func switchRoot(rootfs, subdir string, rmUsr bool) error {
if err := syscall.Unmount(config.OEM, 0); err != nil {
log.Debugf("Not umounting OEM: %v", err)
}
if subdir != "" {
fullRootfs := path.Join(rootfs, subdir)
if _, err := os.Stat(fullRootfs); os.IsNotExist(err) {
if err := os.MkdirAll(fullRootfs, 0755); err != nil {
log.Errorf("Failed to create directory %s: %v", fullRootfs, err)
return err
}
}
log.Debugf("Bind mounting mount %s to %s", fullRootfs, rootfs)
if err := syscall.Mount(fullRootfs, rootfs, "", syscall.MS_BIND, ""); err != nil {
log.Errorf("Failed to bind mount subdir for %s: %v", fullRootfs, err)
return err
}
}
for _, i := range []string{"/dev", "/sys", "/proc", "/run"} {
log.Debugf("Moving mount %s to %s", i, path.Join(rootfs, i))
if err := os.MkdirAll(path.Join(rootfs, i), 0755); err != nil {
return err
}
if err := syscall.Mount(i, path.Join(rootfs, i), "", syscall.MS_MOVE, ""); err != nil {
return err
}
}
if err := copyMoveRoot(rootfs, rmUsr); err != nil {
return err
}
log.Debugf("chdir %s", rootfs)
if err := syscall.Chdir(rootfs); err != nil {
return err
}
log.Debugf("mount MS_MOVE %s", rootfs)
if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
return err
}
log.Debug("chroot .")
if err := syscall.Chroot("."); err != nil {
return err
}
log.Debug("chdir /")
if err := syscall.Chdir("/"); err != nil {
return err
}
log.Debugf("Successfully moved to new root at %s", path.Join(rootfs, subdir))
os.Unsetenv("DOCKER_RAMDISK")
return nil
}
// EnterChroot changes the current directory to the path specified,
// and then calls chroot(2) with the same path. This must be called
// while the process has CAP_SYS_CHROOT.
func EnterChroot(path string) (err error) {
if err = syscall.Chdir(path); err != nil {
return
}
if err = syscall.Chroot(path); err != nil {
return
}
if err = syscall.Chdir("/"); err != nil {
return
}
return
}
func main() {
cwd1 := make([]byte, BUF_SZ)
fmt.Print("This is where I am now: ")
if _, err := syscall.Getcwd(cwd1); err != nil {
log.Fatal("Error: syscall.Getcwd(2): ", err)
}
fmt.Println(string(cwd1))
fmt.Println("chroot(2)ing back to /home/christos")
// Commented out doesn't work for some reason. TODO: Why not?
//cwd_s := string(cwd[:])
//if err := syscall.Chroot(cwd_s); err != nil {
if err := syscall.Chroot("/home/christos"); err != nil {
log.Fatal("Error: syscall.Chroot(2): ", err)
}
fmt.Print("This is where I am now: ")
cwd2 := make([]byte, BUF_SZ)
if _, err := syscall.Getcwd(cwd2); err != nil {
log.Fatal("Error: syscall.Getcwd(2): ", err)
}
fmt.Println(string(cwd2))
fmt.Println("chdir(2)ing to parent")
if err := syscall.Chdir(".."); err != nil {
log.Fatal("Error: syscall.Chdir(2): ", err)
}
fmt.Print("This is where I am now: ")
cwd3 := make([]byte, BUF_SZ)
if _, err := syscall.Getcwd(cwd3); err != nil {
log.Fatal("Error: syscall.Getcwd(2): ", err)
}
fmt.Println(string(cwd3))
fmt.Println("Again, chdir(2)ing to parent")
if err := syscall.Chdir(".."); err != nil {
log.Fatal("Error: syscall.Chdir(2): ", err)
}
fmt.Print("This is where I am now: ")
cwd4 := make([]byte, BUF_SZ)
if _, err := syscall.Getcwd(cwd4); err != nil {
log.Fatal("Error: syscall.Getcwd(2): ", err)
}
fmt.Println(string(cwd4))
return
}
func afterDaemonize(err error) {
// Ignore SIGCHLD signal
signal.Ignore(syscall.SIGCHLD)
// Close STDOUT, STDIN, STDERR
syscall.Close(0)
syscall.Close(1)
syscall.Close(2)
// Become the process group leader
syscall.Setsid()
// // Clear umask
syscall.Umask(022)
// // chdir for root directory
syscall.Chdir("/")
// Notify that the child process started successfuly
pipe := os.NewFile(uintptr(3), "pipe")
if pipe != nil {
defer pipe.Close()
if err == nil {
pipe.Write([]byte{DAEMONIZE_SUCCESS})
} else {
pipe.Write([]byte{DAEMONIZE_FAIL})
}
}
}
// InitializeMountNamespace sets up the devices, mount points, and filesystems for use inside a
// new mount namespace.
func InitializeMountNamespace(rootfs, console string, sysReadonly bool, mountConfig *MountConfig) error {
var (
err error
flag = syscall.MS_PRIVATE
)
if mountConfig.NoPivotRoot {
flag = syscall.MS_SLAVE
}
if err := syscall.Mount("", "/", "", uintptr(flag|syscall.MS_REC), ""); err != nil {
return fmt.Errorf("mounting / with flags %X %s", (flag | syscall.MS_REC), err)
}
if err := syscall.Mount(rootfs, rootfs, "bind", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {
return fmt.Errorf("mouting %s as bind %s", rootfs, err)
}
if err := mountSystem(rootfs, sysReadonly, mountConfig); err != nil {
return fmt.Errorf("mount system %s", err)
}
if err := setupBindmounts(rootfs, mountConfig); err != nil {
return fmt.Errorf("bind mounts %s", err)
}
if err := nodes.CreateDeviceNodes(rootfs, mountConfig.DeviceNodes); err != nil {
return fmt.Errorf("create device nodes %s", err)
}
if err := SetupPtmx(rootfs, console, mountConfig.MountLabel); err != nil {
return err
}
// stdin, stdout and stderr could be pointing to /dev/null from parent namespace.
// Re-open them inside this namespace.
if err := reOpenDevNull(rootfs); err != nil {
return fmt.Errorf("Failed to reopen /dev/null %s", err)
}
if err := setupDevSymlinks(rootfs); err != nil {
return fmt.Errorf("dev symlinks %s", err)
}
if err := syscall.Chdir(rootfs); err != nil {
return fmt.Errorf("chdir into %s %s", rootfs, err)
}
if mountConfig.NoPivotRoot {
err = MsMoveRoot(rootfs)
} else {
err = PivotRoot(rootfs)
}
if err != nil {
return err
}
if mountConfig.ReadonlyFs {
if err := SetReadonly(); err != nil {
return fmt.Errorf("set readonly %s", err)
}
}
syscall.Umask(0022)
return nil
}
func main() {
flag.Usage = usage
flag.Parse()
if flag.NArg() < 1 {
usage()
}
args := flag.Args()
ck(syscall.Chroot(args[0]))
ck(syscall.Chdir("/"))
var cmd *exec.Cmd
if len(args) == 1 {
shell := os.Getenv("SHELL")
if shell == "" {
shell = "/bin/sh"
}
cmd = exec.Command(shell, "-i")
} else {
cmd = exec.Command(args[1], args[2:]...)
}
cmd.Stdin = os.Stdin
cmd.Stderr = os.Stderr
cmd.Stdout = os.Stdout
ck(cmd.Run())
}
func pivotRoot(rootfs, pivotBaseDir string) error {
if pivotBaseDir == "" {
pivotBaseDir = "/"
}
tmpDir := filepath.Join(rootfs, pivotBaseDir)
if err := os.MkdirAll(tmpDir, 0755); err != nil {
return fmt.Errorf("can't create tmp dir %s, error %v", tmpDir, err)
}
pivotDir, err := ioutil.TempDir(tmpDir, ".pivot_root")
if err != nil {
return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
}
if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
return fmt.Errorf("pivot_root %s", err)
}
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("chdir / %s", err)
}
// path to pivot dir now changed, update
pivotDir = filepath.Join(pivotBaseDir, filepath.Base(pivotDir))
// Make pivotDir rprivate to make sure any of the unmounts don't
// propagate to parent.
if err := syscall.Mount("", pivotDir, "", syscall.MS_PRIVATE|syscall.MS_REC, ""); err != nil {
return err
}
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
return fmt.Errorf("unmount pivot_root dir %s", err)
}
return os.Remove(pivotDir)
}
func pivotRoot(root string) error {
// we need this to satisfy restriction:
// "new_root and put_old must not be on the same filesystem as the current root"
if err := syscall.Mount(root, root, "bind", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {
return fmt.Errorf("Mount rootfs to itself error: %v", err)
}
// create rootfs/.pivot_root as path for old_root
pivotDir := filepath.Join(root, ".pivot_root")
if err := os.Mkdir(pivotDir, 0777); err != nil {
return err
}
logrus.Debugf("Pivot root dir: %s", pivotDir)
logrus.Debugf("Pivot root to %s", root)
// pivot_root to rootfs, now old_root is mounted in rootfs/.pivot_root
// mounts from it still can be seen in `mount`
if err := syscall.PivotRoot(root, pivotDir); err != nil {
return fmt.Errorf("pivot_root %v", err)
}
// change working directory to /
// it is recommendation from man-page
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("chdir / %v", err)
}
// path to pivot root now changed, update
pivotDir = filepath.Join("/", ".pivot_root")
// umount rootfs/.pivot_root(which is now /.pivot_root) with all submounts
// now we have only mounts that we mounted ourself in `mount`
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
return fmt.Errorf("unmount pivot_root dir %v", err)
}
// remove temporary directory
return os.Remove(pivotDir)
}
func pivotRoot(rootfs, pivotBaseDir string) error {
if pivotBaseDir == "" {
pivotBaseDir = "/"
}
tmpDir := filepath.Join(rootfs, pivotBaseDir)
if err := os.MkdirAll(tmpDir, 0755); err != nil {
return fmt.Errorf("can't create tmp dir %s, error %v", tmpDir, err)
}
pivotDir, err := ioutil.TempDir(tmpDir, ".pivot_root")
if err != nil {
return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
}
if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
return fmt.Errorf("pivot_root %s", err)
}
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("chdir / %s", err)
}
// path to pivot dir now changed, update
pivotDir = filepath.Join(pivotBaseDir, filepath.Base(pivotDir))
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
return fmt.Errorf("unmount pivot_root dir %s", err)
}
return os.Remove(pivotDir)
}
// Setup working directory
func setupWorkingDirectory(workdir string) {
if workdir == "" {
return
}
if err := syscall.Chdir(workdir); err != nil {
log.Fatalf("Unable to change dir to %v: %v", workdir, err)
}
}
// Setup working directory
func setupWorkingDirectory(args *DockerInitArgs) error {
if args.workDir == "" {
return nil
}
if err := syscall.Chdir(args.workDir); err != nil {
return fmt.Errorf("Unable to change dir to %v: %v", args.workDir, err)
}
return nil
}
func realChroot(path string) error {
if err := syscall.Chroot(path); err != nil {
return fmt.Errorf("Error after fallback to chroot: %v", err)
}
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("Error changing to new root after chroot: %v", err)
}
return nil
}
// setupRootfs sets up the devices, mount points, and filesystems for use inside a
// new mount namespace.
func setupRootfs(config *configs.Config, console *linuxConsole) (err error) {
if err := prepareRoot(config); err != nil {
return newSystemError(err)
}
setupDev := len(config.Devices) == 0
for _, m := range config.Mounts {
for _, precmd := range m.PremountCmds {
if err := mountCmd(precmd); err != nil {
return newSystemError(err)
}
}
if err := mountToRootfs(m, config.Rootfs, config.MountLabel); err != nil {
return newSystemError(err)
}
for _, postcmd := range m.PostmountCmds {
if err := mountCmd(postcmd); err != nil {
return newSystemError(err)
}
}
}
if !setupDev {
if err := createDevices(config); err != nil {
return newSystemError(err)
}
if err := setupPtmx(config, console); err != nil {
return newSystemError(err)
}
if err := setupDevSymlinks(config.Rootfs); err != nil {
return newSystemError(err)
}
}
if err := syscall.Chdir(config.Rootfs); err != nil {
return newSystemError(err)
}
if config.NoPivotRoot {
err = msMoveRoot(config.Rootfs)
} else {
err = pivotRoot(config.Rootfs, config.PivotDir)
}
if err != nil {
return newSystemError(err)
}
if !setupDev {
if err := reOpenDevNull(); err != nil {
return newSystemError(err)
}
}
if config.Readonlyfs {
if err := setReadonly(); err != nil {
return newSystemError(err)
}
}
syscall.Umask(0022)
return nil
}
func msMoveRoot(rootfs string) error {
if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
return err
}
if err := syscall.Chroot("."); err != nil {
return err
}
return syscall.Chdir("/")
}
// Initialises a daemon with recommended values. Called by Daemonize.
//
// Currently, this only calls umask(0) and chdir("/").
func Init() error {
syscall.Umask(0)
err := syscall.Chdir("/")
if err != nil {
return err
}
// setrlimit RLIMIT_CORE
return nil
}
func MsMoveRoot(rootfs string) error {
if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
return fmt.Errorf("mount move %s into / %s", rootfs, err)
}
if err := syscall.Chroot("."); err != nil {
return fmt.Errorf("chroot . %s", err)
}
return syscall.Chdir("/")
}
func containerChroot(fsPath string) error {
err := syscall.Mount(fsPath, "/", "", syscall.MS_MOVE, "")
if err != nil {
return err
}
err = syscall.Chroot(".")
if err != nil {
return err
}
return syscall.Chdir("/")
}
// setupRootfs sets up the devices, mount points, and filesystems for use inside a
// new mount namespace.
func setupRootfs(config *configs.Config, console *linuxConsole) (err error) {
if err := prepareRoot(config); err != nil {
return newSystemError(err)
}
for _, m := range config.Mounts {
for _, precmd := range m.PremountCmds {
if err := mountCmd(precmd); err != nil {
return newSystemError(err)
}
}
if err := mountToRootfs(m, config.Rootfs, config.MountLabel); err != nil {
return newSystemError(err)
}
for _, postcmd := range m.PostmountCmds {
if err := mountCmd(postcmd); err != nil {
return newSystemError(err)
}
}
}
if err := createDevices(config); err != nil {
return newSystemError(err)
}
if err := setupPtmx(config, console); err != nil {
return newSystemError(err)
}
// stdin, stdout and stderr could be pointing to /dev/null from parent namespace.
// re-open them inside this namespace.
if err := reOpenDevNull(config.Rootfs); err != nil {
return newSystemError(err)
}
if err := setupDevSymlinks(config.Rootfs); err != nil {
return newSystemError(err)
}
if err := syscall.Chdir(config.Rootfs); err != nil {
return newSystemError(err)
}
if config.NoPivotRoot {
err = msMoveRoot(config.Rootfs)
} else {
err = pivotRoot(config.Rootfs, config.PivotDir)
}
if err != nil {
return newSystemError(err)
}
if config.Readonlyfs {
if err := setReadonly(); err != nil {
return newSystemError(err)
}
}
syscall.Umask(0022)
return nil
}
// pivotRoot will call pivot_root such that rootfs becomes the new root
// filesystem, and everything else is cleaned up.
func pivotRoot(rootfs string) error {
// While the documentation may claim otherwise, pivot_root(".", ".") is
// actually valid. What this results in is / being the new root but
// /proc/self/cwd being the old root. Since we can play around with the cwd
// with pivot_root this allows us to pivot without creating directories in
// the rootfs. Shout-outs to the LXC developers for giving us this idea.
oldroot, err := syscall.Open("/", syscall.O_DIRECTORY|syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(oldroot)
newroot, err := syscall.Open(rootfs, syscall.O_DIRECTORY|syscall.O_RDONLY, 0)
if err != nil {
return err
}
defer syscall.Close(newroot)
// Change to the new root so that the pivot_root actually acts on it.
if err := syscall.Fchdir(newroot); err != nil {
return err
}
if err := syscall.PivotRoot(".", "."); err != nil {
return fmt.Errorf("pivot_root %s", err)
}
// Currently our "." is oldroot (according to the current kernel code).
// However, purely for safety, we will fchdir(oldroot) since there isn't
// really any guarantee from the kernel what /proc/self/cwd will be after a
// pivot_root(2).
if err := syscall.Fchdir(oldroot); err != nil {
return err
}
// Make oldroot rprivate to make sure our unmounts don't propagate to the
// host (and thus bork the machine).
if err := syscall.Mount("", ".", "", syscall.MS_PRIVATE|syscall.MS_REC, ""); err != nil {
return err
}
// Preform the unmount. MNT_DETACH allows us to unmount /proc/self/cwd.
if err := syscall.Unmount(".", syscall.MNT_DETACH); err != nil {
return err
}
// Switch back to our shiny new root.
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("chdir / %s", err)
}
return nil
}
// Because this function is executed by multicall in a different process, it is not possible to use errwrap to return errors
func extractTarCommand() error {
if len(os.Args) != 5 {
return fmt.Errorf("incorrect number of arguments. Usage: %s DIR {true|false} uidShift uidCount", multicallName)
}
if !sys.HasChrootCapability() {
return fmt.Errorf("chroot capability not available.")
}
dir := os.Args[1]
if !filepath.IsAbs(dir) {
return fmt.Errorf("dir %s must be an absolute path", dir)
}
overwrite, err := strconv.ParseBool(os.Args[2])
if err != nil {
return fmt.Errorf("error parsing overwrite argument: %v", err)
}
us, err := strconv.ParseUint(os.Args[3], 10, 32)
if err != nil {
return fmt.Errorf("error parsing uidShift argument: %v", err)
}
uc, err := strconv.ParseUint(os.Args[4], 10, 32)
if err != nil {
return fmt.Errorf("error parsing uidCount argument: %v", err)
}
uidRange := &user.UidRange{Shift: uint32(us), Count: uint32(uc)}
if err := syscall.Chroot(dir); err != nil {
return fmt.Errorf("failed to chroot in %s: %v", dir, err)
}
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("failed to chdir: %v", err)
}
fileMapFile := os.NewFile(uintptr(fileMapFdNum), "fileMap")
fileMap := map[string]struct{}{}
if err := json.NewDecoder(fileMapFile).Decode(&fileMap); err != nil {
return fmt.Errorf("error decoding fileMap: %v", err)
}
editor, err := NewUidShiftingFilePermEditor(uidRange)
if err != nil {
return fmt.Errorf("error determining current user: %v", err)
}
if err := ExtractTarInsecure(tar.NewReader(os.Stdin), "/", overwrite, fileMap, editor); err != nil {
return fmt.Errorf("error extracting tar: %v", err)
}
// flush remaining bytes
io.Copy(ioutil.Discard, os.Stdin)
return nil
}
func switchRoot(rootfs string) error {
for _, i := range []string{"/dev", "/sys", "/proc", "/run"} {
log.Debugf("Moving mount %s to %s", i, path.Join(rootfs, i))
if err := os.MkdirAll(path.Join(rootfs, i), 0755); err != nil {
return err
}
if err := syscall.Mount(i, path.Join(rootfs, i), "", syscall.MS_MOVE, ""); err != nil {
return err
}
}
if err := copyMoveRoot(rootfs); err != nil {
return err
}
if err := syscall.Chdir(rootfs); err != nil {
return err
}
if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
return err
}
if err := syscall.Chroot("."); err != nil {
return err
}
if err := syscall.Chdir("/"); err != nil {
return err
}
log.Debugf("Successfully moved to new root at %s", rootfs)
os.Unsetenv("DOCKER_RAMDISK")
return nil
}
/* PivotRoot()
*/
func PivotRoot(rootfs string) error {
pivotRoot := filepath.Join(rootfs, ".pivot_root")
if e := BindMount("/dev", filepath.Join(rootfs, "dev")); e != nil {
return fmt.Errorf("Failed to bind mount dev: %v", e)
}
if e := BindMount("/proc", filepath.Join(rootfs, "proc")); e != nil {
return fmt.Errorf("Failed to bind mount dev: %v", e)
}
if e := BindMount("/sys", filepath.Join(rootfs, "sys")); e != nil {
return fmt.Errorf("Failed to mount sysfs: %v", e)
}
if e := BindMount(rootfs, rootfs); e != nil {
return fmt.Errorf("Failed to bind mount rootfs: %v", e)
}
if _, e := os.Stat(pivotRoot); os.IsNotExist(e) {
if e := os.Mkdir(pivotRoot, 755); e != nil {
return fmt.Errorf("Failed to make .pivot_root dir: %v", e)
}
}
if e := syscall.PivotRoot(rootfs, pivotRoot); e != nil {
return fmt.Errorf("Failed to pivot_root: %v", e)
}
if e := syscall.Chdir("/"); e != nil {
return fmt.Errorf("Failed to cd to /: %v", e)
}
if e := syscall.Unmount("/.pivot_root", syscall.MNT_DETACH); e != nil {
return fmt.Errorf("Failed to unmount pivot_root dir: %v", e)
}
if e := os.Remove("/.pivot_root"); e != nil {
return fmt.Errorf("Failed to rmdir /.pivot_root: %v", e)
}
return nil
}
func (t *pty) fork(file string, args, env []string, cwd string, cols, rows, uid, gid int) error {
var winp = new(C.struct_winsize)
winp.ws_col = C.ushort(cols)
winp.ws_row = C.ushort(rows)
winp.ws_xpixel = 0
winp.ws_ypixel = 0
//fork the pty
var master C.int = -1
var name []C.char = make([]C.char, 40)
var pid C.int = C.GoForkpty(&master, &name[0], winp)
t.fd = int(master)
t.pid = int(pid)
t.pty = C.GoString(&name[0])
switch t.pid {
case -1:
return errors.New("forkpty(3) failed")
case 0:
if cwd != "" {
if err := syscall.Chdir(cwd); err != nil {
panic("chdir failed")
}
}
if uid != -1 && gid != -1 {
if err := syscall.Setgid(gid); err != nil {
panic("setgid failed")
}
if err := syscall.Setuid(uid); err != nil {
panic("setuid failed")
}
}
syscall.Exec(file, args, env)
panic("exec failed")
}
return nil
}
// finalizeNamespace drops the caps, sets the correct user
// and working dir, and closes any leaked file descriptors
// before executing the command inside the namespace
func finalizeNamespace(config *initConfig) error {
// Ensure that all unwanted fds we may have accidentally
// inherited are marked close-on-exec so they stay out of the
// container
if err := utils.CloseExecFrom(config.PassedFilesCount + 3); err != nil {
return err
}
capabilities := config.Config.Capabilities
if config.Capabilities != nil {
capabilities = config.Capabilities
}
w, err := newCapWhitelist(capabilities)
if err != nil {
return err
}
// drop capabilities in bounding set before changing user
if err := w.dropBoundingSet(); err != nil {
return err
}
// preserve existing capabilities while we change users
if err := system.SetKeepCaps(); err != nil {
return err
}
if err := setupUser(config); err != nil {
return err
}
if err := system.ClearKeepCaps(); err != nil {
return err
}
// drop all other capabilities
if err := w.drop(); err != nil {
return err
}
if config.Cwd != "" {
if err := syscall.Chdir(config.Cwd); err != nil {
return err
}
}
return nil
}
// Drops privileges to the specified UID and GID.
// This function does nothing and returns no error if all E?[UG]IDs are nonzero.
//
// If chrootDir is not empty, the process is chrooted into it. The directory
// must exist. The function tests that privilege dropping has been successful
// by attempting to setuid(0), which must fail.
//
// The current directory is set to / inside the chroot.
//
// The function ensures that /etc/hosts and /etc/resolv.conf are loaded before
// chrooting, so name service should continue to be available.
func DropPrivileges(UID, GID int, chrootDir string) (chrootErr error, err error) {
// chroot and set UID and GIDs
chrootErr, err = dropPrivileges(UID, GID, chrootDir)
if err != nil {
err = fmt.Errorf("dropPrivileges failed: %v", err)
return
}
err = syscall.Chdir("/")
if err != nil {
return
}
err = ensureNoPrivs()
if err != nil {
err = fmt.Errorf("ensure no privs failed: %v", err)
return
}
return
}
// Drops privileges to the specified UID and GID.
// This function does nothing and returns no error if all E?[UG]IDs are nonzero.
//
// If chrootDir is not empty, the process is chrooted into it. The directory
// must exist. The function tests that privilege dropping has been successful
// by attempting to setuid(0), which must fail.
//
// The current directory is set to / inside the chroot.
//
// The function ensures that /etc/hosts and /etc/resolv.conf are loaded before
// chrooting, so name service should continue to be available.
func DropPrivileges(UID, GID int, chrootDir string) (chrootErr error, err error) {
err = setRlimits()
if err != nil {
err = fmt.Errorf("failed to set rlimits: %v", err)
return
}
err = platformPreDropPrivileges()
if err != nil {
err = fmt.Errorf("platformPreDropPrivileges failed: %v", err)
return
}
// chroot and set UID and GIDs
chrootErr, err = dropPrivileges(UID, GID, chrootDir)
if err != nil {
err = fmt.Errorf("dropPrivileges failed: %v", err)
return
}
err = syscall.Chdir("/")
if err != nil {
return
}
err = ensureNoPrivs()
if err != nil {
err = fmt.Errorf("ensure no privs failed: %v", err)
return
}
err = platformPostDropPrivileges()
if err != nil {
err = fmt.Errorf("platformPostDropPrivileges failed: %v", err)
return
}
err = nil
return
}
func PivotRoot(rootfs string) error {
pivotDir, err := ioutil.TempDir(rootfs, ".pivot_root")
if err != nil {
return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
}
if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
return fmt.Errorf("pivot_root %s", err)
}
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("chdir / %s", err)
}
// path to pivot dir now changed, update
pivotDir = filepath.Join("/", filepath.Base(pivotDir))
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
return fmt.Errorf("unmount pivot_root dir %s", err)
}
return os.Remove(pivotDir)
}
func applyLayer() {
runtime.LockOSThread()
flag.Parse()
if err := syscall.Chroot(flag.Arg(0)); err != nil {
fatal(err)
}
if err := syscall.Chdir("/"); err != nil {
fatal(err)
}
tmpDir, err := ioutil.TempDir("/", "temp-docker-extract")
if err != nil {
fatal(err)
}
os.Setenv("TMPDIR", tmpDir)
if err := archive.ApplyLayer("/", os.Stdin); err != nil {
os.RemoveAll(tmpDir)
fatal(err)
}
os.RemoveAll(tmpDir)
os.Exit(0)
}
// FinalizeNamespace drops the caps, sets the correct user
// and working dir, and closes any leaky file descriptors
// before execing the command inside the namespace
func FinalizeNamespace(container *libcontainer.Config) error {
// Ensure that all non-standard fds we may have accidentally
// inherited are marked close-on-exec so they stay out of the
// container
if err := utils.CloseExecFrom(3); err != nil {
return fmt.Errorf("close open file descriptors %s", err)
}
// drop capabilities in bounding set before changing user
if err := capabilities.DropBoundingSet(container.Capabilities); err != nil {
return fmt.Errorf("drop bounding set %s", err)
}
// preserve existing capabilities while we change users
if err := system.SetKeepCaps(); err != nil {
return fmt.Errorf("set keep caps %s", err)
}
if err := SetupUser(container.User); err != nil {
return fmt.Errorf("setup user %s", err)
}
if err := system.ClearKeepCaps(); err != nil {
return fmt.Errorf("clear keep caps %s", err)
}
// drop all other capabilities
if err := capabilities.DropCapabilities(container.Capabilities); err != nil {
return fmt.Errorf("drop capabilities %s", err)
}
if container.WorkingDir != "" {
if err := syscall.Chdir(container.WorkingDir); err != nil {
return fmt.Errorf("chdir to %s %s", container.WorkingDir, err)
}
}
return nil
}
func daemonize(server *Server) {
pid, err := os.ForkExec("lineupd", []string{}, []string{}, "/var/run", []*os.File{});
if err != nil {
server.Logger().Logf("couldn't fork: %s\n", err);
os.Exit(1);
}
server.Logger().Logf("%d->%d\n", os.Getpid(), pid);
if (pid < 0) {
os.Exit(1);
}
if (pid > 0) {
os.Exit(0);
}
syscall.Setsid();
for i := 0; i < 3; i++ {
syscall.Close(i);
}
for i := 0; i < 3; i++ {
syscall.Open("/dev/null", os.O_RDWR, 0644);
}
syscall.Umask(027);
syscall.Chdir("/var/run");
}
