Add a spamchecker callback to allow or deny room creation based on invites (#10898)

This is in the context of creating new module callbacks that modules in https://github.com/matrix-org/synapse-dinsic can use, in an effort to reconcile the spam checker API in synapse-dinsic with the one in mainline.

This adds a callback that's fairly similar to user_may_create_room except it also allows processing based on the invites sent at room creation.

Author: babolivier

changelog.d/10898.feature

@@ -0,0 +1 @@
+Add a `user_may_create_room_with_invites` spam checker callback to allow modules to allow or deny a room creation request based on the invites and/or 3PID invites it includes.

docs/modules/spam_checker_callbacks.md

@@ -0,0 +1,189 @@
+# Spam checker callbacks
+
+Spam checker callbacks allow module developers to implement spam mitigation actions for
+Synapse instances. Spam checker callbacks can be registered using the module API's
+`register_spam_checker_callbacks` method.
+
+## Callbacks
+
+The available spam checker callbacks are:
+
+### `check_event_for_spam`
+
+```python
+async def check_event_for_spam(event: "synapse.events.EventBase") -> Union[bool, str]
+```
+
+Called when receiving an event from a client or via federation. The module can return
+either a `bool` to indicate whether the event must be rejected because of spam, or a `str`
+to indicate the event must be rejected because of spam and to give a rejection reason to
+forward to clients.
+
+### `user_may_invite`
+
+```python
+async def user_may_invite(inviter: str, invitee: str, room_id: str) -> bool
+```
+
+Called when processing an invitation. The module must return a `bool` indicating whether
+the inviter can invite the invitee to the given room. Both inviter and invitee are
+represented by their Matrix user ID (e.g. `@alice:example.com`).
+
+### `user_may_create_room`
+
+```python
+async def user_may_create_room(user: str) -> bool
+```
+
+Called when processing a room creation request. The module must return a `bool` indicating
+whether the given user (represented by their Matrix user ID) is allowed to create a room.
+
+### `user_may_create_room_with_invites`
+
+```python
+async def user_may_create_room_with_invites(
+    user: str,
+    invites: List[str],
+    threepid_invites: List[Dict[str, str]],
+) -> bool
+```
+
+Called when processing a room creation request (right after `user_may_create_room`).
+The module is given the Matrix user ID of the user trying to create a room, as well as a
+list of Matrix users to invite and a list of third-party identifiers (3PID, e.g. email
+addresses) to invite.
+
+An invited Matrix user to invite is represented by their Matrix user IDs, and an invited
+3PIDs is represented by a dict that includes the 3PID medium (e.g. "email") through its
+`medium` key and its address (e.g. "[email protected]") through its `address` key.
+
+See [the Matrix specification](https://matrix.org/docs/spec/appendices#pid-types) for more
+information regarding third-party identifiers.
+
+If no invite and/or 3PID invite were specified in the room creation request, the
+corresponding list(s) will be empty.
+
+**Note**: This callback is not called when a room is cloned (e.g. during a room upgrade)
+since no invites are sent when cloning a room. To cover this case, modules also need to
+implement `user_may_create_room`.
+
+### `user_may_create_room_alias`
+
+```python
+async def user_may_create_room_alias(user: str, room_alias: "synapse.types.RoomAlias") -> bool
+```
+
+Called when trying to associate an alias with an existing room. The module must return a
+`bool` indicating whether the given user (represented by their Matrix user ID) is allowed
+to set the given alias.
+
+### `user_may_publish_room`
+
+```python
+async def user_may_publish_room(user: str, room_id: str) -> bool
+```
+
+Called when trying to publish a room to the homeserver's public rooms directory. The
+module must return a `bool` indicating whether the given user (represented by their
+Matrix user ID) is allowed to publish the given room.
+
+### `check_username_for_spam`
+
+```python
+async def check_username_for_spam(user_profile: Dict[str, str]) -> bool
+```
+
+Called when computing search results in the user directory. The module must return a
+`bool` indicating whether the given user profile can appear in search results. The profile
+is represented as a dictionary with the following keys:
+
+* `user_id`: The Matrix ID for this user.
+* `display_name`: The user's display name.
+* `avatar_url`: The `mxc://` URL to the user's avatar.
+
+The module is given a copy of the original dictionary, so modifying it from within the
+module cannot modify a user's profile when included in user directory search results.
+
+### `check_registration_for_spam`
+
+```python
+async def check_registration_for_spam(
+    email_threepid: Optional[dict],
+    username: Optional[str],
+    request_info: Collection[Tuple[str, str]],
+    auth_provider_id: Optional[str] = None,
+) -> "synapse.spam_checker_api.RegistrationBehaviour"
+```
+
+Called when registering a new user. The module must return a `RegistrationBehaviour`
+indicating whether the registration can go through or must be denied, or whether the user
+may be allowed to register but will be shadow banned.
+
+The arguments passed to this callback are:
+
+* `email_threepid`: The email address used for registering, if any.
+* `username`: The username the user would like to register. Can be `None`, meaning that
+  Synapse will generate one later.
+* `request_info`: A collection of tuples, which first item is a user agent, and which
+  second item is an IP address. These user agents and IP addresses are the ones that were
+  used during the registration process.
+* `auth_provider_id`: The identifier of the SSO authentication provider, if any.
+
+### `check_media_file_for_spam`
+
+```python
+async def check_media_file_for_spam(
+    file_wrapper: "synapse.rest.media.v1.media_storage.ReadableFileWrapper",
+    file_info: "synapse.rest.media.v1._base.FileInfo",
+) -> bool
+```
+
+Called when storing a local or remote file. The module must return a boolean indicating
+whether the given file can be stored in the homeserver's media store.
+
+## Example
+
+The example below is a module that implements the spam checker callback
+`check_event_for_spam` to deny any message sent by users whose Matrix user IDs are
+mentioned in a configured list, and registers a web resource to the path
+`/_synapse/client/list_spam_checker/is_evil` that returns a JSON object indicating
+whether the provided user appears in that list.
+
+```python
+import json
+from typing import Union
+
+from twisted.web.resource import Resource
+from twisted.web.server import Request
+
+from synapse.module_api import ModuleApi
+
+
+class IsUserEvilResource(Resource):
+    def __init__(self, config):
+        super(IsUserEvilResource, self).__init__()
+        self.evil_users = config.get("evil_users") or []
+
+    def render_GET(self, request: Request):
+        user = request.args.get(b"user")[0].decode()
+        request.setHeader(b"Content-Type", b"application/json")
+        return json.dumps({"evil": user in self.evil_users}).encode()
+
+
+class ListSpamChecker:
+    def __init__(self, config: dict, api: ModuleApi):
+        self.api = api
+        self.evil_users = config.get("evil_users") or []
+
+        self.api.register_spam_checker_callbacks(
+            check_event_for_spam=self.check_event_for_spam,
+        )
+
+        self.api.register_web_resource(
+            path="/_synapse/client/list_spam_checker/is_evil",
+            resource=IsUserEvilResource(config),
+        )
+
+    async def check_event_for_spam(self, event: "synapse.events.EventBase") -> Union[bool, str]:
+        return event.sender not in self.evil_users
+```

synapse/events/spamcheck.py

@@ -44,13 +44,10 @@
     ["synapse.events.EventBase"],
     Awaitable[Union[bool, str]],
 ]
-# FIXME: Callback signature differs from mainline
-USER_MAY_INVITE_CALLBACK = Callable[
-    [str, Optional[str], Optional[dict], str, bool, bool], Awaitable[bool]
-]
-# FIXME: Callback signature differs from mainline
-USER_MAY_CREATE_ROOM_CALLBACK = Callable[
-    [str, List[str], List[dict], bool], Awaitable[bool]
+USER_MAY_INVITE_CALLBACK = Callable[[str, str, str], Awaitable[bool]]
+USER_MAY_CREATE_ROOM_CALLBACK = Callable[[str], Awaitable[bool]]
+USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK = Callable[
+    [str, List[str], List[Dict[str, str]]], Awaitable[bool]
 ]
 USER_MAY_CREATE_ROOM_ALIAS_CALLBACK = Callable[[str, RoomAlias], Awaitable[bool]]
 USER_MAY_PUBLISH_ROOM_CALLBACK = Callable[[str, str], Awaitable[bool]]
@@ -173,6 +170,9 @@ def __init__(self):
         self._check_event_for_spam_callbacks: List[CHECK_EVENT_FOR_SPAM_CALLBACK] = []
         self._user_may_invite_callbacks: List[USER_MAY_INVITE_CALLBACK] = []
         self._user_may_create_room_callbacks: List[USER_MAY_CREATE_ROOM_CALLBACK] = []
+        self._user_may_create_room_with_invites_callbacks: List[
+            USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK
+        ] = []
         self._user_may_create_room_alias_callbacks: List[
             USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
         ] = []
@@ -193,6 +193,9 @@ def register_callbacks(
         check_event_for_spam: Optional[CHECK_EVENT_FOR_SPAM_CALLBACK] = None,
         user_may_invite: Optional[USER_MAY_INVITE_CALLBACK] = None,
         user_may_create_room: Optional[USER_MAY_CREATE_ROOM_CALLBACK] = None,
+        user_may_create_room_with_invites: Optional[
+            USER_MAY_CREATE_ROOM_WITH_INVITES_CALLBACK
+        ] = None,
         user_may_create_room_alias: Optional[
             USER_MAY_CREATE_ROOM_ALIAS_CALLBACK
         ] = None,
@@ -214,6 +217,11 @@ def register_callbacks(
         if user_may_create_room is not None:
             self._user_may_create_room_callbacks.append(user_may_create_room)
 
+        if user_may_create_room_with_invites is not None:
+            self._user_may_create_room_with_invites_callbacks.append(
+                user_may_create_room_with_invites,
+            )
+
         if user_may_create_room_alias is not None:
             self._user_may_create_room_alias_callbacks.append(
                 user_may_create_room_alias,
@@ -338,6 +346,34 @@ async def user_may_create_room(
 
         return True
 
+    async def user_may_create_room_with_invites(
+        self,
+        userid: str,
+        invites: List[str],
+        threepid_invites: List[Dict[str, str]],
+    ) -> bool:
+        """Checks if a given user may create a room with invites
+
+        If this method returns false, the creation request will be rejected.
+
+        Args:
+            userid: The ID of the user attempting to create a room
+            invites: The IDs of the Matrix users to be invited if the room creation is
+                allowed.
+            threepid_invites: The threepids to be invited if the room creation is allowed,
+                as a dict including a "medium" key indicating the threepid's medium (e.g.
+                "email") and an "address" key indicating the threepid's address (e.g.
+                "[email protected]")
+
+        Returns:
+            True if the user may create the room, otherwise False
+        """
+        for callback in self._user_may_create_room_with_invites_callbacks:
+            if await callback(userid, invites, threepid_invites) is False:
+                return False
+
+        return True
+
     async def user_may_create_room_alias(
         self, userid: str, room_alias: RoomAlias
     ) -> bool:

synapse/handlers/room.py

@@ -636,14 +636,16 @@ async def create_room(
             requester, config, is_requester_admin=is_requester_admin
         )
 
-        invite_list = config.get("invite", [])
         invite_3pid_list = config.get("invite_3pid", [])
+        invite_list = config.get("invite", [])
 
-        if not is_requester_admin and not await self.spam_checker.user_may_create_room(
-            user_id,
-            invite_list=invite_list,
-            third_party_invite_list=invite_3pid_list,
-            cloning=False,
+        if not is_requester_admin and not (
+            await self.spam_checker.user_may_create_room(user_id)
+            and await self.spam_checker.user_may_create_room_with_invites(
+                user_id,
+                invite_list,
+                invite_3pid_list,
+            )
         ):
             raise SynapseError(403, "You are not permitted to create rooms")
 
@@ -677,8 +679,6 @@ async def create_room(
             if mapping:
                 raise SynapseError(400, "Room alias already taken", Codes.ROOM_IN_USE)
 
-        invite_3pid_list = config.get("invite_3pid", [])
-        invite_list = config.get("invite", [])
         for i in invite_list:
             try:
                 uid = UserID.from_string(i)