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Date:   Sun, 6 Oct 2019 12:13:38 +0200
From:   Dominick Grift <dac.override@gmail.com>
To:     Laurent Bigonville <bigon@debian.org>,
        selinux-refpolicy@vger.kernel.org
Subject: Re: systemd --user for GDM started as unconfined_t instead of xdm_t
Message-ID: <20191006101338.GD469820@brutus.lan>
Mail-Followup-To: Laurent Bigonville <bigon@debian.org>,
        selinux-refpolicy@vger.kernel.org
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On Sun, Oct 06, 2019 at 12:01:25PM +0200, Dominick Grift wrote:
> On Sun, Oct 06, 2019 at 11:41:56AM +0200, Dominick Grift wrote:
> > On Sun, Oct 06, 2019 at 11:22:00AM +0200, Laurent Bigonville wrote:
> > > Hello,
> > >=20
> > > I discovered today that the GDM own processes are started as unconfin=
ed_t
> > > instead of xdm_t because systemd --user process itself is started in =
that
> > > context.
> > >=20
> > > This is probably related to:
> > >=20
> > > commit da156aea1e89a6ff6025be7e50c9c8173e5a6dcf
> > > Author: Chris PeBenito <Christopher.PeBenito@microsoft.com>
> > > Date:=A0=A0 Fri Apr 19 11:50:59 2019 -0400
> > >=20
> > > =A0=A0=A0 systemd: Add initial policy for systemd --user.
> > >=20
> > > =A0=A0=A0 This is just a start; it does not cover all uses.
> > >=20
> > > =A0=A0=A0 Signed-off-by: Chris PeBenito <Christopher.PeBenito@microso=
ft.com>
> > >=20
> > > Was that expected and/or wanted?
> >=20
> > It just means that gdm hooks into pam, and since 1. your __default__ id=
 is set to unconfined_u and 2. you do not have a private id for gdm (and gn=
ome-initial-setup) systemd will start gdm's systemd --user instance with un=
confined_u:unconfined_r:unconfined_t.
> >=20
> > One (ugly but arguable less ugly than the alternative) solution is to c=
reate a "xdm_u" and allow systemd to run a systemd --user instance on behal=
f of gdm with "xdm_u:system_r:xdm_t"
> >=20
> > That way you can tell selinux that gdm's systemd --user instance should=
 never transition out of xdm_u:system_r:xdm_t
> >=20
> > echo "system_r:init_t:s0 system_r:xdm_t:s0" > /etc/selinux/TYPE/context=
s/users/xdm_u
> >=20
> > Then all processes in the gdm session should stay in xdm_t (but some pr=
ocesses will be associate with xdm_u and other with system_u).
> >=20
> > You would probably also want to add to semanage.conf:
> >=20
> > ignoredirs =3D /var/lib/gdm;/run/gnome-initial-setup
> >=20
> > and make sure that selinux does not relabel /run/user/$(id -u gdm)
>=20
> Just to clarify. The patch you reference is not responsible for the uglyn=
ess that is GDM/Gnome
> Without this patch, the systemd --user instance of GDM (and any other use=
rs) would run in "init_t". This is obviously also not desirable.


I wonder what you happen if you would (would gdm still work?):

sudo systemctl mask user@$(id -u gdm).service user-runtime-dir@$(id -u gdm)=
=2Eservice

>=20
> >=20
> > >=20
> > > Kind regards,
> > >=20
> > > Laurent Bigonville
> > >=20
> >=20
> > --=20
> > Key fingerprint =3D 5F4D 3CDB D3F8 3652 FBD8 02D5 3B6C 5F1D 2C7B 6B02
> > https://sks-keyservers.net/pks/lookup?op=3Dget&search=3D0x3B6C5F1D2C7B6=
B02
> > Dominick Grift
>=20
>=20
>=20
> --=20
> Key fingerprint =3D 5F4D 3CDB D3F8 3652 FBD8 02D5 3B6C 5F1D 2C7B 6B02
> https://sks-keyservers.net/pks/lookup?op=3Dget&search=3D0x3B6C5F1D2C7B6B02
> Dominick Grift


--=20
Key fingerprint =3D 5F4D 3CDB D3F8 3652 FBD8 02D5 3B6C 5F1D 2C7B 6B02
https://sks-keyservers.net/pks/lookup?op=3Dget&search=3D0x3B6C5F1D2C7B6B02
Dominick Grift

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