diff --git a/changelogs/client_server/newsfragments/1550.feature b/changelogs/client_server/newsfragments/1550.feature new file mode 100644 index 00000000..f04fa9ae --- /dev/null +++ b/changelogs/client_server/newsfragments/1550.feature @@ -0,0 +1 @@ +Add server ACLs as an option for controlling federation in a room. diff --git a/event-schemas/examples/m.room.server_acl b/event-schemas/examples/m.room.server_acl new file mode 100644 index 00000000..86da2093 --- /dev/null +++ b/event-schemas/examples/m.room.server_acl @@ -0,0 +1,14 @@ +{ + "age": 242352, + "content": { + "allow_ip_literals": false, + "allow": ["*"], + "deny": ["*.evil.com", "evil.com"] + }, + "state_key": "", + "origin_server_ts": 1431961217939, + "event_id": "$WLGTSEFSEF:localhost", + "type": "m.room.server_acl", + "room_id": "!Cuyf34gef24t:localhost", + "sender": "@example:localhost" +} diff --git a/event-schemas/schema/m.room.server_acl b/event-schemas/schema/m.room.server_acl new file mode 100644 index 00000000..c6adaf05 --- /dev/null +++ b/event-schemas/schema/m.room.server_acl @@ -0,0 +1,88 @@ +--- +title: Server ACL +description: |- + An event to indicate which servers are permitted to participate in the + room. Server ACLs may allow or deny groups of hosts. All servers participating + in the room, including those that are denied, are expected to uphold the + server ACL. Servers that do not uphold the ACLs MUST be added to the denied hosts + list in order for the ACLs to remain effective. + + The ``allow`` and ``deny`` lists are lists of globs supporting ``?`` and ``*`` + as wildcards. When comparing against the server ACLs, the suspect server's port + number must not be considered. Therefore ``evil.com``, ``evil.com:8448``, and + ``evil.com:1234`` would all match rules that apply to ``evil.com``, for example. + + The ACLs are applied to servers when they make requests, and are applied in + the following order: + + 1. If there is no ``m.room.server_acl`` event in the room state, allow. + #. If the server name is an IP address (v4 or v6) literal, and ``allow_ip_literals`` + is present and ``false``, deny. + #. If the server name matches an entry in the ``deny`` list, deny. + #. If the server name matches an entry in the ``allow`` list, allow. + #. Otherwise, deny. + + .. Note:: + Server ACLs do not restrict the events relative to the room DAG via authorisation + rules, but instead act purely at the network layer to determine which servers are + allowed to connect and interact with a given room. + + .. WARNING:: + Failing to provide an ``allow`` rule of some kind will prevent **all** + servers from participating in the room, including the sender. This renders + the room unusable. A common allow rule is ``[ "*" ]`` which would still + permit the use of the ``deny`` list without losing the room. + + .. WARNING:: + All compliant servers must implement server ACLs. However, legacy or noncompliant + servers exist which do not uphold ACLs, and these MUST be manually appended to + the denied hosts list when setting an ACL to prevent them from leaking events from + banned servers into a room. Currently, the only way to determine noncompliant hosts is + to check the ``prev_events`` of leaked events, therefore detecting servers which + are not upholding the ACLs. Server versions can also be used to try to detect hosts that + will not uphold the ACLs, although this is not comprehensive. Server ACLs were added + in Synapse v0.32.0, although other server implementations and versions exist in the world. +allOf: + - $ref: core-event-schema/state_event.yaml +type: object +properties: + content: + properties: + allow_ip_literals: + type: boolean + description: |- + True to allow server names that are IP address literals. False to + deny. Defaults to true if missing or otherwise not a boolean. + + This is strongly recommended to be set to ``false`` as servers running + with IP literal names are strongly discouraged in order to require + legitimate homeservers to be backed by a valid registered domain name. + allow: + type: array + description: |- + The server names to allow in the room, excluding any port information. + Wildcards may be used to cover a wider range of hosts, where ``*`` + matches zero or more characters and ``?`` matches exactly one character. + + **This defaults to an empty list when not provided, effectively disallowing + every server.** + items: + type: string + deny: + type: array + description: |- + The server names to disallow in the room, excluding any port information. + Wildcards may be used to cover a wider range of hosts, where ``*`` + matches zero or more characters and ``?`` matches exactly one character. + + This defaults to an empty list when not provided. + items: + type: string + type: object + state_key: + description: A zero-length string. + pattern: '^$' + type: string + type: + enum: ['m.room.server_acl'] + type: enum diff --git a/specification/modules/server_acls.rst b/specification/modules/server_acls.rst new file mode 100644 index 00000000..2b2d8f35 --- /dev/null +++ b/specification/modules/server_acls.rst @@ -0,0 +1,70 @@ +.. Copyright 2018 New Vector Ltd +.. +.. Licensed under the Apache License, Version 2.0 (the "License"); +.. you may not use this file except in compliance with the License. +.. You may obtain a copy of the License at +.. +.. http://www.apache.org/licenses/LICENSE-2.0 +.. +.. Unless required by applicable law or agreed to in writing, software +.. distributed under the License is distributed on an "AS IS" BASIS, +.. WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +.. See the License for the specific language governing permissions and +.. limitations under the License. + +Server Access Control Lists (ACLs) for rooms +============================================ + +.. _module:server-acls: + +In some scenarios room operators may wish to prevent a malicious or untrusted +server from participating in their room. Sending an `m.room.server_acl`_ state +event into a room is an effective way to prevent the server from participating +in the room at the federation level. + +Server ACLs can also be used to make rooms only federate with a limited set of +servers, or retroactively make the room no longer federate with any other server, +similar to setting the ``m.federate`` value on the `m.room.create`_ event. + +{{m_room_server_acl_event}} + +.. Note:: + Port numbers are not supported because it is unclear to parsers whether a + port number should be matched or an IP address literal. Additionally, it + is unlikely that one would trust a server running on a particular domain's + port but not a different port, especially considering the server host can + easily change ports. + +.. Note:: + CIDR notation is not supported for IP addresses because Matrix does not + encourage the use of IPs for identifying servers. Instead, a blanket + ``allow_ip_literals`` is provided to cover banning them. + +Client behaviour +---------------- +Clients are not expected to perform any additional duties beyond sending the +event. Clients should describe changes to the server ACLs to the user in the +user interface, such as in the timeline. + +Clients may wish to kick affected users from the room prior to denying a server +access to the room to help prevent those servers from participating and to +provide feedback to the users that they have been excluded from the room. + +Server behaviour +---------------- +Servers MUST prevent blacklisted servers from sending events or participating +in the room when an `m.room.server_acl`_ event is present in the room state. +Which APIs are specifically affected are described in the Server-Server API +specification. + +Servers should still send events to denied servers if they are still residents +of the room. + + +Security considerations +----------------------- +Server ACLs are only effective if every server in the room honours them. Servers +that do not honour the ACLs may still permit events sent by denied servers into +the room, leaking them to other servers in the room. To effectively enforce an +ACL in a room, the servers that do not honour the ACLs should be denied in the +room as well. \ No newline at end of file diff --git a/specification/server_server_api.rst b/specification/server_server_api.rst index dbde8b10..439b35f9 100644 --- a/specification/server_server_api.rst +++ b/specification/server_server_api.rst @@ -929,6 +929,32 @@ described in the `Client-Server API`_, being sure to use the ``allow_remote`` parameter (set to ``false``). +Server Access Control Lists (ACLs) +---------------------------------- + +Server ACLs and their purpose are described in the `Server ACLs`_ section of the +Client-Server API. + +When a remote server makes a request, it MUST be verified to be allowed by the +server ACLs. If the server is denied access to a room, the receiving server +MUST reply with a 403 HTTP status code and an ``errcode`` of ``M_FORBIDDEN``. + +The following endpoint prefixes MUST be protected: + +* ``/_matrix/federation/v1/send`` (on a per-PDU basis) +* ``/_matrix/federation/v1/make_join`` +* ``/_matrix/federation/v1/make_leave`` +* ``/_matrix/federation/v1/send_join`` +* ``/_matrix/federation/v1/send_leave`` +* ``/_matrix/federation/v1/invite`` +* ``/_matrix/federation/v1/state`` +* ``/_matrix/federation/v1/state_ids`` +* ``/_matrix/federation/v1/backfill`` +* ``/_matrix/federation/v1/event_auth`` +* ``/_matrix/federation/v1/query_auth`` +* ``/_matrix/federation/v1/get_missing_events`` + + Signing Events -------------- diff --git a/specification/targets.yaml b/specification/targets.yaml index 5480bbc5..acf4b6ac 100644 --- a/specification/targets.yaml +++ b/specification/targets.yaml @@ -67,6 +67,7 @@ groups: # reusable blobs of files when prefixed with 'group:' - modules/report_content.rst - modules/third_party_networks.rst - modules/openid.rst + - modules/server_acls.rst title_styles: ["=", "-", "~", "+", "^", "`", "@", ":"]