From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754699AbaDYU0C (ORCPT ); Fri, 25 Apr 2014 16:26:02 -0400 Received: from out02.mta.xmission.com ([166.70.13.232]:54146 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754532AbaDYUZ7 (ORCPT ); Fri, 25 Apr 2014 16:25:59 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Andy Lutomirski Cc: "linux-kernel\@vger.kernel.org" , "Serge E. Hallyn" , Linux Containers References: <87ha5h42va.fsf@x220.int.ebiederm.org> Date: Fri, 25 Apr 2014 13:25:27 -0700 In-Reply-To: (Andy Lutomirski's message of "Fri, 25 Apr 2014 12:50:49 -0700") Message-ID: <87tx9h2m2w.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1/BnXxdg05Rz1xngAy+X60bDN1p3lFsW0E= X-SA-Exim-Connect-IP: 98.234.51.111 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -0.0 BAYES_20 BODY: Bayes spam probability is 5 to 20% * [score: 0.0738] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa04 1397; Body=1 Fuz1=1 Fuz2=1] X-Spam-DCC: XMission; sa04 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Andy Lutomirski X-Spam-Relay-Country: Subject: Re: pid ns feature request X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 13:58:17 -0700) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andy Lutomirski writes: > On Fri, Apr 25, 2014 at 12:37 PM, Eric W. Biederman > wrote: >> Andy Lutomirski writes: >> >>> Unless I'm missing some trick, it's currently rather painful to mount >>> a namespace /proc. You have to actually be in the pid namespace to >>> mount the correct /proc instance, and you can't unmount the old /proc >>> until you've mounted the new /proc. This means that you have to fork >>> into the new pid namespace before you can finish setting it up. >> >> Yes. You have to be inside just about all namespaces before you can >> finish setting them up. >> >> I don't know the context in which needed to be inside the pid namespace >> is a burden. > > I'm trying to sandbox myself. I unshare everything, setup up new > mounts, pivot_root, umount the old stuff, fork, and wait around for > the child to finish. > > This doesn't work: the parent can't mount the new /proc, and the child > can't either because it's too late. > > The only solution I can think of without kernel changes is to fork the > child (pid 1) before pivot_root, which makes everything more > complicated. I suppose I can unshare, fork immediately, have the > child set up all the mounts, and then wake the parent, but this is an > annoying bit of extra complexity for no obvious gain. Or perhaps just use clone and clone flags. What are you doing with the parent process? What value does it serve? >>> Would it make sense to add a mount option to procfs to request a mount >>> for pid_ns_for_children instead of task_active_pid_ns? >> >> This is about the using setns and unshare? >> >> Adding a proc amount option that takes a pid namespace file descriptor >> would be the general solution, and might be worth implementing. >> >> Getting a pid namespace file descriptors when there are no pids might be >> a challenge. > > Indeed, hence my request for a specific mode to mount /proc for > pid_ns_for_children. > > FWIW, I also tried forking, having the child mount /proc and exit, > then forking again later on. That also doesn't work -- it looks like > you can't recreate pid 1 after it does. Nope. Once pid 1 (init) is dead the pid namespace is dead. Eric