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Creating ACL rules is not exactly easy and existing examples are pretty simple. This patch adds a somewhat complex example which defines several roles. Admins can do everything, operators can do basic operations on any domain and several groups of users who act as operators but only on a limited set of domains. Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
415 lines
13 KiB
XML
415 lines
13 KiB
XML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<body>
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<h1>Polkit access control</h1>
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<p>
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Libvirt's client <a href="acl.html">access control framework</a> allows
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administrators to setup fine grained permission rules across client users,
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managed objects and API operations. This allows client connections
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to be locked down to a minimal set of privileges. The polkit driver
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provides a simple implementation of the access control framework.
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</p>
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<ul id="toc"></ul>
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<h2><a name="intro">Introduction</a></h2>
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<p>
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A default install of libvirt will typically use
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<a href="http://www.freedesktop.org/wiki/Software/polkit/">polkit</a>
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to authenticate the initial user connection to libvirtd. This is a
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very coarse grained check though, either allowing full read-write
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access to all APIs, or just read-only access. The polkit access
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control driver in libvirt builds on this capability to allow for
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fine grained control over the operations a user may perform on an
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object.
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</p>
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<h2><a name="perms">Permission names</a></h2>
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<p>
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The libvirt <a href="acl.html#perms">object names and permission names</a>
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are mapped onto polkit action names using the simple pattern:
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</p>
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<pre>org.libvirt.api.$object.$permission
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</pre>
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<p>
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The only caveat is that any underscore characters in the
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object or permission names are converted to hyphens. So,
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for example, the <code>search_storage_vols</code> permission
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on the <code>storage_pool</code> object maps to the polkit
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action:
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</p>
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<pre>org.libvirt.api.storage-pool.search-storage-vols
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</pre>
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<p>
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The default policy for any permission which corresponds to
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a "read only" operation, is to allow access. All other
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permissions default to deny access.
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</p>
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<h2><a name="attrs">Object identity attributes</a></h2>
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<p>
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To allow polkit authorization rules to be written to match
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against individual object instances, libvirt provides a number
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of authorization detail attributes when performing a permission
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check. The set of attributes varies according to the type
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of object being checked
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</p>
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<h3><a name="object_connect">virConnectPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_domain">virDomainPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>domain_name</td>
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<td>Name of the domain, unique to the local host</td>
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</tr>
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<tr>
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<td>domain_uuid</td>
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<td>UUID of the domain, globally unique</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_interface">virInterfacePtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>interface_name</td>
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<td>Name of the network interface, unique to the local host</td>
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</tr>
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<tr>
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<td>interface_macaddr</td>
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<td>MAC address of the network interface, not unique</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_network">virNetworkPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>network_name</td>
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<td>Name of the network, unique to the local host</td>
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</tr>
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<tr>
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<td>network_uuid</td>
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<td>UUID of the network, globally unique</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_node_device">virNodeDevicePtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>node_device_name</td>
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<td>Name of the node device, unique to the local host</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_nwfilter">virNWFilterPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>nwfilter_name</td>
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<td>Name of the network filter, unique to the local host</td>
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</tr>
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<tr>
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<td>nwfilter_uuid</td>
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<td>UUID of the network filter, globally unique</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_secret">virSecretPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>secret_uuid</td>
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<td>UUID of the secret, globally unique</td>
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</tr>
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<tr>
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<td>secret_usage_volume</td>
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<td>Name of the associated volume, if any</td>
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</tr>
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<tr>
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<td>secret_usage_ceph</td>
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<td>Name of the associated Ceph server, if any</td>
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</tr>
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<tr>
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<td>secret_usage_target</td>
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<td>Name of the associated iSCSI target, if any</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_storage_pool">virStoragePoolPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>pool_name</td>
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<td>Name of the storage pool, unique to the local host</td>
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</tr>
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<tr>
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<td>pool_uuid</td>
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<td>UUID of the storage pool, globally unique</td>
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</tr>
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</tbody>
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</table>
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<h3><a name="object_storage_vol">virStorageVolPtr</a></h3>
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<table class="acl">
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<thead>
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<tr>
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<th>Attribute</th>
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<th>Description</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>connect_driver</td>
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<td>Name of the libvirt connection driver</td>
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</tr>
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<tr>
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<td>pool_name</td>
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<td>Name of the storage pool, unique to the local host</td>
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</tr>
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<tr>
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<td>pool_uuid</td>
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<td>UUID of the storage pool, globally unique</td>
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</tr>
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<tr>
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<td>vol_name</td>
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<td>Name of the storage volume, unique to the pool</td>
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</tr>
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<tr>
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<td>vol_key</td>
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<td>Key of the storage volume, globally unique</td>
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</tr>
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</tbody>
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</table>
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<h2><a name="user">User identity attributes</a></h2>
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<p>
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At this point in time, the only attribute provided by
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libvirt to identify the user invoking the operation
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is the PID of the client program. This means that the
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polkit access control driver is only useful if connections
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to libvirt are restricted to its UNIX domain socket. If
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connections are being made to a TCP socket, no identifying
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information is available and access will be denied.
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Also note that if the client is connecting via an SSH
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tunnel, it is the local SSH user that will be identified.
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In future versions, it is expected that more information
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about the client user will be provided, including the
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SASL / Kerberos username and/or x509 distinguished
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name obtained from the authentication provider in use.
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</p>
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<h2><a name="checks">Writing access control policies</a></h2>
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<p>
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If using versions of polkit prior to 0.106 then it is only
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possible to validate (user, permission) pairs via the <code>.pkla</code>
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files. Fully validation of the (user, permission, object) triple
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requires the new JavaScript <code>.rules</code> support that
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was introduced in version 0.106. The latter is what will be
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described here.
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</p>
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<p>
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Libvirt does not ship any rules files by default. It merely
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provides a definition of the default behaviour for each
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action (permission). As noted earlier, permissions which
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correspond to read-only operations in libvirt will be allowed
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to all users by default; everything else is denied by default.
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Defining custom rules requires creation of a file in the
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<code>/etc/polkit-1/rules.d</code> directory with a name
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chosen by the administrator (<code>100-libvirt-acl.rules</code>
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would be a reasonable choice). See the <code>polkit(8)</code>
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manual page for a description of how to write these files
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in general. The key idea is to create a file containing
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something like
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</p>
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<pre>
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polkit.addRule(function(action, subject) {
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....logic to check 'action' and 'subject'...
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});
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</pre>
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<p>
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In this code snippet above, the <code>action</code> object
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instance will represent the libvirt permission being checked
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along with identifying attributes for the object it is being
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applied to. The <code>subject</code> meanwhile will identify
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the libvirt client app (with the caveat above about it only
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dealing with local clients connected via the UNIX socket).
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On the <code>action</code> object, the permission name is
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accessible via the <code>id</code> attribute, while the
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object identifying attributes are exposed via the
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<code>lookup</code> method.
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</p>
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<p>
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See
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<a href="http://libvirt.org/git/?p=libvirt.git;a=tree;f=examples/polkit;hb=HEAD">source code</a>
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for a more complex example.
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</p>
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<h3><a name="exconnect">Example: restricting ability to connect to drivers</a></h3>
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<p>
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Consider a local user <code>berrange</code>
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who has been granted permission to connect to libvirt in
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full read-write mode. The goal is to only allow them to
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use the <code>QEMU</code> driver and not the Xen or LXC
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drivers which are also available in libvirtd.
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To achieve this we need to write a rule which checks
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whether the <code>connect_driver</code> attribute
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is <code>QEMU</code>, and match on an action
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name of <code>org.libvirt.api.connect.getattr</code>. Using
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the javascript rules format, this ends up written as
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</p>
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<pre>
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polkit.addRule(function(action, subject) {
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if (action.id == "org.libvirt.api.connect.getattr" &&
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subject.user == "berrange") {
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if (action.lookup("connect_driver") == 'QEMU') {
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return polkit.Result.YES;
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} else {
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return polkit.Result.NO;
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}
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}
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});
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</pre>
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<h3><a name="exdomain">Example: restricting access to a single domain</a></h3>
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<p>
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Consider a local user <code>berrange</code>
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who has been granted permission to connect to libvirt in
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full read-write mode. The goal is to only allow them to
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see the domain called <code>demo</code> on the LXC driver.
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To achieve this we need to write a rule which checks
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whether the <code>connect_driver</code> attribute
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is <code>LXC</code> and the <code>domain_name</code>
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attribute is <code>demo</code>, and match on a action
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name of <code>org.libvirt.api.domain.getattr</code>. Using
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the javascript rules format, this ends up written as
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</p>
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<pre>
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polkit.addRule(function(action, subject) {
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if (action.id == "org.libvirt.api.domain.getattr" &&
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subject.user == "berrange") {
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if (action.lookup("connect_driver") == 'LXC' &&
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action.lookup("domain_name") == 'demo') {
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return polkit.Result.YES;
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} else {
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return polkit.Result.NO;
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}
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}
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});
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</pre>
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</body>
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</html>
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