Re: [PATCH] contrib/selinux: use regex instead of non-standard bash macro

[Max Chernoff <git@maxchernoff.ca>]

Hi Stefano,

On Thu, 2025-10-16 at 10:21 +0200, Stefano Brivio wrote:
> On Thu, 16 Oct 2025 13:10:41 +0530
> Danish Prakash <contact@danishpraka.sh> wrote:
> > It might be possible to avoid using non-standard bash macro (%USERID),

It's not a Bash macro, it's a SELinux template. This doesn't seem to be
documented anywhere (which isn't terribly surprising with SELinux), but
it's defined in this file:

    https://github.com/SELinuxProject/selinux/blob/ceb5b221/libsemanage/src/genhomedircon.c

> I wonder if
> Max remembers any reason why we couldn't do this in the first place.

The Fedora SELinux policy always uses %{USERID}, and so I copied it from
there:

    $ grep -RnF '%{USERID}' policy/
    policy/modules/contrib/dbus.fc:29:/run/user/%{USERID}/bus	-s	gen_context(system_u:object_r:session_dbusd_tmp_t,s0)
    policy/modules/contrib/dbus.fc:30:/run/user/%{USERID}/dbus(/.*)? 	gen_context(system_u:object_r:session_dbusd_tmp_t,s0)
    policy/modules/contrib/dbus.fc:31:/run/user/%{USERID}/dbus-1(/.*)? 	gen_context(system_u:object_r:session_dbusd_tmp_t,s0)
    policy/modules/contrib/gnome.fc:25:/run/user/%{USERID}/\.orc(/.*)?		gen_context(system_u:object_r:gstreamer_home_t,s0)
    policy/modules/contrib/gnome.fc:26:/run/user/%{USERID}/dconf(/.*)?	gen_context(system_u:object_r:config_home_t,s0)
    policy/modules/contrib/gnome.fc:27:/run/user/%{USERID}/keyring.*	gen_context(system_u:object_r:gkeyringd_tmp_t,s0)
    policy/modules/kernel/filesystem.fc:17:/run/user/%{USERID}/gvfs		-d	gen_context(system_u:object_r:fusefs_t,s0)
    policy/modules/kernel/filesystem.fc:18:/run/user/%{USERID}/gvfs/.*	<<none>>
    policy/modules/system/userdomain.fc:38:/run/user/%{USERID}	-d	gen_context(system_u:object_r:user_tmp_t,s0)
    policy/modules/system/userdomain.fc:39:/run/user/%{USERID}/.+	<<none>>

    $ grep -RnF '[0-9]+' policy/  | grep -v /dev/
    policy/modules/contrib/rpm.fc:52:/usr/bin/rhn_check-[0-9]+\.[0-9]+		--	gen_context(system_u:object_r:rpm_exec_t,s0)
    policy/modules/contrib/soundserver.fc:12:/run/yiff-[0-9]+\.pid	--	gen_context(system_u:object_r:soundd_var_run_t,s0)
    policy/modules/kernel/devices.if:6958:##	Allow read the hfi1_[0-9]+ devices

> > diff --git a/contrib/fedora/passt.spec b/contrib/fedora/passt.spec
> > index 663289f53d97..d1bcf4a74338 100644
> > --- a/contrib/fedora/passt.spec
> > +++ b/contrib/fedora/passt.spec
> > [...]
>
> At a glance, this looks like a better solution regardless of the
> reported issue. It sounds too good to be true, though

I agree that it looks like a good solution, which makes me wonder why
the base SELinux policies don't do it that way. The containers SELinux
policy appears to do things this way

    $ grep -RnF '[0-9]+'
    container_selinux.8:166:	/run/user/[0-9]+/gvfs
    $ grep -RnF '%{USERID}'; echo $?
    1

so it's probably (?) okay though.

Thanks,
-- Max