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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd">
<chapter id="access-control">
<title>Access Control</title>
<para>
Access to hardware by unprivileged users is traditionally granted
in two ways either by granting access to the <emphasis>special
device file</emphasis> or allowing access through another process,
using IPC acting on behalf of the user. HAL follows the latter
model and uses the system-wide message bus (D-Bus) as the IPC
mechanism. In addition, HAL has support for modifying the ACL's
(access control lists) on a device file to grant/revoke access to
users based on several criteria.
</para>
<sect1 id="access-control-device-file">
<title>Device Files</title>
<para>
If HAL is built with <literal>--enable-acl-management</literal>
(requires both <literal>--enable-console-kit</literal>
and <literal>--enable-policy-kit</literal>) then ACL's on device
objects with the capability <literal>access_control</literal>
are automatically managed according to the properties defined in
<xref linkend="device-properties-access-control"/>. In addition,
for this configuration, HAL ships with a device information file
(normally installed in
<literal>/usr/share/hal/fdi/policy/10osvendor/20-acl-management.fdi</literal>)
that merges this capability on device objects that are normally
accessed by unprivileged users through the device file. This
includes e.g. sound cards, webcams and other devices but
excludes drives and volumes as the latter two are normally
accessed by a user through mounting them into the file system.
</para>
<para>
HAL uses PolicyKit to decide what users should have access
according to PolicyKit configuration; see the PolicyKit
privilege definition
file <literal>/usr/share/PolicyKit/policy/org.freedesktop.hal.device-access.policy</literal>
on a system with HAL installed for the default access suggested
by the HAL package and/or OS vendor.
</para>
<para>
In addition, 3rd party packages can supply device information
files to specify (via
the <literal>access_control.grant_user</literal>
and <literal>access_control.grant_group</literal> properties)
that a given user or group should always have access to a device
file. This is useful for system-wide software (such as AV
streaming management) that runs as an unprivileged system
user. This interface is supposed to be stable so 3rd party
packages can depend on it.
</para>
<sect2 id="access-control-device-file-policies">
<title>Device Files policies</title>
<para>
This is a list of the device file policies/rules delivered with
the HAL package to manage ACL's as defined via <literal>
access_control.type</literal> and the current default Policykit
policies for inactive and active users.
</para>
<informaltable>
<tgroup cols="2">
<thead>
<row>
<entry>Type</entry>
<entry>Description</entry>
<entry>allow_inactive</entry>
<entry>allow_active</entry>
</row>
</thead>
<tbody>
<row>
<entry>
<literal>audio-player</literal>
</entry>
<entry>Directly access audio players.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>camera</literal>
</entry>
<entry>Directly access digital cameras.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>cdrom</literal>
</entry>
<entry>Directly access optical drives.</entry>
<entry>yes</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>dvb</literal>
</entry>
<entry>Directly access DVB devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>fingerprint-reader</literal>
</entry>
<entry>Directly access to fingerprint reader devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>floppy</literal>
</entry>
<entry>Directly access Floppy devices.</entry>
<entry>yes</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>ieee1394-avc</literal>
</entry>
<entry>Directly access Firewire AVC devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>ieee1394-iidc</literal>
</entry>
<entry>Directly access Firewire IIDC devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>smart-card-reader</literal>
</entry>
<entry>Directly access Smart Card Reader security devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>joystick</literal>
</entry>
<entry>Directly access Joystick devices.</entry>
<entry>yes</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>modem</literal>
</entry>
<entry>Directly access serial modem devices.</entry>
<entry>auth_admin_keep_always</entry>
<entry>auth_admin_keep_always</entry>
</row>
<row>
<entry>
<literal>mouse</literal>
</entry>
<entry>Directly access Mouse (input) devices</entry>
<entry>yes</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>obex</literal>
</entry>
<entry>Directly access OBEX devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>pda</literal>
</entry>
<entry>Directly access PDA devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>ppdev</literal>
</entry>
<entry>Directly access parallel port devices.</entry>
<entry>auth_admin_keep_always</entry>
<entry>auth_admin_keep_always</entry>
</row>
<row>
<entry>
<literal>printer</literal>
</entry>
<entry>Directly access printer devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>removable-block</literal>
</entry>
<entry>Directly access removable block devices.</entry>
<entry>no</entry>
<entry>no</entry>
</row>
<row>
<entry>
<literal>scanner</literal>
</entry>
<entry>Directly access scanners.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>sound</literal>
</entry>
<entry>Directly access sound devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>video</literal>
</entry>
<entry>Directly access Video devices.</entry>
<entry>yes</entry>
<entry>yes</entry>
</row>
<row>
<entry>
<literal>video4linux</literal>
</entry>
<entry>Directly access video capture devices.</entry>
<entry>no</entry>
<entry>yes</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</sect2>
</sect1>
<sect1 id="access-control-ipc">
<title>D-Bus Interfaces</title>
<para>
If HAL is built without ConsoleKit support
(e.g. without <literal>--enable-console-kit</literal>) access to
the various D-Bus interfaces that provides mechanisms is only
protected by the D-Bus security configuration files
(e.g. using <literal>at_console</literal> to restrict to console
user on Red Hat systems) and, in certain cases, restricted to
the super user.
</para>
<para>
If ConsoleKit support is enabled, access to D-Bus interfaces is
currently hardcoded to only allow active users at the system
console. If PolicyKit support is enabled, the PolicyKit library
will be in charge of determining access; see the PolicyKit
privilege definition files
in <literal>/etc/PolicyKit/privileges</literal> on a system with
HAL installed for the default access suggested by the HAL
package and/or OS vendor.
</para>
</sect1>
</chapter>
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