linux-kernel - Re: About commit 901ef845fa2469c ("selinux: allow per-file labeling for cgroupfs")

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Date:   Tue, 10 Oct 2017 10:06:52 -0400
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Waiman Long <longman@...hat.com>,
        Antonio Murdaca <runcom@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, selinux@...ho.nsa.gov,
        lkml <linux-kernel@...r.kernel.org>,
        Paul Moore <paul@...l-moore.com>,
        Miroslav Grepl <mgrepl@...hat.com>
Subject: Re: About commit 901ef845fa2469c ("selinux: allow per-file labeling
 for cgroupfs")

On Fri, 2017-10-06 at 13:53 -0400, Waiman Long wrote:
> Antonio,
> 
> I have a question about your 4.14 upstream commit 901ef845fa2469c
> ("selinux: allow per-file labeling for cgroupfs"). With that, I am no
> longer able to mount the cgroup2 filesystem with a 4.14 kernel. The
> problem is that your commit sets the SE_SBGENFS flag, which causes
> selinux to lookup the genfs database for a filesystem type match.
> However, the filesystem type "cgroup2" isn't in the genfs database in
> my
> RHEL7 based test system. The "cgroup" filesystem type is in the genfs
> database,
> so I have no problem with v1 cgroup mount.
> 
> Do you know where the genfs database is defined? I need some way to
> add cgroup2
> as a valid genfs fstype, or I have to manually back out the commit in
> order to
> do my cgroup2 testing.

It is part of the policy; you could add it via a policy module ala:
$ cat cgroup2.cil
(genfscon cgroup2 / (system_u object_r cgroup_t ((s0) (s0))))

$ sudo semodule -i cgroup2.cil

That said, the fact that you can't even mount it without that is
arguably a bug/regression.  I guess this is due to the ENOENT from
security_genfs_sid being propagated all the way up instead of just
leaving it unlabeled and permitting the mount to proceed.