func (daemon *Daemon) mountVolumes(container *container.Container) error {
mounts, err := daemon.setupMounts(container)
if err != nil {
return err
}
for _, m := range mounts {
dest, err := container.GetResourcePath(m.Destination)
if err != nil {
return err
}
var stat os.FileInfo
stat, err = os.Stat(m.Source)
if err != nil {
return err
}
if err = fileutils.CreateIfNotExists(dest, stat.IsDir()); err != nil {
return err
}
opts := "rbind,ro"
if m.Writable {
opts = "rbind,rw"
}
if err := mount.Mount(m.Source, dest, bindMountType, opts); err != nil {
return err
}
// mountVolumes() seems to be called for temporary mounts
// outside the container. Soon these will be unmounted with
// lazy unmount option and given we have mounted the rbind,
// all the submounts will propagate if these are shared. If
// daemon is running in host namespace and has / as shared
// then these unmounts will propagate and unmount original
// mount as well. So make all these mounts rprivate.
// Do not use propagation property of volume as that should
// apply only when mounting happen inside the container.
if err := mount.MakeRPrivate(dest); err != nil {
return err
}
}
return nil
}
// chroot on linux uses pivot_root instead of chroot
// pivot_root takes a new root and an old root.
// Old root must be a sub-dir of new root, it is where the current rootfs will reside after the call to pivot_root.
// New root is where the new rootfs is set to.
// Old root is removed after the call to pivot_root so it is no longer available under the new root.
// This is similar to how libcontainer sets up a container's rootfs
func chroot(path string) (err error) {
if err := syscall.Unshare(syscall.CLONE_NEWNS); err != nil {
return fmt.Errorf("Error creating mount namespace before pivot: %v", err)
}
if err := mount.MakeRPrivate(path); err != nil {
return err
}
// setup oldRoot for pivot_root
pivotDir, err := ioutil.TempDir(path, ".pivot_root")
if err != nil {
return fmt.Errorf("Error setting up pivot dir: %v", err)
}
var mounted bool
defer func() {
if mounted {
// make sure pivotDir is not mounted before we try to remove it
if errCleanup := syscall.Unmount(pivotDir, syscall.MNT_DETACH); errCleanup != nil {
if err == nil {
err = errCleanup
}
return
}
}
errCleanup := os.Remove(pivotDir)
// pivotDir doesn't exist if pivot_root failed and chroot+chdir was successful
// because we already cleaned it up on failed pivot_root
if errCleanup != nil && !os.IsNotExist(errCleanup) {
errCleanup = fmt.Errorf("Error cleaning up after pivot: %v", errCleanup)
if err == nil {
err = errCleanup
}
}
if errCleanup := syscall.Unmount("/", syscall.MNT_DETACH); errCleanup != nil {
if err == nil {
err = fmt.Errorf("error unmounting root: %v", errCleanup)
}
return
}
}()
if err := syscall.PivotRoot(path, pivotDir); err != nil {
// If pivot fails, fall back to the normal chroot after cleaning up temp dir
if err := os.Remove(pivotDir); err != nil {
return fmt.Errorf("Error cleaning up after failed pivot: %v", err)
}
return realChroot(path)
}
mounted = true
// This is the new path for where the old root (prior to the pivot) has been moved to
// This dir contains the rootfs of the caller, which we need to remove so it is not visible during extraction
pivotDir = filepath.Join("/", filepath.Base(pivotDir))
if err := syscall.Chdir("/"); err != nil {
return fmt.Errorf("Error changing to new root: %v", err)
}
// Make the pivotDir (where the old root lives) private so it can be unmounted without propagating to the host
if err := syscall.Mount("", pivotDir, "", syscall.MS_PRIVATE|syscall.MS_REC, ""); err != nil {
return fmt.Errorf("Error making old root private after pivot: %v", err)
}
// Now unmount the old root so it's no longer visible from the new root
if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
return fmt.Errorf("Error while unmounting old root after pivot: %v", err)
}
mounted = false
return nil
}