Features/UsermodeMigration

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Contents

Usermode Migration

Summary

Access control of privileged operations for ordinary users should be handled exclusively by a centrally managed authority. Usermode/consolehelper should be phased out and be replaced entirely by PolicyKit.

Owner

Current status

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

Detailed Description

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

These days, most privileged system operations are already controlled by PolicyKit, a well-established, fine-grained, (possibly) network-transparent service for managing privileged operations by ordinary users. Enterprise environments need to be able to centrally define access control policy for the organization, and automatically apply it to all connected workstations.

  • PolicyKit can be used by privileged processes to decide if it should execute privileged operations on behalf of the requesting user. For directly executed tools, PolicyKit provides a setuid-root helper program called ‘’pkexec’’.The hooks to ask the user for authorizations are well-integrated into text environments, and native in all major graphical environments.
  • The concept of a console user (that usermode/consolehelper implements) is no longer a sufficient concept to derive privileges from. OTOH PolicyKit authorizations can properly distinguish between multiple active sessions and seats: e.g. an untrusted user’s reboot request is only granted if only a single user session runs at that time.

polkit(8) manpage

Benefit to Fedora

  • Consistency of system configuration.
  • Centralization of policy.
  • Cleaner system integration; no implicit interception of tools residing in sbin/ with symlinks in bin/, which is less dependent on $PATH ordering.
  • No difference regarding the hookup between tools installed in bin/ or sbin/.

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 unconverted rest, drop the usermode part and recommend to use pkexec on the command line, like sudo is used to run tools.

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

Release Notes

Comments and Discussion