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From: Lennart Poettering <lennart@poettering.net>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Christian Brauner" <christian.brauner@ubuntu.com>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Christoph Hellwig" <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org,
	"John Johansen" <john.johansen@canonical.com>,
	"James Morris" <jmorris@namei.org>,
	"Mimi Zohar" <zohar@linux.ibm.com>,
	"Dmitry Kasatkin" <dmitry.kasatkin@gmail.com>,
	"Stephen Smalley" <stephen.smalley.work@gmail.com>,
	"Casey Schaufler" <casey@schaufler-ca.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Andreas Dilger" <adilger.kernel@dilger.ca>,
	"OGAWA Hirofumi" <hirofumi@mail.parknet.co.jp>,
	"Geoffrey Thomas" <geofft@ldpreload.com>,
	"Mrunal Patel" <mpatel@redhat.com>,
	"Josh Triplett" <josh@joshtriplett.org>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Amir Goldstein" <amir73il@gmail.com>,
	"Miklos Szeredi" <miklos@szeredi.hu>,
	"Theodore Tso" <tytso@mit.edu>, "Alban Crequy" <alban@kinvolk.io>,
	"Tycho Andersen" <tycho@tycho.ws>,
	"David Howells" <dhowells@redhat.com>,
	"James Bottomley" <James.Bottomley@hansenpartnership.com>,
	"Jann Horn" <jannh@google.com>,
	"Seth Forshee" <seth.forshee@canonical.com>,
	"Stéphane Graber" <stgraber@ubuntu.com>,
	"Aleksa Sarai" <cyphar@cyphar.com>,
	smbarber@chromium.org, "Phil Estes" <estesp@gmail.com>,
	"Serge Hallyn" <serge@hallyn.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Todd Kjos" <tkjos@google.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	containers@lists.linux-foundation.org,
	linux-security-module@vger.kernel.org, linux-api@vger.kernel.org,
	linux-ext4@vger.kernel.org, linux-unionfs@vger.kernel.org,
	linux-audit@redhat.com, linux-integrity@vger.kernel.org,
	selinux@vger.kernel.org
Subject: Re: [PATCH 00/34] fs: idmapped mounts
Date: Thu, 29 Oct 2020 17:05:02 +0100	[thread overview]
Message-ID: <20201029160502.GA333141@gardel-login> (raw)
In-Reply-To: <87pn51ghju.fsf@x220.int.ebiederm.org>

On Do, 29.10.20 10:47, Eric W. Biederman (ebiederm@xmission.com) wrote:

> 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?

Yes, I am very interested in seeing Christian's work succeed, for the
usecase in systemd-homed. In systemd-homed each user gets their own
private file system, and these fs shall be owned by the user's local
UID, regardless in which system it is used. The UID should be an
artifact of the local, individual system in this model, and thus
the UID on of the same user/home on system A might be picked as 1010
and on another as 1543, and on a third as 1323, and it shouldn't
matter. This way, home directories become migratable without having to
universially sync UID assignments: it doesn't matter anymore what the
local UID is.

Right now we do a recursive chown() at login time to ensure the home
dir is properly owned. This has two disadvantages:

1. It's slow. In particular on large home dirs, it takes a while to go
   through the whole user's homedir tree and chown/adjust ACLs for
   everything.

2. Because it is so slow we take a shortcut right now: if the
   top-level home dir inode itself is owned by the correct user, we
   skip the recursive chowning. This means in the typical case where a
   user uses the same system most of the time, and thus the UID is
   stable we can avoid the slowness. But this comes at a drawback: if
   the user for some reason ends up with files in their homedir owned
   by an unrelated user, then we'll never notice or readjust.

> If the goal is to solve fragmented administration of uid assignment I
> suggest that it might be better to solve the administration problem so
> that all of the uids of interest get assigned the same way on all of the
> systems of interest.

Well, the goal is to make things simple and be able to use the home
dir everywhere without any prior preparation, without central UID
assignment authority.

The goal is to have a scheme that requires no administration, by
making the UID management problem go away. Hence, if you suggest
solving this by having a central administrative authority: this is
exactly what the model wants to get away from.

Or to say this differently: just because I personally use three
different computers, I certainly don't want to set up LDAP or sync
UIDs manually.

Lennart

--
Lennart Poettering, Berlin

  parent reply	other threads:[~2020-10-29 16:15 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 [this message]
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
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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