Bug 1470312 - GDM fails to start when SELinux default user is mapped to the guest_u user
Summary: GDM fails to start when SELinux default user is mapped to the guest_u user
Keywords:
Status: CLOSED EOL
Alias: None
Product: Fedora
Classification: Fedora
Component: gdm
Version: 26
Hardware: x86_64
OS: Linux
unspecified
medium
Target Milestone: ---
Assignee: Ray Strode [halfline]
QA Contact: Fedora Extras Quality Assurance
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2017-07-12 17:58 UTC by Richard Berg
Modified: 2018-05-29 12:56 UTC (History)
5 users (show)

Fixed In Version:
Clone Of:
Environment:
Last Closed: 2018-05-29 12:56:57 UTC
Type: Bug
Embargoed:


Attachments (Terms of Use)
logs (7.85 KB, text/plain)
2017-07-12 17:58 UTC, Richard Berg
no flags Details

Description Richard Berg 2017-07-12 17:58:39 UTC
Created attachment 1297141 [details]
logs

Description of problem:
GDM fails to start when SELinux default user is mapped to the guest_u user on Fedora 26. The following error message is shown in the console:
  Failed to start User Manager for UID 42 

UID 42 is gdm:
  getent passwd | grep 42
  gdm:x:42:42::/var/lib/gdm:/sbin/nologin


On Fedora 25 GDM starts without any problems when SELinux default user mapped is to guest_u user.


Version-Release number of selected component (if applicable):
gdm-3.24.2-1.fc26.x86_64

Some other component versions:
pam-1.3.0-2.fc26.x86_64
selinux-policy-targeted-3.13.1-259.fc26.noarch
systemd-pam-233-6.fc26.x86_64
systemd-libs-233-6.fc26.x86_64


How reproducible:
Always.


Steps to Reproduce:
1. Install Fedora 26 Workstation with default settings.
2. Change mapping of default SELinux user to guest_u with the following command:
  semanage login -m -s guest_u __default__
3. Reboot the computer


Actual results:
Computer boot stops in text mode. The following error message is show:
  Failed to start User Manager for UID 42 


Expected results:
Computer booting to GNOME login screen.


Additional info:
It looks like gdm is started with guest_r role and this role is picked because SELinux default user is mapped to guest_u. SELinux default user should not be used for services.

See attachment for journalctl and AVCs output.

Comment 1 Taras 2017-07-18 15:43:52 UTC
Got this problem while upgrading from 25 with DNF system-upgrade plugin. Is it possible to fix it via specifying SELinux settings for GDM manually?

Comment 2 Benjamin Kreuter 2017-09-12 21:10:48 UTC
This also appears to be a problem when the default user is user_u.

Comment 3 Quintin 2017-12-18 18:37:20 UTC
I also have this issue. It seems to be temporarily fixed by first logging in as the xguest user without a desktop environment, then logging in with the desktop environment.

So long as the xguest user is already logged in, selinux seems to allow the user to log in with GDM as well.

Comment 4 Fedora End Of Life 2018-05-03 08:41:37 UTC
This message is a reminder that Fedora 26 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 26. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '26'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 26 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

Comment 5 Fedora End Of Life 2018-05-29 12:56:57 UTC
Fedora 26 changed to end-of-life (EOL) status on 2018-05-29. Fedora 26
is no longer maintained, which means that it will not receive any
further security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.


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