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 61723C433E9 for ; Thu, 14 Jan 2021 21:15:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07A7323A50 for ; Thu, 14 Jan 2021 21:15:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728574AbhANVPp (ORCPT ); Thu, 14 Jan 2021 16:15:45 -0500 Received: from mail107.syd.optusnet.com.au ([211.29.132.53]:57286 "EHLO mail107.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726334AbhANVPp (ORCPT ); Thu, 14 Jan 2021 16:15:45 -0500 Received: from dread.disaster.area (pa49-179-167-107.pa.nsw.optusnet.com.au [49.179.167.107]) by mail107.syd.optusnet.com.au (Postfix) with ESMTPS id 84A94D5E47A; Fri, 15 Jan 2021 07:43:35 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1l09Sw-006UW3-9I; Fri, 15 Jan 2021 07:43:34 +1100 Date: Fri, 15 Jan 2021 07:43:34 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: Christian Brauner , Alexander Viro , Christoph Hellwig , linux-fsdevel@vger.kernel.org, John Johansen , James Morris , Mimi Zohar , Dmitry Kasatkin , Stephen Smalley , Casey Schaufler , Arnd Bergmann , Andreas Dilger , OGAWA Hirofumi , Geoffrey Thomas , Mrunal Patel , Josh Triplett , Andy Lutomirski , Theodore Tso , Alban Crequy , Tycho Andersen , David Howells , James Bottomley , Seth Forshee , =?iso-8859-1?Q?St=E9phane?= Graber , Linus Torvalds , Aleksa Sarai , Lennart Poettering , "Eric W. Biederman" , smbarber@chromium.org, Phil Estes , Serge Hallyn , Kees Cook , Todd Kjos , Paul Moore , Jonathan Corbet , containers@lists.linux-foundation.org, linux-security-module@vger.kernel.org, linux-api@vger.kernel.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, linux-integrity@vger.kernel.org, selinux@vger.kernel.org Subject: Re: [PATCH v5 00/42] idmapped mounts Message-ID: <20210114204334.GK331610@dread.disaster.area> References: <20210112220124.837960-1-christian.brauner@ubuntu.com> <20210114171241.GA1164240@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210114171241.GA1164240@magnolia> X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=F8MpiZpN c=1 sm=1 tr=0 cx=a_idp_d a=+wqVUQIkAh0lLYI+QRsciw==:117 a=+wqVUQIkAh0lLYI+QRsciw==:17 a=kj9zAlcOel0A:10 a=EmqxpYm9HcoA:10 a=7-415B0cAAAA:8 a=In5g3teRgiYIkOrEuZ4A:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Precedence: bulk List-ID: X-Mailing-List: selinux@vger.kernel.org On Thu, Jan 14, 2021 at 09:12:41AM -0800, Darrick J. Wong wrote: > On Tue, Jan 12, 2021 at 11:00:42PM +0100, Christian Brauner wrote: > > Hey everyone, > > > > The only major change is the inclusion of hch's patch to port XFS to > > support idmapped mounts. Thanks to Christoph for doing that work. > > Yay :) > > > (For a full list of major changes between versions see the end of this > > cover letter. > > Please also note the large xfstests testsuite in patch 42 that has been > > kept as part of this series. It verifies correct vfs behavior with and > > without idmapped mounts including covering newer vfs features such as > > io_uring. > > I currently still plan to target the v5.12 merge window.) > > > > With this patchset we make it possible to attach idmappings to mounts, > > i.e. simply put different bind mounts can expose the same file or > > directory with different ownership. > > Shifting of ownership on a per-mount basis handles a wide range of > > long standing use-cases. Here are just a few: > > - Shifting of a subset of ownership-less filesystems (vfat) for use by > > multiple users, effectively allowing for DAC on such devices > > (systemd, Android, ...) > > - Allow remapping uid/gid on external filesystems or paths (USB sticks, > > network filesystem, ...) to match the local system's user and groups. > > (David Howells intends to port AFS as a first candidate.) > > - Shifting of a container rootfs or base image without having to mangle > > every file (runc, Docker, containerd, k8s, LXD, systemd ...) > > - Sharing of data between host or privileged containers with > > unprivileged containers (runC, Docker, containerd, k8s, LXD, ...) > > - Data sharing between multiple user namespaces with incompatible maps > > (LXD, k8s, ...) > > That sounds neat. AFAICT, the VFS passes the filesystem a mount userns > structure, which is then carried down the call stack to whatever > functions actually care about mapping kernel [ug]ids to their ondisk > versions? > > Does quota still work after this patchset is applied? There isn't any > mention of that in the cover letter and I don't see a code patch, so > does that mean everything just works? I'm particularly curious about > whether there can exist processes with CAP_SYS_ADMIN and an idmapped > mount? Syscalls like bulkstat and quotactl present file [ug]ids to > programs, but afaict there won't be any translating going on? bulkstat is not allowed inside user namespaces. It's an init namespace only thing because it provides unchecked/unbounded access to all inodes in the filesystem, not just those contained within a specific mount container. Hence I don't think bulkstat output (and other initns+root only filesystem introspection APIs) should be subject to or concerned about idmapping. Cheers, Dave. -- Dave Chinner david@fromorbit.com