From 187d2837a9fc9d5b9e585f3a7f0f54f2ceac7d1b Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Mon, 17 Jun 2019 15:48:57 +0100
Subject: [PATCH 1/2] Add third party rules hook into create room

---
 synapse/events/third_party_rules.py | 27 ++++++++++++++++++++++++---
 synapse/handlers/room.py            | 25 ++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
index 9f98d51523..ee7b97ad39 100644
--- a/synapse/events/third_party_rules.py
+++ b/synapse/events/third_party_rules.py
@@ -17,8 +17,8 @@ from twisted.internet import defer
 
 
 class ThirdPartyEventRules(object):
-    """Allows server admins to provide a Python module implementing an extra set of rules
-    to apply when processing events.
+    """Allows server admins to provide a Python module implementing an extra
+    set of rules to apply when processing events.
 
     This is designed to help admins of closed federations with enforcing custom
     behaviours.
@@ -46,7 +46,7 @@ class ThirdPartyEventRules(object):
             context (synapse.events.snapshot.EventContext): The context of the event.
 
         Returns:
-            defer.Deferred(bool), True if the event should be allowed, False if not.
+            defer.Deferred[bool]: True if the event should be allowed, False if not.
         """
         if self.third_party_rules is None:
             defer.returnValue(True)
@@ -60,3 +60,24 @@ class ThirdPartyEventRules(object):
 
         ret = yield self.third_party_rules.check_event_allowed(event, state_events)
         defer.returnValue(ret)
+
+    @defer.inlineCallbacks
+    def on_create_room(self, requester, config, is_requester_admin):
+        """Intercept requests to create room to allow, deny or update the
+        request config.
+
+        Args:
+            requester (Requester)
+            config (dict): The creation config from the client.
+            is_requester_admin (bool): If the requester is an admin
+
+        Returns:
+            defer.Deferred
+        """
+
+        if self.third_party_rules is None:
+            return
+
+        yield self.third_party_rules.on_create_room(
+            requester, config, is_requester_admin
+        )
diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 4a17911a87..74793bab33 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -75,6 +75,10 @@ class RoomCreationHandler(BaseHandler):
         # linearizer to stop two upgrades happening at once
         self._upgrade_linearizer = Linearizer("room_upgrade_linearizer")
 
+        self._server_notices_mxid = hs.config.server_notices_mxid
+
+        self.third_party_event_rules = hs.get_third_party_event_rules()
+
     @defer.inlineCallbacks
     def upgrade_room(self, requester, old_room_id, new_version):
         """Replace a room with a new room with a different version
@@ -470,7 +474,26 @@ class RoomCreationHandler(BaseHandler):
 
         yield self.auth.check_auth_blocking(user_id)
 
-        if not self.spam_checker.user_may_create_room(user_id):
+        if (self._server_notices_mxid is not None and
+                requester.user.to_string() == self._server_notices_mxid):
+            # allow the server notices mxid to create rooms
+            is_requester_admin = True
+        else:
+            is_requester_admin = yield self.auth.is_server_admin(
+                requester.user,
+            )
+
+        # Check whether the third party rules allows/changes the room create
+        # request.
+        yield self.third_party_event_rules.on_create_room(
+            requester,
+            config,
+            is_requester_admin=is_requester_admin,
+        )
+
+        if not is_requester_admin and not self.spam_checker.user_may_create_room(
+            user_id,
+        ):
             raise SynapseError(403, "You are not permitted to create rooms")
 
         if ratelimit:

From 2d6308a043153b149ead23b1a6567a03ae20496b Mon Sep 17 00:00:00 2001
From: Erik Johnston <erik@matrix.org>
Date: Mon, 17 Jun 2019 15:52:15 +0100
Subject: [PATCH 2/2] Newsfile

---
 changelog.d/5474.feature | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/5474.feature

diff --git a/changelog.d/5474.feature b/changelog.d/5474.feature
new file mode 100644
index 0000000000..63d9b58734
--- /dev/null
+++ b/changelog.d/5474.feature
@@ -0,0 +1 @@
+Allow server admins to define implementations of extra rules for allowing or denying incoming events.