Changes/RemovePamConsole

Remove pam_console

Summary

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

Owner

• Name: Iker Pedrosa
• Email: ipedrosa@redhat.com

Current status

• Targeted release: Fedora Linux 39
• Last updated: 2023-02-02
• devel thread
• FESCo issue: #2945
• Tracker bug: #2166692
• Release notes tracker: #965

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 Write Display Managers and Write Desktop Environments.

In 2007 there was a 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.

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:

1. Provide PRs to remove pam_console from the PAM stack of the identified software packages (see Dependencies).
2. Remove pam_console from pam-redhat project and rebuild the PAM package without it.

• Other developers:

1. Identified software package maintainers should review and merge the pam_console removal PRs.

• Release engineering: #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.