linux-kernel - Re: Login broken with old userspace (was Re: [PATCH v2] selinux: introduce an initial SID for early boot processes)

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Date:   Sat, 29 Jul 2023 18:10:36 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ondrej Mosnacek <omosnace@...hat.com>
Cc:     Paul Moore <paul@...l-moore.com>, selinux@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-next@...r.kernel.org
Subject: Re: Login broken with old userspace (was Re: [PATCH v2] selinux:
 introduce an initial SID for early boot processes)

Ondrej Mosnacek <omosnace@...hat.com> writes:
> On Fri, Jul 28, 2023 at 4:12 AM Michael Ellerman <mpe@...erman.id.au> wrote:
>>
>> Ondrej Mosnacek <omosnace@...hat.com> writes:
>> > Currently, SELinux doesn't allow distinguishing between kernel threads
>> > and userspace processes that are started before the policy is first
>> > loaded - both get the label corresponding to the kernel SID. The only
>> > way a process that persists from early boot can get a meaningful label
>> > is by doing a voluntary dyntransition or re-executing itself.
>>
>> Hi,
>>
>> This commit breaks login for me when booting linux-next kernels with old
>> userspace, specifically Ubuntu 16.04 on ppc64le. 18.04 is OK.
>>
>> The symptom is that login never accepts the root password, it just
>> always says "Login incorrect".
>>
>> Bisect points to this commit.
>>
>> Reverting this commit on top of next-20230726, fixes the problem
>> (ie. login works again).
>>
>> Booting with selinux=0 also fixes the problem.
>>
>> Is this expected? The change log below suggests backward compatibility
>> was considered, is 16.04 just too old?
>
> Hi Michael,
>
> I can reproduce it on Fedora 38 when I boot with SELINUX=disabled in
> /etc/selinux/config (+ a kernel including that commit), so it likely
> isn't caused by the userspace being old. Can you check what you have
> in /etc/selinux/config (or if it exists at all)?

Not sure if you still need it, but /etc/selinux/config doesn't exist in
the 16.04 image.

cheers