From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752477Ab3HOVXt (ORCPT ); Thu, 15 Aug 2013 17:23:49 -0400 Received: from mail-ob0-f179.google.com ([209.85.214.179]:64424 "EHLO mail-ob0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751439Ab3HOVXr convert rfc822-to-8bit (ORCPT ); Thu, 15 Aug 2013 17:23:47 -0400 Date: Thu, 15 Aug 2013 16:23:45 -0500 From: Rob Landley Subject: Re: DoS with unprivileged mounts To: Miklos Szeredi Cc: "Eric W. Biederman" , "Serge E. Hallyn" , Al Viro , Linux-Fsdevel , Kernel Mailing List References: In-Reply-To: (from miklos@szeredi.hu on Wed Aug 14 12:42:19 2013) X-Mailer: Balsa 2.4.11 Message-Id: <1376601825.2737.37@driftwood> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; DelSp=Yes; Format=Flowed Content-Disposition: inline Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/14/2013 12:42:19 PM, Miklos Szeredi wrote: > There's a simple and effective way to prevent unlink(2) and rename(2) > from operating on any file or directory by simply mounting something > on it. In any mount instance in any namespace. > > Was this considered in the unprivileged mount design? > > The solution is also theoretically simple: mounts in unpriv namespaces > are marked "volatile" and are dissolved on an unlink type operation. > > Such volatile mounts would be useful in general too. Would that "anonymous inode" thing that wandered by recently help, letting umount move the mount to one side so you could keep the mount point as the root of your per-process hierarchy but not have it glued to other people's namespaces? Rob