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helper: separate pipes from Helper 

Upcoming bwrap helper implementation requires two sets of pipes to be managed, fd will also no longer be constant.

Signed-off-by: Ophestra Umiker <cat@ophivana.moe>
This commit is contained in:
Ophestra Umiker 2024-10-07 12:48:20 +09:00
parent 18d9ce733e
commit 9647eb6a6b
Signed by: cat
SSH Key Fingerprint: SHA256:gQ67O0enBZ7UdZypgtspB2FDM1g3GVw8nX0XSdcFw8Q
7 changed files with 231 additions and 140 deletions
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2
dbus/dbus_test.go
View File

@ -164,7 +164,7 @@ func TestProxy_Start_Wait_Close_String(t *testing.T) {
}
t.Run("started string of "+id, func(t *testing.T) {
wantSubstr := binPath + " --args=3 --fd=4"
wantSubstr := binPath + " --args=3"
if got := p.String(); !strings.Contains(got, wantSubstr) {
t.Errorf("String() = %v, want %v",
p.String(), wantSubstr)

11
dbus/run.go
View File

@ -3,6 +3,7 @@ package dbus
import (
"errors"
"io"
"strconv"
"git.ophivana.moe/cat/fortify/helper"
)
@ -18,9 +19,13 @@ func (p *Proxy) Start(ready chan error, output io.Writer) error {
}
h := helper.New(p.seal, p.path,
// Helper: Args is always 3 and status if set is always 4.
"--args=3",
"--fd=4",
func(argsFD, statFD int) []string {
if statFD == -1 {
return []string{"--args=" + strconv.Itoa(argsFD)}
} else {
return []string{"--args=" + strconv.Itoa(argsFD), "--fd=" + strconv.Itoa(statFD)}
}
},
)
// xdg-dbus-proxy does not need to inherit the environment
h.Env = []string{}

10
helper/args.go
View File

@ -10,11 +10,11 @@ var (
ErrContainsNull = errors.New("argument contains null character")
)
type argsFD []string
type argsWt []string
// checks whether any element contains the null character
// must be called before args use and args must not be modified after call
func (a argsFD) check() error {
func (a argsWt) check() error {
for _, arg := range a {
for _, b := range arg {
if b == '\x00' {
@ -26,7 +26,7 @@ func (a argsFD) check() error {
return nil
}
func (a argsFD) WriteTo(w io.Writer) (int64, error) {
func (a argsWt) WriteTo(w io.Writer) (int64, error) {
// assuming already checked
nt := 0
@ -43,13 +43,13 @@ func (a argsFD) WriteTo(w io.Writer) (int64, error) {
return int64(nt), nil
}
func (a argsFD) String() string {
func (a argsWt) String() string {
return strings.Join(a, " ")
}
// NewCheckedArgs returns a checked argument writer for args.
// Callers must not retain any references to args.
func NewCheckedArgs(args []string) (io.WriterTo, error) {
a := argsFD(args)
a := argsWt(args)
return a, a.check()
}

138
helper/helper.go
View File

@ -6,7 +6,6 @@ package helper
import (
"errors"
"io"
"os"
"os/exec"
"sync"
)
@ -17,27 +16,21 @@ var (
)
const (
// FortifyHelper is set for the process launched by Helper.
FortifyHelper = "FORTIFY_HELPER"
// FortifyStatus is 1 when sync fd is enabled and 0 otherwise.
FortifyStatus = "FORTIFY_STATUS"
)
// Helper wraps *exec.Cmd and manages status and args fd.
// Args is always 3 and status if set is always 4.
type Helper struct {
args io.WriterTo
p *pipes
statP [2]*os.File
argsP [2]*os.File
ready chan error
// ExtraFiles specifies additional open files to be inherited by the
// new process. It does not include standard input, standard output, or
// standard error. If non-nil, entry i becomes file descriptor 5+i.
ExtraFiles []*os.File
argF func(argsFD, statFD int) []string
*exec.Cmd
lock sync.RWMutex
*exec.Cmd
}
func (h *Helper) StartNotify(ready chan error) error {
@ -50,95 +43,24 @@ func (h *Helper) StartNotify(ready chan error) error {
return errors.New("exec: already started")
}
// create pipes
if pr, pw, err := os.Pipe(); err != nil {
h.p.ready = ready
if argsFD, statFD, err := h.p.prepareCmd(h.Cmd); err != nil {
return err
} else {
h.argsP[0], h.argsP[1] = pr, pw
h.Cmd.Args = append(h.Cmd.Args, h.argF(argsFD, statFD)...)
}
// create status pipes if ready signal is requested
var sv string
if ready != nil {
if pr, pw, err := os.Pipe(); err != nil {
return err
} else {
h.statP[0], h.statP[1] = pr, pw
}
sv = FortifyStatus + "=1"
if ready != nil {
h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=1")
} else {
sv = FortifyStatus + "=0"
h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=0")
}
// prepare extra files from caller
el := len(h.ExtraFiles)
if ready != nil {
el += 2
} else {
el++
}
ef := make([]*os.File, 0, el)
ef = append(ef, h.argsP[0])
if ready != nil {
ef = append(ef, h.statP[1])
}
ef = append(ef, h.ExtraFiles...)
// prepare and start process
h.Cmd.ExtraFiles = ef
h.Cmd.Env = append(h.Cmd.Env, FortifyHelper+"=1", sv)
if err := h.Cmd.Start(); err != nil {
return err
}
statsP, argsP := h.statP[0], h.argsP[1]
// write arguments and close args pipe
if _, err := h.args.WriteTo(argsP); err != nil {
if err1 := h.Cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
if err := h.p.readyWriteArgs(); err != nil {
return err
} else {
if err = argsP.Close(); err != nil {
if err1 := h.Cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
return err
}
}
if ready != nil {
h.ready = ready
// monitor stat pipe
go func() {
n, err := statsP.Read(make([]byte, 1))
switch n {
case -1:
if err1 := h.Cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
// ensure error is not nil
if err == nil {
err = ErrStatusFault
}
ready <- err
case 0:
// ensure error is not nil
if err == nil {
err = ErrStatusRead
}
ready <- err
case 1:
ready <- nil
default:
panic("unreachable") // unexpected read count
}
}()
}
return nil
@ -155,38 +77,12 @@ func (h *Helper) Wait() error {
return errors.New("exec: Wait was already called")
}
// ensure pipe close
defer func() {
if err := h.argsP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if err := h.argsP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if h.ready != nil {
if err := h.statP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if err := h.statP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
}
}()
defer h.p.mustClosePipes()
return h.Cmd.Wait()
}
func (h *Helper) Close() error {
if h.ready == nil {
panic("attempted to close helper with no status pipe")
}
return h.statP[0].Close()
return h.p.closeStatus()
}
func (h *Helper) Start() error {
@ -195,10 +91,12 @@ func (h *Helper) Start() error {
var execCommand = exec.Command
func New(wt io.WriterTo, name string, arg ...string) *Helper {
// New initialises a new Helper instance with wt as the null-terminated argument writer.
// Function argF returns an array of arguments passed directly to the child process.
func New(wt io.WriterTo, name string, argF func(argsFD, statFD int) []string) *Helper {
if wt == nil {
panic("attempted to create helper with invalid argument writer")
}
return &Helper{args: wt, Cmd: execCommand(name, arg...)}
return &Helper{p: &pipes{args: wt}, argF: argF, Cmd: execCommand(name)}
}

43
helper/helper_test.go
View File

@ -4,9 +4,11 @@ import (
"errors"
"io"
"os"
"strconv"
"strings"
"sync"
"testing"
"time"
"git.ophivana.moe/cat/fortify/helper"
)
@ -36,12 +38,20 @@ func prepareArgs() {
}
}
func argF(argsFD int, _ int) []string {
return []string{"--args", strconv.Itoa(argsFD)}
}
func argFStatus(argsFD int, statFD int) []string {
return []string{"--args", strconv.Itoa(argsFD), "--fd", strconv.Itoa(statFD)}
}
func TestHelper_StartNotify_Close_Wait(t *testing.T) {
helper.InternalReplaceExecCommand(t)
argsOnce.Do(prepareArgs)
t.Run("start non-existent helper path", func(t *testing.T) {
h := helper.New(argsWt, "/nonexistent")
h := helper.New(argsWt, "/nonexistent", argF)
if err := h.Start(); !errors.Is(err, os.ErrNotExist) {
t.Errorf("Start() error = %v, wantErr %v",
@ -50,7 +60,7 @@ func TestHelper_StartNotify_Close_Wait(t *testing.T) {
})
t.Run("start helper with status channel", func(t *testing.T) {
h := helper.New(argsWt, "crash-test-dummy", "--args=3", "--fd=4")
h := helper.New(argsWt, "crash-test-dummy", argFStatus)
ready := make(chan error, 1)
stdout, stderr := new(strings.Builder), new(strings.Builder)
@ -66,6 +76,7 @@ func TestHelper_StartNotify_Close_Wait(t *testing.T) {
}
})
t.Log("starting helper stub")
if err := h.StartNotify(ready); err != nil {
t.Errorf("StartNotify(%v) error = %v",
ready,
@ -83,17 +94,31 @@ func TestHelper_StartNotify_Close_Wait(t *testing.T) {
}
})
if err := <-ready; err != nil {
t.Errorf("StartNotify(%v) latent error = %v",
ready,
err)
t.Log("waiting on status channel with timeout")
select {
case <-time.NewTimer(5 * time.Second).C:
t.Errorf("never got a ready response")
t.Errorf("stdout:\n%s", stdout.String())
t.Errorf("stderr:\n%s", stderr.String())
if err := h.Cmd.Process.Kill(); err != nil {
panic(err.Error())
}
return
case err := <-ready:
if err != nil {
t.Errorf("StartNotify(%v) latent error = %v",
ready,
err)
}
}
t.Log("closing status pipe")
if err := h.Close(); err != nil {
t.Errorf("Close() error = %v",
err)
}
t.Log("waiting on helper")
if err := h.Wait(); err != nil {
t.Errorf("Wait() err = %v stderr = %s",
err, stderr)
@ -131,7 +156,7 @@ func TestHelper_Start_Close_Wait(t *testing.T) {
}
t.Run("start helper", func(t *testing.T) {
h := helper.New(wt, "crash-test-dummy", "--args=3")
h := helper.New(wt, "crash-test-dummy", argF)
stdout, stderr := new(strings.Builder), new(strings.Builder)
h.Stdout, h.Stderr = stdout, stderr
@ -172,7 +197,7 @@ func TestHelper_Start_Close_Wait(t *testing.T) {
func TestNew(t *testing.T) {
t.Run("valid new helper nil check", func(t *testing.T) {
swt, _ := helper.NewCheckedArgs(make([]string, 1))
if got := helper.New(swt, "fortify"); got == nil {
if got := helper.New(swt, "fortify", argF); got == nil {
t.Errorf("New(%q, %q) got nil",
swt, "fortify")
return
@ -188,6 +213,6 @@ func TestNew(t *testing.T) {
}
}()
helper.New(nil, "fortify")
helper.New(nil, "fortify", argF)
})
}

150
helper/pipe.go Normal file
View File

@ -0,0 +1,150 @@
package helper
import (
"errors"
"io"
"os"
"os/exec"
)
type pipes struct {
args io.WriterTo
statP [2]*os.File
argsP [2]*os.File
ready chan error
cmd *exec.Cmd
}
func (p *pipes) pipe() error {
if p.statP[0] != nil || p.statP[1] != nil ||
p.argsP[0] != nil || p.argsP[1] != nil {
panic("attempted to pipe twice")
}
if p.args == nil {
panic("attempted to pipe without args")
}
// create pipes
if pr, pw, err := os.Pipe(); err != nil {
return err
} else {
p.argsP[0], p.argsP[1] = pr, pw
}
// create status pipes if ready signal is requested
if p.ready != nil {
if pr, pw, err := os.Pipe(); err != nil {
return err
} else {
p.statP[0], p.statP[1] = pr, pw
}
}
return nil
}
// calls pipe to create pipes and sets them up as ExtraFiles, returning their fd
func (p *pipes) prepareCmd(cmd *exec.Cmd) (int, int, error) {
if err := p.pipe(); err != nil {
return -1, -1, err
}
// save a reference of cmd for future use
p.cmd = cmd
// ExtraFiles: If non-nil, entry i becomes file descriptor 3+i.
argsFd := 3 + len(cmd.ExtraFiles)
cmd.ExtraFiles = append(cmd.ExtraFiles, p.argsP[0])
if p.ready != nil {
cmd.ExtraFiles = append(cmd.ExtraFiles, p.statP[1])
return argsFd, argsFd + 1, nil
} else {
return argsFd, -1, nil
}
}
func (p *pipes) readyWriteArgs() error {
statsP, argsP := p.statP[0], p.argsP[1]
// write arguments and close args pipe
if _, err := p.args.WriteTo(argsP); err != nil {
if err1 := p.cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
return err
} else {
if err = argsP.Close(); err != nil {
if err1 := p.cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
return err
}
}
if p.ready != nil {
// monitor stat pipe
go func() {
n, err := statsP.Read(make([]byte, 1))
switch n {
case -1:
if err1 := p.cmd.Process.Kill(); err1 != nil {
// should be unreachable
panic(err1.Error())
}
// ensure error is not nil
if err == nil {
err = ErrStatusFault
}
p.ready <- err
case 0:
// ensure error is not nil
if err == nil {
err = ErrStatusRead
}
p.ready <- err
case 1:
p.ready <- nil
default:
panic("unreachable") // unexpected read count
}
}()
}
return nil
}
func (p *pipes) mustClosePipes() {
if err := p.argsP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if err := p.argsP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if p.ready != nil {
if err := p.statP[0].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
if err := p.statP[1].Close(); err != nil && !errors.Is(err, os.ErrClosed) {
// unreachable
panic(err.Error())
}
}
}
func (p *pipes) closeStatus() error {
if p.ready == nil {
panic("attempted to close helper with no status pipe")
}
return p.statP[0].Close()
}

17
helper/stub.go
View File

@ -1,6 +1,7 @@
package helper
import (
"flag"
"io"
"os"
"os/exec"
@ -17,9 +18,17 @@ func InternalChildStub() {
return
}
argsFD := flag.Int("args", -1, "")
statFD := flag.Int("fd", -1, "")
_ = flag.CommandLine.Parse(os.Args[4:])
// simulate args pipe behaviour
func() {
f := os.NewFile(3, "|0")
if *argsFD == -1 {
panic("attempted to start helper without passing args pipe fd")
}
f := os.NewFile(uintptr(*argsFD), "|0")
if f == nil {
panic("attempted to start helper without args pipe")
}
@ -33,9 +42,13 @@ func InternalChildStub() {
// simulate status pipe behaviour
if os.Getenv(FortifyStatus) == "1" {
if *statFD == -1 {
panic("attempted to start helper with status reporting without passing status pipe fd")
}
wait = make(chan struct{})
go func() {
f := os.NewFile(4, "|1")
f := os.NewFile(uintptr(*statFD), "|1")
if f == nil {
panic("attempted to start with status reporting without status pipe")
}