From: "Ludovic Courtès" <ludo@gnu.org>
To: Mark H Weaver <mhw@netris.org>
Cc: Brendan Tildesley <btild@mailbox.org>, 36508@debbugs.gnu.org
Subject: bug#36508: GDM files have incorrect owner after temporarily removing service
Date: Wed, 14 Apr 2021 12:32:48 +0200 [thread overview]
Message-ID: <875z0pgnqn.fsf@gnu.org> (raw)
In-Reply-To: <87czuxsya5.fsf@netris.org> (Mark H. Weaver's message of "Tue, 13 Apr 2021 16:51:35 -0400")
Hi Mark,
Mark H Weaver <mhw@netris.org> skribis:
> Brendan Tildesley via Bug reports for GNU Guix <bug-guix@gnu.org>
> writes:
>
>> I recently encountered what is likely the same bug. The directory /var/lib/gdm
>> had the correct permissions gdm:gdm, but all the files inside had something like
>> 973:gdm
>
> The underlying problem here, which I've also experienced, is that if you
> reconfigure your system with fewer users/groups, and then later add
> those users/groups back, there is no guarantee that they will be
> assigned the same UIDs and GIDs.
Yes.
The patch Brendan posted LGTM (though I’m surprised the directory itself
can have the right UID/GID while files inside it don’t; perhaps this was
made possible by 2161820ebbbab62a5ce76c9101ebaec54dc61586, which chowns
the home directory unconditionally.)
Note that there are other places, in addition to GDM, where we
forcefully reset the UID/GID of the home directory (e.g., for the
‘knot-resolver’ service.)
My preferred solution to this would be to unconditionally chown -R home
directories upon activation (for efficiency, it would be best if we
could do that if and only if the home directory itself has wrong
ownership). Thoughts?
systemd-homed does something like that. The intuition here is that
UIDs/GIDs are implementation details that should get out of the way.
> There's some discussion of this issue at <https://bugs.gnu.org/44944>,
> although I'm not sure that Danny's suggested solution is practical.
>
> Here's one idea: when activating a system, *never* delete users or
> groups if files still exist that are owned by those users/groups.
> Checking all filesystems would likely be too expensive, but perhaps it
> would be sufficient to check certain directories such as /var, /etc, and
> possibly the top directory of /home.
How would you determine which directories to look at though? What if we
miss an important one?
Note that the ID allocation strategy in (gnu build accounts) ensures
UIDs/GIDs aren’t reused right away (same strategy as implemented by
Shadow, etc.). So if you remove “bob”, then add “alice”, “alice” won’t
be able to access the left-behind /home/bob because it has a different
UID.
Ludo’.
next prev parent reply other threads:[~2021-04-14 10:34 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-05 8:36 bug#36508: GDM files have incorrect owner after temporarily replacing with SDDM ison
2021-04-13 13:24 ` bug#36508: GDM files have incorrect owner after temporarily removing service Brendan Tildesley via Bug reports for GNU Guix
2021-04-13 20:51 ` Mark H Weaver
2021-04-14 4:31 ` Brendan Tildesley via Bug reports for GNU Guix
2021-04-15 18:09 ` Mark H Weaver
2021-04-14 10:32 ` Ludovic Courtès [this message]
2021-04-14 12:21 ` Brendan Tildesley via Bug reports for GNU Guix
2021-04-15 14:24 ` Ludovic Courtès
2021-04-15 18:30 ` Mark H Weaver
2021-04-15 20:05 ` Ludovic Courtès
2021-04-15 22:22 ` Mark H Weaver
2021-04-16 15:18 ` Ludovic Courtès
2021-04-17 16:16 ` Mark H Weaver
2021-04-15 23:04 ` Mark H Weaver
2021-04-16 15:14 ` Ludovic Courtès
2021-04-15 18:35 ` Mark H Weaver
2021-04-15 18:58 ` Mark H Weaver
2021-04-16 10:42 ` Maxime Devos
2021-04-17 16:28 ` Mark H Weaver
2022-09-18 12:22 ` bug#36508: [DRAFT PATCH] Stable allocation of uids, by keeping a historical mapping Maxime Devos
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