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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build freebsd || linux
package syscall_test
import (
"bufio"
"fmt"
"internal/testenv"
"io"
"os"
"os/exec"
"os/signal"
"os/user"
"path/filepath"
"strconv"
"strings"
"syscall"
"testing"
)
// TestDeathSignalSetuid verifies that a command run with a different UID still
// receives PDeathsig; it is a regression test for https://go.dev/issue/9686.
func TestDeathSignalSetuid(t *testing.T) {
if testing.Short() {
t.Skipf("skipping test that copies its binary into temp dir")
}
// Copy the test binary to a location that another user can read/execute
// after we drop privileges.
//
// TODO(bcmills): Why do we believe that another users will be able to
// execute a binary in this directory? (It could be mounted noexec.)
tempDir, err := os.MkdirTemp("", "TestDeathSignal")
if err != nil {
t.Fatalf("cannot create temporary directory: %v", err)
}
defer os.RemoveAll(tempDir)
os.Chmod(tempDir, 0755)
tmpBinary := filepath.Join(tempDir, filepath.Base(os.Args[0]))
src, err := os.Open(os.Args[0])
if err != nil {
t.Fatalf("cannot open binary %q, %v", os.Args[0], err)
}
defer src.Close()
dst, err := os.OpenFile(tmpBinary, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0755)
if err != nil {
t.Fatalf("cannot create temporary binary %q, %v", tmpBinary, err)
}
if _, err := io.Copy(dst, src); err != nil {
t.Fatalf("failed to copy test binary to %q, %v", tmpBinary, err)
}
err = dst.Close()
if err != nil {
t.Fatalf("failed to close test binary %q, %v", tmpBinary, err)
}
cmd := testenv.Command(t, tmpBinary)
cmd.Env = append(cmd.Environ(), "GO_DEATHSIG_PARENT=1")
chldStdin, err := cmd.StdinPipe()
if err != nil {
t.Fatalf("failed to create new stdin pipe: %v", err)
}
chldStdout, err := cmd.StdoutPipe()
if err != nil {
t.Fatalf("failed to create new stdout pipe: %v", err)
}
stderr := new(strings.Builder)
cmd.Stderr = stderr
err = cmd.Start()
defer func() {
chldStdin.Close()
cmd.Wait()
if stderr.Len() > 0 {
t.Logf("stderr:\n%s", stderr)
}
}()
if err != nil {
t.Fatalf("failed to start first child process: %v", err)
}
chldPipe := bufio.NewReader(chldStdout)
if got, err := chldPipe.ReadString('\n'); got == "start\n" {
syscall.Kill(cmd.Process.Pid, syscall.SIGTERM)
want := "ok\n"
if got, err = chldPipe.ReadString('\n'); got != want {
t.Fatalf("expected %q, received %q, %v", want, got, err)
}
} else if got == "skip\n" {
t.Skipf("skipping: parent could not run child program as selected user")
} else {
t.Fatalf("did not receive start from child, received %q, %v", got, err)
}
}
func deathSignalParent() {
var (
u *user.User
err error
)
if os.Getuid() == 0 {
tryUsers := []string{"nobody"}
if testenv.Builder() != "" {
tryUsers = append(tryUsers, "gopher")
}
for _, name := range tryUsers {
u, err = user.Lookup(name)
if err == nil {
break
}
fmt.Fprintf(os.Stderr, "Lookup(%q): %v\n", name, err)
}
}
if u == nil {
// If we couldn't find an unprivileged user to run as, try running as
// the current user. (Empirically this still causes the call to Start to
// fail with a permission error if running as a non-root user on Linux.)
u, err = user.Current()
if err != nil {
fmt.Fprintln(os.Stderr, err)
os.Exit(1)
}
}
uid, err := strconv.ParseUint(u.Uid, 10, 32)
if err != nil {
fmt.Fprintf(os.Stderr, "invalid UID: %v\n", err)
os.Exit(1)
}
gid, err := strconv.ParseUint(u.Gid, 10, 32)
if err != nil {
fmt.Fprintf(os.Stderr, "invalid GID: %v\n", err)
os.Exit(1)
}
cmd := exec.Command(os.Args[0])
cmd.Env = append(os.Environ(),
"GO_DEATHSIG_PARENT=",
"GO_DEATHSIG_CHILD=1",
)
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
attrs := syscall.SysProcAttr{
Pdeathsig: syscall.SIGUSR1,
Credential: &syscall.Credential{Uid: uint32(uid), Gid: uint32(gid)},
}
cmd.SysProcAttr = &attrs
fmt.Fprintf(os.Stderr, "starting process as user %q\n", u.Username)
if err := cmd.Start(); err != nil {
fmt.Fprintln(os.Stderr, err)
if testenv.SyscallIsNotSupported(err) {
fmt.Println("skip")
os.Exit(0)
}
os.Exit(1)
}
cmd.Wait()
os.Exit(0)
}
func deathSignalChild() {
c := make(chan os.Signal, 1)
signal.Notify(c, syscall.SIGUSR1)
go func() {
<-c
fmt.Println("ok")
os.Exit(0)
}()
fmt.Println("start")
buf := make([]byte, 32)
os.Stdin.Read(buf)
// We expected to be signaled before stdin closed
fmt.Println("not ok")
os.Exit(1)
}
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