From: "Ludovic Courtès" <ludo@gnu.org>
To: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Cc: othacehe@gnu.org, 54786@debbugs.gnu.org
Subject: bug#54786: Installation tests are failing
Date: Tue, 07 Jun 2022 16:00:54 +0200 [thread overview]
Message-ID: <877d5sbmjt.fsf@gnu.org> (raw)
In-Reply-To: <874k11ujqq.fsf@gmail.com> (Maxim Cournoyer's message of "Sat, 04 Jun 2022 00:37:33 -0400")
Hi!
Maxim Cournoyer <maxim.cournoyer@gmail.com> skribis:
> Ludovic Courtès <ludo@gnu.org> writes:
[...]
>>> I reviewed how that works, and it'd be easy; I just didn't see the
>>> incentive yet (there's no composition needed for the service, and it'd
>>> make the definition slightly less readable). If you tell me
>>> mark+forkexec-constructor/container is going the way of the Dodo though,
>>> that's a good enough incentive :-).
>
> That turns out to be bit problematic; dbus-daemon must not run in its
> own user namespace (CLONE_NEWUSER) as it wants to validate user/group
> IDs. That's probably the reason it was working with
> 'make-forkexec-constructor/container', as this was dropping the user and
> net namespaces, contrary to least-authority, which uses them all.
>
> The problem then seems to be that since we need CAP_SYS_ADMIN when
> dropping the user namespace, as CLONE_NEWUSER is what gives us
> superpowers. Per 'man user_namespaces':
>
> The child process created by clone(2) with the CLONE_NEWUSER flag starts
> out with a complete set of capabilities in the new user namespace.
>
> Which means that if we combine something like (untested):
>
> (make-forkexec-constructor
> (least-authority
> (list (file-append coreutils "/bin/true"))
> (mappings (delq 'user %namespaces))
> #:user "nobody"
> #:group "nobody"))
>
> the make-forkexec-constructor will switch to the non-privileged user
> before the clone call is made, and it will fail with EPERM.
>
> When using 'make-forkexec-constructor/container', the clone(2) call
> happens before switching user, thus as 'root' in Shepherd, which
> explains why it works.
Damnit, that’s right. For example the result of:
(lower-object (least-authority-wrapper (file-append coreutils "/bin/uname")
#:namespaces (delq 'user %namespaces)))
won’t run as an unprivileged user:
--8<---------------cut here---------------start------------->8---
$ $(guix build /gnu/store/hy8rd8p8pid67ac27dwm63svl5bqn0a1-pola-wrapper.drv)
substitute: updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://bordeaux.guix.gnu.org'... 100.0%
substitute: updating substitutes from 'https://guix.bordeaux.inria.fr'... 100.0%
The following derivations will be built:
/gnu/store/hy8rd8p8pid67ac27dwm63svl5bqn0a1-pola-wrapper.drv
/gnu/store/bd63i07rvvsw7xgsig0cbdsw7fpznd1k-references.drv
building /gnu/store/bd63i07rvvsw7xgsig0cbdsw7fpznd1k-references.drv...
successfully built /gnu/store/bd63i07rvvsw7xgsig0cbdsw7fpznd1k-references.drv
building /gnu/store/hy8rd8p8pid67ac27dwm63svl5bqn0a1-pola-wrapper.drv...
successfully built /gnu/store/hy8rd8p8pid67ac27dwm63svl5bqn0a1-pola-wrapper.drv
Backtrace:
5 (primitive-load "/gnu/store/ifsh87aifh2k8pqzhkjxncq3vskpwx3l-pola-wrapper")
In ice-9/eval.scm:
191:35 4 (_ #f)
In gnu/build/linux-container.scm:
300:8 3 (call-with-temporary-directory #<procedure 7f9aa3a674b0 at gnu/build/linux-container.scm:396:3 (root)>)
397:16 2 (_ "/tmp/guix-directory.K9gBNH")
239:7 1 (run-container "/tmp/guix-directory.K9gBNH" (#<<file-system> device: "/gnu/store/jkjs0inmzhj4vsvclbf08nmh0shm7lrf-attr-2.5…> …) …)
In guix/build/syscalls.scm:
1099:12 0 (_ 1845624849)
guix/build/syscalls.scm:1099:12: In procedure clone: 1845624849: Operation not permitted
--8<---------------cut here---------------end--------------->8---
> I'm not sure how it could be fixed; it seems the user changing business
> would need to be handled by the least-authority-wrapper code? And the
> make-forkexec-constructor would probably need to detect that command is
> a pola wrapper and then avoid changing the user/group itself to not
> interfere.
I think we would add #:user and #:group to ‘least-authority-wrapper’ and
have it call setuid/setgid. ‘make-forkexec-constructor’ doesn’t need to
be modified, but the user simply won’t pass #:user and #:group to it.
Thanks,
Ludo’.
next prev parent reply other threads:[~2022-06-07 14:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-08 9:51 bug#54786: Installation tests are failing Mathieu Othacehe
2022-04-08 15:10 ` Mathieu Othacehe
2022-04-28 7:22 ` Mathieu Othacehe
2022-04-28 19:19 ` Ludovic Courtès
2022-04-29 19:50 ` Ludovic Courtès
2022-04-30 13:02 ` Mathieu Othacehe
2022-05-01 13:26 ` Ludovic Courtès
2022-05-25 3:43 ` Maxim Cournoyer
2022-05-28 21:29 ` Ludovic Courtès
2022-05-31 16:44 ` bug#54786: [PATCH] services: jami: Modernize to adjust to Shepherd 0.9+ changes Maxim Cournoyer
2022-06-01 9:54 ` bug#54786: Installation tests are failing Ludovic Courtès
2022-06-01 13:10 ` Maxim Cournoyer
2022-06-02 13:13 ` Ludovic Courtès
2022-06-02 17:24 ` Maxim Cournoyer
2022-06-02 20:43 ` Ludovic Courtès
2022-06-04 4:37 ` Maxim Cournoyer
2022-06-07 14:00 ` Ludovic Courtès [this message]
2022-06-08 0:58 ` bokr
2022-06-11 4:18 ` Maxim Cournoyer
2022-08-09 14:20 ` Mathieu Othacehe
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