code: func validatePathNoBacksteps(targetPath string, fldPath *field.Path) field.ErrorList {
  	allErrs := field.ErrorList{}
  	parts := strings.Split(filepath.ToSlash(targetPath), "/")
  	for _, item := range parts {
  		if item == ".." {
  			allErrs = append(allErrs, field.Invalid(fldPath, targetPath, "must not contain '..'"))
  			break // even for `../../..`, one error is sufficient to make the point
  		}
  	}
  	return allErrs
  }
docs: // validatePathNoBacksteps makes sure the targetPath does not have any `..` path elements when split
  //
  // This assumes the OS of the apiserver and the nodes are the same. The same check should be done
  // on the node to ensure there are no backsteps.