Handle malformed values of notification.room in power level events (#14942)

* Better test for bad values in power levels events

The previous test only checked that Synapse didn't raise an exception,
but didn't check that we had correctly interpreted the value of the
dodgy power level.

It also conflated two things: bad room notification levels, and bad user
levels. There _is_ logic for converting the latter to integers, but we
should test it separately.

* Check we ignore types that don't convert to int

* Handle `None` values in `notifications.room`

* Changelog

* Also test that bad values are rejected by event auth

* Docstring

* linter scripttttttttt

Author: David Robertson

changelog.d/14942.bugfix

@@ -0,0 +1 @@
+Fix a bug introduced in Synapse 1.68.0 where we were unable to service remote joins in rooms with `@room` notification levels set to `null` in their (malformed) power levels.

synapse/push/bulk_push_rule_evaluator.py

@@ -69,6 +69,9 @@
 }
 
 
+SENTINEL = object()
+
+
 def _should_count_as_unread(event: EventBase, context: EventContext) -> bool:
     # Exclude rejected and soft-failed events.
     if context.rejected or event.internal_metadata.is_soft_failed():
@@ -343,11 +346,21 @@ async def _action_for_event_by_user(
         related_events = await self._related_events(event)
 
         # It's possible that old room versions have non-integer power levels (floats or
-        # strings). Workaround this by explicitly converting to int.
+        # strings; even the occasional `null`). For old rooms, we interpret these as if
+        # they were integers. Do this here for the `@room` power level threshold.
+        # Note that this is done automatically for the sender's power level by
+        # _get_power_levels_and_sender_level in its call to get_user_power_level
+        # (even for room V10.)
         notification_levels = power_levels.get("notifications", {})
         if not event.room_version.msc3667_int_only_power_levels:
-            for user_id, level in notification_levels.items():
-                notification_levels[user_id] = int(level)
+            keys = list(notification_levels.keys())
+            for key in keys:
+                level = notification_levels.get(key, SENTINEL)
+                if level is not SENTINEL and type(level) is not int:
+                    try:
+                        notification_levels[key] = int(level)
+                    except (TypeError, ValueError):
+                        del notification_levels[key]
 
         # Pull out any user and room mentions.
         mentions = event.content.get(EventContentFields.MSC3952_MENTIONS)

tests/push/test_bulk_push_rule_evaluator.py

@@ -15,6 +15,8 @@
 from typing import Any
 from unittest.mock import patch
 
+from parameterized import parameterized
+
 from twisted.test.proto_helpers import MemoryReactor
 
 from synapse.api.constants import EventContentFields
@@ -48,35 +50,84 @@ def prepare(
         self.requester = create_requester(self.alice)
 
         self.room_id = self.helper.create_room_as(
-            self.alice, room_version=RoomVersions.V9.identifier, tok=self.token
+            # This is deliberately set to V9, because we want to test the logic which
+            # handles stringy power levels. Stringy power levels were outlawed in V10.
+            self.alice,
+            room_version=RoomVersions.V9.identifier,
+            tok=self.token,
         )
 
         self.event_creation_handler = self.hs.get_event_creation_handler()
 
-    def test_action_for_event_by_user_handles_noninteger_power_levels(self) -> None:
-        """We should convert floats and strings to integers before passing to Rust.
+    @parameterized.expand(
+        [
+            # The historically-permitted bad values. Alice's notification should be
+            # allowed if this threshold is at or below her power level (60)
+            ("100", False),
+            ("0", True),
+            (12.34, True),
+            (60.0, True),
+            (67.89, False),
+            # Values that int(...) would not successfully cast should be ignored.
+            # The room notification level should then default to 50, per the spec, so
+            # Alice's notification is allowed.
+            (None, True),
+            # We haven't seen `"room": []` or `"room": {}` in the wild (yet), but
+            # let's check them for paranoia's sake.
+            ([], True),
+            ({}, True),
+        ]
+    )
+    def test_action_for_event_by_user_handles_noninteger_room_power_levels(
+        self, bad_room_level: object, should_permit: bool
+    ) -> None:
+        """We should convert strings in `room` to integers before passing to Rust.
+
+        Test this as follows:
+        - Create a room as Alice and invite two other users Bob and Charlie.
+        - Set PLs so that Alice has PL 60 and `notifications.room` is set to a bad value.
+        - Have Alice create a message notifying @room.
+        - Evaluate notification actions for that message. This should not raise.
+        - Look in the DB to see if that message triggered a highlight for Bob.
+
+        The test is parameterised with two arguments:
+        - the bad power level value for "room", before JSON serisalistion
+        - whether Bob should expect the message to be highlighted
 
         Reproduces #14060.
 
         A lack of validation: the gift that keeps on giving.
         """
-
-        # Alter the power levels in that room to include stringy and floaty levels.
-        # We need to suppress the validation logic or else it will reject these dodgy
-        # values. (Presumably this validation was not always present.)
+        # Join another user to the room, so that there is someone to see Alice's
+        # @room notification.
+        bob = self.register_user("bob", "pass")
+        bob_token = self.login(bob, "pass")
+        self.helper.join(self.room_id, bob, tok=bob_token)
+
+        # Alter the power levels in that room to include the bad @room notification
+        # level. We need to suppress
+        #
+        # - canonicaljson validation, because canonicaljson forbids floats;
+        # - the event jsonschema validation, because it will forbid bad values; and
+        # - the auth rules checks, because they stop us from creating power levels
+        #   with `"room": null`. (We want to test this case, because we have seen it
+        #   in the wild.)
+        #
+        # We have seen stringy and null values for "room" in the wild, so presumably
+        # some of this validation was missing in the past.
         with patch("synapse.events.validator.validate_canonicaljson"), patch(
             "synapse.events.validator.jsonschema.validate"
-        ):
-            self.helper.send_state(
+        ), patch("synapse.handlers.event_auth.check_state_dependent_auth_rules"):
+            pl_event_id = self.helper.send_state(
                 self.room_id,
                 "m.room.power_levels",
                 {
-                    "users": {self.alice: "100"},  # stringy
-                    "notifications": {"room": 100.0},  # float
+                    "users": {self.alice: 60},
+                    "notifications": {"room": bad_room_level},
                 },
                 self.token,
                 state_key="",
-            )
+            )["event_id"]
 
         # Create a new message event, and try to evaluate it under the dodgy
         # power level event.
@@ -88,17 +139,33 @@ def test_action_for_event_by_user_handles_noninteger_power_levels(self) -> None:
                     "room_id": self.room_id,
                     "content": {
                         "msgtype": "m.text",
-                        "body": "helo",
+                        "body": "helo @room",
                     },
                     "sender": self.alice,
                 },
+                prev_event_ids=[pl_event_id],
             )
         )
 
         bulk_evaluator = BulkPushRuleEvaluator(self.hs)
         # should not raise
         self.get_success(bulk_evaluator.action_for_events_by_user([(event, context)]))
 
+        # Did Bob see Alice's @room notification?
+        highlighted_actions = self.get_success(
+            self.hs.get_datastores().main.db_pool.simple_select_list(
+                table="event_push_actions_staging",
+                keyvalues={
+                    "event_id": event.event_id,
+                    "user_id": bob,
+                    "highlight": 1,
+                },
+                retcols=("*",),
+                desc="get_event_push_actions_staging",
+            )
+        )
+        self.assertEqual(len(highlighted_actions), int(should_permit))
+
     @override_config({"push": {"enabled": False}})
     def test_action_for_event_by_user_disabled_by_config(self) -> None:
         """Ensure that push rules are not calculated when disabled in the config"""

tests/test_event_auth.py

@@ -13,7 +13,7 @@
 # limitations under the License.
 
 import unittest
-from typing import Collection, Dict, Iterable, List, Optional
+from typing import Any, Collection, Dict, Iterable, List, Optional
 
 from parameterized import parameterized
 
@@ -728,6 +728,36 @@ def test_room_v10_rejects_string_power_levels(self) -> None:
                 pl_event.room_version, pl_event2, {("fake_type", "fake_key"): pl_event}
             )
 
+    def test_room_v10_rejects_other_non_integer_power_levels(self) -> None:
+        """We should reject PLs that are non-integer, non-string JSON values.
+
+        test_room_v10_rejects_string_power_levels above handles the string case.
+        """
+
+        def create_event(pl_event_content: Dict[str, Any]) -> EventBase:
+            return make_event_from_dict(
+                {
+                    "room_id": TEST_ROOM_ID,
+                    **_maybe_get_event_id_dict_for_room_version(RoomVersions.V10),
+                    "type": "m.room.power_levels",
+                    "sender": "@test:test.com",
+                    "state_key": "",
+                    "content": pl_event_content,
+                    "signatures": {"test.com": {"ed25519:0": "some9signature"}},
+                },
+                room_version=RoomVersions.V10,
+            )
+
+        contents: Iterable[Dict[str, Any]] = [
+            {"notifications": {"room": None}},
+            {"users": {"@alice:wonderland": []}},
+            {"users_default": {}},
+        ]
+        for content in contents:
+            event = create_event(content)
+            with self.assertRaises(SynapseError):
+                event_auth._check_power_levels(event.room_version, event, {})
+
 
 # helpers for making events
 TEST_DOMAIN = "example.com"