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-rw-r--r--synapse/api/auth.py28
-rw-r--r--synapse/api/errors.py3
-rw-r--r--synapse/config/key.py6
-rw-r--r--synapse/config/server.py41
-rw-r--r--synapse/crypto/context_factory.py8
-rw-r--r--synapse/federation/federation_client.py36
-rw-r--r--synapse/federation/transport/client.py31
-rw-r--r--synapse/handlers/auth.py2
-rw-r--r--synapse/handlers/directory.py1
-rw-r--r--synapse/handlers/e2e_keys.py7
-rw-r--r--synapse/handlers/federation.py25
-rw-r--r--synapse/handlers/room_member.py84
-rw-r--r--synapse/http/federation/matrix_federation_agent.py16
-rw-r--r--synapse/push/baserules.py8
-rw-r--r--synapse/storage/roommember.py2
-rw-r--r--synapse/storage/schema/delta/56/current_state_events_membership.sql3
-rw-r--r--synapse/storage/schema/delta/56/current_state_events_membership_mk2.sql24
17 files changed, 262 insertions, 63 deletions
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 351790cca4..179644852a 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -410,21 +410,16 @@ class Auth(object):
         try:
             user_id = self.get_user_id_from_macaroon(macaroon)
 
-            has_expiry = False
             guest = False
             for caveat in macaroon.caveats:
-                if caveat.caveat_id.startswith("time "):
-                    has_expiry = True
-                elif caveat.caveat_id == "guest = true":
+                if caveat.caveat_id == "guest = true":
                     guest = True
 
-            self.validate_macaroon(
-                macaroon, rights, self.hs.config.expire_access_token, user_id=user_id
-            )
+            self.validate_macaroon(macaroon, rights, user_id=user_id)
         except (pymacaroons.exceptions.MacaroonException, TypeError, ValueError):
             raise InvalidClientTokenError("Invalid macaroon passed.")
 
-        if not has_expiry and rights == "access":
+        if rights == "access":
             self.token_cache[token] = (user_id, guest)
 
         return user_id, guest
@@ -450,7 +445,7 @@ class Auth(object):
                 return caveat.caveat_id[len(user_prefix) :]
         raise InvalidClientTokenError("No user caveat in macaroon")
 
-    def validate_macaroon(self, macaroon, type_string, verify_expiry, user_id):
+    def validate_macaroon(self, macaroon, type_string, user_id):
         """
         validate that a Macaroon is understood by and was signed by this server.
 
@@ -458,7 +453,6 @@ class Auth(object):
             macaroon(pymacaroons.Macaroon): The macaroon to validate
             type_string(str): The kind of token required (e.g. "access",
                               "delete_pusher")
-            verify_expiry(bool): Whether to verify whether the macaroon has expired.
             user_id (str): The user_id required
         """
         v = pymacaroons.Verifier()
@@ -471,19 +465,7 @@ class Auth(object):
         v.satisfy_exact("type = " + type_string)
         v.satisfy_exact("user_id = %s" % user_id)
         v.satisfy_exact("guest = true")
-
-        # verify_expiry should really always be True, but there exist access
-        # tokens in the wild which expire when they should not, so we can't
-        # enforce expiry yet (so we have to allow any caveat starting with
-        # 'time < ' in access tokens).
-        #
-        # On the other hand, short-term login tokens (as used by CAS login, for
-        # example) have an expiry time which we do want to enforce.
-
-        if verify_expiry:
-            v.satisfy_general(self._verify_expiry)
-        else:
-            v.satisfy_general(lambda c: c.startswith("time < "))
+        v.satisfy_general(self._verify_expiry)
 
         # access_tokens include a nonce for uniqueness: any value is acceptable
         v.satisfy_general(lambda c: c.startswith("nonce = "))
diff --git a/synapse/api/errors.py b/synapse/api/errors.py
index ad3e262041..cf1ebf1af2 100644
--- a/synapse/api/errors.py
+++ b/synapse/api/errors.py
@@ -61,6 +61,7 @@ class Codes(object):
     INCOMPATIBLE_ROOM_VERSION = "M_INCOMPATIBLE_ROOM_VERSION"
     WRONG_ROOM_KEYS_VERSION = "M_WRONG_ROOM_KEYS_VERSION"
     EXPIRED_ACCOUNT = "ORG_MATRIX_EXPIRED_ACCOUNT"
+    USER_DEACTIVATED = "M_USER_DEACTIVATED"
 
 
 class CodeMessageException(RuntimeError):
@@ -151,7 +152,7 @@ class UserDeactivatedError(SynapseError):
             msg (str): The human-readable error message
         """
         super(UserDeactivatedError, self).__init__(
-            code=http_client.FORBIDDEN, msg=msg, errcode=Codes.UNKNOWN
+            code=http_client.FORBIDDEN, msg=msg, errcode=Codes.USER_DEACTIVATED
         )
 
 
diff --git a/synapse/config/key.py b/synapse/config/key.py
index 8fc74f9cdf..fe8386985c 100644
--- a/synapse/config/key.py
+++ b/synapse/config/key.py
@@ -116,8 +116,6 @@ class KeyConfig(Config):
             seed = bytes(self.signing_key[0])
             self.macaroon_secret_key = hashlib.sha256(seed).digest()
 
-        self.expire_access_token = config.get("expire_access_token", False)
-
         # a secret which is used to calculate HMACs for form values, to stop
         # falsification of values
         self.form_secret = config.get("form_secret", None)
@@ -144,10 +142,6 @@ class KeyConfig(Config):
         #
         %(macaroon_secret_key)s
 
-        # Used to enable access token expiration.
-        #
-        #expire_access_token: False
-
         # a secret which is used to calculate HMACs for form values, to stop
         # falsification of values. Must be specified for the User Consent
         # forms to work.
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 00170f1393..15449695d1 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -18,6 +18,7 @@
 import logging
 import os.path
 
+import attr
 from netaddr import IPSet
 
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS
@@ -38,6 +39,12 @@ DEFAULT_BIND_ADDRESSES = ["::", "0.0.0.0"]
 
 DEFAULT_ROOM_VERSION = "4"
 
+ROOM_COMPLEXITY_TOO_GREAT = (
+    "Your homeserver is unable to join rooms this large or complex. "
+    "Please speak to your server administrator, or upgrade your instance "
+    "to join this room."
+)
+
 
 class ServerConfig(Config):
     def read_config(self, config, **kwargs):
@@ -247,6 +254,23 @@ class ServerConfig(Config):
 
         self.gc_thresholds = read_gc_thresholds(config.get("gc_thresholds", None))
 
+        @attr.s
+        class LimitRemoteRoomsConfig(object):
+            enabled = attr.ib(
+                validator=attr.validators.instance_of(bool), default=False
+            )
+            complexity = attr.ib(
+                validator=attr.validators.instance_of((int, float)), default=1.0
+            )
+            complexity_error = attr.ib(
+                validator=attr.validators.instance_of(str),
+                default=ROOM_COMPLEXITY_TOO_GREAT,
+            )
+
+        self.limit_remote_rooms = LimitRemoteRoomsConfig(
+            **config.get("limit_remote_rooms", {})
+        )
+
         bind_port = config.get("bind_port")
         if bind_port:
             if config.get("no_tls", False):
@@ -617,6 +641,23 @@ class ServerConfig(Config):
         # Used by phonehome stats to group together related servers.
         #server_context: context
 
+        # Resource-constrained Homeserver Settings
+        #
+        # If limit_remote_rooms.enabled is True, the room complexity will be
+        # checked before a user joins a new remote room. If it is above
+        # limit_remote_rooms.complexity, it will disallow joining or
+        # instantly leave.
+        #
+        # limit_remote_rooms.complexity_error can be set to customise the text
+        # displayed to the user when a room above the complexity threshold has
+        # its join cancelled.
+        #
+        # Uncomment the below lines to enable:
+        #limit_remote_rooms:
+        #  enabled: True
+        #  complexity: 1.0
+        #  complexity_error: "This room is too complex."
+
         # Whether to require a user to be in the room to add an alias to it.
         # Defaults to 'true'.
         #
diff --git a/synapse/crypto/context_factory.py b/synapse/crypto/context_factory.py
index 4f48e8e88d..06e63a96b5 100644
--- a/synapse/crypto/context_factory.py
+++ b/synapse/crypto/context_factory.py
@@ -31,6 +31,7 @@ from twisted.internet.ssl import (
     platformTrust,
 )
 from twisted.python.failure import Failure
+from twisted.web.iweb import IPolicyForHTTPS
 
 logger = logging.getLogger(__name__)
 
@@ -74,6 +75,7 @@ class ServerContextFactory(ContextFactory):
         return self._context
 
 
+@implementer(IPolicyForHTTPS)
 class ClientTLSOptionsFactory(object):
     """Factory for Twisted SSLClientConnectionCreators that are used to make connections
     to remote servers for federation.
@@ -146,6 +148,12 @@ class ClientTLSOptionsFactory(object):
             f = Failure()
             tls_protocol.failVerification(f)
 
+    def creatorForNetloc(self, hostname, port):
+        """Implements the IPolicyForHTTPS interace so that this can be passed
+        directly to agents.
+        """
+        return self.get_options(hostname)
+
 
 @implementer(IOpenSSLClientConnectionCreator)
 class SSLClientConnectionCreator(object):
diff --git a/synapse/federation/federation_client.py b/synapse/federation/federation_client.py
index 25ed1257f1..6e03ce21af 100644
--- a/synapse/federation/federation_client.py
+++ b/synapse/federation/federation_client.py
@@ -993,3 +993,39 @@ class FederationClient(FederationBase):
                 )
 
         raise RuntimeError("Failed to send to any server.")
+
+    @defer.inlineCallbacks
+    def get_room_complexity(self, destination, room_id):
+        """
+        Fetch the complexity of a remote room from another server.
+
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+
+        Returns:
+            Deferred[dict] or Deferred[None]: Dict contains the complexity
+            metric versions, while None means we could not fetch the complexity.
+        """
+        try:
+            complexity = yield self.transport_layer.get_room_complexity(
+                destination=destination, room_id=room_id
+            )
+            defer.returnValue(complexity)
+        except CodeMessageException as e:
+            # We didn't manage to get it -- probably a 404. We are okay if other
+            # servers don't give it to us.
+            logger.debug(
+                "Failed to fetch room complexity via %s for %s, got a %d",
+                destination,
+                room_id,
+                e.code,
+            )
+        except Exception:
+            logger.exception(
+                "Failed to fetch room complexity via %s for %s", destination, room_id
+            )
+
+        # If we don't manage to find it, return None. It's not an error if a
+        # server doesn't give it to us.
+        defer.returnValue(None)
diff --git a/synapse/federation/transport/client.py b/synapse/federation/transport/client.py
index 2a6709ff48..0cea0d2a10 100644
--- a/synapse/federation/transport/client.py
+++ b/synapse/federation/transport/client.py
@@ -21,7 +21,11 @@ from six.moves import urllib
 from twisted.internet import defer
 
 from synapse.api.constants import Membership
-from synapse.api.urls import FEDERATION_V1_PREFIX, FEDERATION_V2_PREFIX
+from synapse.api.urls import (
+    FEDERATION_UNSTABLE_PREFIX,
+    FEDERATION_V1_PREFIX,
+    FEDERATION_V2_PREFIX,
+)
 from synapse.logging.utils import log_function
 
 logger = logging.getLogger(__name__)
@@ -935,6 +939,23 @@ class TransportLayerClient(object):
             destination=destination, path=path, data=content, ignore_backoff=True
         )
 
+    def get_room_complexity(self, destination, room_id):
+        """
+        Args:
+            destination (str): The remote server
+            room_id (str): The room ID to ask about.
+        """
+        path = _create_path(FEDERATION_UNSTABLE_PREFIX, "/rooms/%s/complexity", room_id)
+
+        return self.client.get_json(destination=destination, path=path)
+
+
+def _create_path(federation_prefix, path, *args):
+    """
+    Ensures that all args are url encoded.
+    """
+    return federation_prefix + path % tuple(urllib.parse.quote(arg, "") for arg in args)
+
 
 def _create_v1_path(path, *args):
     """Creates a path against V1 federation API from the path template and
@@ -951,9 +972,7 @@ def _create_v1_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V1_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V1_PREFIX, path, *args)
 
 
 def _create_v2_path(path, *args):
@@ -971,6 +990,4 @@ def _create_v2_path(path, *args):
     Returns:
         str
     """
-    return FEDERATION_V2_PREFIX + path % tuple(
-        urllib.parse.quote(arg, "") for arg in args
-    )
+    return _create_path(FEDERATION_V2_PREFIX, path, *args)
diff --git a/synapse/handlers/auth.py b/synapse/handlers/auth.py
index 05be5b7c48..0f3ebf7ef8 100644
--- a/synapse/handlers/auth.py
+++ b/synapse/handlers/auth.py
@@ -860,7 +860,7 @@ class AuthHandler(BaseHandler):
         try:
             macaroon = pymacaroons.Macaroon.deserialize(login_token)
             user_id = auth_api.get_user_id_from_macaroon(macaroon)
-            auth_api.validate_macaroon(macaroon, "login", True, user_id)
+            auth_api.validate_macaroon(macaroon, "login", user_id)
         except Exception:
             raise AuthError(403, "Invalid token", errcode=Codes.FORBIDDEN)
         self.ratelimit_login_per_account(user_id)
diff --git a/synapse/handlers/directory.py b/synapse/handlers/directory.py
index 0fd423197c..526379c6f7 100644
--- a/synapse/handlers/directory.py
+++ b/synapse/handlers/directory.py
@@ -278,7 +278,6 @@ class DirectoryHandler(BaseHandler):
             servers = list(servers)
 
         return {"room_id": room_id, "servers": servers}
-        return
 
     @defer.inlineCallbacks
     def on_directory_query(self, args):
diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 366a0bc68b..1f90b0d278 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -25,6 +25,7 @@ from twisted.internet import defer
 from synapse.api.errors import CodeMessageException, SynapseError
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.types import UserID, get_domain_from_id
+from synapse.util import unwrapFirstError
 from synapse.util.retryutils import NotRetryingDestination
 
 logger = logging.getLogger(__name__)
@@ -161,9 +162,7 @@ class E2eKeysHandler(object):
                         results[user_id] = {device["device_id"]: device["keys"]}
                     user_ids_updated.append(user_id)
                 except Exception as e:
-                    failures[destination] = failures.get(destination, []).append(
-                        _exception_to_failure(e)
-                    )
+                    failures[destination] = _exception_to_failure(e)
 
             if len(destination_query) == len(user_ids_updated):
                 # We've updated all the users in the query and we do not need to
@@ -194,7 +193,7 @@ class E2eKeysHandler(object):
                     for destination in remote_queries_not_in_cache
                 ],
                 consumeErrors=True,
-            )
+            ).addErrback(unwrapFirstError)
         )
 
         return {"device_keys": results, "failures": failures}
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index c70f12092a..c86903b98b 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -2799,3 +2799,28 @@ class FederationHandler(BaseHandler):
             )
         else:
             return user_joined_room(self.distributor, user, room_id)
+
+    @defer.inlineCallbacks
+    def get_room_complexity(self, remote_room_hosts, room_id):
+        """
+        Fetch the complexity of a remote room over federation.
+
+        Args:
+            remote_room_hosts (list[str]): The remote servers to ask.
+            room_id (str): The room ID to ask about.
+
+        Returns:
+            Deferred[dict] or Deferred[None]: Dict contains the complexity
+            metric versions, while None means we could not fetch the complexity.
+        """
+
+        for host in remote_room_hosts:
+            res = yield self.federation_client.get_room_complexity(host, room_id)
+
+            # We got a result, return it.
+            if res:
+                defer.returnValue(res)
+
+        # We fell off the bottom, couldn't get the complexity from anyone. Oh
+        # well.
+        defer.returnValue(None)
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index baea08ddd0..249a6d9c5d 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -26,8 +26,7 @@ from unpaddedbase64 import decode_base64
 
 from twisted.internet import defer
 
-import synapse.server
-import synapse.types
+from synapse import types
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import AuthError, Codes, HttpResponseException, SynapseError
 from synapse.types import RoomID, UserID
@@ -543,7 +542,7 @@ class RoomMemberHandler(object):
             ), "Sender (%s) must be same as requester (%s)" % (sender, requester.user)
             assert self.hs.is_mine(sender), "Sender must be our own: %s" % (sender,)
         else:
-            requester = synapse.types.create_requester(target_user)
+            requester = types.create_requester(target_user)
 
         prev_event = yield self.event_creation_handler.deduplicate_state_event(
             event, context
@@ -946,13 +945,53 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         self.distributor.declare("user_left_room")
 
     @defer.inlineCallbacks
+    def _is_remote_room_too_complex(self, room_id, remote_room_hosts):
+        """
+        Check if complexity of a remote room is too great.
+
+        Args:
+            room_id (str)
+            remote_room_hosts (list[str])
+
+        Returns: bool of whether the complexity is too great, or None
+            if unable to be fetched
+        """
+        max_complexity = self.hs.config.limit_remote_rooms.complexity
+        complexity = yield self.federation_handler.get_room_complexity(
+            remote_room_hosts, room_id
+        )
+
+        if complexity:
+            if complexity["v1"] > max_complexity:
+                return True
+            return False
+        return None
+
+    @defer.inlineCallbacks
+    def _is_local_room_too_complex(self, room_id):
+        """
+        Check if the complexity of a local room is too great.
+
+        Args:
+            room_id (str)
+
+        Returns: bool
+        """
+        max_complexity = self.hs.config.limit_remote_rooms.complexity
+        complexity = yield self.store.get_room_complexity(room_id)
+
+        if complexity["v1"] > max_complexity:
+            return True
+
+        return False
+
+    @defer.inlineCallbacks
     def _remote_join(self, requester, remote_room_hosts, room_id, user, content):
         """Implements RoomMemberHandler._remote_join
         """
         # filter ourselves out of remote_room_hosts: do_invite_join ignores it
         # and if it is the only entry we'd like to return a 404 rather than a
         # 500.
-
         remote_room_hosts = [
             host for host in remote_room_hosts if host != self.hs.hostname
         ]
@@ -960,6 +999,18 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         if len(remote_room_hosts) == 0:
             raise SynapseError(404, "No known servers")
 
+        if self.hs.config.limit_remote_rooms.enabled:
+            # Fetch the room complexity
+            too_complex = yield self._is_remote_room_too_complex(
+                room_id, remote_room_hosts
+            )
+            if too_complex is True:
+                raise SynapseError(
+                    code=400,
+                    msg=self.hs.config.limit_remote_rooms.complexity_error,
+                    errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+                )
+
         # We don't do an auth check if we are doing an invite
         # join dance for now, since we're kinda implicitly checking
         # that we are allowed to join when we decide whether or not we
@@ -969,6 +1020,31 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         )
         yield self._user_joined_room(user, room_id)
 
+        # Check the room we just joined wasn't too large, if we didn't fetch the
+        # complexity of it before.
+        if self.hs.config.limit_remote_rooms.enabled:
+            if too_complex is False:
+                # We checked, and we're under the limit.
+                return
+
+            # Check again, but with the local state events
+            too_complex = yield self._is_local_room_too_complex(room_id)
+
+            if too_complex is False:
+                # We're under the limit.
+                return
+
+            # The room is too large. Leave.
+            requester = types.create_requester(user, None, False, None)
+            yield self.update_membership(
+                requester=requester, target=user, room_id=room_id, action="leave"
+            )
+            raise SynapseError(
+                code=400,
+                msg=self.hs.config.limit_remote_rooms.complexity_error,
+                errcode=Codes.RESOURCE_LIMIT_EXCEEDED,
+            )
+
     @defer.inlineCallbacks
     def _remote_reject_invite(self, requester, remote_room_hosts, room_id, target):
         """Implements RoomMemberHandler._remote_reject_invite
diff --git a/synapse/http/federation/matrix_federation_agent.py b/synapse/http/federation/matrix_federation_agent.py
index c03ddb724f..a0d5139839 100644
--- a/synapse/http/federation/matrix_federation_agent.py
+++ b/synapse/http/federation/matrix_federation_agent.py
@@ -64,10 +64,6 @@ class MatrixFederationAgent(object):
         tls_client_options_factory (ClientTLSOptionsFactory|None):
             factory to use for fetching client tls options, or none to disable TLS.
 
-        _well_known_tls_policy (IPolicyForHTTPS|None):
-            TLS policy to use for fetching .well-known files. None to use a default
-            (browser-like) implementation.
-
         _srv_resolver (SrvResolver|None):
             SRVResolver impl to use for looking up SRV records. None to use a default
             implementation.
@@ -81,7 +77,6 @@ class MatrixFederationAgent(object):
         self,
         reactor,
         tls_client_options_factory,
-        _well_known_tls_policy=None,
         _srv_resolver=None,
         _well_known_cache=well_known_cache,
     ):
@@ -98,13 +93,12 @@ class MatrixFederationAgent(object):
         self._pool.maxPersistentPerHost = 5
         self._pool.cachedConnectionTimeout = 2 * 60
 
-        agent_args = {}
-        if _well_known_tls_policy is not None:
-            # the param is called 'contextFactory', but actually passing a
-            # contextfactory is deprecated, and it expects an IPolicyForHTTPS.
-            agent_args["contextFactory"] = _well_known_tls_policy
         _well_known_agent = RedirectAgent(
-            Agent(self._reactor, pool=self._pool, **agent_args)
+            Agent(
+                self._reactor,
+                pool=self._pool,
+                contextFactory=tls_client_options_factory,
+            )
         )
         self._well_known_agent = _well_known_agent
 
diff --git a/synapse/push/baserules.py b/synapse/push/baserules.py
index 134bf805eb..286374d0b5 100644
--- a/synapse/push/baserules.py
+++ b/synapse/push/baserules.py
@@ -245,7 +245,13 @@ BASE_APPEND_OVERRIDE_RULES = [
                 "key": "type",
                 "pattern": "m.room.tombstone",
                 "_id": "_tombstone",
-            }
+            },
+            {
+                "kind": "event_match",
+                "key": "state_key",
+                "pattern": "",
+                "_id": "_tombstone_statekey",
+            },
         ],
         "actions": ["notify", {"set_tweak": "highlight", "value": True}],
     },
diff --git a/synapse/storage/roommember.py b/synapse/storage/roommember.py
index e60409ed73..eecb276465 100644
--- a/synapse/storage/roommember.py
+++ b/synapse/storage/roommember.py
@@ -935,7 +935,7 @@ class RoomMemberStore(RoomMemberWorkerStore):
             while processed < batch_size:
                 txn.execute(
                     """
-                        SELECT MIN(room_id) FROM rooms WHERE room_id > ?
+                        SELECT MIN(room_id) FROM current_state_events WHERE room_id > ?
                     """,
                     (last_processed_room,),
                 )
diff --git a/synapse/storage/schema/delta/56/current_state_events_membership.sql b/synapse/storage/schema/delta/56/current_state_events_membership.sql
index b2e08cd85d..473018676f 100644
--- a/synapse/storage/schema/delta/56/current_state_events_membership.sql
+++ b/synapse/storage/schema/delta/56/current_state_events_membership.sql
@@ -20,6 +20,3 @@
 -- for membership events. (Will also be null for membership events until the
 -- background update job has finished).
 ALTER TABLE current_state_events ADD membership TEXT;
-
-INSERT INTO background_updates (update_name, progress_json) VALUES
-  ('current_state_events_membership', '{}');
diff --git a/synapse/storage/schema/delta/56/current_state_events_membership_mk2.sql b/synapse/storage/schema/delta/56/current_state_events_membership_mk2.sql
new file mode 100644
index 0000000000..3133d42d4a
--- /dev/null
+++ b/synapse/storage/schema/delta/56/current_state_events_membership_mk2.sql
@@ -0,0 +1,24 @@
+/* Copyright 2019 The Matrix.org Foundation C.I.C.
+ *
+ * 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.
+ */
+
+-- We add membership to current state so that we don't need to join against
+-- room_memberships, which can be surprisingly costly (we do such queries
+-- very frequently).
+-- This will be null for non-membership events and the content.membership key
+-- for membership events. (Will also be null for membership events until the
+-- background update job has finished).
+
+INSERT INTO background_updates (update_name, progress_json) VALUES
+  ('current_state_events_membership', '{}');