From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6A1C5C55179 for ; Thu, 29 Oct 2020 16:48:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1C31B21582 for ; Thu, 29 Oct 2020 16:48:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728086AbgJ2Qo6 (ORCPT ); Thu, 29 Oct 2020 12:44:58 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:60340 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727966AbgJ2Qo5 (ORCPT ); Thu, 29 Oct 2020 12:44:57 -0400 Received: from in01.mta.xmission.com ([166.70.13.51]) by out01.mta.xmission.com with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.93) (envelope-from ) id 1kYB2Q-009eVE-Gs; Thu, 29 Oct 2020 10:44:34 -0600 Received: from ip68-227-160-95.om.om.cox.net ([68.227.160.95] helo=x220.xmission.com) by in01.mta.xmission.com with esmtpsa (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.87) (envelope-from ) id 1kYB2N-0000rc-Un; Thu, 29 Oct 2020 10:44:34 -0600 From: ebiederm@xmission.com (Eric W. Biederman) To: Tycho Andersen Cc: Christian Brauner , Lennart Poettering , Mimi Zohar , David Howells , Andreas Dilger , containers@lists.linux-foundation.org, Miklos Szeredi , smbarber@chromium.org, Christoph Hellwig , linux-ext4@vger.kernel.org, Mrunal Patel , Kees Cook , Arnd Bergmann , Jann Horn , selinux@vger.kernel.org, Josh Triplett , linux-fsdevel@vger.kernel.org, Alexander Viro , Andy Lutomirski , OGAWA Hirofumi , Geoffrey Thomas , James Bottomley , John Johansen , Theodore Tso , Seth Forshee , Dmitry Kasatkin , Stephen Smalley , Jonathan Corbet , linux-unionfs@vger.kernel.org, linux-security-module@vger.kernel.org, linux-audit@redhat.com, linux-api@vger.kernel.org, Casey Schaufler , Alban Crequy , linux-integrity@vger.kernel.org, Todd Kjos References: <20201029003252.2128653-1-christian.brauner@ubuntu.com> <87pn51ghju.fsf@x220.int.ebiederm.org> <20201029161231.GA108315@cisco> Date: Thu, 29 Oct 2020 11:44:33 -0500 In-Reply-To: <20201029161231.GA108315@cisco> (Tycho Andersen's message of "Thu, 29 Oct 2020 10:12:31 -0600") Message-ID: <87blglc77y.fsf@x220.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1kYB2N-0000rc-Un;;;mid=<87blglc77y.fsf@x220.int.ebiederm.org>;;;hst=in01.mta.xmission.com;;;ip=68.227.160.95;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX18l/ky6v0TPp3RfG1uVSiI/idjNvZVspy0= X-SA-Exim-Connect-IP: 68.227.160.95 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: Re: [PATCH 00/34] fs: idmapped mounts X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-unionfs@vger.kernel.org Tycho Andersen writes: > Hi Eric, > > On Thu, Oct 29, 2020 at 10:47:49AM -0500, Eric W. Biederman wrote: >> Christian Brauner writes: >> >> > Hey everyone, >> > >> > I vanished for a little while to focus on this work here so sorry for >> > not being available by mail for a while. >> > >> > Since quite a long time we have issues with sharing mounts between >> > multiple unprivileged containers with different id mappings, sharing a >> > rootfs between multiple containers with different id mappings, and also >> > sharing regular directories and filesystems between users with different >> > uids and gids. The latter use-cases have become even more important with >> > the availability and adoption of systemd-homed (cf. [1]) to implement >> > portable home directories. >> >> Can you walk us through the motivating use case? >> >> As of this year's LPC I had the distinct impression that the primary use >> case for such a feature was due to the RLIMIT_NPROC problem where two >> containers with the same users still wanted different uid mappings to >> the disk because the users were conflicting with each other because of >> the per user rlimits. >> >> Fixing rlimits is straight forward to implement, and easier to manage >> for implementations and administrators. > > Our use case is to have the same directory exposed to several > different containers which each have disjoint ID mappings. Why do the you have disjoint ID mappings for the users that are writing to disk with the same ID? >> Reading up on systemd-homed it appears to be a way to have encrypted >> home directories. Those home directories can either be encrypted at the >> fs or at the block level. Those home directories appear to have the >> goal of being luggable between systems. If the systems in question >> don't have common administration of uids and gids after lugging your >> encrypted home directory to another system chowning the files is >> required. >> >> Is that the use case you are looking at removing the need for >> systemd-homed to avoid chowning after lugging encrypted home directories >> from one system to another? Why would it be desirable to avoid the >> chown? > > Not just systemd-homed, but LXD has to do this, I asked why the same disk users are assigned different kuids and the only reason I have heard that LXD does this is the RLIMIT_NPROC problem. Perhaps there is another reason. In part this is why I am eager to hear peoples use case, and why I was trying very hard to make certain we get the requirements. I want the real requirements though and some thought, not just we did this and it hurts. Changning the uids on write is a very hard problem, and not just in implementating it but also in maintaining and understanding what is going on. Eric