Support MSC3757: Restricting who can overwrite a state event

changelog.d/17513.feature

@@ -0,0 +1 @@
+Add implementation of restricting who can overwrite a state event as proposed by [MSC3757](https://github.com/matrix-org/matrix-spec-proposals/pull/3757).

synapse/api/room_versions.py

@@ -107,6 +107,8 @@ class RoomVersion:
     # support the flag. Unknown flags are ignored by the evaluator, making conditions
     # fail if used.
     msc3931_push_features: Tuple[str, ...]  # values from PushRuleRoomFlag
+    # MSC3757: Restricting who can overwrite a state event
+    msc3757_enabled: bool
 
 
 class RoomVersions:
@@ -128,6 +130,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V2 = RoomVersion(
         "2",
@@ -147,6 +150,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V3 = RoomVersion(
         "3",
@@ -166,6 +170,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V4 = RoomVersion(
         "4",
@@ -185,6 +190,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V5 = RoomVersion(
         "5",
@@ -204,6 +210,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V6 = RoomVersion(
         "6",
@@ -223,6 +230,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V7 = RoomVersion(
         "7",
@@ -242,6 +250,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V8 = RoomVersion(
         "8",
@@ -261,6 +270,7 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     V9 = RoomVersion(
         "9",
@@ -280,6 +290,28 @@ class RoomVersions:
         knock_restricted_join_rule=False,
         enforce_int_power_levels=False,
         msc3931_push_features=(),
+        msc3757_enabled=False,
+    )
+    MSC3757v9 = RoomVersion(
+        # MSC3757 (Restricting who can overwrite a state event) based on room version "9"
+        "org.matrix.msc3757.9",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V4_PLUS,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=False,
+        updated_redaction_rules=False,
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=False,
+        enforce_int_power_levels=False,
+        msc3931_push_features=(),
+        msc3757_enabled=True,
     )
     V10 = RoomVersion(
         "10",
@@ -299,6 +331,7 @@ class RoomVersions:
         knock_restricted_join_rule=True,
         enforce_int_power_levels=True,
         msc3931_push_features=(),
+        msc3757_enabled=False,
     )
     MSC1767v10 = RoomVersion(
         # MSC1767 (Extensible Events) based on room version "10"
@@ -319,6 +352,28 @@ class RoomVersions:
         knock_restricted_join_rule=True,
         enforce_int_power_levels=True,
         msc3931_push_features=(PushRuleRoomFlag.EXTENSIBLE_EVENTS,),
+        msc3757_enabled=False,
+    )
+    MSC3757v10 = RoomVersion(
+        # MSC3757 (Restricting who can overwrite a state event) based on room version "10"
+        "org.matrix.msc3757.10",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V4_PLUS,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=False,
+        updated_redaction_rules=False,
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=True,
+        enforce_int_power_levels=True,
+        msc3931_push_features=(),
+        msc3757_enabled=True,
     )
     V11 = RoomVersion(
         "11",
@@ -338,6 +393,28 @@ class RoomVersions:
         knock_restricted_join_rule=True,
         enforce_int_power_levels=True,
         msc3931_push_features=(),
+        msc3757_enabled=False,
+    )
+    MSC3757v11 = RoomVersion(
+        # MSC3757 (Restricting who can overwrite a state event) based on room version "11"
+        "org.matrix.msc3757.11",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.ROOM_V4_PLUS,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=True,  # Used by MSC3820
+        updated_redaction_rules=True,  # Used by MSC3820
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=True,
+        enforce_int_power_levels=True,
+        msc3931_push_features=(),
+        msc3757_enabled=True,
     )
 
 
@@ -355,6 +432,9 @@ class RoomVersions:
         RoomVersions.V9,
         RoomVersions.V10,
         RoomVersions.V11,
+        RoomVersions.MSC3757v9,
+        RoomVersions.MSC3757v10,
+        RoomVersions.MSC3757v11,
     )
 }
 

synapse/event_auth.py

@@ -386,8 +386,10 @@ def check_state_dependent_auth_rules(
     RoomVersions.V7,
     RoomVersions.V8,
     RoomVersions.V9,
+    RoomVersions.MSC3757v9,
     RoomVersions.V10,
     RoomVersions.MSC1767v10,
+    RoomVersions.MSC3757v10,
 }
 
 
@@ -790,9 +792,10 @@ def get_send_level(
 
 
 def _can_send_event(event: "EventBase", auth_events: StateMap["EventBase"]) -> bool:
+    state_key = event.get_state_key()
     power_levels_event = get_power_level_event(auth_events)
 
-    send_level = get_send_level(event.type, event.get("state_key"), power_levels_event)
+    send_level = get_send_level(event.type, state_key, power_levels_event)
     user_level = get_user_power_level(event.user_id, auth_events)
 
     if user_level < send_level:
@@ -803,11 +806,30 @@ def _can_send_event(event: "EventBase", auth_events: StateMap["EventBase"]) -> b
             errcode=Codes.INSUFFICIENT_POWER,
         )
 
-    # Check state_key
-    if hasattr(event, "state_key"):
-        if event.state_key.startswith("@"):
-            if event.state_key != event.user_id:
-                raise AuthError(403, "You are not allowed to set others state")
+    if (
+        state_key is not None
+        and state_key.startswith("@")
+        and state_key != event.user_id
+    ):
+        if event.room_version.msc3757_enabled:
+            state_key_user_id: Union[str, None] = None
+            colon_idx = state_key.find(":", 1)
+            if colon_idx != -1:
+                suffix_idx = state_key.find("_", colon_idx + 1)
+                state_key_user_id = (
+                    state_key[:suffix_idx] if suffix_idx != -1 else state_key
+                )
+            if state_key_user_id is None or not UserID.is_valid(state_key_user_id):
+                raise SynapseError(
+                    400,
+                    "State key neither equals a valid user ID, nor starts with one plus an underscore",
+                    errcode=Codes.BAD_JSON,
+                )
+            if state_key_user_id == event.user_id or user_level > get_user_power_level(
+                state_key_user_id, auth_events
+            ):
+                return True
+        raise AuthError(403, "You are not allowed to set others state")
 
     return True
 

tests/rest/client/test_power_levels.py

@@ -19,10 +19,14 @@
 #
 #
 from http import HTTPStatus
+from typing import Optional
+
+from parameterized import parameterized_class
 
 from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.errors import Codes
+from synapse.api.room_versions import RoomVersions
 from synapse.events.utils import CANONICALJSON_MAX_INT, CANONICALJSON_MIN_INT
 from synapse.rest import admin
 from synapse.rest.client import login, room, sync
@@ -32,9 +36,10 @@
 from tests.unittest import HomeserverTestCase
 
 
-class PowerLevelsTestCase(HomeserverTestCase):
+class BasePowerLevelsTestCase(HomeserverTestCase):
     """Tests that power levels are enforced in various situations"""
 
+    room_version: Optional[str] = None
     servlets = [
         admin.register_servlets,
         room.register_servlets,
@@ -58,7 +63,9 @@ def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
 
         # Create a room
         self.room_id = self.helper.create_room_as(
-            self.admin_user_id, tok=self.admin_access_token
+            self.admin_user_id,
+            tok=self.admin_access_token,
+            room_version=self.room_version,
         )
 
         # Invite the other users
@@ -100,6 +107,8 @@ def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
             tok=self.admin_access_token,
         )
 
+
+class PowerLevelsTestCase(BasePowerLevelsTestCase):
     def test_non_admins_cannot_enable_room_encryption(self) -> None:
         # have the mod try to enable room encryption
         self.helper.send_state(
@@ -149,7 +158,9 @@ def test_non_admins_cannot_send_server_acl(self) -> None:
     def test_non_admins_cannot_tombstone_room(self) -> None:
         # Create another room that will serve as our "upgraded room"
         self.upgraded_room_id = self.helper.create_room_as(
-            self.admin_user_id, tok=self.admin_access_token
+            self.admin_user_id,
+            tok=self.admin_access_token,
+            room_version=self.room_version,
         )
 
         # have the mod try to send a tombstone event
@@ -203,7 +214,9 @@ def test_admins_can_send_server_acl(self) -> None:
     def test_admins_can_tombstone_room(self) -> None:
         # Create another room that will serve as our "upgraded room"
         self.upgraded_room_id = self.helper.create_room_as(
-            self.admin_user_id, tok=self.admin_access_token
+            self.admin_user_id,
+            tok=self.admin_access_token,
+            room_version=self.room_version,
         )
 
         # have the admin try to send a tombstone event
@@ -293,3 +306,76 @@ def test_cannot_set_unsafe_small_power_levels(self) -> None:
             Codes.BAD_JSON,
             body,
         )
+
+
+@parameterized_class(
+    ("room_version", "allows_owned_state"),
+    [
+        (rv.identifier, rv.msc3757_enabled)
+        for rv in [
+            RoomVersions.V10,
+            RoomVersions.MSC3757v10,
+        ]
+    ],
+)
+class MSC3757PowerLevelsTestCase(BasePowerLevelsTestCase):
+    _STATE_EVENT_TYPE = "org.matrix.msc3757.test"
+
+    allows_owned_state: bool
+
+    def test_can_set_own_state(self) -> None:
+        self.helper.send_state(
+            self.room_id,
+            self._STATE_EVENT_TYPE,
+            {},
+            state_key=f"{self.mod_user_id}_suffix",
+            tok=self.mod_access_token,
+            expect_code=(
+                HTTPStatus.OK if self.allows_owned_state else HTTPStatus.FORBIDDEN
+            ),
+        )
+
+    def test_admins_can_set_others_state(self) -> None:
+        self.helper.send_state(
+            self.room_id,
+            self._STATE_EVENT_TYPE,
+            {},
+            state_key=f"{self.mod_user_id}_suffix",
+            tok=self.admin_access_token,
+            expect_code=(
+                HTTPStatus.OK if self.allows_owned_state else HTTPStatus.FORBIDDEN
+            ),
+        )
+
+    def test_non_admins_cannot_set_others_state(self) -> None:
+        self.helper.send_state(
+            self.room_id,
+            self._STATE_EVENT_TYPE,
+            {},
+            state_key=f"{self.admin_user_id}_suffix",
+            tok=self.mod_access_token,
+            expect_code=HTTPStatus.FORBIDDEN,
+        )
+
+    def test_cannot_set_state_with_non_user_id_key(self) -> None:
+        if self.allows_owned_state:
+            expect_code = HTTPStatus.BAD_REQUEST
+            errcode = Codes.BAD_JSON
+        else:
+            expect_code = HTTPStatus.FORBIDDEN
+            errcode = Codes.FORBIDDEN
+
+        body = self.helper.send_state(
+            self.room_id,
+            self._STATE_EVENT_TYPE,
+            {},
+            state_key=f"{self.admin_user_id}@suffix",
+            tok=self.admin_access_token,
+            expect_code=expect_code,
+        )
+
+        self.assertEqual(
+            body["errcode"],
+            errcode,
+            body,
+        )