From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030847AbXDMVoU (ORCPT ); Fri, 13 Apr 2007 17:44:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1030848AbXDMVoT (ORCPT ); Fri, 13 Apr 2007 17:44:19 -0400 Received: from e3.ny.us.ibm.com ([32.97.182.143]:52489 "EHLO e3.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030847AbXDMVoR (ORCPT ); Fri, 13 Apr 2007 17:44:17 -0400 Date: Fri, 13 Apr 2007 16:44:15 -0500 From: "Serge E. Hallyn" To: Miklos Szeredi Cc: serue@us.ibm.com, linuxram@us.ibm.com, akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org, containers@lists.osdl.org, util-linux-ng@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [patch 0/8] unprivileged mount syscall Message-ID: <20070413214415.GA28629@sergelap.austin.ibm.com> References: <20070409143802.GB4891@sergelap.austin.ibm.com> <20070409170743.GF24415@sergelap.austin.ibm.com> <1176194285.2903.67.camel@ram.us.ibm.com> <1176316116.2811.39.camel@ram.us.ibm.com> <20070413132832.GA1483@sergelap.austin.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Quoting Miklos Szeredi (miklos@szeredi.hu): > > > Thinking a bit more about this, I'm quite sure most users wouldn't > > > even want private namespaces. It would be enough to > > > > > > chroot /share/$USER > > > > > > and be done with it. > > > > > > Private namespaces are only good for keeping a bunch of mounts > > > referenced by a group of processes. But my guess is, that the natural > > > behavior for users is to see a persistent set of mounts. > > > > > > If for example they mount something on a remote machine, then log out > > > from the ssh session and later log back in, they would want to see > > > their previous mount still there. > > > > > > Miklos > > > > Agreed on desired behavior, but not on chroot sufficing. It actually > > sounds like you want exactly what was outlined in the OLS paper. > > > > Users still need to be in a different mounts namespace from the admin > > user so long as we consider the deluser and backup problems > > I don't think it matters, because /share/$USER duplicates a part or > the whole of the user's namespace. > > So backup would have to be taught about /share anyway, and deluser > operates on /home/$USER and not on /share/*, so there shouldn't be any > problem. In what I was thinking of, /share/$USER is bind mounted to ~$USER/share, so it would have to be done in a private namespace in order for deluser to not be tricked. > There's actually very little difference between rbind+chroot, and > CLONE_NEWNS. In a private namespace: > > 1) when no more processes reference the namespace, the tree will be > disbanded > > 2) the mount tree won't be accessible from outside the namespace But it *can* be, if properly set up. That's part of the point of the example in the OLS paper. When a user logs in, sshd clones a new namespace, then bind-mounts /share/$USER into ~$USER/share. So assuming that /share/$USER was --make-shared'd, it and ~$USER are now in the same peer group, and any changes made by the user under ~$USER will be reflected back into /share/$USER. > Wanting a persistent namespace contradicts 1). Not necessarily, see above. > Wanting a per-user (as opposed to per-session) namespace contradicts > 2). The namespace _has_ to be accessible from outside, so that a new > session can access/copy it. Again, I *think* you are wrong that private namespace contradicts this requirement. > So both requirements point to the rbind/chroot solution. It all points to a combination of the two :-) -serge