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Date: Fri, 15 Jan 2021 07:43:34 +1100 From: Dave Chinner <david@...morbit.com> To: "Darrick J. Wong" <djwong@...nel.org> Cc: Christian Brauner <christian.brauner@...ntu.com>, Alexander Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@...radead.org>, linux-fsdevel@...r.kernel.org, John Johansen <john.johansen@...onical.com>, James Morris <jmorris@...ei.org>, Mimi Zohar <zohar@...ux.ibm.com>, Dmitry Kasatkin <dmitry.kasatkin@...il.com>, Stephen Smalley <stephen.smalley.work@...il.com>, Casey Schaufler <casey@...aufler-ca.com>, Arnd Bergmann <arnd@...db.de>, Andreas Dilger <adilger.kernel@...ger.ca>, OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>, Geoffrey Thomas <geofft@...reload.com>, Mrunal Patel <mpatel@...hat.com>, Josh Triplett <josh@...htriplett.org>, Andy Lutomirski <luto@...nel.org>, Theodore Tso <tytso@....edu>, Alban Crequy <alban@...volk.io>, Tycho Andersen <tycho@...ho.ws>, David Howells <dhowells@...hat.com>, James Bottomley <James.Bottomley@...senpartnership.com>, Seth Forshee <seth.forshee@...onical.com>, Stéphane Graber <stgraber@...ntu.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Aleksa Sarai <cyphar@...har.com>, Lennart Poettering <lennart@...ttering.net>, "Eric W. Biederman" <ebiederm@...ssion.com>, smbarber@...omium.org, Phil Estes <estesp@...il.com>, Serge Hallyn <serge@...lyn.com>, Kees Cook <keescook@...omium.org>, Todd Kjos <tkjos@...gle.com>, Paul Moore <paul@...l-moore.com>, Jonathan Corbet <corbet@....net>, containers@...ts.linux-foundation.org, linux-security-module@...r.kernel.org, linux-api@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, linux-integrity@...r.kernel.org, selinux@...r.kernel.org Subject: Re: [PATCH v5 00/42] idmapped mounts 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@...morbit.com
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