Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752087AbcCGDp0 (ORCPT ); Sun, 6 Mar 2016 22:45:26 -0500 Received: from h2.hallyn.com ([78.46.35.8]:43102 "EHLO h2.hallyn.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751809AbcCGDpS (ORCPT ); Sun, 6 Mar 2016 22:45:18 -0500 Date: Sun, 6 Mar 2016 21:45:16 -0600 From: "Serge E. Hallyn" To: Andy Lutomirski Cc: "Eric W. Biederman" , "Serge E. Hallyn" , Serge Hallyn , Seth Forshee , lkml , =?iso-8859-1?Q?St=E9phane?= Graber Subject: Re: user namespace and fully visible proc and sys mounts Message-ID: <20160307034516.GA11489@mail.hallyn.com> References: <20160306082820.GA1917@mail.hallyn.com> <87oaar2ryz.fsf@x220.int.ebiederm.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3227 Lines: 72 On Sun, Mar 06, 2016 at 06:24:23PM -0800, Andy Lutomirski wrote: > On Mar 6, 2016 2:03 PM, "Eric W. Biederman" wrote: > > > > "Serge E. Hallyn" writes: > > > > > Hi, > > > > > > So we've been over this many times... but unfortunately there is more > > > breakage to report. Regular privileged and unprivileged containers > > > work all right for us. But running an unprivileged container inside a > > > privileged container is blocked. > > > > > > When creating privileged containers, lxc by default does a few things: > > > it mounts some fuse.lxcfs files over procfiles include /proc/meminfo and > > > /proc/uptime. It mounts proc rw but /proc/sysrq-trigger ro as well as > > > moves /proc/sys/net out of the way, bind-mounts /proc/sys readonly > > > (because this container is not in a user namespace) then moves > > > /proc/sys/net back. Finally it mounts sys ro but bind-mounts > > > /sys/devices/virtual/net as writeable. > > > > > > If any of these are left enabled, unprivileged containers can't be > > > started. If all are disabled, then they can be. > > > > > > Can we find a way to make these not block remounts in child user > > > namespaces? A boot flag, a procfs and sysfs mount option, a sysctl? > > > > Are any of these overmounts done for the purpose of security? It > > appears the /proc/sys and /sys mounts being made read-only is for that > > purpose. > > > > If none of the mounts are for secuirty the easy solution that works > > today is to also mount /proc and /sys somewhere else in your container > > so that the permission check for mounting a new copy passes. > > Can we use the big hammer approach on /proc/sys? Specifically, what > if we made it so that /proc mounts created in a non-root namespace > *only* see things that are scoped to the active namespaces, and only > those over which the mounter has capabilities? We could have mount > options for this. Of course the problem is precisely non-user-namespaced containers which do own and have capabilities over the /proc/sys/files. For user-namespaced containers /proc/sys/ isn't really an issue. Better namespacing of sysctls and maybe some way to say "I relinquish the ability to update *those* sysctls for myself and all children" could help. > /proc/sys utterly sucks for namespaces things. So does the uid_map > and similar crap. The API is simply awful. > > On a related note, can we *please* find a way to constrain namespace > creation in a way that might satisfy the RHEL crowd? > > > > > That said /proc/sys appears to be a show stopper in this scheme. As the > > root of your privileged container can enter your unprivileged container > > it can bypass your read-only /proc/sys by mounting a new copy of proc if > > we allow the relaxation you are requesting. > > > > Therefore the only choice on the table (and I don't have a clue how > > realistic it is) is to have a variant of proc with just files describing > > processes. Call it processfs. That would not need the current > > restrictions. > > > > As for sysfs I am drawing a blank about what might be possible. > > Lovely. Yet another vaguely-namespaced thing in a pseudo-filesystem. > > --Andy `