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From:   Dominick Grift <dominick.grift@defensec.nl>
To:     Chris PeBenito <pebenito@ieee.org>
Cc:     Russell Coker <russell@coker.com.au>,
        selinux-refpolicy@vger.kernel.org
Subject: Re: machinectl shell policy
References: <8322849.62pqQp6Oog@liv> <1723812.Y751QtlBzf@liv>
        <ypjl8s9m5nbi.fsf@defensec.nl> <5735537.jZnottUgFY@liv>
        <f142c9ee-ce7e-7f7d-dec4-9d93ddd49c43@ieee.org>
        <ypjlmtxo4uhn.fsf@defensec.nl>
Date:   Mon, 04 Jan 2021 16:06:22 +0100
In-Reply-To: <ypjlmtxo4uhn.fsf@defensec.nl> (Dominick Grift's message of "Mon,
        04 Jan 2021 16:00:52 +0100")
Message-ID: <ypjlim8c4u8h.fsf@defensec.nl>
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Dominick Grift <dominick.grift@defensec.nl> writes:

> Chris PeBenito <pebenito@ieee.org> writes:
>
>> On 12/25/20 4:16 AM, Russell Coker wrote:
>>> On Friday, 25 December 2020 6:58:41 PM AEDT Dominick Grift wrote:
>>>> Russell Coker <russell@coker.com.au> writes:
>>>>> On Thursday, 24 December 2020 7:37:50 PM AEDT Dominick Grift wrote:
>>>>>>> To enable "machinectl shell" on recent versions of systemd we need
>>>>>>> something like the above policy (which is not complete or ideal, still
>>>>>>> doesn't work so no point polishing it) and something for the below.
>>>>>>> What
>>>>>>> is the below about?
>>>>>>
>>>>>> this should be thoroughly addressed. machined creates a login pty that
>>>>>> gets relabeled on login as per type_change rules.
>>>>>
>>>>> Currently it's not being relabeled on Debian, but that's a separate issue.
>>>>
>>>> Maybe the required type_change rules arent present?
>>> Here is all the policy to make it work.  Maybe we should have a type
>>> like
>>> system_dbusd_devpts_t for this.  This is not policy for inclusion, this is
>>> policy to discuss before writing that policy.
>>> term_user_pty(user_systemd_t, user_devpts_t)
>>> term_login_pty(devpts_t)
>>> allow user_systemd_t user_devpts_t:chr_file rw_file_perms;
>>> # for machinectl shell
>>> allow sysadm_t systemd_machined_t:dbus send_msg;
>>> systemd_manage_userdb_runtime_dirs(systemd_machined_t)
>>> systemd_manage_userdb_runtime_sock_files(systemd_machined_t)
>>> term_use_ptmx(systemd_machined_t)
>>> dev_getattr_fs(systemd_machined_t)
>>> term_getattr_pty_fs(systemd_machined_t)
>>> allow systemd_machined_t sysadm_t:dbus send_msg;
>>> allow systemd_machined_t devpts_t:chr_file rw_file_perms;
>>> allow system_dbusd_t systemd_machined_t:fd use;
>>> allow system_dbusd_t devpts_t:chr_file { read write };
>>> allow system_dbusd_t ptmx_t:chr_file { read write };
>>> allow sysadm_t systemd_machined_t:fd use;
>>> allow user_systemd_t shell_exec_t:file entrypoint;
>>
>> The pty stuff seems to make sense, but I'm curious why there is a
>> transition into user_systemd_t for the shell.
>
> The policy above is referencing "devpts_t", that is sub-optimal. there
> shouldnt be any pty chr files with the devpts_t filesystem type

And I agree that then user_systemd_t shell_exec_t entrypoint should be
there.

>
>
>>
>>> allow user_systemd_t systemd_machined_t:fd use;
>>> allow user_systemd_t self:process signal;
>>> allow user_t systemd_machined_t:fd use;
>>> allow user_t user_systemd_t:fifo_file { getattr write };
>>> allow user_t init_t:process signal;
>>
>>
>>
>>>>> https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=892001
>>>>>
>>>>> We have work in progress on dbus-broker in Debian.  Would it make sense to
>>>>> only support dbus-broker in SE Linux policy?  Being forced to use only 1
>>>>> of
>>>>> the 2 dbus programs (and the newer and faster 1 of the 2) is a very small
>>>>> trade-off, smaller than some of the other trade-offs for running SE Linux.
>>
>> I'd prefer to keep both unless it becomes onerous.
>>
>>
>>>> should probably be able to support both (conditionally) but could get messy
>>> Currently we have a heap of ifdef systemd in the policy, as probably
>>> the only
>>> people not wanting dbus-broker will be the ones not wanting systemd we could
>>> include it in the same ifdef rules.
>>
>> The "else" of the ifdef can work.

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Dominick Grift