PolicyKit Reference Manual |
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pklocalauthoritypklocalauthority — PolicyKit Local Authority |
DESCRIPTION
The Local Authority is the default PolicyKit authority implementation. Configuration for the Local Authority and information pertaining to authorization decisions are read from local files on the disk. One design goal of the Local Authority is to split configuration items into separate files such that 3rd party packages and users won't conflict trying to edit the same files. This policy also ensures smooth upgrades when distributing PolicyKit using a package management system.
Files shipped with PolicyKit and 3rd party packages (e.g. under package manager control) typically have comments (such as “DO NOT EDIT THIS FILE, it will be overwritten on update”) telling the system administrator that changes will be overwritten on update.
ADMINISTRATOR AUTHENTICATION
PolicyKit makes a distinction between user authentication (to make the user in front of the system prove he really is the user) and administrator authentication (to make the user in front of the system prove he really is an administrator). Since various operating systems (or even flavors of the same operating system) has different ways of defining "administrator", the Local Authority provides a way to specify what "administrator authentication" means.
By default, "administrator authentication" is defined as asking for the root password. Since some systems, for usability reasons, don't have a root password and instead rely on a group of users being member of an administrative group that gives them super-user privileges, the Local Authority can be configured to support this use-case as well.
Configuration for the Local Authority is read from files in
the /etc/polkit-1/localauthority.conf.d
directory. All files are read in lexigraphical order (using the
C locale) meaning that later files can override earlier
ones. The file 50-localauthority.conf
contains the settings provided by the OS vendor. Users and 3rd
party packages can drop configuration files with a priority
higher than 60 to change the defaults. The configuration file
format is simple. Each configuration file is a key
file (also commonly known as a ini
file) with a single group
called [Configuration]
. Only a single
key, AdminIdentities
is read. The value of
this key is a semi-colon separated list of identities that can
be used when administrator authentication is required. Users are
specified by prefixing the user name with
unix-user:
and groups of users are specified
by prefixing with unix-group:
. See
the section called “EXAMPLES” for an example of a
configuration file.
DIRECTORY STRUCTURE
The Local Authority reads files with .pkla
extension from all directories located inside the
/etc/polkit-1/localauthority
and /var/lib/polkit-1/localauthority
directories. By default, the following sub-directories are installed.
/etc/polkit-1/ `-- localauthority |-- 10-vendor.d |-- 20-org.d |-- 30-site.d |-- 50-local.d `-- 90-mandatory.d
and
/var/lib/polkit-1/ `-- localauthority |-- 10-vendor.d |-- 20-org.d |-- 30-site.d |-- 50-local.d `-- 90-mandatory.d
The /etc/polkit-1/localauthority
hierarchy
is inteded for local configuration and
the /var/lib/polkit-1/localauthority
is
intended for 3rd party packages.
Each .pkla
file contains one or more
authorization entries. If the underlying filesystem supports
file monitoring, the Local Authority will reload information
whenever .pkla
files are added, removed or
changed.
Each directory is intended for a specific audience
10-vendor.d |
Intended for use by the OS vendor. |
20-org.d |
Intended for the organization deploying the OS. |
30-site.d |
Intended for the site deploying the system. |
50-local.d |
Intended for local usage. |
90-mandatory.d |
Intended for the organization deploying the OS. |
and new directories can be added/removed as needed.
As to regards to the content, each .pkla
file is a standard key file and contains
key/value pairs in one or more groups with each group
representing an authorization entry.
A .pkla
file MUST be named by using a
scheme to ensure that the name is unique, e.g. reverse DNS
notation or similar. For example, if the organization is
“Acme Corp” needs to modify policy for the
product “Frobnicator”, a name
like com.acme.frobnicator.pkla
would be
suitable.
AUTHORIZATION ENTRY
Each group in a .pkla
file must have a name
that is unique within the file it belongs to. The following keys
are are recognized:
Identity |
A semi-colon separated list of globs to match identities. Each glob
should start with |
Action |
A semi-colon separated list of globs to match action identifiers. |
ResultActive |
The result to return for subjects in an active local
session that matches one or more of the given identities.
Allowed values are similar to what can be used in
the defaults section
of |
ResultInactive |
Like ResultActive but instead applies to subjects in inactive local sessions. |
ResultAny |
Like ResultActive but instead applies to any subject. |
ReturnValue |
A semi-colon separated list of key/value pairs (of the form key=value) that are added to the details of authorization result on positive matches. |
All keys specified above are required except that only at least one of ResultAny, ResultInactive and ResultActive must be present. The ReturnValue key is optional.
EVALUATION ORDER
When a Mechanism requests services from the Authority to check if a given Subject is authorized for a given Action, the authorization entries discussed above are consulted using the following algorithm.
The authorization entries from all .pkla files are ordered using
the following rules. First all the basename of all
sub-directories (e.g. 30-site.d) from both
the /etc/polkit-1/localauthority
and /var/lib/polkit-1/localauthority
directories are enumerated and sorted (using the C locale). If a
name exists in both /etc
and /var
, the one
in /etc
takes precedence. Then
all .pkla
files are read in order from this
list of sub-directories. For each .pkla
file, authorizations from each file are appended in order resulting
in an ordered list of authorization entries.
For example, given the following files
/var/lib/polkit-1 └── localauthority ├── 10-vendor.d │ └── 10-desktop-policy.pkla ├── 20-org.d ├── 30-site.d ├── 50-local.d ├── 55-org.my.company.d │ └── 10-org.my.company.product.pkla └── 90-mandatory.d /etc/polkit-1 └── localauthority ├── 10-vendor.d │ └── 01-some-changes-from-a-subvendor.pkla ├── 20-org.d ├── 30-site.d ├── 50-local.d ├── 55-org.my.company.d │ └── 10-org.my.company.product.pkla └── 90-mandatory.d
the evaluation order of the .pkla
files is:
10-desktop-policy.pkla
01-some-changes-from-a-subvendor.pkla
10-org.my.company.product.pkla
(the/var
one)10-org.my.company.product.pkla
(the/etc
one)
When the list of authorization entries has been calculated, the authorization check can be made. First, the user of the Subject is determined and the groups that the user belongs are looked up. For each group identity, the authorization entries are consulted in order. If the authorization check matches the data from the authorization check, then the authorization result from RequireAny, RequireInactive or RequireActive is used and ReturnValue is added to the authorization result.
Finally, the authorization entries are consulted using the user identity in the same manner.
Note that processing continues even after a match. This allows for socalled “negative authorizations”, see the section called “EXAMPLES” for further discussion.
EXAMPLES
The following .conf
file
[Configuration] AdminIdentities=unix-group:desktop_admin_r
that any user in the desktop_admin_r
UNIX
group can be used for authentication when administrator
authentication is needed. This file would typically be installed
in the /etc/polkit-1/localauthority.conf.d
directory and given the
name 60-desktop-policy.conf
to ensure that
it is evaluted after
the 50-localauthority.conf
file shipped
with PolicyKit. If the local administrator wants to override this (suppose 60-desktop-policy.conf
was shipped as part of the OS) he can simply create a file 99-my-admin-configuration.conf
with the following content
[Configuration] AdminIdentities=unix-user:lisa;unix-user:marge
to specify that only the users lisa
and marge
can authenticate when
administrator authentication is needed.
The following .pkla
file grants
authorization to all users in the staff
group
for actions matching the
glob com.example.awesomeproduct.*
provided
they are in an active session on the local console:
[Normal Staff Permissions] Identity=unix-group:staff Action=com.example.awesomeproduct.* ResultAny=no ResultInactive=no ResultActive=yes
If the users homer
and grimes
are member of
the staff
group but policy requires that an
administrator needs to authenticate every time authorization for
any action
matching com.example.awesomeproduct.*
is
required, one would add
[Exclude Some Problematic Users] Identity=unix-user:homer;unix-user:grimes Action=com.example.awesomeproduct.* ResultAny=no ResultInactive=no ResultActive=auth_admin
and make sure this authorization entry is after the first one.
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.