Travis Ralston
6 years ago
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GitHub
commit
4e885c3f77
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Add server ACLs as an option for controlling federation in a room.
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{
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"age": 242352,
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"content": {
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"allow_ip_literals": false,
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"allow": ["*"],
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"deny": ["*.evil.com", "evil.com"]
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},
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"state_key": "",
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"origin_server_ts": 1431961217939,
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"event_id": "$WLGTSEFSEF:localhost",
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"type": "m.room.server_acl",
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"room_id": "!Cuyf34gef24t:localhost",
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"sender": "@example:localhost"
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}
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---
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title: Server ACL
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description: |-
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An event to indicate which servers are permitted to participate in the
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room. Server ACLs may allow or deny groups of hosts. All servers participating
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in the room, including those that are denied, are expected to uphold the
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server ACL. Servers that do not uphold the ACLs MUST be added to the denied hosts
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list in order for the ACLs to remain effective.
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The ``allow`` and ``deny`` lists are lists of globs supporting ``?`` and ``*``
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as wildcards. When comparing against the server ACLs, the suspect server's port
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number must not be considered. Therefore ``evil.com``, ``evil.com:8448``, and
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``evil.com:1234`` would all match rules that apply to ``evil.com``, for example.
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The ACLs are applied to servers when they make requests, and are applied in
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the following order:
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1. If there is no ``m.room.server_acl`` event in the room state, allow.
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#. If the server name is an IP address (v4 or v6) literal, and ``allow_ip_literals``
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is present and ``false``, deny.
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#. If the server name matches an entry in the ``deny`` list, deny.
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#. If the server name matches an entry in the ``allow`` list, allow.
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#. Otherwise, deny.
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.. Note::
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Server ACLs do not restrict the events relative to the room DAG via authorisation
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rules, but instead act purely at the network layer to determine which servers are
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allowed to connect and interact with a given room.
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.. WARNING::
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Failing to provide an ``allow`` rule of some kind will prevent **all**
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servers from participating in the room, including the sender. This renders
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the room unusable. A common allow rule is ``[ "*" ]`` which would still
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permit the use of the ``deny`` list without losing the room.
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.. WARNING::
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All compliant servers must implement server ACLs. However, legacy or noncompliant
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servers exist which do not uphold ACLs, and these MUST be manually appended to
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the denied hosts list when setting an ACL to prevent them from leaking events from
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banned servers into a room. Currently, the only way to determine noncompliant hosts is
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to check the ``prev_events`` of leaked events, therefore detecting servers which
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are not upholding the ACLs. Server versions can also be used to try to detect hosts that
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will not uphold the ACLs, although this is not comprehensive. Server ACLs were added
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in Synapse v0.32.0, although other server implementations and versions exist in the world.
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allOf:
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- $ref: core-event-schema/state_event.yaml
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type: object
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properties:
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content:
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properties:
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allow_ip_literals:
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type: boolean
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description: |-
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True to allow server names that are IP address literals. False to
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deny. Defaults to true if missing or otherwise not a boolean.
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This is strongly recommended to be set to ``false`` as servers running
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with IP literal names are strongly discouraged in order to require
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legitimate homeservers to be backed by a valid registered domain name.
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allow:
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type: array
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description: |-
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The server names to allow in the room, excluding any port information.
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Wildcards may be used to cover a wider range of hosts, where ``*``
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matches zero or more characters and ``?`` matches exactly one character.
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**This defaults to an empty list when not provided, effectively disallowing
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every server.**
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items:
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type: string
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deny:
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type: array
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description: |-
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The server names to disallow in the room, excluding any port information.
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Wildcards may be used to cover a wider range of hosts, where ``*``
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matches zero or more characters and ``?`` matches exactly one character.
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This defaults to an empty list when not provided.
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items:
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type: string
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type: object
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state_key:
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description: A zero-length string.
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pattern: '^$'
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type: string
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type:
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enum: ['m.room.server_acl']
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type: enum
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@ -0,0 +1,70 @@
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.. Copyright 2018 New Vector Ltd
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..
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.. Licensed under the Apache License, Version 2.0 (the "License");
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.. you may not use this file except in compliance with the License.
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.. You may obtain a copy of the License at
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..
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.. http://www.apache.org/licenses/LICENSE-2.0
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..
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.. Unless required by applicable law or agreed to in writing, software
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.. distributed under the License is distributed on an "AS IS" BASIS,
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.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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.. See the License for the specific language governing permissions and
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.. limitations under the License.
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Server Access Control Lists (ACLs) for rooms
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============================================
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.. _module:server-acls:
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In some scenarios room operators may wish to prevent a malicious or untrusted
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server from participating in their room. Sending an `m.room.server_acl`_ state
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event into a room is an effective way to prevent the server from participating
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in the room at the federation level.
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Server ACLs can also be used to make rooms only federate with a limited set of
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servers, or retroactively make the room no longer federate with any other server,
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similar to setting the ``m.federate`` value on the `m.room.create`_ event.
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{{m_room_server_acl_event}}
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.. Note::
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Port numbers are not supported because it is unclear to parsers whether a
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port number should be matched or an IP address literal. Additionally, it
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is unlikely that one would trust a server running on a particular domain's
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port but not a different port, especially considering the server host can
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easily change ports.
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.. Note::
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CIDR notation is not supported for IP addresses because Matrix does not
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encourage the use of IPs for identifying servers. Instead, a blanket
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``allow_ip_literals`` is provided to cover banning them.
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Client behaviour
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----------------
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Clients are not expected to perform any additional duties beyond sending the
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event. Clients should describe changes to the server ACLs to the user in the
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user interface, such as in the timeline.
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Clients may wish to kick affected users from the room prior to denying a server
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access to the room to help prevent those servers from participating and to
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provide feedback to the users that they have been excluded from the room.
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Server behaviour
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----------------
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Servers MUST prevent blacklisted servers from sending events or participating
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in the room when an `m.room.server_acl`_ event is present in the room state.
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Which APIs are specifically affected are described in the Server-Server API
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specification.
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Servers should still send events to denied servers if they are still residents
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of the room.
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Security considerations
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-----------------------
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Server ACLs are only effective if every server in the room honours them. Servers
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that do not honour the ACLs may still permit events sent by denied servers into
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the room, leaking them to other servers in the room. To effectively enforce an
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ACL in a room, the servers that do not honour the ACLs should be denied in the
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room as well.
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