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Subject: Re: /run/systemd/inaccessible
To:     Dominick Grift <dac.override@gmail.com>,
        Russell Coker <russell@coker.com.au>
Cc:     selinux-refpolicy@vger.kernel.org
References: <6385652.IY5x3zMeex@xev> <87zhd4b4ri.fsf@gmail.com>
From:   Topi Miettinen <toiwoton@gmail.com>
Message-ID: <a908d824-8503-73ab-0d8f-d2465c06d1de@gmail.com>
Date:   Thu, 27 Feb 2020 20:13:29 +0200
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On 27.2.2020 14.20, Dominick Grift wrote:
> Russell Coker <russell@coker.com.au> writes:
> 
>> allow systemd_logind_t init_var_run_t:chr_file write;
>>
>> audit2allow shows me that the above is attempted on Debian/Unstable.  What's
>> this inaccessible directory about anyway?
> 
> systemd-userruntimedir (245) now also creates it in /run/user/%{USERID}

The relevant code has this comment:

/* Set up inaccessible nodes now so they're available if we decide to 
use them with user namespaces. */

> probably used for InaccessiblePath= directive but I am not sure.

Yes, these are bind mounted over the path which is wanted inaccessible. 
Perhaps this could be improved by giving them a dedicated label and then 
some new TE rules could prevent anything other than PID1 from managing 
them. Now if a service has CAP_SYS_ADMIN and is not blocked by seccomp 
filters from using mount and umount system calls, it could dismantle the 
bind mount.

-Topi

>>
>> # ls -lZ /run/systemd/inaccessible
>> total 0
>> b---------. 1 root root system_u:object_r:init_var_run_t:s0 0, 0 Feb 27 13:36
>> blk
>> c---------. 1 root root system_u:object_r:init_var_run_t:s0 0, 0 Feb 27 13:36
>> chr
>> d---------. 2 root root system_u:object_r:init_var_run_t:s0   40 Feb 27 13:36
>> dir
>> p---------. 1 root root system_u:object_r:init_var_run_t:s0    0 Feb 27 13:36
>> fifo
>> ----------. 1 root root system_u:object_r:init_var_run_t:s0    0 Feb 27 13:36
>> reg
>> s---------. 1 root root system_u:object_r:init_var_run_t:s0    0 Feb 27 13:36
>> sock
>