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Source file src/syscall/exec_linux_test.go

Documentation: syscall

     1  // Copyright 2015 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // +build linux
     6  
     7  package syscall_test
     8  
     9  import (
    10  	"flag"
    11  	"fmt"
    12  	"internal/testenv"
    13  	"io"
    14  	"io/ioutil"
    15  	"os"
    16  	"os/exec"
    17  	"os/user"
    18  	"path/filepath"
    19  	"runtime"
    20  	"strconv"
    21  	"strings"
    22  	"syscall"
    23  	"testing"
    24  	"unsafe"
    25  )
    26  
    27  func isDocker() bool {
    28  	_, err := os.Stat("/.dockerenv")
    29  	return err == nil
    30  }
    31  
    32  func isLXC() bool {
    33  	return os.Getenv("container") == "lxc"
    34  }
    35  
    36  func skipInContainer(t *testing.T) {
    37  	if isDocker() {
    38  		t.Skip("skip this test in Docker container")
    39  	}
    40  	if isLXC() {
    41  		t.Skip("skip this test in LXC container")
    42  	}
    43  }
    44  
    45  // Check if we are in a chroot by checking if the inode of / is
    46  // different from 2 (there is no better test available to non-root on
    47  // linux).
    48  func isChrooted(t *testing.T) bool {
    49  	root, err := os.Stat("/")
    50  	if err != nil {
    51  		t.Fatalf("cannot stat /: %v", err)
    52  	}
    53  	return root.Sys().(*syscall.Stat_t).Ino != 2
    54  }
    55  
    56  func checkUserNS(t *testing.T) {
    57  	skipInContainer(t)
    58  	if _, err := os.Stat("/proc/self/ns/user"); err != nil {
    59  		if os.IsNotExist(err) {
    60  			t.Skip("kernel doesn't support user namespaces")
    61  		}
    62  		if os.IsPermission(err) {
    63  			t.Skip("unable to test user namespaces due to permissions")
    64  		}
    65  		t.Fatalf("Failed to stat /proc/self/ns/user: %v", err)
    66  	}
    67  	if isChrooted(t) {
    68  		// create_user_ns in the kernel (see
    69  		// https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/kernel/user_namespace.c)
    70  		// forbids the creation of user namespaces when chrooted.
    71  		t.Skip("cannot create user namespaces when chrooted")
    72  	}
    73  	// On some systems, there is a sysctl setting.
    74  	if os.Getuid() != 0 {
    75  		data, errRead := ioutil.ReadFile("/proc/sys/kernel/unprivileged_userns_clone")
    76  		if errRead == nil && data[0] == '0' {
    77  			t.Skip("kernel prohibits user namespace in unprivileged process")
    78  		}
    79  	}
    80  	// On Centos 7 make sure they set the kernel parameter user_namespace=1
    81  	// See issue 16283 and 20796.
    82  	if _, err := os.Stat("/sys/module/user_namespace/parameters/enable"); err == nil {
    83  		buf, _ := ioutil.ReadFile("/sys/module/user_namespace/parameters/enabled")
    84  		if !strings.HasPrefix(string(buf), "Y") {
    85  			t.Skip("kernel doesn't support user namespaces")
    86  		}
    87  	}
    88  
    89  	// On Centos 7.5+, user namespaces are disabled if user.max_user_namespaces = 0
    90  	if _, err := os.Stat("/proc/sys/user/max_user_namespaces"); err == nil {
    91  		buf, errRead := ioutil.ReadFile("/proc/sys/user/max_user_namespaces")
    92  		if errRead == nil && buf[0] == '0' {
    93  			t.Skip("kernel doesn't support user namespaces")
    94  		}
    95  	}
    96  
    97  	// When running under the Go continuous build, skip tests for
    98  	// now when under Kubernetes. (where things are root but not quite)
    99  	// Both of these are our own environment variables.
   100  	// See Issue 12815.
   101  	if os.Getenv("GO_BUILDER_NAME") != "" && os.Getenv("IN_KUBERNETES") == "1" {
   102  		t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
   103  	}
   104  }
   105  
   106  func whoamiCmd(t *testing.T, uid, gid int, setgroups bool) *exec.Cmd {
   107  	checkUserNS(t)
   108  	cmd := exec.Command("whoami")
   109  	cmd.SysProcAttr = &syscall.SysProcAttr{
   110  		Cloneflags: syscall.CLONE_NEWUSER,
   111  		UidMappings: []syscall.SysProcIDMap{
   112  			{ContainerID: 0, HostID: uid, Size: 1},
   113  		},
   114  		GidMappings: []syscall.SysProcIDMap{
   115  			{ContainerID: 0, HostID: gid, Size: 1},
   116  		},
   117  		GidMappingsEnableSetgroups: setgroups,
   118  	}
   119  	return cmd
   120  }
   121  
   122  func testNEWUSERRemap(t *testing.T, uid, gid int, setgroups bool) {
   123  	cmd := whoamiCmd(t, uid, gid, setgroups)
   124  	out, err := cmd.CombinedOutput()
   125  	if err != nil {
   126  		t.Fatalf("Cmd failed with err %v, output: %s", err, out)
   127  	}
   128  	sout := strings.TrimSpace(string(out))
   129  	want := "root"
   130  	if sout != want {
   131  		t.Fatalf("whoami = %q; want %q", out, want)
   132  	}
   133  }
   134  
   135  func TestCloneNEWUSERAndRemapRootDisableSetgroups(t *testing.T) {
   136  	if os.Getuid() != 0 {
   137  		t.Skip("skipping root only test")
   138  	}
   139  	testNEWUSERRemap(t, 0, 0, false)
   140  }
   141  
   142  func TestCloneNEWUSERAndRemapRootEnableSetgroups(t *testing.T) {
   143  	if os.Getuid() != 0 {
   144  		t.Skip("skipping root only test")
   145  	}
   146  	testNEWUSERRemap(t, 0, 0, true)
   147  }
   148  
   149  func TestCloneNEWUSERAndRemapNoRootDisableSetgroups(t *testing.T) {
   150  	if os.Getuid() == 0 {
   151  		t.Skip("skipping unprivileged user only test")
   152  	}
   153  	testNEWUSERRemap(t, os.Getuid(), os.Getgid(), false)
   154  }
   155  
   156  func TestCloneNEWUSERAndRemapNoRootSetgroupsEnableSetgroups(t *testing.T) {
   157  	if os.Getuid() == 0 {
   158  		t.Skip("skipping unprivileged user only test")
   159  	}
   160  	cmd := whoamiCmd(t, os.Getuid(), os.Getgid(), true)
   161  	err := cmd.Run()
   162  	if err == nil {
   163  		t.Skip("probably old kernel without security fix")
   164  	}
   165  	if !os.IsPermission(err) {
   166  		t.Fatalf("Unprivileged gid_map rewriting with GidMappingsEnableSetgroups must fail")
   167  	}
   168  }
   169  
   170  func TestEmptyCredGroupsDisableSetgroups(t *testing.T) {
   171  	cmd := whoamiCmd(t, os.Getuid(), os.Getgid(), false)
   172  	cmd.SysProcAttr.Credential = &syscall.Credential{}
   173  	if err := cmd.Run(); err != nil {
   174  		t.Fatal(err)
   175  	}
   176  }
   177  
   178  func TestUnshare(t *testing.T) {
   179  	skipInContainer(t)
   180  	// Make sure we are running as root so we have permissions to use unshare
   181  	// and create a network namespace.
   182  	if os.Getuid() != 0 {
   183  		t.Skip("kernel prohibits unshare in unprivileged process, unless using user namespace")
   184  	}
   185  
   186  	// When running under the Go continuous build, skip tests for
   187  	// now when under Kubernetes. (where things are root but not quite)
   188  	// Both of these are our own environment variables.
   189  	// See Issue 12815.
   190  	if os.Getenv("GO_BUILDER_NAME") != "" && os.Getenv("IN_KUBERNETES") == "1" {
   191  		t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
   192  	}
   193  
   194  	path := "/proc/net/dev"
   195  	if _, err := os.Stat(path); err != nil {
   196  		if os.IsNotExist(err) {
   197  			t.Skip("kernel doesn't support proc filesystem")
   198  		}
   199  		if os.IsPermission(err) {
   200  			t.Skip("unable to test proc filesystem due to permissions")
   201  		}
   202  		t.Fatal(err)
   203  	}
   204  	if _, err := os.Stat("/proc/self/ns/net"); err != nil {
   205  		if os.IsNotExist(err) {
   206  			t.Skip("kernel doesn't support net namespace")
   207  		}
   208  		t.Fatal(err)
   209  	}
   210  
   211  	orig, err := ioutil.ReadFile(path)
   212  	if err != nil {
   213  		t.Fatal(err)
   214  	}
   215  	origLines := strings.Split(strings.TrimSpace(string(orig)), "\n")
   216  
   217  	cmd := exec.Command("cat", path)
   218  	cmd.SysProcAttr = &syscall.SysProcAttr{
   219  		Unshareflags: syscall.CLONE_NEWNET,
   220  	}
   221  	out, err := cmd.CombinedOutput()
   222  	if err != nil {
   223  		if strings.Contains(err.Error(), "operation not permitted") {
   224  			// Issue 17206: despite all the checks above,
   225  			// this still reportedly fails for some users.
   226  			// (older kernels?). Just skip.
   227  			t.Skip("skipping due to permission error")
   228  		}
   229  		t.Fatalf("Cmd failed with err %v, output: %s", err, out)
   230  	}
   231  
   232  	// Check there is only the local network interface
   233  	sout := strings.TrimSpace(string(out))
   234  	if !strings.Contains(sout, "lo:") {
   235  		t.Fatalf("Expected lo network interface to exist, got %s", sout)
   236  	}
   237  
   238  	lines := strings.Split(sout, "\n")
   239  	if len(lines) >= len(origLines) {
   240  		t.Fatalf("Got %d lines of output, want <%d", len(lines), len(origLines))
   241  	}
   242  }
   243  
   244  func TestGroupCleanup(t *testing.T) {
   245  	if os.Getuid() != 0 {
   246  		t.Skip("we need root for credential")
   247  	}
   248  	cmd := exec.Command("id")
   249  	cmd.SysProcAttr = &syscall.SysProcAttr{
   250  		Credential: &syscall.Credential{
   251  			Uid: 0,
   252  			Gid: 0,
   253  		},
   254  	}
   255  	out, err := cmd.CombinedOutput()
   256  	if err != nil {
   257  		t.Fatalf("Cmd failed with err %v, output: %s", err, out)
   258  	}
   259  	strOut := strings.TrimSpace(string(out))
   260  	expected := "uid=0(root) gid=0(root)"
   261  	// Just check prefix because some distros reportedly output a
   262  	// context parameter; see https://golang.org/issue/16224.
   263  	// Alpine does not output groups; see https://golang.org/issue/19938.
   264  	if !strings.HasPrefix(strOut, expected) {
   265  		t.Errorf("id command output: %q, expected prefix: %q", strOut, expected)
   266  	}
   267  }
   268  
   269  func TestGroupCleanupUserNamespace(t *testing.T) {
   270  	if os.Getuid() != 0 {
   271  		t.Skip("we need root for credential")
   272  	}
   273  	checkUserNS(t)
   274  	cmd := exec.Command("id")
   275  	uid, gid := os.Getuid(), os.Getgid()
   276  	cmd.SysProcAttr = &syscall.SysProcAttr{
   277  		Cloneflags: syscall.CLONE_NEWUSER,
   278  		Credential: &syscall.Credential{
   279  			Uid: uint32(uid),
   280  			Gid: uint32(gid),
   281  		},
   282  		UidMappings: []syscall.SysProcIDMap{
   283  			{ContainerID: 0, HostID: uid, Size: 1},
   284  		},
   285  		GidMappings: []syscall.SysProcIDMap{
   286  			{ContainerID: 0, HostID: gid, Size: 1},
   287  		},
   288  	}
   289  	out, err := cmd.CombinedOutput()
   290  	if err != nil {
   291  		t.Fatalf("Cmd failed with err %v, output: %s", err, out)
   292  	}
   293  	strOut := strings.TrimSpace(string(out))
   294  
   295  	// Strings we've seen in the wild.
   296  	expected := []string{
   297  		"uid=0(root) gid=0(root) groups=0(root)",
   298  		"uid=0(root) gid=0(root) groups=0(root),65534(nobody)",
   299  		"uid=0(root) gid=0(root) groups=0(root),65534(nogroup)",
   300  		"uid=0(root) gid=0(root) groups=0(root),65534",
   301  		"uid=0(root) gid=0(root) groups=0(root),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody),65534(nobody)", // Alpine; see https://golang.org/issue/19938
   302  	}
   303  	for _, e := range expected {
   304  		if strOut == e {
   305  			return
   306  		}
   307  	}
   308  	t.Errorf("id command output: %q, expected one of %q", strOut, expected)
   309  }
   310  
   311  // TestUnshareHelperProcess isn't a real test. It's used as a helper process
   312  // for TestUnshareMountNameSpace.
   313  func TestUnshareMountNameSpaceHelper(*testing.T) {
   314  	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
   315  		return
   316  	}
   317  	defer os.Exit(0)
   318  	if err := syscall.Mount("none", flag.Args()[0], "proc", 0, ""); err != nil {
   319  		fmt.Fprintf(os.Stderr, "unshare: mount %v failed: %v", os.Args, err)
   320  		os.Exit(2)
   321  	}
   322  }
   323  
   324  // Test for Issue 38471: unshare fails because systemd has forced / to be shared
   325  func TestUnshareMountNameSpace(t *testing.T) {
   326  	skipInContainer(t)
   327  	// Make sure we are running as root so we have permissions to use unshare
   328  	// and create a network namespace.
   329  	if os.Getuid() != 0 {
   330  		t.Skip("kernel prohibits unshare in unprivileged process, unless using user namespace")
   331  	}
   332  
   333  	// When running under the Go continuous build, skip tests for
   334  	// now when under Kubernetes. (where things are root but not quite)
   335  	// Both of these are our own environment variables.
   336  	// See Issue 12815.
   337  	if os.Getenv("GO_BUILDER_NAME") != "" && os.Getenv("IN_KUBERNETES") == "1" {
   338  		t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
   339  	}
   340  
   341  	d, err := ioutil.TempDir("", "unshare")
   342  	if err != nil {
   343  		t.Fatalf("tempdir: %v", err)
   344  	}
   345  
   346  	cmd := exec.Command(os.Args[0], "-test.run=TestUnshareMountNameSpaceHelper", d)
   347  	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
   348  	cmd.SysProcAttr = &syscall.SysProcAttr{Unshareflags: syscall.CLONE_NEWNS}
   349  
   350  	o, err := cmd.CombinedOutput()
   351  	if err != nil {
   352  		if strings.Contains(err.Error(), ": permission denied") {
   353  			t.Skipf("Skipping test (golang.org/issue/19698); unshare failed due to permissions: %s, %v", o, err)
   354  		}
   355  		t.Fatalf("unshare failed: %s, %v", o, err)
   356  	}
   357  
   358  	// How do we tell if the namespace was really unshared? It turns out
   359  	// to be simple: just try to remove the directory. If it's still mounted
   360  	// on the rm will fail with EBUSY. Then we have some cleanup to do:
   361  	// we must unmount it, then try to remove it again.
   362  
   363  	if err := os.Remove(d); err != nil {
   364  		t.Errorf("rmdir failed on %v: %v", d, err)
   365  		if err := syscall.Unmount(d, syscall.MNT_FORCE); err != nil {
   366  			t.Errorf("Can't unmount %v: %v", d, err)
   367  		}
   368  		if err := os.Remove(d); err != nil {
   369  			t.Errorf("rmdir after unmount failed on %v: %v", d, err)
   370  		}
   371  	}
   372  }
   373  
   374  // Test for Issue 20103: unshare fails when chroot is used
   375  func TestUnshareMountNameSpaceChroot(t *testing.T) {
   376  	skipInContainer(t)
   377  	// Make sure we are running as root so we have permissions to use unshare
   378  	// and create a network namespace.
   379  	if os.Getuid() != 0 {
   380  		t.Skip("kernel prohibits unshare in unprivileged process, unless using user namespace")
   381  	}
   382  
   383  	// When running under the Go continuous build, skip tests for
   384  	// now when under Kubernetes. (where things are root but not quite)
   385  	// Both of these are our own environment variables.
   386  	// See Issue 12815.
   387  	if os.Getenv("GO_BUILDER_NAME") != "" && os.Getenv("IN_KUBERNETES") == "1" {
   388  		t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
   389  	}
   390  
   391  	d, err := ioutil.TempDir("", "unshare")
   392  	if err != nil {
   393  		t.Fatalf("tempdir: %v", err)
   394  	}
   395  
   396  	// Since we are doing a chroot, we need the binary there,
   397  	// and it must be statically linked.
   398  	x := filepath.Join(d, "syscall.test")
   399  	cmd := exec.Command(testenv.GoToolPath(t), "test", "-c", "-o", x, "syscall")
   400  	cmd.Env = append(os.Environ(), "CGO_ENABLED=0")
   401  	if o, err := cmd.CombinedOutput(); err != nil {
   402  		t.Fatalf("Build of syscall in chroot failed, output %v, err %v", o, err)
   403  	}
   404  
   405  	cmd = exec.Command("/syscall.test", "-test.run=TestUnshareMountNameSpaceHelper", "/")
   406  	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
   407  	cmd.SysProcAttr = &syscall.SysProcAttr{Chroot: d, Unshareflags: syscall.CLONE_NEWNS}
   408  
   409  	o, err := cmd.CombinedOutput()
   410  	if err != nil {
   411  		if strings.Contains(err.Error(), ": permission denied") {
   412  			t.Skipf("Skipping test (golang.org/issue/19698); unshare failed due to permissions: %s, %v", o, err)
   413  		}
   414  		t.Fatalf("unshare failed: %s, %v", o, err)
   415  	}
   416  
   417  	// How do we tell if the namespace was really unshared? It turns out
   418  	// to be simple: just try to remove the executable. If it's still mounted
   419  	// on, the rm will fail. Then we have some cleanup to do:
   420  	// we must force unmount it, then try to remove it again.
   421  
   422  	if err := os.Remove(x); err != nil {
   423  		t.Errorf("rm failed on %v: %v", x, err)
   424  		if err := syscall.Unmount(d, syscall.MNT_FORCE); err != nil {
   425  			t.Fatalf("Can't unmount %v: %v", d, err)
   426  		}
   427  		if err := os.Remove(x); err != nil {
   428  			t.Fatalf("rm failed on %v: %v", x, err)
   429  		}
   430  	}
   431  
   432  	if err := os.Remove(d); err != nil {
   433  		t.Errorf("rmdir failed on %v: %v", d, err)
   434  	}
   435  }
   436  
   437  type capHeader struct {
   438  	version uint32
   439  	pid     int
   440  }
   441  
   442  type capData struct {
   443  	effective   uint32
   444  	permitted   uint32
   445  	inheritable uint32
   446  }
   447  
   448  const CAP_SYS_TIME = 25
   449  
   450  type caps struct {
   451  	hdr  capHeader
   452  	data [2]capData
   453  }
   454  
   455  func getCaps() (caps, error) {
   456  	var c caps
   457  
   458  	// Get capability version
   459  	if _, _, errno := syscall.Syscall(syscall.SYS_CAPGET, uintptr(unsafe.Pointer(&c.hdr)), uintptr(unsafe.Pointer(nil)), 0); errno != 0 {
   460  		return c, fmt.Errorf("SYS_CAPGET: %v", errno)
   461  	}
   462  
   463  	// Get current capabilities
   464  	if _, _, errno := syscall.Syscall(syscall.SYS_CAPGET, uintptr(unsafe.Pointer(&c.hdr)), uintptr(unsafe.Pointer(&c.data[0])), 0); errno != 0 {
   465  		return c, fmt.Errorf("SYS_CAPGET: %v", errno)
   466  	}
   467  
   468  	return c, nil
   469  }
   470  
   471  func mustSupportAmbientCaps(t *testing.T) {
   472  	var uname syscall.Utsname
   473  	if err := syscall.Uname(&uname); err != nil {
   474  		t.Fatalf("Uname: %v", err)
   475  	}
   476  	var buf [65]byte
   477  	for i, b := range uname.Release {
   478  		buf[i] = byte(b)
   479  	}
   480  	ver := string(buf[:])
   481  	if i := strings.Index(ver, "\x00"); i != -1 {
   482  		ver = ver[:i]
   483  	}
   484  	if strings.HasPrefix(ver, "2.") ||
   485  		strings.HasPrefix(ver, "3.") ||
   486  		strings.HasPrefix(ver, "4.1.") ||
   487  		strings.HasPrefix(ver, "4.2.") {
   488  		t.Skipf("kernel version %q predates required 4.3; skipping test", ver)
   489  	}
   490  }
   491  
   492  // TestAmbientCapsHelper isn't a real test. It's used as a helper process for
   493  // TestAmbientCaps.
   494  func TestAmbientCapsHelper(*testing.T) {
   495  	if os.Getenv("GO_WANT_HELPER_PROCESS") != "1" {
   496  		return
   497  	}
   498  	defer os.Exit(0)
   499  
   500  	caps, err := getCaps()
   501  	if err != nil {
   502  		fmt.Fprintln(os.Stderr, err)
   503  		os.Exit(2)
   504  	}
   505  	if caps.data[0].effective&(1<<uint(CAP_SYS_TIME)) == 0 {
   506  		fmt.Fprintln(os.Stderr, "CAP_SYS_TIME unexpectedly not in the effective capability mask")
   507  		os.Exit(2)
   508  	}
   509  }
   510  
   511  func TestAmbientCaps(t *testing.T) {
   512  	skipInContainer(t)
   513  	// Make sure we are running as root so we have permissions to use unshare
   514  	// and create a network namespace.
   515  	if os.Getuid() != 0 {
   516  		t.Skip("kernel prohibits unshare in unprivileged process, unless using user namespace")
   517  	}
   518  	mustSupportAmbientCaps(t)
   519  
   520  	// When running under the Go continuous build, skip tests for
   521  	// now when under Kubernetes. (where things are root but not quite)
   522  	// Both of these are our own environment variables.
   523  	// See Issue 12815.
   524  	if os.Getenv("GO_BUILDER_NAME") != "" && os.Getenv("IN_KUBERNETES") == "1" {
   525  		t.Skip("skipping test on Kubernetes-based builders; see Issue 12815")
   526  	}
   527  
   528  	// skip on android, due to lack of lookup support
   529  	if runtime.GOOS == "android" {
   530  		t.Skip("skipping test on android; see Issue 27327")
   531  	}
   532  
   533  	caps, err := getCaps()
   534  	if err != nil {
   535  		t.Fatal(err)
   536  	}
   537  
   538  	// Add CAP_SYS_TIME to the permitted and inheritable capability mask,
   539  	// otherwise we will not be able to add it to the ambient capability mask.
   540  	caps.data[0].permitted |= 1 << uint(CAP_SYS_TIME)
   541  	caps.data[0].inheritable |= 1 << uint(CAP_SYS_TIME)
   542  
   543  	if _, _, errno := syscall.Syscall(syscall.SYS_CAPSET, uintptr(unsafe.Pointer(&caps.hdr)), uintptr(unsafe.Pointer(&caps.data[0])), 0); errno != 0 {
   544  		t.Fatalf("SYS_CAPSET: %v", errno)
   545  	}
   546  
   547  	u, err := user.Lookup("nobody")
   548  	if err != nil {
   549  		t.Fatal(err)
   550  	}
   551  	uid, err := strconv.ParseInt(u.Uid, 0, 32)
   552  	if err != nil {
   553  		t.Fatal(err)
   554  	}
   555  	gid, err := strconv.ParseInt(u.Gid, 0, 32)
   556  	if err != nil {
   557  		t.Fatal(err)
   558  	}
   559  
   560  	// Copy the test binary to a temporary location which is readable by nobody.
   561  	f, err := ioutil.TempFile("", "gotest")
   562  	if err != nil {
   563  		t.Fatal(err)
   564  	}
   565  	defer os.Remove(f.Name())
   566  	defer f.Close()
   567  	e, err := os.Open(os.Args[0])
   568  	if err != nil {
   569  		t.Fatal(err)
   570  	}
   571  	defer e.Close()
   572  	if _, err := io.Copy(f, e); err != nil {
   573  		t.Fatal(err)
   574  	}
   575  	if err := f.Chmod(0755); err != nil {
   576  		t.Fatal(err)
   577  	}
   578  	if err := f.Close(); err != nil {
   579  		t.Fatal(err)
   580  	}
   581  
   582  	cmd := exec.Command(f.Name(), "-test.run=TestAmbientCapsHelper")
   583  	cmd.Env = []string{"GO_WANT_HELPER_PROCESS=1"}
   584  	cmd.Stdout = os.Stdout
   585  	cmd.Stderr = os.Stderr
   586  	cmd.SysProcAttr = &syscall.SysProcAttr{
   587  		Credential: &syscall.Credential{
   588  			Uid: uint32(uid),
   589  			Gid: uint32(gid),
   590  		},
   591  		AmbientCaps: []uintptr{CAP_SYS_TIME},
   592  	}
   593  	if err := cmd.Run(); err != nil {
   594  		t.Fatal(err.Error())
   595  	}
   596  }
   597  

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