src/syscall/syscall_linux_test.go - go - Git at Google

 // 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.

 package syscall_test

 import (
 	"fmt"
 	"io"
 	"io/fs"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
 	"sort"
 	"strconv"
 	"strings"
 	"syscall"
 	"testing"
 	"unsafe"
 )

 // chtmpdir changes the working directory to a new temporary directory and
 // provides a cleanup function. Used when PWD is read-only.
 func chtmpdir(t *testing.T) func() {
 	oldwd, err := os.Getwd()
 	if err != nil {
 		t.Fatalf("chtmpdir: %v", err)
 	}
 	d, err := os.MkdirTemp("", "test")
 	if err != nil {
 		t.Fatalf("chtmpdir: %v", err)
 	}
 	if err := os.Chdir(d); err != nil {
 		t.Fatalf("chtmpdir: %v", err)
 	}
 	return func() {
 		if err := os.Chdir(oldwd); err != nil {
 			t.Fatalf("chtmpdir: %v", err)
 		}
 		os.RemoveAll(d)
 	}
 }

 func touch(t *testing.T, name string) {
 	f, err := os.Create(name)
 	if err != nil {
 		t.Fatal(err)
 	}
 	if err := f.Close(); err != nil {
 		t.Fatal(err)
 	}
 }

 const (
 	_AT_SYMLINK_NOFOLLOW = 0x100
 	_AT_FDCWD            = -0x64
 	_AT_EACCESS          = 0x200
 	_F_OK                = 0
 	_R_OK                = 4
 )

 func TestFaccessat(t *testing.T) {
 	defer chtmpdir(t)()
 	touch(t, "file1")

 	err := syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, 0)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, 2)
 	if err != syscall.EINVAL {
 		t.Errorf("Faccessat: unexpected error: %v, want EINVAL", err)
 	}

 	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, _AT_EACCESS)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = os.Symlink("file1", "symlink1")
 	if err != nil {
 		t.Fatal(err)
 	}

 	err = syscall.Faccessat(_AT_FDCWD, "symlink1", _R_OK, _AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		t.Errorf("Faccessat SYMLINK_NOFOLLOW: unexpected error %v", err)
 	}

 	// We can't really test _AT_SYMLINK_NOFOLLOW, because there
 	// doesn't seem to be any way to change the mode of a symlink.
 	// We don't test _AT_EACCESS because such tests are only
 	// meaningful if run as root.

 	err = syscall.Fchmodat(_AT_FDCWD, "file1", 0, 0)
 	if err != nil {
 		t.Errorf("Fchmodat: unexpected error %v", err)
 	}

 	err = syscall.Faccessat(_AT_FDCWD, "file1", _F_OK, _AT_SYMLINK_NOFOLLOW)
 	if err != nil {
 		t.Errorf("Faccessat: unexpected error: %v", err)
 	}

 	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, _AT_SYMLINK_NOFOLLOW)
 	if err != syscall.EACCES {
 		if syscall.Getuid() != 0 {
 			t.Errorf("Faccessat: unexpected error: %v, want EACCES", err)
 		}
 	}
 }

 func TestFchmodat(t *testing.T) {
 	defer chtmpdir(t)()

 	touch(t, "file1")
 	os.Symlink("file1", "symlink1")

 	err := syscall.Fchmodat(_AT_FDCWD, "symlink1", 0444, 0)
 	if err != nil {
 		t.Fatalf("Fchmodat: unexpected error: %v", err)
 	}

 	fi, err := os.Stat("file1")
 	if err != nil {
 		t.Fatal(err)
 	}

 	if fi.Mode() != 0444 {
 		t.Errorf("Fchmodat: failed to change mode: expected %v, got %v", 0444, fi.Mode())
 	}

 	err = syscall.Fchmodat(_AT_FDCWD, "symlink1", 0444, _AT_SYMLINK_NOFOLLOW)
 	if err != syscall.EOPNOTSUPP {
 		t.Fatalf("Fchmodat: unexpected error: %v, expected EOPNOTSUPP", err)
 	}
 }

 func TestMain(m *testing.M) {
 	if os.Getenv("GO_DEATHSIG_PARENT") == "1" {
 		deathSignalParent()
 	} else if os.Getenv("GO_DEATHSIG_CHILD") == "1" {
 		deathSignalChild()
 	} else if os.Getenv("GO_SYSCALL_NOERROR") == "1" {
 		syscallNoError()
 	}

 	os.Exit(m.Run())
 }

 func TestParseNetlinkMessage(t *testing.T) {
 	for i, b := range [][]byte{
 		{103, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 5, 8, 0, 3,
 			0, 8, 0, 6, 0, 0, 0, 0, 1, 63, 0, 10, 0, 69, 16, 0, 59, 39, 82, 64, 0, 64, 6, 21, 89, 127, 0, 0,
 			1, 127, 0, 0, 1, 230, 228, 31, 144, 32, 186, 155, 211, 185, 151, 209, 179, 128, 24, 1, 86,
 			53, 119, 0, 0, 1, 1, 8, 10, 0, 17, 234, 12, 0, 17, 189, 126, 107, 106, 108, 107, 106, 13, 10,
 		},
 		{106, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 3, 8, 0, 3,
 			0, 8, 0, 6, 0, 0, 0, 0, 1, 66, 0, 10, 0, 69, 0, 0, 62, 230, 255, 64, 0, 64, 6, 85, 184, 127, 0, 0,
 			1, 127, 0, 0, 1, 237, 206, 31, 144, 73, 197, 128, 65, 250, 60, 192, 97, 128, 24, 1, 86, 253, 21, 0,
 			0, 1, 1, 8, 10, 0, 51, 106, 89, 0, 51, 102, 198, 108, 104, 106, 108, 107, 104, 108, 107, 104, 10,
 		},
 		{102, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 1, 8, 0, 3, 0,
 			8, 0, 6, 0, 0, 0, 0, 1, 62, 0, 10, 0, 69, 0, 0, 58, 231, 2, 64, 0, 64, 6, 85, 185, 127, 0, 0, 1, 127,
 			0, 0, 1, 237, 206, 31, 144, 73, 197, 128, 86, 250, 60, 192, 97, 128, 24, 1, 86, 104, 64, 0, 0, 1, 1, 8,
 			10, 0, 52, 198, 200, 0, 51, 135, 232, 101, 115, 97, 103, 103, 10,
 		},
 	} {
 		m, err := syscall.ParseNetlinkMessage(b)
 		if err != syscall.EINVAL {
 			t.Errorf("#%d: got %v; want EINVAL", i, err)
 		}
 		if m != nil {
 			t.Errorf("#%d: got %v; want nil", i, m)
 		}
 	}
 }

 func TestSyscallNoError(t *testing.T) {
 	// On Linux there are currently no syscalls which don't fail and return
 	// a value larger than 0xfffffffffffff001 so we could test RawSyscall
 	// vs. RawSyscallNoError on 64bit architectures.
 	if unsafe.Sizeof(uintptr(0)) != 4 {
 		t.Skip("skipping on non-32bit architecture")
 	}

 	// See https://golang.org/issue/35422
 	// On MIPS, Linux returns whether the syscall had an error in a separate
 	// register (R7), not using a negative return value as on other
 	// architectures.
 	if runtime.GOARCH == "mips" || runtime.GOARCH == "mipsle" {
 		t.Skipf("skipping on %s", runtime.GOARCH)
 	}

 	if os.Getuid() != 0 {
 		t.Skip("skipping root only test")
 	}

 	if runtime.GOOS == "android" {
 		t.Skip("skipping on rooted android, see issue 27364")
 	}

 	// Copy the test binary to a location that a non-root user can read/execute
 	// after we drop privileges
 	tempDir, err := os.MkdirTemp("", "TestSyscallNoError")
 	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)
 	}

 	uid := uint32(0xfffffffe)
 	err = os.Chown(tmpBinary, int(uid), -1)
 	if err != nil {
 		t.Fatalf("failed to chown test binary %q, %v", tmpBinary, err)
 	}

 	err = os.Chmod(tmpBinary, 0755|fs.ModeSetuid)
 	if err != nil {
 		t.Fatalf("failed to set setuid bit on test binary %q, %v", tmpBinary, err)
 	}

 	cmd := exec.Command(tmpBinary)
 	cmd.Env = append(os.Environ(), "GO_SYSCALL_NOERROR=1")

 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("failed to start first child process: %v", err)
 	}

 	got := strings.TrimSpace(string(out))
 	want := strconv.FormatUint(uint64(uid)+1, 10) + " / " +
 		strconv.FormatUint(uint64(-uid), 10) + " / " +
 		strconv.FormatUint(uint64(uid), 10)
 	if got != want {
 		if filesystemIsNoSUID(tmpBinary) {
 			t.Skip("skipping test when temp dir is mounted nosuid")
 		}
 		// formatted so the values are aligned for easier comparison
 		t.Errorf("expected %s,\ngot      %s", want, got)
 	}
 }

 // filesystemIsNoSUID reports whether the filesystem for the given
 // path is mounted nosuid.
 func filesystemIsNoSUID(path string) bool {
 	var st syscall.Statfs_t
 	if syscall.Statfs(path, &st) != nil {
 		return false
 	}
 	return st.Flags&syscall.MS_NOSUID != 0
 }

 func syscallNoError() {
 	// Test that the return value from SYS_GETEUID32 (which cannot fail)
 	// doesn't get treated as an error (see https://golang.org/issue/22924)
 	euid1, _, e := syscall.RawSyscall(syscall.Sys_GETEUID, 0, 0, 0)
 	euid2, _ := syscall.RawSyscallNoError(syscall.Sys_GETEUID, 0, 0, 0)

 	fmt.Println(uintptr(euid1), "/", int(e), "/", uintptr(euid2))
 	os.Exit(0)
 }

 // reference uapi/linux/prctl.h
 const (
 	PR_GET_KEEPCAPS uintptr = 7
 	PR_SET_KEEPCAPS         = 8
 )

 // TestAllThreadsSyscall tests that the go runtime can perform
 // syscalls that execute on all OSThreads - with which to support
 // POSIX semantics for security state changes.
 func TestAllThreadsSyscall(t *testing.T) {
 	if _, _, err := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, 0, 0); err == syscall.ENOTSUP {
 		t.Skip("AllThreadsSyscall disabled with cgo")
 	}

 	fns := []struct {
 		label string
 		fn    func(uintptr) error
 	}{
 		{
 			label: "prctl<3-args>",
 			fn: func(v uintptr) error {
 				_, _, e := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, v, 0)
 				if e != 0 {
 					return e
 				}
 				return nil
 			},
 		},
 		{
 			label: "prctl<6-args>",
 			fn: func(v uintptr) error {
 				_, _, e := syscall.AllThreadsSyscall6(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, v, 0, 0, 0, 0)
 				if e != 0 {
 					return e
 				}
 				return nil
 			},
 		},
 	}

 	waiter := func(q <-chan uintptr, r chan<- uintptr, once bool) {
 		for x := range q {
 			runtime.LockOSThread()
 			v, _, e := syscall.Syscall(syscall.SYS_PRCTL, PR_GET_KEEPCAPS, 0, 0)
 			if e != 0 {
 				t.Errorf("tid=%d prctl(PR_GET_KEEPCAPS) failed: %v", syscall.Gettid(), e)
 			} else if x != v {
 				t.Errorf("tid=%d prctl(PR_GET_KEEPCAPS) mismatch: got=%d want=%d", syscall.Gettid(), v, x)
 			}
 			r <- v
 			if once {
 				break
 			}
 			runtime.UnlockOSThread()
 		}
 	}

 	// launches per fns member.
 	const launches = 11
 	question := make(chan uintptr)
 	response := make(chan uintptr)
 	defer close(question)

 	routines := 0
 	for i, v := range fns {
 		for j := 0; j < launches; j++ {
 			// Add another goroutine - the closest thing
 			// we can do to encourage more OS thread
 			// creation - while the test is running.  The
 			// actual thread creation may or may not be
 			// needed, based on the number of available
 			// unlocked OS threads at the time waiter
 			// calls runtime.LockOSThread(), but the goal
 			// of doing this every time through the loop
 			// is to race thread creation with v.fn(want)
 			// being executed. Via the once boolean we
 			// also encourage one in 5 waiters to return
 			// locked after participating in only one
 			// question response sequence. This allows the
 			// test to race thread destruction too.
 			once := routines%5 == 4
 			go waiter(question, response, once)

 			// Keep a count of how many goroutines are
 			// going to participate in the
 			// question/response test. This will count up
 			// towards 2*launches minus the count of
 			// routines that have been invoked with
 			// once=true.
 			routines++

 			// Decide what value we want to set the
 			// process-shared KEEPCAPS. Note, there is
 			// an explicit repeat of 0 when we change the
 			// variant of the syscall being used.
 			want := uintptr(j & 1)

 			// Invoke the AllThreadsSyscall* variant.
 			if err := v.fn(want); err != nil {
 				t.Errorf("[%d,%d] %s(PR_SET_KEEPCAPS, %d, ...): %v", i, j, v.label, j&1, err)
 			}

 			// At this point, we want all launched Go
 			// routines to confirm that they see the
 			// wanted value for KEEPCAPS.
 			for k := 0; k < routines; k++ {
 				question <- want
 			}

 			// At this point, we should have a large
 			// number of locked OS threads all wanting to
 			// reply.
 			for k := 0; k < routines; k++ {
 				if got := <-response; got != want {
 					t.Errorf("[%d,%d,%d] waiter result got=%d, want=%d", i, j, k, got, want)
 				}
 			}

 			// Provide an explicit opportunity for this Go
 			// routine to change Ms.
 			runtime.Gosched()

 			if once {
 				// One waiter routine will have exited.
 				routines--
 			}

 			// Whatever M we are now running on, confirm
 			// we see the wanted value too.
 			if v, _, e := syscall.Syscall(syscall.SYS_PRCTL, PR_GET_KEEPCAPS, 0, 0); e != 0 {
 				t.Errorf("[%d,%d] prctl(PR_GET_KEEPCAPS) failed: %v", i, j, e)
 			} else if v != want {
 				t.Errorf("[%d,%d] prctl(PR_GET_KEEPCAPS) gave wrong value: got=%v, want=1", i, j, v)
 			}
 		}
 	}
 }

 // compareStatus is used to confirm the contents of the thread
 // specific status files match expectations.
 func compareStatus(filter, expect string) error {
 	expected := filter + expect
 	pid := syscall.Getpid()
 	fs, err := os.ReadDir(fmt.Sprintf("/proc/%d/task", pid))
 	if err != nil {
 		return fmt.Errorf("unable to find %d tasks: %v", pid, err)
 	}
 	expectedProc := fmt.Sprintf("Pid:\t%d", pid)
 	foundAThread := false
 	for _, f := range fs {
 		tf := fmt.Sprintf("/proc/%s/status", f.Name())
 		d, err := os.ReadFile(tf)
 		if err != nil {
 			// There are a surprising number of ways this
 			// can error out on linux.  We've seen all of
 			// the following, so treat any error here as
 			// equivalent to the "process is gone":
 			//    os.IsNotExist(err),
 			//    "... : no such process",
 			//    "... : bad file descriptor.
 			continue
 		}
 		lines := strings.Split(string(d), "\n")
 		for _, line := range lines {
 			// Different kernel vintages pad differently.
 			line = strings.TrimSpace(line)
 			if strings.HasPrefix(line, "Pid:\t") {
 				// On loaded systems, it is possible
 				// for a TID to be reused really
 				// quickly. As such, we need to
 				// validate that the thread status
 				// info we just read is a task of the
 				// same process PID as we are
 				// currently running, and not a
 				// recently terminated thread
 				// resurfaced in a different process.
 				if line != expectedProc {
 					break
 				}
 				// Fall through in the unlikely case
 				// that filter at some point is
 				// "Pid:\t".
 			}
 			if strings.HasPrefix(line, filter) {
 				if line == expected {
 					foundAThread = true
 					break
 				}
 				if filter == "Groups:" && strings.HasPrefix(line, "Groups:\t") {
 					// https://github.com/golang/go/issues/46145
 					// Containers don't reliably output this line in sorted order so manually sort and compare that.
 					a := strings.Split(line[8:], " ")
 					sort.Strings(a)
 					got := strings.Join(a, " ")
 					if got == expected[8:] {
 						foundAThread = true
 						break
 					}

 				}
 				return fmt.Errorf("%q got:%q want:%q (bad) [pid=%d file:'%s' %v]\n", tf, line, expected, pid, string(d), expectedProc)
 			}
 		}
 	}
 	if !foundAThread {
 		return fmt.Errorf("found no thread /proc/<TID>/status files for process %q", expectedProc)
 	}
 	return nil
 }

 // killAThread locks the goroutine to an OS thread and exits; this
 // causes an OS thread to terminate.
 func killAThread(c <-chan struct{}) {
 	runtime.LockOSThread()
 	<-c
 	return
 }

 // TestSetuidEtc performs tests on all of the wrapped system calls
 // that mirror to the 9 glibc syscalls with POSIX semantics. The test
 // here is considered authoritative and should compile and run
 // CGO_ENABLED=0 or 1. Note, there is an extended copy of this same
 // test in ../../misc/cgo/test/issue1435.go which requires
 // CGO_ENABLED=1 and launches pthreads from C that run concurrently
 // with the Go code of the test - and the test validates that these
 // pthreads are also kept in sync with the security state changed with
 // the syscalls. Care should be taken to mirror any enhancements to
 // this test here in that file too.
 func TestSetuidEtc(t *testing.T) {
 	if syscall.Getuid() != 0 {
 		t.Skip("skipping root only test")
 	}
 	vs := []struct {
 		call           string
 		fn             func() error
 		filter, expect string
 	}{
 		{call: "Setegid(1)", fn: func() error { return syscall.Setegid(1) }, filter: "Gid:", expect: "\t0\t1\t0\t1"},
 		{call: "Setegid(0)", fn: func() error { return syscall.Setegid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

 		{call: "Seteuid(1)", fn: func() error { return syscall.Seteuid(1) }, filter: "Uid:", expect: "\t0\t1\t0\t1"},
 		{call: "Setuid(0)", fn: func() error { return syscall.Setuid(0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

 		{call: "Setgid(1)", fn: func() error { return syscall.Setgid(1) }, filter: "Gid:", expect: "\t1\t1\t1\t1"},
 		{call: "Setgid(0)", fn: func() error { return syscall.Setgid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

 		{call: "Setgroups([]int{0,1,2,3})", fn: func() error { return syscall.Setgroups([]int{0, 1, 2, 3}) }, filter: "Groups:", expect: "\t0 1 2 3"},
 		{call: "Setgroups(nil)", fn: func() error { return syscall.Setgroups(nil) }, filter: "Groups:", expect: ""},
 		{call: "Setgroups([]int{0})", fn: func() error { return syscall.Setgroups([]int{0}) }, filter: "Groups:", expect: "\t0"},

 		{call: "Setregid(101,0)", fn: func() error { return syscall.Setregid(101, 0) }, filter: "Gid:", expect: "\t101\t0\t0\t0"},
 		{call: "Setregid(0,102)", fn: func() error { return syscall.Setregid(0, 102) }, filter: "Gid:", expect: "\t0\t102\t102\t102"},
 		{call: "Setregid(0,0)", fn: func() error { return syscall.Setregid(0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

 		{call: "Setreuid(1,0)", fn: func() error { return syscall.Setreuid(1, 0) }, filter: "Uid:", expect: "\t1\t0\t0\t0"},
 		{call: "Setreuid(0,2)", fn: func() error { return syscall.Setreuid(0, 2) }, filter: "Uid:", expect: "\t0\t2\t2\t2"},
 		{call: "Setreuid(0,0)", fn: func() error { return syscall.Setreuid(0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

 		{call: "Setresgid(101,0,102)", fn: func() error { return syscall.Setresgid(101, 0, 102) }, filter: "Gid:", expect: "\t101\t0\t102\t0"},
 		{call: "Setresgid(0,102,101)", fn: func() error { return syscall.Setresgid(0, 102, 101) }, filter: "Gid:", expect: "\t0\t102\t101\t102"},
 		{call: "Setresgid(0,0,0)", fn: func() error { return syscall.Setresgid(0, 0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

 		{call: "Setresuid(1,0,2)", fn: func() error { return syscall.Setresuid(1, 0, 2) }, filter: "Uid:", expect: "\t1\t0\t2\t0"},
 		{call: "Setresuid(0,2,1)", fn: func() error { return syscall.Setresuid(0, 2, 1) }, filter: "Uid:", expect: "\t0\t2\t1\t2"},
 		{call: "Setresuid(0,0,0)", fn: func() error { return syscall.Setresuid(0, 0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},
 	}

 	for i, v := range vs {
 		// Generate some thread churn as we execute the tests.
 		c := make(chan struct{})
 		go killAThread(c)
 		close(c)

 		if err := v.fn(); err != nil {
 			t.Errorf("[%d] %q failed: %v", i, v.call, err)
 			continue
 		}
 		if err := compareStatus(v.filter, v.expect); err != nil {
 			t.Errorf("[%d] %q comparison: %v", i, v.call, err)
 		}
 	}
 }
	// 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.

	package syscall_test

	import (
	"fmt"
	"io"
	"io/fs"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"sort"
	"strconv"
	"strings"
	"syscall"
	"testing"
	"unsafe"
	)

	// chtmpdir changes the working directory to a new temporary directory and
	// provides a cleanup function. Used when PWD is read-only.
	func chtmpdir(t *testing.T) func() {
	oldwd, err := os.Getwd()
	if err != nil {
	t.Fatalf("chtmpdir: %v", err)
	}
	d, err := os.MkdirTemp("", "test")
	if err != nil {
	t.Fatalf("chtmpdir: %v", err)
	}
	if err := os.Chdir(d); err != nil {
	t.Fatalf("chtmpdir: %v", err)
	}
	return func() {
	if err := os.Chdir(oldwd); err != nil {
	t.Fatalf("chtmpdir: %v", err)
	}
	os.RemoveAll(d)
	}
	}

	func touch(t *testing.T, name string) {
	f, err := os.Create(name)
	if err != nil {
	t.Fatal(err)
	}
	if err := f.Close(); err != nil {
	t.Fatal(err)
	}
	}

	const (
	_AT_SYMLINK_NOFOLLOW = 0x100
	_AT_FDCWD = -0x64
	_AT_EACCESS = 0x200
	_F_OK = 0
	_R_OK = 4
	)

	func TestFaccessat(t *testing.T) {
	defer chtmpdir(t)()
	touch(t, "file1")

	err := syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, 0)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, 2)
	if err != syscall.EINVAL {
	t.Errorf("Faccessat: unexpected error: %v, want EINVAL", err)
	}

	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, _AT_EACCESS)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = os.Symlink("file1", "symlink1")
	if err != nil {
	t.Fatal(err)
	}

	err = syscall.Faccessat(_AT_FDCWD, "symlink1", _R_OK, _AT_SYMLINK_NOFOLLOW)
	if err != nil {
	t.Errorf("Faccessat SYMLINK_NOFOLLOW: unexpected error %v", err)
	}

	// We can't really test _AT_SYMLINK_NOFOLLOW, because there
	// doesn't seem to be any way to change the mode of a symlink.
	// We don't test _AT_EACCESS because such tests are only
	// meaningful if run as root.

	err = syscall.Fchmodat(_AT_FDCWD, "file1", 0, 0)
	if err != nil {
	t.Errorf("Fchmodat: unexpected error %v", err)
	}

	err = syscall.Faccessat(_AT_FDCWD, "file1", _F_OK, _AT_SYMLINK_NOFOLLOW)
	if err != nil {
	t.Errorf("Faccessat: unexpected error: %v", err)
	}

	err = syscall.Faccessat(_AT_FDCWD, "file1", _R_OK, _AT_SYMLINK_NOFOLLOW)
	if err != syscall.EACCES {
	if syscall.Getuid() != 0 {
	t.Errorf("Faccessat: unexpected error: %v, want EACCES", err)
	}
	}
	}

	func TestFchmodat(t *testing.T) {
	defer chtmpdir(t)()

	touch(t, "file1")
	os.Symlink("file1", "symlink1")

	err := syscall.Fchmodat(_AT_FDCWD, "symlink1", 0444, 0)
	if err != nil {
	t.Fatalf("Fchmodat: unexpected error: %v", err)
	}

	fi, err := os.Stat("file1")
	if err != nil {
	t.Fatal(err)
	}

	if fi.Mode() != 0444 {
	t.Errorf("Fchmodat: failed to change mode: expected %v, got %v", 0444, fi.Mode())
	}

	err = syscall.Fchmodat(_AT_FDCWD, "symlink1", 0444, _AT_SYMLINK_NOFOLLOW)
	if err != syscall.EOPNOTSUPP {
	t.Fatalf("Fchmodat: unexpected error: %v, expected EOPNOTSUPP", err)
	}
	}

	func TestMain(m *testing.M) {
	if os.Getenv("GO_DEATHSIG_PARENT") == "1" {
	deathSignalParent()
	} else if os.Getenv("GO_DEATHSIG_CHILD") == "1" {
	deathSignalChild()
	} else if os.Getenv("GO_SYSCALL_NOERROR") == "1" {
	syscallNoError()
	}

	os.Exit(m.Run())
	}

	func TestParseNetlinkMessage(t *testing.T) {
	for i, b := range [][]byte{
	{103, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 5, 8, 0, 3,
	0, 8, 0, 6, 0, 0, 0, 0, 1, 63, 0, 10, 0, 69, 16, 0, 59, 39, 82, 64, 0, 64, 6, 21, 89, 127, 0, 0,
	1, 127, 0, 0, 1, 230, 228, 31, 144, 32, 186, 155, 211, 185, 151, 209, 179, 128, 24, 1, 86,
	53, 119, 0, 0, 1, 1, 8, 10, 0, 17, 234, 12, 0, 17, 189, 126, 107, 106, 108, 107, 106, 13, 10,
	},
	{106, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 3, 8, 0, 3,
	0, 8, 0, 6, 0, 0, 0, 0, 1, 66, 0, 10, 0, 69, 0, 0, 62, 230, 255, 64, 0, 64, 6, 85, 184, 127, 0, 0,
	1, 127, 0, 0, 1, 237, 206, 31, 144, 73, 197, 128, 65, 250, 60, 192, 97, 128, 24, 1, 86, 253, 21, 0,
	0, 1, 1, 8, 10, 0, 51, 106, 89, 0, 51, 102, 198, 108, 104, 106, 108, 107, 104, 108, 107, 104, 10,
	},
	{102, 0, 0, 0, 0, 3, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 2, 0, 0, 2, 11, 0, 1, 0, 0, 0, 0, 1, 8, 0, 3, 0,
	8, 0, 6, 0, 0, 0, 0, 1, 62, 0, 10, 0, 69, 0, 0, 58, 231, 2, 64, 0, 64, 6, 85, 185, 127, 0, 0, 1, 127,
	0, 0, 1, 237, 206, 31, 144, 73, 197, 128, 86, 250, 60, 192, 97, 128, 24, 1, 86, 104, 64, 0, 0, 1, 1, 8,
	10, 0, 52, 198, 200, 0, 51, 135, 232, 101, 115, 97, 103, 103, 10,
	},
	} {
	m, err := syscall.ParseNetlinkMessage(b)
	if err != syscall.EINVAL {
	t.Errorf("#%d: got %v; want EINVAL", i, err)
	}
	if m != nil {
	t.Errorf("#%d: got %v; want nil", i, m)
	}
	}
	}

	func TestSyscallNoError(t *testing.T) {
	// On Linux there are currently no syscalls which don't fail and return
	// a value larger than 0xfffffffffffff001 so we could test RawSyscall
	// vs. RawSyscallNoError on 64bit architectures.
	if unsafe.Sizeof(uintptr(0)) != 4 {
	t.Skip("skipping on non-32bit architecture")
	}

	// See https://golang.org/issue/35422
	// On MIPS, Linux returns whether the syscall had an error in a separate
	// register (R7), not using a negative return value as on other
	// architectures.
	if runtime.GOARCH == "mips" \|\| runtime.GOARCH == "mipsle" {
	t.Skipf("skipping on %s", runtime.GOARCH)
	}

	if os.Getuid() != 0 {
	t.Skip("skipping root only test")
	}

	if runtime.GOOS == "android" {
	t.Skip("skipping on rooted android, see issue 27364")
	}

	// Copy the test binary to a location that a non-root user can read/execute
	// after we drop privileges
	tempDir, err := os.MkdirTemp("", "TestSyscallNoError")
	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)
	}

	uid := uint32(0xfffffffe)
	err = os.Chown(tmpBinary, int(uid), -1)
	if err != nil {
	t.Fatalf("failed to chown test binary %q, %v", tmpBinary, err)
	}

	err = os.Chmod(tmpBinary, 0755\|fs.ModeSetuid)
	if err != nil {
	t.Fatalf("failed to set setuid bit on test binary %q, %v", tmpBinary, err)
	}

	cmd := exec.Command(tmpBinary)
	cmd.Env = append(os.Environ(), "GO_SYSCALL_NOERROR=1")

	out, err := cmd.CombinedOutput()
	if err != nil {
	t.Fatalf("failed to start first child process: %v", err)
	}

	got := strings.TrimSpace(string(out))
	want := strconv.FormatUint(uint64(uid)+1, 10) + " / " +
	strconv.FormatUint(uint64(-uid), 10) + " / " +
	strconv.FormatUint(uint64(uid), 10)
	if got != want {
	if filesystemIsNoSUID(tmpBinary) {
	t.Skip("skipping test when temp dir is mounted nosuid")
	}
	// formatted so the values are aligned for easier comparison
	t.Errorf("expected %s,\ngot %s", want, got)
	}
	}

	// filesystemIsNoSUID reports whether the filesystem for the given
	// path is mounted nosuid.
	func filesystemIsNoSUID(path string) bool {
	var st syscall.Statfs_t
	if syscall.Statfs(path, &st) != nil {
	return false
	}
	return st.Flags&syscall.MS_NOSUID != 0
	}

	func syscallNoError() {
	// Test that the return value from SYS_GETEUID32 (which cannot fail)
	// doesn't get treated as an error (see https://golang.org/issue/22924)
	euid1, _, e := syscall.RawSyscall(syscall.Sys_GETEUID, 0, 0, 0)
	euid2, _ := syscall.RawSyscallNoError(syscall.Sys_GETEUID, 0, 0, 0)

	fmt.Println(uintptr(euid1), "/", int(e), "/", uintptr(euid2))
	os.Exit(0)
	}

	// reference uapi/linux/prctl.h
	const (
	PR_GET_KEEPCAPS uintptr = 7
	PR_SET_KEEPCAPS = 8
	)

	// TestAllThreadsSyscall tests that the go runtime can perform
	// syscalls that execute on all OSThreads - with which to support
	// POSIX semantics for security state changes.
	func TestAllThreadsSyscall(t *testing.T) {
	if _, _, err := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, 0, 0); err == syscall.ENOTSUP {
	t.Skip("AllThreadsSyscall disabled with cgo")
	}

	fns := []struct {
	label string
	fn func(uintptr) error
	}{
	{
	label: "prctl<3-args>",
	fn: func(v uintptr) error {
	_, _, e := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, v, 0)
	if e != 0 {
	return e
	}
	return nil
	},
	},
	{
	label: "prctl<6-args>",
	fn: func(v uintptr) error {
	_, _, e := syscall.AllThreadsSyscall6(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, v, 0, 0, 0, 0)
	if e != 0 {
	return e
	}
	return nil
	},
	},
	}

	waiter := func(q <-chan uintptr, r chan<- uintptr, once bool) {
	for x := range q {
	runtime.LockOSThread()
	v, _, e := syscall.Syscall(syscall.SYS_PRCTL, PR_GET_KEEPCAPS, 0, 0)
	if e != 0 {
	t.Errorf("tid=%d prctl(PR_GET_KEEPCAPS) failed: %v", syscall.Gettid(), e)
	} else if x != v {
	t.Errorf("tid=%d prctl(PR_GET_KEEPCAPS) mismatch: got=%d want=%d", syscall.Gettid(), v, x)
	}
	r <- v
	if once {
	break
	}
	runtime.UnlockOSThread()
	}
	}

	// launches per fns member.
	const launches = 11
	question := make(chan uintptr)
	response := make(chan uintptr)
	defer close(question)

	routines := 0
	for i, v := range fns {
	for j := 0; j < launches; j++ {
	// Add another goroutine - the closest thing
	// we can do to encourage more OS thread
	// creation - while the test is running. The
	// actual thread creation may or may not be
	// needed, based on the number of available
	// unlocked OS threads at the time waiter
	// calls runtime.LockOSThread(), but the goal
	// of doing this every time through the loop
	// is to race thread creation with v.fn(want)
	// being executed. Via the once boolean we
	// also encourage one in 5 waiters to return
	// locked after participating in only one
	// question response sequence. This allows the
	// test to race thread destruction too.
	once := routines%5 == 4
	go waiter(question, response, once)

	// Keep a count of how many goroutines are
	// going to participate in the
	// question/response test. This will count up
	// towards 2*launches minus the count of
	// routines that have been invoked with
	// once=true.
	routines++

	// Decide what value we want to set the
	// process-shared KEEPCAPS. Note, there is
	// an explicit repeat of 0 when we change the
	// variant of the syscall being used.
	want := uintptr(j & 1)

	// Invoke the AllThreadsSyscall* variant.
	if err := v.fn(want); err != nil {
	t.Errorf("[%d,%d] %s(PR_SET_KEEPCAPS, %d, ...): %v", i, j, v.label, j&1, err)
	}

	// At this point, we want all launched Go
	// routines to confirm that they see the
	// wanted value for KEEPCAPS.
	for k := 0; k < routines; k++ {
	question <- want
	}

	// At this point, we should have a large
	// number of locked OS threads all wanting to
	// reply.
	for k := 0; k < routines; k++ {
	if got := <-response; got != want {
	t.Errorf("[%d,%d,%d] waiter result got=%d, want=%d", i, j, k, got, want)
	}
	}

	// Provide an explicit opportunity for this Go
	// routine to change Ms.
	runtime.Gosched()

	if once {
	// One waiter routine will have exited.
	routines--
	}

	// Whatever M we are now running on, confirm
	// we see the wanted value too.
	if v, _, e := syscall.Syscall(syscall.SYS_PRCTL, PR_GET_KEEPCAPS, 0, 0); e != 0 {
	t.Errorf("[%d,%d] prctl(PR_GET_KEEPCAPS) failed: %v", i, j, e)
	} else if v != want {
	t.Errorf("[%d,%d] prctl(PR_GET_KEEPCAPS) gave wrong value: got=%v, want=1", i, j, v)
	}
	}
	}
	}

	// compareStatus is used to confirm the contents of the thread
	// specific status files match expectations.
	func compareStatus(filter, expect string) error {
	expected := filter + expect
	pid := syscall.Getpid()
	fs, err := os.ReadDir(fmt.Sprintf("/proc/%d/task", pid))
	if err != nil {
	return fmt.Errorf("unable to find %d tasks: %v", pid, err)
	}
	expectedProc := fmt.Sprintf("Pid:\t%d", pid)
	foundAThread := false
	for _, f := range fs {
	tf := fmt.Sprintf("/proc/%s/status", f.Name())
	d, err := os.ReadFile(tf)
	if err != nil {
	// There are a surprising number of ways this
	// can error out on linux. We've seen all of
	// the following, so treat any error here as
	// equivalent to the "process is gone":
	// os.IsNotExist(err),
	// "... : no such process",
	// "... : bad file descriptor.
	continue
	}
	lines := strings.Split(string(d), "\n")
	for _, line := range lines {
	// Different kernel vintages pad differently.
	line = strings.TrimSpace(line)
	if strings.HasPrefix(line, "Pid:\t") {
	// On loaded systems, it is possible
	// for a TID to be reused really
	// quickly. As such, we need to
	// validate that the thread status
	// info we just read is a task of the
	// same process PID as we are
	// currently running, and not a
	// recently terminated thread
	// resurfaced in a different process.
	if line != expectedProc {
	break
	}
	// Fall through in the unlikely case
	// that filter at some point is
	// "Pid:\t".
	}
	if strings.HasPrefix(line, filter) {
	if line == expected {
	foundAThread = true
	break
	}
	if filter == "Groups:" && strings.HasPrefix(line, "Groups:\t") {
	// https://github.com/golang/go/issues/46145
	// Containers don't reliably output this line in sorted order so manually sort and compare that.
	a := strings.Split(line[8:], " ")
	sort.Strings(a)
	got := strings.Join(a, " ")
	if got == expected[8:] {
	foundAThread = true
	break
	}

	}
	return fmt.Errorf("%q got:%q want:%q (bad) [pid=%d file:'%s' %v]\n", tf, line, expected, pid, string(d), expectedProc)
	}
	}
	}
	if !foundAThread {
	return fmt.Errorf("found no thread /proc/<TID>/status files for process %q", expectedProc)
	}
	return nil
	}

	// killAThread locks the goroutine to an OS thread and exits; this
	// causes an OS thread to terminate.
	func killAThread(c <-chan struct{}) {
	runtime.LockOSThread()
	<-c
	return
	}

	// TestSetuidEtc performs tests on all of the wrapped system calls
	// that mirror to the 9 glibc syscalls with POSIX semantics. The test
	// here is considered authoritative and should compile and run
	// CGO_ENABLED=0 or 1. Note, there is an extended copy of this same
	// test in ../../misc/cgo/test/issue1435.go which requires
	// CGO_ENABLED=1 and launches pthreads from C that run concurrently
	// with the Go code of the test - and the test validates that these
	// pthreads are also kept in sync with the security state changed with
	// the syscalls. Care should be taken to mirror any enhancements to
	// this test here in that file too.
	func TestSetuidEtc(t *testing.T) {
	if syscall.Getuid() != 0 {
	t.Skip("skipping root only test")
	}
	vs := []struct {
	call string
	fn func() error
	filter, expect string
	}{
	{call: "Setegid(1)", fn: func() error { return syscall.Setegid(1) }, filter: "Gid:", expect: "\t0\t1\t0\t1"},
	{call: "Setegid(0)", fn: func() error { return syscall.Setegid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

	{call: "Seteuid(1)", fn: func() error { return syscall.Seteuid(1) }, filter: "Uid:", expect: "\t0\t1\t0\t1"},
	{call: "Setuid(0)", fn: func() error { return syscall.Setuid(0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

	{call: "Setgid(1)", fn: func() error { return syscall.Setgid(1) }, filter: "Gid:", expect: "\t1\t1\t1\t1"},
	{call: "Setgid(0)", fn: func() error { return syscall.Setgid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

	{call: "Setgroups([]int{0,1,2,3})", fn: func() error { return syscall.Setgroups([]int{0, 1, 2, 3}) }, filter: "Groups:", expect: "\t0 1 2 3"},
	{call: "Setgroups(nil)", fn: func() error { return syscall.Setgroups(nil) }, filter: "Groups:", expect: ""},
	{call: "Setgroups([]int{0})", fn: func() error { return syscall.Setgroups([]int{0}) }, filter: "Groups:", expect: "\t0"},

	{call: "Setregid(101,0)", fn: func() error { return syscall.Setregid(101, 0) }, filter: "Gid:", expect: "\t101\t0\t0\t0"},
	{call: "Setregid(0,102)", fn: func() error { return syscall.Setregid(0, 102) }, filter: "Gid:", expect: "\t0\t102\t102\t102"},
	{call: "Setregid(0,0)", fn: func() error { return syscall.Setregid(0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

	{call: "Setreuid(1,0)", fn: func() error { return syscall.Setreuid(1, 0) }, filter: "Uid:", expect: "\t1\t0\t0\t0"},
	{call: "Setreuid(0,2)", fn: func() error { return syscall.Setreuid(0, 2) }, filter: "Uid:", expect: "\t0\t2\t2\t2"},
	{call: "Setreuid(0,0)", fn: func() error { return syscall.Setreuid(0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},

	{call: "Setresgid(101,0,102)", fn: func() error { return syscall.Setresgid(101, 0, 102) }, filter: "Gid:", expect: "\t101\t0\t102\t0"},
	{call: "Setresgid(0,102,101)", fn: func() error { return syscall.Setresgid(0, 102, 101) }, filter: "Gid:", expect: "\t0\t102\t101\t102"},
	{call: "Setresgid(0,0,0)", fn: func() error { return syscall.Setresgid(0, 0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},

	{call: "Setresuid(1,0,2)", fn: func() error { return syscall.Setresuid(1, 0, 2) }, filter: "Uid:", expect: "\t1\t0\t2\t0"},
	{call: "Setresuid(0,2,1)", fn: func() error { return syscall.Setresuid(0, 2, 1) }, filter: "Uid:", expect: "\t0\t2\t1\t2"},
	{call: "Setresuid(0,0,0)", fn: func() error { return syscall.Setresuid(0, 0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},
	}

	for i, v := range vs {
	// Generate some thread churn as we execute the tests.
	c := make(chan struct{})
	go killAThread(c)
	close(c)

	if err := v.fn(); err != nil {
	t.Errorf("[%d] %q failed: %v", i, v.call, err)
	continue
	}
	if err := compareStatus(v.filter, v.expect); err != nil {
	t.Errorf("[%d] %q comparison: %v", i, v.call, err)
	}
	}
	}