Re: systemd --user for GDM started as unconfined_t instead of xdm_t

Dominick Grift <[email protected]> Sun, 6 Oct 2019 12:13:38 +0200
Newsgroups	org.kernel.vger.selinux-refpolicy
Message-ID	<[email protected]>
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,
> > > 
> > > I discovered today that the GDM own processes are started as unconfined_t
> > > instead of xdm_t because systemd --user process itself is started in that
> > > context.
> > > 
> > > This is probably related to:
> > > 
> > > commit da156aea1e89a6ff6025be7e50c9c8173e5a6dcf
> > > Author: Chris PeBenito <[email protected]>
> > > Date:   Fri Apr 19 11:50:59 2019 -0400
> > > 
> > >     systemd: Add initial policy for systemd --user.
> > > 
> > >     This is just a start; it does not cover all uses.
> > > 
> > >     Signed-off-by: Chris PeBenito <[email protected]>
> > > 
> > > Was that expected and/or wanted?
> > 
> > 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 gnome-initial-setup) systemd will start gdm's systemd --user instance with unconfined_u:unconfined_r:unconfined_t.
> > 
> > One (ugly but arguable less ugly than the alternative) solution is to create a "xdm_u" and allow systemd to run a systemd --user instance on behalf of gdm with "xdm_u:system_r:xdm_t"
> > 
> > That way you can tell selinux that gdm's systemd --user instance should never transition out of xdm_u:system_r:xdm_t
> > 
> > echo "system_r:init_t:s0 system_r:xdm_t:s0" > /etc/selinux/TYPE/contexts/users/xdm_u
> > 
> > Then all processes in the gdm session should stay in xdm_t (but some processes will be associate with xdm_u and other with system_u).
> > 
> > You would probably also want to add to semanage.conf:
> > 
> > ignoredirs = /var/lib/gdm;/run/gnome-initial-setup
> > 
> > and make sure that selinux does not relabel /run/user/$(id -u gdm)
> 
> Just to clarify. The patch you reference is not responsible for the uglyness that is GDM/Gnome
> Without this patch, the systemd --user instance of GDM (and any other users) 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).service

> 
> > 
> > > 
> > > Kind regards,
> > > 
> > > Laurent Bigonville
> > > 
> > 
> > -- 
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> > Dominick Grift
> 
> 
> 
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> Dominick Grift



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