Beware of non-empty state_keys on special events

synapse/api/constants.py

@@ -132,6 +132,23 @@ class EventTypes:
     CallInvite: Final = "m.call.invite"
 
 
+ZERO_LENGTH_STATE_KEY_EVENT_TYPES = {
+    EventTypes.CanonicalAlias,
+    EventTypes.Create,
+    EventTypes.JoinRules,
+    EventTypes.PowerLevels,
+    EventTypes.Name,
+    EventTypes.Topic,
+    EventTypes.RoomAvatar,
+    EventTypes.Pinned,
+    EventTypes.RoomEncryption,
+    EventTypes.RoomHistoryVisibility,
+    EventTypes.GuestAccess,
+    EventTypes.ServerACL,
+    EventTypes.Tombstone,
+}
+
+
 class ToDeviceEventTypes:
     RoomKeyRequest: Final = "m.room_key_request"
 

synapse/event_auth.py

@@ -46,6 +46,7 @@ from unpaddedbase64 import decode_base64
 
 from synapse.api.constants import (
     MAX_PDU_SIZE,
+    ZERO_LENGTH_STATE_KEY_EVENT_TYPES,
     EventContentFields,
     EventTypes,
     JoinRules,
@@ -794,6 +795,7 @@ def get_send_level(
                 state_key == msc_3779_sender
                 or state_key.startswith(msc_3779_sender + "_")
             )
+            and etype not in ZERO_LENGTH_STATE_KEY_EVENT_TYPES
         )
         if state_key is not None and not is_owned_state_event:
             send_level = power_levels_content.get("state_default", 50)