Strictly enforce canonicaljson requirements in a new room version

changelog.d/7381.bugfix

@@ -0,0 +1 @@
+Add an experimental room version which strictly adheres to the canonical JSON specification.

synapse/api/room_versions.py

@@ -59,7 +59,11 @@ class RoomVersion(object):
 
     # bool: before MSC2261/MSC2432, m.room.aliases had special auth rules and redaction rules
     special_case_aliases_auth = attr.ib(type=bool)
-
+    # Strictly enforce canonicaljson, do not allow:
+    # * Integers outside the range of [-2 ^ 53 + 1, 2 ^ 53 - 1]
+    # * Floats
+    # * NaN, Infinity, -Infinity
+    strict_canonicaljson = attr.ib(type=bool)
     # bool: MSC2209: Check 'notifications' key while verifying
     # m.room.power_levels auth rules.
     limit_notifications_power_levels = attr.ib(type=bool)
@@ -73,6 +77,7 @@ class RoomVersions(object):
         StateResolutionVersions.V1,
         enforce_key_validity=False,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=False,
     )
     V2 = RoomVersion(
@@ -82,6 +87,7 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=False,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=False,
     )
     V3 = RoomVersion(
@@ -91,6 +97,7 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=False,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=False,
     )
     V4 = RoomVersion(
@@ -100,6 +107,7 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=False,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=False,
     )
     V5 = RoomVersion(
@@ -109,6 +117,7 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=True,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=False,
     )
     MSC2432_DEV = RoomVersion(
@@ -118,6 +127,17 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=True,
         special_case_aliases_auth=False,
+        strict_canonicaljson=False,
+        limit_notifications_power_levels=False,
+    )
+    STRICT_CANONICALJSON = RoomVersion(
+        "org.matrix.strict_canonicaljson",
+        RoomDisposition.UNSTABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
+        special_case_aliases_auth=True,
+        strict_canonicaljson=True,
         limit_notifications_power_levels=False,
     )
     MSC2209_DEV = RoomVersion(
@@ -127,6 +147,7 @@ class RoomVersions(object):
         StateResolutionVersions.V2,
         enforce_key_validity=True,
         special_case_aliases_auth=True,
+        strict_canonicaljson=False,
         limit_notifications_power_levels=True,
     )
 
@@ -140,6 +161,7 @@ class RoomVersions(object):
         RoomVersions.V4,
         RoomVersions.V5,
         RoomVersions.MSC2432_DEV,
+        RoomVersions.STRICT_CANONICALJSON,
         RoomVersions.MSC2209_DEV,
     )
 }  # type: Dict[str, RoomVersion]

synapse/events/utils.py

@@ -14,7 +14,7 @@
 # limitations under the License.
 import collections
 import re
-from typing import Mapping, Union
+from typing import Any, Mapping, Union
 
 from six import string_types
 
@@ -23,6 +23,7 @@
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, RelationTypes
+from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import RoomVersion
 from synapse.util.async_helpers import yieldable_gather_results
 
@@ -449,3 +450,35 @@ def copy_power_levels_contents(
         raise TypeError("Invalid power_levels value for %s: %r" % (k, v))
 
     return power_levels
+
+
+def validate_canonicaljson(value: Any):
+    """
+    Ensure that the JSON object is valid according to the rules of canonical JSON.
+
+    See the appendix section 3.1: Canonical JSON.
+
+    This rejects JSON that has:
+    * An integer outside the range of [-2 ^ 53 + 1, 2 ^ 53 - 1]
+    * Floats
+    * NaN, Infinity, -Infinity
+    """
+    if isinstance(value, int):
+        if value <= -(2 ** 53) or 2 ** 53 <= value:
+            raise SynapseError(400, "JSON integer out of range", Codes.BAD_JSON)
+
+    elif isinstance(value, float):
+        # Note that Infinity, -Infinity, and NaN are also considered floats.
+        raise SynapseError(400, "Bad JSON value: float", Codes.BAD_JSON)
+
+    elif isinstance(value, (dict, frozendict)):
+        for v in value.values():
+            validate_canonicaljson(v)
+
+    elif isinstance(value, (list, tuple)):
+        for i in value:
+            validate_canonicaljson(i)
+
+    elif not isinstance(value, (bool, str)) and value is not None:
+        # Other potential JSON values (bool, None, str) are safe.
+        raise SynapseError(400, "Unknown JSON value", Codes.BAD_JSON)

synapse/events/validator.py

@@ -18,6 +18,7 @@
 from synapse.api.constants import MAX_ALIAS_LENGTH, EventTypes, Membership
 from synapse.api.errors import Codes, SynapseError
 from synapse.api.room_versions import EventFormatVersions
+from synapse.events.utils import validate_canonicaljson
 from synapse.types import EventID, RoomID, UserID
 
 
@@ -55,6 +56,12 @@ def validate_new(self, event, config):
             if not isinstance(getattr(event, s), string_types):
                 raise SynapseError(400, "'%s' not a string type" % (s,))
 
+        # Depending on the room version, ensure the data is spec compliant JSON.
+        if event.room_version.strict_canonicaljson:
+            # Note that only the client controlled portion of the event is
+            # checked, since we trust the portions of the event we created.
+            validate_canonicaljson(event.content)
+
         if event.type == EventTypes.Aliases:
             if "aliases" in event.content:
                 for alias in event.content["aliases"]:

synapse/federation/federation_base.py

@@ -29,7 +29,7 @@
 from synapse.crypto.event_signing import check_event_content_hash
 from synapse.crypto.keyring import Keyring
 from synapse.events import EventBase, make_event_from_dict
-from synapse.events.utils import prune_event
+from synapse.events.utils import prune_event, validate_canonicaljson
 from synapse.http.servlet import assert_params_in_dict
 from synapse.logging.context import (
     PreserveLoggingContext,
@@ -302,6 +302,10 @@ def event_from_pdu_json(
     elif depth > MAX_DEPTH:
         raise SynapseError(400, "Depth too large", Codes.BAD_JSON)
 
+    # Validate that the JSON conforms to the specification.
+    if room_version.strict_canonicaljson:
+        validate_canonicaljson(pdu_json)
+
     event = make_event_from_dict(pdu_json, room_version)
     event.internal_metadata.outlier = outlier
 

synapse/util/frozenutils.py

@@ -65,5 +65,5 @@ def _handle_frozendict(obj):
     )
 
 
-# A JSONEncoder which is capable of encoding frozendics without barfing
+# A JSONEncoder which is capable of encoding frozendicts without barfing
 frozendict_json_encoder = json.JSONEncoder(default=_handle_frozendict)

tests/handlers/test_federation.py

@@ -13,9 +13,12 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 import logging
+from unittest import TestCase
 
 from synapse.api.constants import EventTypes
-from synapse.api.errors import AuthError, Codes
+from synapse.api.errors import AuthError, Codes, SynapseError
+from synapse.api.room_versions import RoomVersions
+from synapse.events import EventBase
 from synapse.federation.federation_base import event_from_pdu_json
 from synapse.logging.context import LoggingContext, run_in_background
 from synapse.rest import admin
@@ -207,3 +210,65 @@ def _build_and_send_join_event(self, other_server, other_user, room_id):
         self.assertEqual(r[(EventTypes.Member, other_user)], join_event.event_id)
 
         return join_event
+
+
+class EventFromPduTestCase(TestCase):
+    def test_valid_json(self):
+        """Valid JSON should be turned into an event."""
+        ev = event_from_pdu_json(
+            {
+                "type": EventTypes.Message,
+                "content": {"bool": True, "null": None, "int": 1, "str": "foobar"},
+                "room_id": "!room:test",
+                "sender": "@user:test",
+                "depth": 1,
+                "prev_events": [],
+                "auth_events": [],
+                "origin_server_ts": 1234,
+            },
+            RoomVersions.STRICT_CANONICALJSON,
+        )
+
+        self.assertIsInstance(ev, EventBase)
+
+    def test_invalid_numbers(self):
+        """Invalid values for an integer should be rejected, all floats should be rejected."""
+        for value in [
+            -(2 ** 53),
+            2 ** 53,
+            1.0,
+            float("inf"),
+            float("-inf"),
+            float("nan"),
+        ]:
+            with self.assertRaises(SynapseError):
+                event_from_pdu_json(
+                    {
+                        "type": EventTypes.Message,
+                        "content": {"foo": value},
+                        "room_id": "!room:test",
+                        "sender": "@user:test",
+                        "depth": 1,
+                        "prev_events": [],
+                        "auth_events": [],
+                        "origin_server_ts": 1234,
+                    },
+                    RoomVersions.STRICT_CANONICALJSON,
+                )
+
+    def test_invalid_nested(self):
+        """List and dictionaries are recursively searched."""
+        with self.assertRaises(SynapseError):
+            event_from_pdu_json(
+                {
+                    "type": EventTypes.Message,
+                    "content": {"foo": [{"bar": 2 ** 56}]},
+                    "room_id": "!room:test",
+                    "sender": "@user:test",
+                    "depth": 1,
+                    "prev_events": [],
+                    "auth_events": [],
+                    "origin_server_ts": 1234,
+                },
+                RoomVersions.STRICT_CANONICALJSON,
+            )