Merge commit 'de119063f' into anoa/dinsic_release_1_18_x

* commit 'de119063f': (31 commits)
  Convert room list handler to async/await. (#7912)
  Element CSS and logo in email templates (#7919)
  Lint the contrib/ directory in CI and linting scripts, add synctl to linting script (#7914)
  Remove unused code from synapse.logging.utils. (#7897)
  Fix a typo in the sample config. (#7890)
  Fix deprecation warning: import ABC from collections.abc (#7892)
  Change sample config's postgres user to synapse_user (#7889)
  Fix deprecation warning due to invalid escape sequences (#7895)
  Remove Ubuntu Eoan that is now EOL (#7888)
  Fix the trace function for async functions. (#7872)
  Add help for creating a user via docker (#7885)
  Switch to Debian:Slim from Alpine for the docker image (#7839)
  Stop using 'device_max_stream_id' (#7882)
  Fix TypeError in synapse.notifier (#7880)
  Add a default limit (of 100) to get/sync operations. (#7858)
  Change "unknown room ver" logging to warning. (#7881)
  Convert device handler to async/await (#7871)
  Convert synapse.app to async/await. (#7868)
  Convert _base, profile, and _receipts handlers to async/await (#7860)
  Add admin endpoint to get members in a room. (#7842)
  ...

1 files changed, 14 insertions, 3 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py

index 52499c679d..1178af6920 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -19,7 +19,7 @@
 
 import itertools
 import logging
-from collections import Container
+from collections.abc import Container
 from http import HTTPStatus
 from typing import Dict, Iterable, List, Optional, Sequence, Tuple, Union
 
@@ -44,6 +44,7 @@ from synapse.api.errors import (
     FederationDeniedError,
     FederationError,
     HttpResponseException,
+    NotFoundError,
     RequestSendFailed,
     SynapseError,
 )
@@ -1442,10 +1443,20 @@ class FederationHandler(BaseHandler):
             )
             raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
 
-        event_content = {"membership": Membership.JOIN}
-
+        # checking the room version will check that we've actually heard of the room
+        # (and return a 404 otherwise)
         room_version = await self.store.get_room_version_id(room_id)
 
+        # now check that we are *still* in the room
+        is_in_room = await self.auth.check_host_in_room(room_id, self.server_name)
+        if not is_in_room:
+            logger.info(
+                "Got /make_join request for room %s we are no longer in", room_id,
+            )
+            raise NotFoundError("Not an active room on this server")
+
+        event_content = {"membership": Membership.JOIN}
+
         builder = self.event_builder_factory.new(
             room_version,
             {