F39 proposal: Remove pam_console (System-Wide Change proposal)

[Ben Cotton]

https://fedoraproject.org/wiki/Changes/RemovePamConsole

This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

== Summary ==
Remove pam_console as it is not enabled by default, can be replaced by
systemd and has security issues.

== Owner ==
* Name: [[User:ipedrosa| Iker Pedrosa]]
* Email: ipedrosa(a)redhat.com


== Detailed Description ==
pam_console give users at the physical console additional capabilities
when authenticating, and removes those capabilities when the user logs
out. The module changes the permissions and ownership of files and
devices.

pam_console has some limitations and flaws:
* Only one user can have those additional capabilities at the same
time (no multi-seat)
* Potential security problems of device file ownership if the PAM
conversation ending isn't executed
* Remove ACL and call revoke() on device nodes for
fast-user-switching. This is to prevent the user of the inactive
session B spying on the user of the active session A using webcam,
sound cards, etc.
* As of today the module does nothing because one of the configuration
files use to define the permissions (50-default.perms) is not
installed in the distribution. Other packages may install their own
configuration files to specify the permissions, but I haven't found
any.

These additional capabilities that pam_console provides are useful to
simplify the work for console users. Usually, the permissions are set
for devices like the CD/DVD reader, or the disk drives. This
functionality is still useful today, and it should be managed with
systemd-logind, rather than with a PAM module. This systemd service
takes care of user sessions, multi-seat management, device access
management... This would increase the security level of the system,
and enable multi-seat for the file and device permissions. For more
information on systemd-logind implementation refer to the
documentation on how to
[https://www.freedesktop.org/wiki/Software/systemd/writing-display-managers/
Write Display Managers] and
[https://www.freedesktop.org/wiki/Software/systemd/writing-desktop-environ...
Write Desktop Environments].

In 2007 there was a [[Releases/FeatureRemovePAMConsole|System-Wide
Change]] proposal to remove pam_console, but it wasn't finished. My
plan is to continue that work and remove the pam_console module.


== Feedback ==


== Benefit to Fedora ==
By removing pam_console and moving to systemd-logind the distribution
would benefit from the multi-seat functionality and higher security
levels.

== Scope ==
* Proposal owners:
# Provide PRs to remove pam_console from the PAM stack of the
identified software packages (see Dependencies).
# Remove pam_console from [https://pagure.io/pam-redhat pam-redhat]
project and rebuild the PAM package without it.

* Other developers:
# Identified software package maintainers should review and merge the
pam_console removal PRs.

* Release engineering: [https://pagure.io/releng/issue/11223 #11223]

* Policies and guidelines: N/A

* Trademark approval: N/A

* Alignment with Objectives: N/A

== Upgrade/compatibility impact ==
No impact is expected.


== How To Test ==
No special hardware or configuration is required to test this change.
Once the change is in place, check that the pam_console isn't
installed in your system (default location:
/lib64/security/pam_console.so) and do a user authentication (i.e.
graphical interface, su, ssh, and whatever else comes to your mind).


== User Experience ==
Users won't experience any change.

== Dependencies ==
This change depends on other packages removing pam_console from their
PAM stack. I have identified five packages and I have opened a
bugzilla for all of them:
* xorg-x11-server - https://bugzilla.redhat.com/show_bug.cgi?id=1822209
* lxdm - https://bugzilla.redhat.com/show_bug.cgi?id=1822227
* xorg-x11-xdm - https://bugzilla.redhat.com/show_bug.cgi?id=1822225
* slim - https://bugzilla.redhat.com/show_bug.cgi?id=1822229
* gdm - https://bugzilla.redhat.com/show_bug.cgi?id=1822228

From the above list only the first item is a blocker as it requires
pam_console to succeed in the authentication. In all other cases it is
optional, so not removing the module from their PAM stack will only
cause a message printed in the security file.


== Contingency Plan ==

* Contingency mechanism: Postpone to the next release.
* Contingency deadline: Beta freeze.
* Blocks release? No.


== Documentation ==
No documentation.


== Release Notes ==
No need to update the release notes for this change.


-- 
Ben Cotton
He / Him / His
Fedora Program Manager
Red Hat
TZ=America/Indiana/Indianapolis

[Kevin Kofler]

>  * As of today the module does nothing because one of the
> configuration
>  files use to define the permissions (50-default.perms) is not
>  installed in the distribution. Other packages may install their own
>  configuration files to specify the permissions, but I haven't found
>  any. 
So basically, pam_console was obsoleted by systemd-logind eons ago. Not sure 
why we still ship it then. I guess it can just go away.

For the record, the one third-party RPM I maintain that used to use 
pam_console for device permissions (libticables2) switched away from 
pam_console back in 2009! (I had to rework the ACL handling several times 
between 2009 and 2012, with HAL and ConsoleKit coming and going, then it 
stabilized on udev rules, using systemd-logind internally.)

pam_console used to be a great selling point for Fedora over other 
distributions back when it was introduced, but by now, systemd-logind has 
completely subsumed its functionality.

        Kevin Kofler

[Dmitry Butskoy]

Ben Cotton wrote:
>  == Summary ==
>  Remove pam_console as it is not enabled by default, can be replaced by
>  systemd and has security issues. 
Just to make sure -- pam_console provided an "auth" feature (see 
https://bugzilla.redhat.com/show_bug.cgi?id=137802 ), which allows to 
log just once when working on several virtual consoles (and yes, it was 
19 years ago :) ). Is it possible with systemd-logind now?


~buc

[Iker Pedrosa]

Hi Dmitry,

If I understand it correctly, what you mean is that once a user is
authenticated in a system with pam_console, then all subsequent
authentication attempts by this user are successful without having to input
the password. This is kind of dangerous, as somebody could open a session
for an already authenticated user without them knowing it. I'd recommend
you to use pam_timestamp instead, as it offers the same functionality with
additional security features (authentication origin, timeout, etc.).

On Tue, Jan 17, 2023 at 3:48 PM Dmitry Butskoy <buc(a)buc.me&gt; wrote:

>  Ben Cotton wrote:
>  > == Summary ==
>  > Remove pam_console as it is not enabled by default, can be replaced by
>  > systemd and has security issues.
>
>  Just to make sure -- pam_console provided an "auth" feature (see
>  https://bugzilla.redhat.com/show_bug.cgi?id=137802 ), which allows to
>  log just once when working on several virtual consoles (and yes, it was
>  19 years ago :) ). Is it possible with systemd-logind now?
>
>
>  ~buc
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-- 

Iker Pedrosa

Software Engineer, Identity Management team

Red Hat <https://www.redhat.com>

Txapela (gorria) buruan eta ibili munduan

(Red) hat on his head and walk the world

Basque proverb
<https://www.redhat.com>