Usermode Migration

Summary

All granting of privileged operations to ordinary users should exclusively be handled by centrally-managed polit policy. Usermode/userhelper should be phased-out and entirely replaced by polkit.

Owner

Name: Harald Hoyer
Email: harald@redhat.com

Name: Kay Sievers
Email: kay@redhat.com

Current status

Targeted release: Fedora 18
Last updated: 2012-04-03
Percentage of completion: 20%

Detailed Description

The usermode/userhelper program is a setuid-root wrapper around a couple of tools, to provide superuser privileges to ordinary users. Its policy is controlled by text files in /etc.

Most privileged user operations are already controlled by polkit today, a well-established, fine-grained, possible network-transparent infrastructure to manage privileged operations by ordinary users. Enterprise environments should be able to centrally define the domain’s policy, and automatically apply it to all connected workstations.

Polkit can be used by privileged process to decide if it should execute privileged operations on behalf of the requesting user. For directly executed tools, polkit provides a setuid-root helper program called ‘’pkexec’’.The hooks to ask the user for authorizations are well-integrated into text, and natively into all major graphical environments.
Polkit auth can properly distinguish between multiple sessions: e.g. untrusted user reboot request reboot only allowed when only a single user session runs.

| Polkit(8) manpage

Benefit to Fedora

Consistency of system configuration.
Centralization of policy.
Cleaner system integration, no interception of tools in sbin/ with symlinks in bin/, which results in dependencies on $PATH ordering

Scope

document how to convert consolehelper to polkit:
- python: put pkexec in the wrapper shell
- C tools: re-exec with pkexec in C code
- C tools: move original to /usr/lib/<pkg>/<tool>, and wrap /usr/bin/<tool> with a pkexec shell (ugly!)
open tracker bug and file bugs against all individual packages
convert all packages, where it makes sense to use polkit, to pkexec
for the rest, drop usermode and recommend to use pkexec like sudo

How to convert

A fast and easy way to convert a former consolehelper program is the use of pkexec.

As an example, we convert system-config-date to PolicyKit:

# ls -l /usr/bin/system-config-date
lrwxrwxrwx 1 root root 13  5. Feb 02:34 /usr/bin/system-config-date -> consolehelper

# rm /usr/bin/system-config-date
# cat /etc/security/console.apps/system-config-date
. config-util
PROGRAM=/usr/share/system-config-date/system-config-date.py
SESSION=true

Ok, running /usr/bin/system-config-date would have executed /usr/share/system-config-date/system-config-date.py, so we create /usr/bin/system-config-date like the following:

# cat /usr/bin/system-config-date
#!/bin/sh
exec /usr/bin/pkexec /usr/share/system-config-date/system-config-date.py

This will not export the DISPLAY variable, so we have to add a policy file, although starting a GUI as root is not encouraged. The important part is: <annotate key="org.freedesktop.policykit.exec.allow_gui">true</annotate>

/usr/share/polkit-1/actions/org.fedoraproject.config.date.policy:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policyconfig PUBLIC
"-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
"http://www.freedesktop.org/standards/PolicyKit/1/policyconfig.dtd">
<policyconfig>

 <vendor>System Config Date</vendor>
 <vendor_url>http://fedorahosted.org/system-config-date</vendor_url>

 <action id="org.fedoraproject.config.date.pkexec.run">
    <description>Run System Config Date</description>
    <message>Authentication is required to run system-config-date</message>
    <icon_name>system-config-date</icon_name>
    <defaults>
     <allow_any>no</allow_any>
     <allow_inactive>no</allow_inactive>
     <allow_active>auth_self_keep</allow_active>
    </defaults>
    <annotate key="org.freedesktop.policykit.exec.path">/usr/share/system-config-date/system-config-date.py</annotate>
    <annotate key="org.freedesktop.policykit.exec.allow_gui">true</annotate>
 </action>
</policyconfig>

How To Test

# yum remove usermode usermode-gtk

should succeed for an installation with all Fedora packages installed.

# repoquery --whatrequires usermode --whatrequires usermode-gtk
usermode-gtk-....

should not output a single package, except the usermode-gtk package.

Make sure, you can call all the tools, which used to use usermode and be asked the appropriate password.

User Experience

The user should experience no noticeable changes.

Dependencies

anaconda
audit-viewer
authconfig-gtk
backintime-gnome
backintime-kde
beesu
bootconf-gui
chkrootkit
driftnet
drobo-utils-gui
eclipse-oprofile
ejabberd
fwfstab
galternatives
gsmartcontrol
hddtemp
kdenetwork-kppp
kismet
liveusb-creator
livna-config-display
lshw-gui
mock
mtr-gtk
netgo
nmap-frontend
ntfs-config
policycoreutils-gui
preupgrade
pure-ftpd
qtparted
realcrypt
revisor-cli
rhn-setup
rhn-setup-gnome
sabayon
setools-gui
setuptool
smart-gui
subscription-manager-gnome
synaptic
system-config-audit
system-config-bind
system-config-boot
system-config-date
system-config-httpd
system-config-kdump
system-config-keyboard
system-config-language
system-config-lvm
system-config-network
system-config-network-tui
system-config-nfs
system-config-rootpassword
system-config-users
system-switch-displaymanager
system-switch-java
system-switch-mail
system-switch-mail-gnome
tuned
usermode-gtk
vpnc-consoleuser
wifi-radar
wlassistant
xawtv
yumex
zyx-liveinstaller

Contingency Plan

Even, if we cannot drop usermode, the changes in the packages do not have to be reverted.

Documentation

| Polkit(8) manpage

Release Notes

Comments and Discussion

See Talk:Features/UsermodeMigration

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