Modify the auth rules and redaction rules for aliases.

changelog.d/7037.feature

@@ -0,0 +1 @@
+Implement updated authorization rules and redaction rules for aliases events, from [MSC2261](https://github.com/matrix-org/matrix-doc/pull/2261) and [MSC2432](https://github.com/matrix-org/matrix-doc/pull/2432).

synapse/api/room_versions.py

@@ -57,7 +57,7 @@ class RoomVersion(object):
     state_res = attr.ib()  # int; one of the StateResolutionVersions
     enforce_key_validity = attr.ib()  # bool
 
-    # bool: before MSC2260, anyone was allowed to send an aliases event
+    # bool: before MSC2261/MSC2432, m.room.aliases had special auth rules and redaction rules
     special_case_aliases_auth = attr.ib(type=bool, default=False)
 
 
@@ -102,12 +102,13 @@ class RoomVersions(object):
         enforce_key_validity=True,
         special_case_aliases_auth=True,
     )
-    MSC2260_DEV = RoomVersion(
-        "org.matrix.msc2260",
+    MSC2432_DEV = RoomVersion(
+        "org.matrix.msc2432",
         RoomDisposition.UNSTABLE,
         EventFormatVersions.V3,
         StateResolutionVersions.V2,
         enforce_key_validity=True,
+        special_case_aliases_auth=True,
     )
 
 
@@ -119,6 +120,6 @@ class RoomVersions(object):
         RoomVersions.V3,
         RoomVersions.V4,
         RoomVersions.V5,
-        RoomVersions.MSC2260_DEV,
+        RoomVersions.MSC2432_DEV,
     )
 }  # type: Dict[str, RoomVersion]

synapse/crypto/event_signing.py

@@ -140,7 +140,7 @@ def compute_event_signature(
     Returns:
         a dictionary in the same format of an event's signatures field.
     """
-    redact_json = prune_event_dict(event_dict)
+    redact_json = prune_event_dict(room_version, event_dict)
     redact_json.pop("age_ts", None)
     redact_json.pop("unsigned", None)
     if logger.isEnabledFor(logging.DEBUG):

synapse/event_auth.py

@@ -137,7 +137,7 @@ def check(
             raise AuthError(403, "This room has been marked as unfederatable.")
 
     # 4. If type is m.room.aliases
-    if event.type == EventTypes.Aliases:
+    if event.type == EventTypes.Aliases and room_version_obj.special_case_aliases_auth:
         # 4a. If event has no state_key, reject
         if not event.is_state():
             raise AuthError(403, "Alias event must be a state event")
@@ -152,10 +152,8 @@ def check(
             )
 
         # 4c. Otherwise, allow.
-        # This is removed by https://github.com/matrix-org/matrix-doc/pull/2260
-        if room_version_obj.special_case_aliases_auth:
-            logger.debug("Allowing! %s", event)
-            return
+        logger.debug("Allowing! %s", event)
+        return
 
     if logger.isEnabledFor(logging.DEBUG):
         logger.debug("Auth events: %s", [a.event_id for a in auth_events.values()])

synapse/events/utils.py

@@ -23,6 +23,7 @@
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.room_versions import RoomVersion
 from synapse.util.async_helpers import yieldable_gather_results
 
 from . import EventBase
@@ -43,7 +44,7 @@ def prune_event(event: EventBase) -> EventBase:
     the user has specified, but we do want to keep necessary information like
     type, state_key etc.
     """
-    pruned_event_dict = prune_event_dict(event.get_dict())
+    pruned_event_dict = prune_event_dict(event.room_version, event.get_dict())
 
     from . import make_event_from_dict
 
@@ -57,15 +58,12 @@ def prune_event(event: EventBase) -> EventBase:
     return pruned_event
 
 
-def prune_event_dict(event_dict):
+def prune_event_dict(room_version: RoomVersion, event_dict: dict) -> dict:
     """Redacts the event_dict in the same way as `prune_event`, except it
     operates on dicts rather than event objects
 
-    Args:
-        event_dict (dict)
-
     Returns:
-        dict: A copy of the pruned event dict
+        A copy of the pruned event dict
     """
 
     allowed_keys = [
@@ -112,7 +110,7 @@ def add_fields(*fields):
             "kick",
             "redact",
         )
-    elif event_type == EventTypes.Aliases:
+    elif event_type == EventTypes.Aliases and room_version.special_case_aliases_auth:
         add_fields("aliases")
     elif event_type == EventTypes.RoomHistoryVisibility:
         add_fields("history_visibility")

synapse/storage/data_stores/main/events.py

@@ -1168,7 +1168,11 @@ async def _censor_redactions(self):
                 and original_event.internal_metadata.is_redacted()
             ):
                 # Redaction was allowed
-                pruned_json = encode_json(prune_event_dict(original_event.get_dict()))
+                pruned_json = encode_json(
+                    prune_event_dict(
+                        original_event.room_version, original_event.get_dict()
+                    )
+                )
             else:
                 # Redaction wasn't allowed
                 pruned_json = None
@@ -1929,7 +1933,9 @@ def delete_expired_event_txn(txn):
                 return
 
             # Prune the event's dict then convert it to JSON.
-            pruned_json = encode_json(prune_event_dict(event.get_dict()))
+            pruned_json = encode_json(
+                prune_event_dict(event.room_version, event.get_dict())
+            )
 
             # Update the event_json table to replace the event's JSON with the pruned
             # JSON.