netwatch/internal/reportbuf/datadir_test.go

package reportbuf_test

import (
	"errors"
	"io/fs"
	"os"
	"os/user"
	"path/filepath"
	"strconv"
	"syscall"
	"testing"

	"sneak.berlin/go/netwatch/internal/reportbuf"
)

// reports is the last part of DATA_DIR in these tests, as in the
// image's /data/reports.
const reports = "reports"

// currentUser is the user the test runs as, the only owner a test not
// run as root can give files to.
func currentUser() *user.User {
	return &user.User{
		Uid: strconv.Itoa(os.Getuid()),
		Gid: strconv.Itoa(os.Getgid()),
	}
}

// tempDirMode700 is a new directory in a t.TempDir with mode 0700, so
// a test can tell that PrepareDataDir left its mode alone.
func tempDirMode700(t *testing.T) string {
	t.Helper()

	dir := filepath.Join(t.TempDir(), "d")

	err := os.Mkdir(dir, 0o700)
	if err != nil {
		t.Fatal(err)
	}

	return dir
}

func requireMode(t *testing.T, path string, want fs.FileMode) {
	t.Helper()

	info, err := os.Stat(path)
	if err != nil {
		t.Fatal(err)
	}

	if info.Mode() != want {
		t.Errorf("%s: mode %v, want %v", path, info.Mode(), want)
	}
}

func requireMissing(t *testing.T, path string) {
	t.Helper()

	_, err := os.Lstat(path)
	if !errors.Is(err, fs.ErrNotExist) {
		t.Errorf("%s: created, or Lstat failed: %v", path, err)
	}
}

func requireOwner(t *testing.T, path string, uid, gid uint32) {
	t.Helper()

	info, err := os.Lstat(path)
	if err != nil {
		t.Fatal(err)
	}

	stat, _ := info.Sys().(*syscall.Stat_t)
	if stat.Uid != uid || stat.Gid != gid {
		t.Errorf("%s: owner %d:%d, want %d:%d", path, stat.Uid, stat.Gid,
			uid, gid)
	}
}

func TestPrepareDataDirCreatesDataDir(t *testing.T) {
	t.Parallel()

	volume := t.TempDir()
	dir := filepath.Join(volume, "a", reports)

	err := reportbuf.PrepareDataDir(volume, dir, currentUser())
	if err != nil {
		t.Fatal(err)
	}

	requireMode(t, volume, fs.ModeDir|0o750)
	requireMode(t, dir, fs.ModeDir|0o750)
}

// TestPrepareDataDirSetsModeOfExistingDataDir: a DATA_DIR already on
// the host with another mode gets the mode too, not only a new one.
func TestPrepareDataDirSetsModeOfExistingDataDir(t *testing.T) {
	t.Parallel()

	volume := t.TempDir()
	dir := filepath.Join(volume, reports)

	err := os.Mkdir(dir, 0o700)
	if err != nil {
		t.Fatal(err)
	}

	err = reportbuf.PrepareDataDir(volume, dir, currentUser())
	if err != nil {
		t.Fatal(err)
	}

	requireMode(t, dir, fs.ModeDir|0o750)
}

func TestPrepareDataDirTakesTheVolumeItself(t *testing.T) {
	t.Parallel()

	volume := t.TempDir()

	err := reportbuf.PrepareDataDir(volume, volume, currentUser())
	if err != nil {
		t.Fatal(err)
	}

	requireMode(t, volume, fs.ModeDir|0o750)
}

// TestPrepareDataDirRefusesDataDirOutsideVolume covers a DATA_DIR that
// is relative, outside the volume, or not written in full.
func TestPrepareDataDirRefusesDataDirOutsideVolume(t *testing.T) {
	t.Parallel()

	volume := tempDirMode700(t)
	for _, dir := range []string{
		reports, volume + "/../new", volume + "/", volume + "//" + reports,
		volume + "/./" + reports, volume + "/" + reports + "/..", volume + "x",
		"/etc",
	} {
		err := reportbuf.PrepareDataDir(volume, dir, currentUser())
		if !errors.Is(err, reportbuf.ErrDataDirOutsideVolume) {
			t.Errorf("%q: error = %v, want ErrDataDirOutsideVolume", dir, err)
		}
	}

	requireMissing(t, filepath.Join(filepath.Dir(volume), "new"))
	requireMode(t, volume, fs.ModeDir|0o700)
}

// TestPrepareDataDirRefusesLinkOutOfVolume puts a symbolic link to a
// directory outside the volume on the path to DATA_DIR, written as a
// full path and as one that climbs out with '..', and as DATA_DIR
// itself, where the mode would be set through it.
func TestPrepareDataDirRefusesLinkOutOfVolume(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		name      string
		climbsOut bool
		link, dir string
	}{
		{"full path", false, "x", "x/reports"},
		{"climbs out", true, "x", "x/reports"},
		{"DATA_DIR itself", false, reports, reports},
	} {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			outside := tempDirMode700(t)
			volume := t.TempDir()

			climbOut, err := filepath.Rel(volume, outside)
			if err != nil {
				t.Fatal(err)
			}

			target := outside
			if tc.climbsOut {
				target = climbOut
			}

			err = os.Symlink(target, filepath.Join(volume, tc.link))
			if err != nil {
				t.Fatal(err)
			}

			err = reportbuf.PrepareDataDir(volume,
				filepath.Join(volume, tc.dir), currentUser())
			if err == nil {
				t.Error("no error")
			}

			requireMissing(t, filepath.Join(outside, reports))
			requireMode(t, outside, fs.ModeDir|0o700)
		})
	}
}

// TestPrepareDataDirRefusesDanglingLink: DATA_DIR is a symbolic link
// to a name in the volume that does not exist, which is not created.
func TestPrepareDataDirRefusesDanglingLink(t *testing.T) {
	t.Parallel()

	volume := t.TempDir()

	err := os.Symlink("missing", filepath.Join(volume, reports))
	if err != nil {
		t.Fatal(err)
	}

	err = reportbuf.PrepareDataDir(volume, filepath.Join(volume, reports),
		currentUser())
	if err == nil {
		t.Error("no error")
	}

	requireMissing(t, filepath.Join(volume, "missing"))
}

// TestPrepareDataDirTakesDirectoryNamedInLatin1: a host directory can
// hold names that are not valid UTF-8, here "café" written in Latin-1.
// A test not run as root can only check that PrepareDataDir goes into
// such a directory and gives it, and what it holds, to the current
// user.
func TestPrepareDataDirTakesDirectoryNamedInLatin1(t *testing.T) {
	t.Parallel()

	volume := t.TempDir()
	latin1 := filepath.Join(volume, "caf\xe9")

	err := os.Mkdir(latin1, 0o700)
	if err != nil {
		t.Fatal(err)
	}

	err = os.WriteFile(filepath.Join(latin1, "f"), nil, 0o600)
	if err != nil {
		t.Fatal(err)
	}

	owner := currentUser()

	err = reportbuf.PrepareDataDir(volume, filepath.Join(volume, reports),
		owner)
	if err != nil {
		t.Fatal(err)
	}

	uid, _ := strconv.ParseUint(owner.Uid, 10, 32)
	gid, _ := strconv.ParseUint(owner.Gid, 10, 32)

	requireOwner(t, latin1, uint32(uid), uint32(gid))
	requireOwner(t, filepath.Join(latin1, "f"), uint32(uid), uint32(gid))
}

// TestPrepareDataDirGivesVolumeToOwner gives the directories, regular
// files and symbolic links in the volume to a uid and gid that own
// nothing, which only root can do. A symbolic link in the volume to a
// directory outside it is given to them itself; what it points to is
// left as it was. A hard link to a file outside the volume, and one to
// a symbolic link outside it, are left as they were.
func TestPrepareDataDirGivesVolumeToOwner(t *testing.T) {
	t.Parallel()

	if os.Geteuid() != 0 {
		t.Skip("only root can give files to another uid")
	}

	outside := t.TempDir()
	volume := t.TempDir()
	old := filepath.Join(volume, "old")

	err := os.WriteFile(filepath.Join(outside, "f"), nil, 0o600)
	if err != nil {
		t.Fatal(err)
	}

	err = os.Mkdir(old, 0o700)
	if err != nil {
		t.Fatal(err)
	}

	err = os.WriteFile(filepath.Join(old, "f"), nil, 0o600)
	if err != nil {
		t.Fatal(err)
	}

	err = os.Symlink(outside, filepath.Join(old, "link"))
	if err != nil {
		t.Fatal(err)
	}

	err = os.Link(filepath.Join(outside, "f"), filepath.Join(old, "hardlink"))
	if err != nil {
		t.Fatal(err)
	}

	// os.Link does not follow a symbolic link: it gives the link itself
	// a second name.
	err = os.Symlink("f", filepath.Join(outside, "link"))
	if err != nil {
		t.Fatal(err)
	}

	err = os.Link(filepath.Join(outside, "link"),
		filepath.Join(old, "hardlink-to-link"))
	if err != nil {
		t.Fatal(err)
	}

	err = reportbuf.PrepareDataDir(volume, filepath.Join(volume, reports),
		&user.User{Uid: "4242", Gid: "4343"})
	if err != nil {
		t.Fatal(err)
	}

	for _, path := range []string{
		volume, filepath.Join(volume, reports), old, filepath.Join(old, "f"),
		filepath.Join(old, "link"),
	} {
		requireOwner(t, path, 4242, 4343)
	}

	for _, path := range []string{
		outside, filepath.Join(outside, "f"), filepath.Join(outside, "link"),
	} {
		requireOwner(t, path, 0, 0)
	}
}