From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754175AbXDPBML (ORCPT ); Sun, 15 Apr 2007 21:12:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754240AbXDPBMK (ORCPT ); Sun, 15 Apr 2007 21:12:10 -0400 Received: from e33.co.us.ibm.com ([32.97.110.151]:35927 "EHLO e33.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753647AbXDPBMI (ORCPT ); Sun, 15 Apr 2007 21:12:08 -0400 Date: Sun, 15 Apr 2007 20:11:53 -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: <20070416011153.GA10120@sergelap.austin.ibm.com> References: <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> <20070413214415.GA28629@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): > > > > 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. > > But /share/$USER is surely not bind mounted to ~$USER/share in the > _global_ namespace, is it? I can't see any sense in that. No it's not, only in the private namespace. > > > 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. > > I acknowledge, that it can be done. My point was that it can be done > more simply _without_ using CLONE_NS. Seems like a matter of preference, but I see what you're saying. > > > 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. > > I'm not saying there's any contradiction, I'm saying rbind+chroot is a > better fit. Ok, I see. > I haven't yet heard a single reason why a per-session namespace with > parts shared per-user is better than just a per-user namespace. In fact I suspect we could show that they are functionally equivalent (for your purposes) by drawing the fs tree and peer groups from current->fs->root on up for both methods. And not using private namespaces leaves the admin (at least for now) better able to diagnose the state of the system. -serge