NAME
polkit - Authorization Framework
OVERVIEW
PolicyKit provides an authorization API intended to be used by
privileged programs ("MECHANISMS") offering service to unprivileged
programs ("CLIENTS") through some form of IPC mechanism such as D-Bus
or Unix pipes. In this scenario, the mechanism typically treats the
client as untrusted. For every request from a client, the mechanism
needs to determine if the request is authorized or if it should refuse
to service the client. Using the PolicyKit API, a mechanism can offload
this decision to a trusted party: The PolicyKit Authority.
In addition to acting as an authority, PolicyKit allows users to obtain
temporary authorization through authenticating either an administrative
user or the owner of the session the client belongs to. This is useful
for scenarios where a mechanism needs to verify that the operator of
the system really is the user or really is an administrative user.
SYSTEM ARCHITECTURE
The system architecture of PolicyKit is comprised of the Authority
(implemented as a service on the system message bus) and a
Authentication Agent per user session (provided and started by the user
session e.g. GNOME or KDE). Additionally, PolicyKit supports a number
of extension points - specifically, vendors and/or sites can write
extensions to completely control authorization policy. In a block
diagram, the architecture looks like this:
[IMAGE][1]
+-------------------+
| Authentication |
| Agent |
+-------------------+
| libpolkit-agent-1 |
+-------------------+
^ +--------+
| | Client |
+--------------+ +--------+
| ^
| |
User Session | |
=======================|========================|=============
System Context | |
| |
| +---+
V |
/------------\ |
| System Bus | |
\------------/ |
^ ^ V
| | +---------------------+
+--------------+ | | Mechanism |
| | +---------------------+
V +----> | libpolkit-gobject-1 |
+------------------+ +---------------------+
| org.freedesktop. |
| PolicyKit1 |
+------------------+
| Backends and |
| Extensions |
+------------------+
For convenience, the libpolkit-gobject-1 library wraps the PolicyKit
D-Bus API using GObject. However, a mechanism can also use the D-Bus
API or the pkcheck(1) command to check authorizations.
The libpolkit-agent-1 library provides an abstraction of the native
authentication system, e.g. pam(8) and also facilities registration
and communication with the PolicyKit D-Bus service.
PolicyKit extensions and authority backends are implemented using the
libpolkit-backend-1 library.
See the developer documentation[2] for more information about using and
extending PolicyKit.
See pklocalauthority(8) for information about the Local Authority - the
default authority implementation shipped with PolicyKit.
AUTHENTICATION AGENTS
An authentication agent is used to make the user of a session prove
that the user of the session really is the user (by authenticating as
the user) or an administrative user (by authenticating as a
administrator). In order to integrate well with the rest of the user
session (e.g. match the look and feel), authentication agents are meant
to be provided by the user session that the user uses. For example, an
authentication agent may look like this:
[IMAGE][3]
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is required to run ATA SMART |
| self tests |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| as the super user is required to perform this |
| action. |
| |
| Password for root: [_________________________] |
| |
| [V] Details: |
| Drive: ATA INTEL SSDSA2MH08 (045C) |
| Device: /dev/sda |
| Action: org.fd.devicekit.disks.drive-ata-smart-selftest |
| Vendor: The DeviceKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
If the system is configured without a root account it may allow you to
select the administrative user who is authenticating:
[IMAGE][4]
+----------------------------------------------------------+
| Authenticate [X] |
+----------------------------------------------------------+
| |
| [Icon] Authentication is required to run ATA SMART |
| self tests |
| |
| An application is attempting to perform an |
| action that requires privileges. Authentication |
| as one of the users below is required to |
| perform this action. |
| |
| [[Face] Patrick Bateman (bateman) [V]] |
| |
| Password for bateman: [______________________] |
| |
| [V] Details: |
| Drive: ATA INTEL SSDSA2MH08 (045C) |
| Device: /dev/sda |
| Action: org.fd.devicekit.disks.drive-ata-smart-selftest |
| Vendor: The DeviceKit Project |
| |
| [Cancel] [Authenticate] |
+----------------------------------------------------------+
See pklocalauthority(8) on how to set up the local authority
implemention for systems without a root account.
DECLARING ACTIONS
A mechanism need to declare a set of "ACTIONS" in order to use
PolicyKit. Actions correspond to operations that clients can request
the mechanism to carry out and are defined in XML files that the
mechanism installs into the /usr/share/polkit-1/actions directory.
PolicyKit actions are namespaced and can only contain the characters
[a-z][0-9].- e.g. lower-case ASCII, digits, period and hyphen. Each XML
file can contain more than one action but all actions need to be in the
same namespace and the file needs to be named after the namespace and
have the extension .policy.
The XML file must have the following doctype declaration
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE policyconfig PUBLIC "-//freedesktop//DTD PolicyKit Policy Configuration 1.0//EN"
"http://www.freedesktop.org/standards/PolicyKit/1.0/policyconfig.dtd">
The policyconfig element must be present exactly once. Elements that
can be used inside policyconfig includes:
vendor
The name of the project or vendor that is supplying the actions in
the XML document. Optional.
vendor_url
A URL to the project or vendor that is supplying the actions in the
XML document. Optional.
icon_name
An icon representing the project or vendor that is supplying the
actions in the XML document. The icon name must adhere to the
Freedesktop.org Icon Naming Specification[5]. Optional.
action
Declares an action. The action name is specified using the id
attribute and can only contain the characters [a-z][0-9].- e.g.
lower-case ASCII, digits, period and hyphen.
Elements that can be used inside action includes:
description
A human readable description of the action, e.g. "Install unsigned
software".
message
A human readable message displayed to the user when asking for
credentials when authentication is needed, e.g. "Installing
unsigned software requires authentication".
defaults
This element is used to specify implicit authorizations for
clients.
Elements that can be used inside defaults includes:
allow_any
Implicit authorizations that apply to any client. Optional.
allow_inactive
Implicit authorizations that apply to clients in inactive
sessions on local consoles. Optional.
allow_active
Implicit authorizations that apply to clients in active
sessions on local consoles. Optional.
Each of the allow_any, allow_inactive and allow_active elements can
contain the following values:
no
Not authorized.
yes
Authorized.
auth_self
Authentication by the owner of the session that the client
originates from is required.
auth_admin
Authentication by an administrative user is required.
auth_self_keep
Like auth_self but the authorization is kept for a brief
period.
auth_admin_keep
Like auth_admin but the authorization is kept for a brief
period.
annotate
Used for annotating an action with a key/value pair. The key is
specified using the the key attribute and the value is specified
using the value attribute. This element may appear zero or more
times. See pkexec(1) for an example of how this can be used.
vendor
Used for overriding the vendor on a per-action basis. Optional.
vendor_url
Used for overriding the vendor URL on a per-action basis. Optional.
icon_name
Used for overriding the icon name on a per-action basis. Optional.
For localization, description and message elements may occur multiple
times with different xml:lang attributes.
To list installed PolicyKit actions, use the pkaction(1) command.
AUTHOR
Written by David Zeuthen davidz@redhat.com with a lot of help from many
others.
BUGS
Please send bug reports to either the distribution or the polkit-devel
mailing list, see the link
http://lists.freedesktop.org/mailman/listinfo/polkit-devel on how to
subscribe.
SEE ALSO
pklocalauthority(8) polkitd(8) pkaction(1), pkcheck(1), pkexec(1),
NOTES
1. /usr/share/gtk-doc/html/polkit-1/polkit-architecture.png
2. developer documentation
file:///usr/share/gtk-doc/html/polkit-1/index.html
3. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-
example.png
4. /usr/share/gtk-doc/html/polkit-1/polkit-authentication-agent-
example-wheel.png
5. Freedesktop.org Icon Naming Specification
http://standards.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html