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=False,
     )
 
 
@@ -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.

tests/events/test_utils.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+from synapse.api.room_versions import RoomVersions
 from synapse.events import make_event_from_dict
 from synapse.events.utils import (
     copy_power_levels_contents,
@@ -36,9 +37,9 @@ class PruneEventTestCase(unittest.TestCase):
     """ Asserts that a new event constructed with `evdict` will look like
     `matchdict` when it is redacted. """
 
-    def run_test(self, evdict, matchdict):
+    def run_test(self, evdict, matchdict, **kwargs):
         self.assertEquals(
-            prune_event(make_event_from_dict(evdict)).get_dict(), matchdict
+            prune_event(make_event_from_dict(evdict, **kwargs)).get_dict(), matchdict
         )
 
     def test_minimal(self):
@@ -128,6 +129,36 @@ def test_content(self):
             },
         )
 
+    def test_alias_event(self):
+        """Alias events have special behavior up through room version 6."""
+        self.run_test(
+            {
+                "type": "m.room.aliases",
+                "event_id": "$test:domain",
+                "content": {"aliases": ["test"]},
+            },
+            {
+                "type": "m.room.aliases",
+                "event_id": "$test:domain",
+                "content": {"aliases": ["test"]},
+                "signatures": {},
+                "unsigned": {},
+            },
+        )
+
+    def test_msc2432_alias_event(self):
+        """After MSC2432, alias events have no special behavior."""
+        self.run_test(
+            {"type": "m.room.aliases", "content": {"aliases": ["test"]}},
+            {
+                "type": "m.room.aliases",
+                "content": {},
+                "signatures": {},
+                "unsigned": {},
+            },
+            room_version=RoomVersions.MSC2432_DEV,
+        )
+
 
 class SerializeEventTestCase(unittest.TestCase):
     def serialize(self, ev, fields):

tests/test_event_auth.py

@@ -19,6 +19,7 @@
 from synapse.api.errors import AuthError
 from synapse.api.room_versions import RoomVersions
 from synapse.events import make_event_from_dict
+from synapse.types import get_domain_from_id
 
 
 class EventAuthTestCase(unittest.TestCase):
@@ -51,7 +52,7 @@ def test_random_users_cannot_send_state_before_first_pl(self):
             _random_state_event(joiner),
             auth_events,
             do_sig_check=False,
-        ),
+        )
 
     def test_state_default_level(self):
         """
@@ -87,6 +88,83 @@ def test_state_default_level(self):
             RoomVersions.V1, _random_state_event(king), auth_events, do_sig_check=False,
         )
 
+    def test_alias_event(self):
+        """Alias events have special behavior up through room version 6."""
+        creator = "@creator:example.com"
+        other = "@other:example.com"
+        auth_events = {
+            ("m.room.create", ""): _create_event(creator),
+            ("m.room.member", creator): _join_event(creator),
+        }
+
+        # creator should be able to send aliases
+        event_auth.check(
+            RoomVersions.V1, _alias_event(creator), auth_events, do_sig_check=False,
+        )
+
+        # Reject an event with no state key.
+        with self.assertRaises(AuthError):
+            event_auth.check(
+                RoomVersions.V1,
+                _alias_event(creator, state_key=""),
+                auth_events,
+                do_sig_check=False,
+            )
+
+        # If the domain of the sender does not match the state key, reject.
+        with self.assertRaises(AuthError):
+            event_auth.check(
+                RoomVersions.V1,
+                _alias_event(creator, state_key="test.com"),
+                auth_events,
+                do_sig_check=False,
+            )
+
+        # Note that the member does *not* need to be in the room.
+        event_auth.check(
+            RoomVersions.V1, _alias_event(other), auth_events, do_sig_check=False,
+        )
+
+    def test_msc2432_alias_event(self):
+        """After MSC2432, alias events have no special behavior."""
+        creator = "@creator:example.com"
+        other = "@other:example.com"
+        auth_events = {
+            ("m.room.create", ""): _create_event(creator),
+            ("m.room.member", creator): _join_event(creator),
+        }
+
+        # creator should be able to send aliases
+        event_auth.check(
+            RoomVersions.MSC2432_DEV,
+            _alias_event(creator),
+            auth_events,
+            do_sig_check=False,
+        )
+
+        # No particular checks are done on the state key.
+        event_auth.check(
+            RoomVersions.MSC2432_DEV,
+            _alias_event(creator, state_key=""),
+            auth_events,
+            do_sig_check=False,
+        )
+        event_auth.check(
+            RoomVersions.MSC2432_DEV,
+            _alias_event(creator, state_key="test.com"),
+            auth_events,
+            do_sig_check=False,
+        )
+
+        # Per standard auth rules, the member must be in the room.
+        with self.assertRaises(AuthError):
+            event_auth.check(
+                RoomVersions.MSC2432_DEV,
+                _alias_event(other),
+                auth_events,
+                do_sig_check=False,
+            )
+
 
 # helpers for making events
 
@@ -131,6 +209,19 @@ def _power_levels_event(sender, content):
     )
 
 
+def _alias_event(sender, **kwargs):
+    data = {
+        "room_id": TEST_ROOM_ID,
+        "event_id": _get_event_id(),
+        "type": "m.room.aliases",
+        "sender": sender,
+        "state_key": get_domain_from_id(sender),
+        "content": {"aliases": []},
+    }
+    data.update(**kwargs)
+    return make_event_from_dict(data)
+
+
 def _random_state_event(sender):
     return make_event_from_dict(
         {