polkit

summary

This subchapter looks at polkit, a UNIX (and Linux) command.

polkit is used to control system-wide privileges.

polkit

This subchapter looks at polkit, a UNIX (and Linux) command.

polkit is used to control system-wide privileges.

running privileged commands

polkit can be used to run privileged commands by typing pkexec, followed by the intended command:

$ pkexec cat README

sudo alternative

It is generally recommended to use sudo rather than pkexec, because sudo provides greater flexibity and security.

Mac OS X

While polkit is not part of the official Mac OS X release from Apple, it can be installed on mac OS X.

security

pkexec never does any validation of the ARGUMENTS passed to a program.

graphic programs

X11 (and other graphic) programs won’t run by default with polkit because the $DISPLAY environment variable is not set. The following information from the pkexec manual describes how to set pkexec so that it can run a graphic program.

To specify what kind of authorization is needed to execute the program
 /usr/bin/pk-example-frobnicate as another user, simply write an action
 definition file like this
 <?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>Examples for the PolicyKit Project</vendor>
 <vendor_url>http://hal.freedesktop.org/docs/PolicyKit/</vendor_url>
 <action id="org.freedesktop.policykit.example.pkexec.run-frobnicate">
 <description>Run the PolicyKit example program Frobnicate</description>
 <description xml:lang="da">Kør PolicyKit eksemplet Frobnicate</description>
 <message>Authentication is required to run the PolicyKit example program Frobnicate</message>
 <message xml:lang="da">Autorisering er påkrævet for at afvikle PolicyKit eksemplet Frobnicate</message>
 <icon_name>audio-x-generic</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/bin/pk-example-frobnicate</annotate>
 </action>
 </policyconfig>
 and drop it in the /usr/share/polkit-1/actions directory under a
 suitable name (e.g. matching the namespace of the action). Note that in
 addition to specifying the program, the authentication message,
 description, icon and defaults can be specified. For example, for the
 action defined above, the following authentication dialog will be
 shown:
 [IMAGE][2]
 +----------------------------------------------------------+
 | Authenticate [X] |
 +----------------------------------------------------------+
 | |
 | [Icon] Authentication is required to run the PolicyKit |
 | example program Frobnicate |
 | |
 | An application is attempting to perform an |
 | action that requires privileges. Authentication |
 | is required to perform this action. |
 | |
 | Password: [__________________________________] |
 | |
 | [V] Details: |
 | Command: /usr/bin/pk-example-frobnicate |
 | Run As: Super User (root) |
 | Action: org.fd.pk.example.pkexec.run-frobnicate |
 | Vendor: Examples for the PolicyKit Project |
 | |
 | [Cancel] [Authenticate] |
 +----------------------------------------------------------+
 If the user is using the da_DK locale, the dialog looks like this:
 [IMAGE][3]
 +----------------------------------------------------------+
 | Autorisering [X] |
 +----------------------------------------------------------+
 | |
 | [Icon] Autorisering er pŒkrƒZvet for at afvikle |
 | PolicyKit eksemplet Frobnicate |
 | |
 | Et program forsƒ\ger at udfƒ\re en handling der |
 | krƒZver privilegier. Autorisering er pŒkrƒZvet. |
 | |
 | Kodeord: [___________________________________] |
 | |
 | [V] Detaljer: |
 | Bruger: Super User (root) |
 | Program: /usr/bin/pk-example-frobnicate |
 | Handling: org.fd.pk.example.pkexec.run-frobnicate |
 | Vendor: Examples for the PolicyKit Project |
 | |
 | [AnnullŽr] [Autorisering] |
 +----------------------------------------------------------+
 Note that pkexec does no validation of the ARGUMENTS passed to PROGRAM.
 In the normal case (where administrator authentication is required
 every time pkexec is used), this is not a problem since if the user is
 an administrator he might as well just run pkexec bash to get root.
 However, if an action is used for which the user can retain
 authorization (or if the user is implicitly authorized), such as with
 pk-example-frobnicate above, this could be a security hole. Therefore,
 as a rule of thumb, programs for which the default required
 authorization is changed, should never implicitly trust user input
 (e.g. like any other well-written suid program).