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From: ebiederm@xmission.com (Eric W. Biederman)
To: Tycho Andersen <tycho@tycho.pizza>
Cc: Christian Brauner <christian.brauner@ubuntu.com>,
	Lennart Poettering <lennart@poettering.net>,
	Mimi Zohar <zohar@linux.ibm.com>,
	David Howells <dhowells@redhat.com>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	containers@lists.linux-foundation.org,
	Miklos Szeredi <miklos@szeredi.hu>,
	smbarber@chromium.org, Christoph Hellwig <hch@infradead.org>,
	linux-ext4@vger.kernel.org, Mrunal Patel <mpatel@redhat.com>,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Jann Horn <jannh@google.com>,
	selinux@vger.kernel.org, Josh Triplett <josh@joshtriplett.org>,
	linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Andy Lutomirski <luto@kernel.org>,
	OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
	Geoffrey Thomas <geofft@ldpreload.com>,
	James Bottomley <James.Bottomley@hansenpartnership.com>,
	John Johansen <john.johansen@canonical.com>,
	Theodore Tso <tytso@mit.edu>,
	Seth Forshee <seth.forshee@canonical.com>,
	Dmitry Kasatkin <dmitry.kasatkin@gmail.com>,
	Stephen Smalley <stephen.smalley.work@gmail.com>,
	Jonathan Corbet <corbet@lwn.net>,
	linux-unionfs@vger.kernel.org,
	linux-security-module@vger.kernel.org, linux-audit@redhat.com,
	linux-api@vger.kernel.org,
	Casey Schaufler <casey@schaufler-ca.com>,
	Alban Crequy <alban@kinvolk.io>,
	linux-integrity@vger.kernel.org, Todd Kjos <tkjos@google.com>
Subject: Re: [PATCH 00/34] fs: idmapped mounts
Date: Thu, 29 Oct 2020 11:44:33 -0500	[thread overview]
Message-ID: <87blglc77y.fsf@x220.int.ebiederm.org> (raw)
In-Reply-To: <20201029161231.GA108315@cisco> (Tycho Andersen's message of "Thu, 29 Oct 2020 10:12:31 -0600")

Tycho Andersen <tycho@tycho.pizza> writes:

> Hi Eric,
>
> On Thu, Oct 29, 2020 at 10:47:49AM -0500, Eric W. Biederman wrote:
>> Christian Brauner <christian.brauner@ubuntu.com> 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

  parent reply	other threads:[~2020-10-29 16:48 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-29  0:32 [PATCH 00/34] fs: idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 01/34] namespace: take lock_mount_hash() directly when changing flags Christian Brauner
2020-11-01 14:41   ` Christoph Hellwig
2020-11-02 13:33     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 02/34] namespace: only take read lock in do_reconfigure_mnt() Christian Brauner
2020-10-29  0:32 ` [PATCH 03/34] fs: add mount_setattr() Christian Brauner
2020-11-01 14:42   ` Christoph Hellwig
2020-11-02 13:34     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 04/34] tests: add mount_setattr() selftests Christian Brauner
2020-10-29  0:32 ` [PATCH 05/34] fs: introduce MOUNT_ATTR_IDMAP Christian Brauner
2020-11-01 14:45   ` Christoph Hellwig
2020-11-02 13:29     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 06/34] fs: add id translation helpers Christian Brauner
2020-11-01 14:46   ` Christoph Hellwig
2020-11-02 13:25     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 07/34] capability: handle idmapped mounts Christian Brauner
2020-11-01 14:48   ` Christoph Hellwig
2020-11-02 13:23     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 08/34] namei: add idmapped mount aware permission helpers Christian Brauner
2020-10-29  0:32 ` [PATCH 09/34] inode: add idmapped mount aware init and " Christian Brauner
2020-10-29  0:32 ` [PATCH 10/34] attr: handle idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 11/34] acl: " Christian Brauner
2020-10-29  0:32 ` [PATCH 12/34] xattr: " Christian Brauner
2020-10-29  0:32 ` [PATCH 13/34] selftests: add idmapped mounts xattr selftest Christian Brauner
2020-10-29  0:32 ` [PATCH 14/34] commoncap: handle idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 15/34] stat: add mapped_generic_fillattr() Christian Brauner
2020-10-29  0:32 ` [PATCH 16/34] namei: handle idmapped mounts in may_*() helpers Christian Brauner
2020-10-29  0:32 ` [PATCH 17/34] namei: introduce struct renamedata Christian Brauner
2020-10-29  0:32 ` [PATCH 18/34] namei: prepare for idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 19/34] namei: add lookup helpers with idmapped mounts aware permission checking Christian Brauner
2020-10-29  0:32 ` [PATCH 20/34] open: handle idmapped mounts in do_truncate() Christian Brauner
2020-10-29  0:32 ` [PATCH 21/34] open: handle idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 22/34] af_unix: " Christian Brauner
2020-10-29  0:32 ` [PATCH 23/34] utimes: " Christian Brauner
2020-10-29  0:32 ` [PATCH 24/34] would_dump: " Christian Brauner
2020-10-29  0:32 ` [PATCH 25/34] exec: " Christian Brauner
2020-10-29  0:32 ` [PATCH 26/34] fs: add helpers for idmap mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 27/34] apparmor: handle idmapped mounts Christian Brauner
2020-10-29  0:32 ` [PATCH 28/34] audit: " Christian Brauner
2020-10-29  0:32 ` [PATCH 29/34] ima: " Christian Brauner
2020-10-29  0:32 ` [PATCH 30/34] ext4: support " Christian Brauner
2020-10-29  0:32 ` [PATCH 31/34] expfs: handle " Christian Brauner
2020-10-29  0:32 ` [PATCH 32/34] overlayfs: handle idmapped lower directories Christian Brauner
2020-10-30 11:10   ` Amir Goldstein
2020-10-30 11:52     ` Christian Brauner
2020-10-29  0:32 ` [PATCH 33/34] overlayfs: handle idmapped merged mounts Christian Brauner
2020-10-30  9:57   ` Amir Goldstein
2020-10-29  0:32 ` [PATCH 34/34] fat: handle idmapped mounts Christian Brauner
2020-10-29  2:27 ` [PATCH 00/34] fs: " Dave Chinner
2020-10-29 16:19   ` Christian Brauner
2020-10-29  7:20 ` Sargun Dhillon
2020-10-29 15:47 ` Eric W. Biederman
2020-10-29 15:51   ` Aleksa Sarai
2020-10-29 16:37     ` Eric W. Biederman
2020-10-30  2:18       ` Serge E. Hallyn
2020-10-30 15:07       ` Seth Forshee
2020-10-30 16:03         ` Serge E. Hallyn
2020-11-03 14:10       ` Alban Crequy
2020-10-29 16:05   ` Lennart Poettering
2020-10-29 16:36     ` Sargun Dhillon
2020-10-29 16:54     ` Eric W. Biederman
     [not found]   ` <20201029161231.GA108315@cisco>
2020-10-29 16:23     ` Serge E. Hallyn
2020-10-29 16:44     ` Eric W. Biederman [this message]
2020-10-29 18:04       ` Stéphane Graber
2020-10-29 21:58 ` Andy Lutomirski
2020-10-30 12:01   ` Christian Brauner
2020-10-30 16:17     ` Serge E. Hallyn
2020-10-31 17:43     ` Andy Lutomirski

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