.Itoa(v)} }
+func newID(id *fst.ID) *stringPair[fst.ID] { return &stringPair[fst.ID]{*id, id.String()} }
+
+// stringPair stores a value and its string representation.
+type stringPair[T comparable] struct {
+	v T
+	s string
+}
+
+func (s *stringPair[T]) unwrap() T      { return s.v }
+func (s *stringPair[T]) String() string { return s.s }

internal/app/system.go

@@ -21,9 +21,7 @@ type appSealSys struct {
 	user appUser
 
 	// mapped uid and gid in user namespace
-	mappedID int
-	// string representation of mappedID
-	mappedIDString string
+	mapuid *stringPair[int]
 
 	needRevert bool
 	saveState  bool
@@ -33,19 +31,14 @@ type appSealSys struct {
 }
 
 type appUser struct {
-	// full uid resolved by fsu
-	uid int
-	// string representation of uid
-	us string
+	// application id
+	aid *stringPair[int]
+	// target uid resolved by fid:aid
+	uid *stringPair[int]
 
 	// supplementary group ids
 	supp []string
 
-	// application id
-	aid int
-	// string representation of aid
-	as string
-
 	// home directory host path
 	data string
 	// app user home directory