fortify/internal/app/system.go

379 lines
10 KiB
Go

package app
import (
"errors"
"fmt"
"io/fs"
"os"
"os/user"
"git.ophivana.moe/cat/fortify/acl"
"git.ophivana.moe/cat/fortify/dbus"
"git.ophivana.moe/cat/fortify/internal"
"git.ophivana.moe/cat/fortify/internal/state"
"git.ophivana.moe/cat/fortify/internal/verbose"
"git.ophivana.moe/cat/fortify/xcb"
)
// appSeal seals the application with child-related information
type appSeal struct {
// application unique identifier
id *appID
// freedesktop application ID
fid string
// argv to start process with in the final confined environment
command []string
// environment variables of fortified process
env []string
// persistent process state store
store state.Store
// uint8 representation of launch method sealed from config
launchOption uint8
// process-specific share directory path
share string
// process-specific share directory path local to XDG_RUNTIME_DIR
shareLocal string
// path to launcher program
toolPath string
// pass-through enablement tracking from config
et state.Enablements
// prevents sharing from happening twice
shared bool
// seal system-level component
sys *appSealTx
// used in various sealing operations
internal.SystemConstants
// protected by upstream mutex
}
// appendEnv appends an environment variable for the child process
func (seal *appSeal) appendEnv(k, v string) {
seal.env = append(seal.env, k+"="+v)
}
// appSealTx contains the system-level component of the app seal
type appSealTx struct {
// reference to D-Bus proxy instance, nil if disabled
dbus *dbus.Proxy
// notification from goroutine waiting for dbus.Proxy
dbusWait chan struct{}
// upstream address/downstream path used to initialise dbus.Proxy
dbusAddr *[2][2]string
// whether system bus proxy is enabled
dbusSystem bool
// paths to append/strip ACLs (of target user) from
acl []*appACLEntry
// X11 ChangeHosts commands to perform
xhost []string
// paths of directories to ensure
mkdir []appEnsureEntry
// dst, src pairs of temporarily shared files
tmpfiles [][2]string
// dst, src pairs of temporarily hard linked files
hardlinks [][2]string
// sealed path to fortify executable, used by shim
executable string
// target user UID as an integer
uid int
// target user sealed from config
*user.User
// prevents commit from happening twice
complete bool
// prevents cleanup from happening twice
closed bool
// protected by upstream mutex
}
type appEnsureEntry struct {
path string
perm os.FileMode
remove bool
}
// ensure appends a directory ensure action
func (tx *appSealTx) ensure(path string, perm os.FileMode) {
tx.mkdir = append(tx.mkdir, appEnsureEntry{path, perm, false})
}
// ensureEphemeral appends a directory ensure action with removal in rollback
func (tx *appSealTx) ensureEphemeral(path string, perm os.FileMode) {
tx.mkdir = append(tx.mkdir, appEnsureEntry{path, perm, true})
}
// appACLEntry contains information for applying/reverting an ACL entry
type appACLEntry struct {
path string
perms []acl.Perm
}
func (e *appACLEntry) String() string {
var s = []byte("---")
for _, p := range e.perms {
switch p {
case acl.Read:
s[0] = 'r'
case acl.Write:
s[1] = 'w'
case acl.Execute:
s[2] = 'x'
}
}
return string(s)
}
// updatePerm appends an acl update action
func (tx *appSealTx) updatePerm(path string, perms ...acl.Perm) {
tx.acl = append(tx.acl, &appACLEntry{path, perms})
}
// changeHosts appends target username of an X11 ChangeHosts action
func (tx *appSealTx) changeHosts(username string) {
tx.xhost = append(tx.xhost, username)
}
// 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)
}
// link appends a hardlink action
func (tx *appSealTx) link(oldname, newname string) {
tx.hardlinks = append(tx.hardlinks, [2]string{oldname, newname})
}
type (
ChangeHostsError BaseError
EnsureDirError BaseError
TmpfileError BaseError
DBusStartError BaseError
ACLUpdateError BaseError
)
// commit applies recorded actions
// order: xhost, mkdir, tmpfiles, hardlinks, dbus, acl
func (tx *appSealTx) commit() error {
if tx.complete {
panic("seal transaction committed twice")
}
tx.complete = true
txp := &appSealTx{}
defer func() {
// rollback partial commit
if txp != nil {
// global changes (x11, ACLs) are always repeated and check for other launchers cannot happen here
// attempting cleanup here will cause other fortified processes to lose access to them
// a better (and more secure) fix is to proxy access to these resources and eliminate the ACLs altogether
if err := txp.revert(false); err != nil {
fmt.Println("fortify: errors returned reverting partial commit:", err)
}
}
}()
// insert xhost entries
for _, username := range tx.xhost {
verbose.Printf("inserting XHost entry SI:localuser:%s\n", username)
if err := xcb.ChangeHosts(xcb.HostModeInsert, xcb.FamilyServerInterpreted, "localuser\x00"+username); err != nil {
return (*ChangeHostsError)(wrapError(err,
fmt.Sprintf("cannot insert XHost entry SI:localuser:%s, %s", username, err)))
} else {
// register partial commit
txp.changeHosts(username)
}
}
// ensure directories
for _, dir := range tx.mkdir {
verbose.Println("ensuring directory mode:", dir.perm.String(), "path:", dir.path)
if err := os.Mkdir(dir.path, dir.perm); err != nil && !errors.Is(err, fs.ErrExist) {
return (*EnsureDirError)(wrapError(err,
fmt.Sprintf("cannot create directory '%s': %s", dir.path, err)))
} else {
// only ephemeral dirs require rollback
if dir.remove {
// register partial commit
txp.ensureEphemeral(dir.path, dir.perm)
}
}
}
// publish tmpfiles
for _, tmpfile := range tx.tmpfiles {
verbose.Println("publishing tmpfile", tmpfile[0], "from", tmpfile[1])
if err := copyFile(tmpfile[0], tmpfile[1]); err != nil {
return (*TmpfileError)(wrapError(err,
fmt.Sprintf("cannot publish tmpfile '%s' from '%s': %s", tmpfile[0], tmpfile[1], err)))
} else {
// register partial commit
txp.copyFile(tmpfile[0], tmpfile[1])
}
}
// create hardlinks
for _, link := range tx.hardlinks {
verbose.Println("creating hardlink", link[1], "from", link[0])
if err := os.Link(link[0], link[1]); err != nil {
return (*TmpfileError)(wrapError(err,
fmt.Sprintf("cannot create hardlink '%s' from '%s': %s", link[1], link[0], err)))
} else {
// register partial commit
txp.link(link[0], link[1])
}
}
if tx.dbus != nil {
// start dbus proxy
verbose.Printf("session bus proxy on '%s' for upstream '%s'\n", tx.dbusAddr[0][1], tx.dbusAddr[0][0])
if tx.dbusSystem {
verbose.Printf("system bus proxy on '%s' for upstream '%s'\n", tx.dbusAddr[1][1], tx.dbusAddr[1][0])
}
if err := tx.startDBus(); err != nil {
return (*DBusStartError)(wrapError(err, "cannot start message bus proxy:", err))
} else {
txp.dbus = tx.dbus
txp.dbusAddr = tx.dbusAddr
txp.dbusSystem = tx.dbusSystem
txp.dbusWait = tx.dbusWait
}
}
// apply ACLs
for _, e := range tx.acl {
verbose.Println("applying ACL", e, "uid:", tx.Uid, "path:", e.path)
if err := acl.UpdatePerm(e.path, tx.uid, e.perms...); err != nil {
return (*ACLUpdateError)(wrapError(err,
fmt.Sprintf("cannot apply ACL to '%s': %s", e.path, err)))
} else {
// register partial commit
txp.updatePerm(e.path, e.perms...)
}
}
// disarm partial commit rollback
txp = nil
return nil
}
// revert rolls back recorded actions
// order: acl, dbus, hardlinks, tmpfiles, mkdir, xhost
// errors are printed but not treated as fatal
func (tx *appSealTx) revert(global bool) error {
if tx.closed {
panic("seal transaction reverted twice")
}
tx.closed = true
// will be slightly over-sized with ephemeral dirs
errs := make([]error, 0, len(tx.acl)+1+len(tx.tmpfiles)+len(tx.mkdir)+len(tx.xhost))
joinError := func(err error, a ...any) {
var e error
if err != nil {
e = wrapError(err, a...)
}
errs = append(errs, e)
}
if global {
// revert ACLs
for _, e := range tx.acl {
verbose.Println("stripping ACL", e, "uid:", tx.Uid, "path:", e.path)
err := acl.UpdatePerm(e.path, tx.uid)
joinError(err, fmt.Sprintf("cannot strip ACL entry from '%s': %s", e.path, err))
}
}
if tx.dbus != nil {
// stop dbus proxy
verbose.Println("terminating message bus proxy")
err := tx.stopDBus()
joinError(err, "cannot stop message bus proxy:", err)
}
// remove hardlinks
for _, link := range tx.hardlinks {
verbose.Println("removing hardlink", link[1])
err := os.Remove(link[1])
joinError(err, fmt.Sprintf("cannot remove hardlink '%s': %s", link[1], err))
}
// remove tmpfiles
for _, tmpfile := range tx.tmpfiles {
verbose.Println("removing tmpfile", tmpfile[0])
err := os.Remove(tmpfile[0])
joinError(err, fmt.Sprintf("cannot remove tmpfile '%s': %s", tmpfile[0], err))
}
// remove (empty) ephemeral directories
for i := len(tx.mkdir); i > 0; i-- {
dir := tx.mkdir[i-1]
if !dir.remove {
continue
}
verbose.Println("destroying ephemeral directory mode:", dir.perm.String(), "path:", dir.path)
err := os.Remove(dir.path)
joinError(err, fmt.Sprintf("cannot remove ephemeral directory '%s': %s", dir.path, err))
}
if global {
// rollback xhost insertions
for _, username := range tx.xhost {
verbose.Printf("deleting XHost entry SI:localuser:%s\n", username)
err := xcb.ChangeHosts(xcb.HostModeDelete, xcb.FamilyServerInterpreted, "localuser\x00"+username)
joinError(err, "cannot remove XHost entry:", err)
}
}
return errors.Join(errs...)
}
// shareAll calls all share methods in sequence
func (seal *appSeal) shareAll(bus [2]*dbus.Config) error {
if seal.shared {
panic("seal shared twice")
}
seal.shared = true
seal.shareRuntime()
if err := seal.shareDisplay(); err != nil {
return err
}
if err := seal.sharePulse(); err != nil {
return err
}
// ensure dbus session bus defaults
if bus[0] == nil {
bus[0] = dbus.NewConfig(seal.fid, true, true)
}
if err := seal.shareDBus(bus); err != nil {
return err
} else if seal.sys.dbusAddr != nil { // set if D-Bus enabled and share successful
verbose.Println("sealed session proxy", bus[0].Args(seal.sys.dbusAddr[0]))
if bus[1] != nil {
verbose.Println("sealed system proxy", bus[1].Args(seal.sys.dbusAddr[1]))
}
verbose.Println("message bus proxy final args:", seal.sys.dbus)
}
// workaround for launch method sudo
if seal.launchOption == LaunchMethodSudo {
targetRuntime := seal.shareRuntimeChild()
verbose.Printf("child runtime data dir '%s' configured\n", targetRuntime)
}
return nil
}