From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: Introspecting userns relationships to other namespaces? Date: Fri, 8 Jul 2016 13:11:42 +0200 Message-ID: <48c8d759-97e7-1de1-16b5-20d9f7bc928d@gmail.com> References: <87r3b7pxja.fsf@x220.int.ebiederm.org> <20160706141348.GB20728@mail.hallyn.com> <20160707133631.GA2994@mail.hallyn.com> <1467903712.2347.16.camel@HansenPartnership.com> <1467919055.2322.36.camel@HansenPartnership.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1467919055.2322.36.camel-d9PhHud1JfjCXq6kfMZ53/egYHeGw8Jk@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: James Bottomley Cc: "Eric W. Biederman" , Linux API , Containers , lkml , Andy Lutomirski , criu-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org, mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org List-Id: linux-api@vger.kernel.org On 07/07/2016 09:17 PM, James Bottomley wrote: > On Thu, 2016-07-07 at 20:21 +0200, Michael Kerrisk (man-pages) wrote: >> On 7 July 2016 at 17:01, James Bottomley >> wrote: > [Serge already answered the parenting issue] >>> On Thu, 2016-07-07 at 08:36 -0500, Serge E. Hallyn wrote: >>>> Hm. Probably best-effort based on the process hierarchy. So >>>> yeah you could probably get a tree into a state that would be >>>> wrongly recreated. Create a new netns, bind mount it, exit; Have >>>> another task create a new user_ns, bind mount it, exit; Third >>>> task setns()s first to the new netns then to the new user_ns. I >>>> suspect criu will recreate that wrongly. >>> >>> This is a bit pathological, and you have to be root to do it: so >>> root can set up a nesting hierarchy, bind it and destroy the pids >>> but I know of no current orchestration system which does this. >>> >>> Actually, I have to back pedal a bit: the way I currently set up >>> architecture emulation containers does precisely this: I set up the >>> namespaces unprivileged with child mount namespaces, but then I ask >>> root to bind the userns and kill the process that created it so I >>> have a permanent handle to enter the namespace by, so I suspect >>> that when our current orchestration systems get more sophisticated, >>> they might eventually want to do something like this as well. >>> >>> In theory, we could get nsfs to show this information as an option >>> (just add a show_options entry to the superblock ops), but the >>> problem is that although each namespace has a parent user_ns, >>> there's no way to get it without digging in the namespace specific >>> structure. Probably we should restructure to move it into >>> ns_common, then we could display it (and enforce all namespaces >>> having owning user_ns) but it would be a >> >> I'm missing something here. Is it not already the case that all >> namespaces have an owning user_ns? > > Um, yes, I don't believe I said they don't. The problem I thought you > were having is that there's no way of seeing what it is. Your words "and enforce all namespaces having owning user_ns" were what left me puzzled--it sounded to me that the implication was that this is not "enforced" right now. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/