helper: implementation of helper.Helper using bwrap
Signed-off-by: Ophestra Umiker <cat@ophivana.moe>
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@ -0,0 +1,144 @@
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package helper
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import (
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"errors"
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"io"
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"os/exec"
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"strconv"
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"sync"
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"git.ophivana.moe/cat/fortify/helper/bwrap"
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)
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// BubblewrapName is the file name or path to bubblewrap.
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var BubblewrapName = "bwrap"
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type bubblewrap struct {
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// bwrap child file name
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name string
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// bwrap pipes
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p *pipes
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// sealed bwrap config
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config *bwrap.Config
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// returns an array of arguments passed directly
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// to the child process spawned by bwrap
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argF func(argsFD, statFD int) []string
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// pipes received by the child
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// nil if no pipes are required
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cp *pipes
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lock sync.RWMutex
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*exec.Cmd
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}
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func (b *bubblewrap) StartNotify(ready chan error) error {
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b.lock.Lock()
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defer b.lock.Unlock()
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if ready != nil && b.cp == nil {
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panic("attempted to start with status monitoring on a bwrap child initialised without pipes")
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}
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// Check for doubled Start calls before we defer failure cleanup. If the prior
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// call to Start succeeded, we don't want to spuriously close its pipes.
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if b.Cmd.Process != nil {
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return errors.New("exec: already started")
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}
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// prepare bwrap pipe and args
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if argsFD, _, err := b.p.prepareCmd(b.Cmd); err != nil {
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return err
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} else {
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b.Cmd.Args = append(b.Cmd.Args, "--args", strconv.Itoa(argsFD), "--", b.name)
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}
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// prepare child args and pipes if enabled
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if b.cp != nil {
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b.cp.ready = ready
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if argsFD, statFD, err := b.cp.prepareCmd(b.Cmd); err != nil {
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return err
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} else {
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b.Cmd.Args = append(b.Cmd.Args, b.argF(argsFD, statFD)...)
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}
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} else {
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b.Cmd.Args = append(b.Cmd.Args, b.argF(-1, -1)...)
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}
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if ready != nil {
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b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=1")
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} else if b.cp != nil {
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b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=0")
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} else {
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b.Cmd.Env = append(b.Cmd.Env, FortifyHelper+"=1", FortifyStatus+"=-1")
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}
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if err := b.Cmd.Start(); err != nil {
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return err
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}
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// write bwrap args first
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if err := b.p.readyWriteArgs(); err != nil {
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return err
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}
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// write child args if enabled
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if b.cp != nil {
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if err := b.cp.readyWriteArgs(); err != nil {
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return err
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}
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}
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return nil
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}
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func (b *bubblewrap) Close() error {
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if b.cp == nil {
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panic("attempted to close bwrap child initialised without pipes")
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}
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return b.cp.closeStatus()
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}
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func (b *bubblewrap) Start() error {
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return b.StartNotify(nil)
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}
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func (b *bubblewrap) Unwrap() *exec.Cmd {
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return b.Cmd
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}
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// MustNewBwrap initialises a new Bwrap instance with wt as the null-terminated argument writer.
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// If wt is nil, the child process spawned by bwrap will not get an argument pipe.
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// Function argF returns an array of arguments passed directly to the child process.
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func MustNewBwrap(conf *bwrap.Config, wt io.WriterTo, name string, argF func(argsFD, statFD int) []string) Helper {
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b, err := NewBwrap(conf, wt, name, argF)
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if err != nil {
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panic(err.Error())
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} else {
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return b
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}
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}
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// NewBwrap initialises a new Bwrap instance with wt as the null-terminated argument writer.
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// If wt is nil, the child process spawned by bwrap will not get an argument pipe.
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// Function argF returns an array of arguments passed directly to the child process.
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func NewBwrap(conf *bwrap.Config, wt io.WriterTo, name string, argF func(argsFD, statFD int) []string) (Helper, error) {
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b := new(bubblewrap)
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if args, err := NewCheckedArgs(conf.Args()); err != nil {
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return nil, err
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} else {
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b.p = &pipes{args: args}
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}
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b.argF = argF
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b.name = name
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if wt != nil {
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b.cp = &pipes{args: wt}
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}
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b.Cmd = execCommand(BubblewrapName)
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return b, nil
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}
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@ -0,0 +1,112 @@
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package helper_test
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import (
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"errors"
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"fmt"
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"os"
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"strings"
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"testing"
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"git.ophivana.moe/cat/fortify/helper"
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"git.ophivana.moe/cat/fortify/helper/bwrap"
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)
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func TestBwrap(t *testing.T) {
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sc := &bwrap.Config{
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Unshare: nil,
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Net: true,
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UserNS: false,
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Hostname: "localhost",
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Chdir: "/nonexistent",
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Clearenv: true,
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NewSession: true,
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DieWithParent: true,
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AsInit: true,
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}
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t.Run("nonexistent bwrap name", func(t *testing.T) {
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bubblewrapName := helper.BubblewrapName
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helper.BubblewrapName = "/nonexistent"
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t.Cleanup(func() {
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helper.BubblewrapName = bubblewrapName
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})
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h := helper.MustNewBwrap(sc, argsWt, "fortify", argF)
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if err := h.Start(); !errors.Is(err, os.ErrNotExist) {
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t.Errorf("Start() error = %v, wantErr %v",
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err, os.ErrNotExist)
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}
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})
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t.Run("valid new helper nil check", func(t *testing.T) {
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if got := helper.MustNewBwrap(sc, argsWt, "fortify", argF); got == nil {
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t.Errorf("MustNewBwrap(%#v, %#v, %#v) got nil",
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sc, argsWt, "fortify")
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return
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}
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})
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t.Run("invalid bwrap config new helper panic", func(t *testing.T) {
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defer func() {
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wantPanic := "argument contains null character"
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if r := recover(); r != wantPanic {
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t.Errorf("MustNewBwrap: panic = %q, want %q",
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r, wantPanic)
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}
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}()
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helper.MustNewBwrap(&bwrap.Config{Hostname: "\x00"}, nil, "fortify", argF)
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})
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t.Run("start notify without pipes panic", func(t *testing.T) {
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defer func() {
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wantPanic := "attempted to start with status monitoring on a bwrap child initialised without pipes"
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if r := recover(); r != wantPanic {
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t.Errorf("StartNotify: panic = %q, want %q",
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r, wantPanic)
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}
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}()
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panic(fmt.Sprintf("unreachable: %v",
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helper.MustNewBwrap(sc, nil, "fortify", argF).StartNotify(make(chan error))))
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})
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t.Run("start without pipes", func(t *testing.T) {
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helper.InternalReplaceExecCommand(t)
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h := helper.MustNewBwrap(sc, nil, "crash-test-dummy", argFChecked)
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cmd := h.Unwrap()
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stdout, stderr := new(strings.Builder), new(strings.Builder)
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cmd.Stdout, cmd.Stderr = stdout, stderr
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t.Run("close without pipes panic", func(t *testing.T) {
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defer func() {
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wantPanic := "attempted to close bwrap child initialised without pipes"
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if r := recover(); r != wantPanic {
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t.Errorf("Close: panic = %q, want %q",
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r, wantPanic)
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}
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}()
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panic(fmt.Sprintf("unreachable: %v",
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h.Close()))
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})
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if err := h.Start(); err != nil {
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t.Errorf("Start() error = %v",
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err)
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return
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}
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if err := h.Wait(); err != nil {
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t.Errorf("Wait() err = %v stderr = %s",
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err, stderr)
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}
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})
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t.Run("implementation compliance", func(t *testing.T) {
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testHelper(t, func() helper.Helper { return helper.MustNewBwrap(sc, argsWt, "crash-test-dummy", argF) })
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})
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}
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@ -23,11 +23,15 @@ var (
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argsWt = helper.MustNewCheckedArgs(wantArgs)
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)
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func argF(argsFD int, statFD int) []string {
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func argF(argsFD, statFD int) []string {
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if argsFD == -1 {
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panic("invalid args fd")
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}
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return argFChecked(argsFD, statFD)
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}
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func argFChecked(argsFD, statFD int) []string {
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if statFD == -1 {
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return []string{"--args", strconv.Itoa(argsFD)}
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} else {
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@ -6,15 +6,19 @@ import (
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"os"
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"os/exec"
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"strconv"
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"strings"
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"syscall"
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"testing"
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"git.ophivana.moe/cat/fortify/helper/bwrap"
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)
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// InternalChildStub is an internal function but exported because it is cross-package;
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// it is part of the implementation of the helper stub.
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func InternalChildStub() {
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// this test mocks the helper process
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if os.Getenv(FortifyHelper) != "1" {
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if os.Getenv(FortifyHelper) != "1" ||
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os.Getenv(FortifyStatus) == "-1" { // this indicates the stub is being invoked as a bwrap child without pipes
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return
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}
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@ -22,6 +26,35 @@ func InternalChildStub() {
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statFD := flag.Int("fd", -1, "")
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_ = flag.CommandLine.Parse(os.Args[4:])
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switch os.Args[3] {
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case "bwrap":
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bwrapStub(argsFD, statFD)
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default:
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genericStub(argsFD, statFD)
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}
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os.Exit(0)
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}
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// InternalReplaceExecCommand is an internal function but exported because it is cross-package;
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// it is part of the implementation of the helper stub.
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func InternalReplaceExecCommand(t *testing.T) {
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t.Cleanup(func() {
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execCommand = exec.Command
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})
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// replace execCommand to have the resulting *exec.Cmd launch TestHelperChildStub
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execCommand = func(name string, arg ...string) *exec.Cmd {
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// pass through nonexistent path
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if name == "/nonexistent" && len(arg) == 0 {
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return exec.Command(name)
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}
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return exec.Command(os.Args[0], append([]string{"-test.run=TestHelperChildStub", "--", name}, arg...)...)
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}
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}
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func genericStub(argsFD, statFD *int) {
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// simulate args pipe behaviour
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func() {
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if *argsFD == -1 {
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@ -89,20 +122,53 @@ func InternalChildStub() {
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}
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}
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// InternalReplaceExecCommand is an internal function but exported because it is cross-package;
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// it is part of the implementation of the helper stub.
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func InternalReplaceExecCommand(t *testing.T) {
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t.Cleanup(func() {
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execCommand = exec.Command
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})
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func bwrapStub(argsFD, statFD *int) {
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// the bwrap launcher does not ever launch with sync fd
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if *statFD != -1 {
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panic("attempted to launch bwrap with status monitoring")
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}
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// replace execCommand to have the resulting *exec.Cmd launch TestHelperChildStub
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execCommand = func(name string, arg ...string) *exec.Cmd {
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// pass through nonexistent path
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if name == "/nonexistent" && len(arg) == 0 {
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return exec.Command(name)
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// test args pipe behaviour
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func() {
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if *argsFD == -1 {
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panic("attempted to start bwrap without passing args pipe fd")
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}
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return exec.Command(os.Args[0], append([]string{"-test.run=TestHelperChildStub", "--", name}, arg...)...)
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f := os.NewFile(uintptr(*argsFD), "|0")
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if f == nil {
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panic("attempted to start helper without args pipe")
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}
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got, want := new(strings.Builder), new(strings.Builder)
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if _, err := io.Copy(got, f); err != nil {
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panic("cannot read args: " + err.Error())
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}
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// hardcoded bwrap configuration used by test
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if _, err := MustNewCheckedArgs((&bwrap.Config{
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Unshare: nil,
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Net: true,
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UserNS: false,
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Hostname: "localhost",
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Chdir: "/nonexistent",
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Clearenv: true,
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NewSession: true,
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DieWithParent: true,
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AsInit: true,
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}).Args()).WriteTo(want); err != nil {
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panic("cannot read want: " + err.Error())
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}
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if got.String() != want.String() {
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panic("bad bwrap args\ngot: " + got.String() + "\nwant: " + want.String())
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}
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}()
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if err := syscall.Exec(
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os.Args[0],
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append([]string{os.Args[0], "-test.run=TestHelperChildStub", "--"}, flag.CommandLine.Args()...),
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os.Environ()); err != nil {
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panic("cannot start general stub: " + err.Error())
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}
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}
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