Check for space membership during a remote join of a restricted room (#9814)

When receiving a /send_join request for a room with join rules set to 'restricted',
check if the user is a member of the spaces defined in the 'allow' key of the join rules.

This only applies to an experimental room version, as defined in MSC3083.

1 files changed, 3 insertions, 59 deletions

diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 2bbfac6471..2c5bada1d8 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -19,7 +19,7 @@ from http import HTTPStatus
 from typing import TYPE_CHECKING, Iterable, List, Optional, Tuple
 
 from synapse import types
-from synapse.api.constants import AccountDataTypes, EventTypes, JoinRules, Membership
+from synapse.api.constants import AccountDataTypes, EventTypes, Membership
 from synapse.api.errors import (
     AuthError,
     Codes,
@@ -28,7 +28,6 @@ from synapse.api.errors import (
     SynapseError,
 )
 from synapse.api.ratelimiting import Ratelimiter
-from synapse.api.room_versions import RoomVersion
 from synapse.events import EventBase
 from synapse.events.snapshot import EventContext
 from synapse.types import JsonDict, Requester, RoomAlias, RoomID, StateMap, UserID
@@ -64,6 +63,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         self.profile_handler = hs.get_profile_handler()
         self.event_creation_handler = hs.get_event_creation_handler()
         self.account_data_handler = hs.get_account_data_handler()
+        self.event_auth_handler = hs.get_event_auth_handler()
 
         self.member_linearizer = Linearizer(name="member")
 
@@ -178,62 +178,6 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
 
         await self._invites_per_user_limiter.ratelimit(requester, invitee_user_id)
 
-    async def _can_join_without_invite(
-        self, state_ids: StateMap[str], room_version: RoomVersion, user_id: str
-    ) -> bool:
-        """
-        Check whether a user can join a room without an invite.
-
-        When joining a room with restricted joined rules (as defined in MSC3083),
-        the membership of spaces must be checked during join.
-
-        Args:
-            state_ids: The state of the room as it currently is.
-            room_version: The room version of the room being joined.
-            user_id: The user joining the room.
-
-        Returns:
-            True if the user can join the room, false otherwise.
-        """
-        # This only applies to room versions which support the new join rule.
-        if not room_version.msc3083_join_rules:
-            return True
-
-        # If there's no join rule, then it defaults to public (so this doesn't apply).
-        join_rules_event_id = state_ids.get((EventTypes.JoinRules, ""), None)
-        if not join_rules_event_id:
-            return True
-
-        # If the join rule is not restricted, this doesn't apply.
-        join_rules_event = await self.store.get_event(join_rules_event_id)
-        if join_rules_event.content.get("join_rule") != JoinRules.MSC3083_RESTRICTED:
-            return True
-
-        # If allowed is of the wrong form, then only allow invited users.
-        allowed_spaces = join_rules_event.content.get("allow", [])
-        if not isinstance(allowed_spaces, list):
-            return False
-
-        # Get the list of joined rooms and see if there's an overlap.
-        joined_rooms = await self.store.get_rooms_for_user(user_id)
-
-        # Pull out the other room IDs, invalid data gets filtered.
-        for space in allowed_spaces:
-            if not isinstance(space, dict):
-                continue
-
-            space_id = space.get("space")
-            if not isinstance(space_id, str):
-                continue
-
-            # The user was joined to one of the spaces specified, they can join
-            # this room!
-            if space_id in joined_rooms:
-                return True
-
-        # The user was not in any of the required spaces.
-        return False
-
     async def _local_membership_update(
         self,
         requester: Requester,
@@ -302,7 +246,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             if (
                 newly_joined
                 and not user_is_invited
-                and not await self._can_join_without_invite(
+                and not await self.event_auth_handler.can_join_without_invite(
                     prev_state_ids, event.room_version, user_id
                 )
             ):