diff options
| -rw-r--r-- | changelog.d/8535.feature | 1 | ||||
| -rw-r--r-- | synapse/events/__init__.py | 6 | ||||
| -rw-r--r-- | synapse/events/third_party_rules.py | 19 | ||||
| -rw-r--r-- | synapse/handlers/federation.py | 66 | ||||
| -rw-r--r-- | synapse/handlers/message.py | 79 | ||||
| -rw-r--r-- | tests/rest/client/test_third_party_rules.py | 28 |
6 files changed, 118 insertions, 81 deletions
diff --git a/changelog.d/8535.feature b/changelog.d/8535.feature new file mode 100644 index 0000000000..45342e66ad --- /dev/null +++ b/changelog.d/8535.feature @@ -0,0 +1 @@ +Support modifying event content in `ThirdPartyRules` modules. diff --git a/synapse/events/__init__.py b/synapse/events/__init__.py index 7a51d0a22f..65df62107f 100644 --- a/synapse/events/__init__.py +++ b/synapse/events/__init__.py @@ -312,6 +312,12 @@ class EventBase(metaclass=abc.ABCMeta): """ return [e for e, _ in self.auth_events] + def freeze(self): + """'Freeze' the event dict, so it cannot be modified by accident""" + + # this will be a no-op if the event dict is already frozen. + self._dict = freeze(self._dict) + class FrozenEvent(EventBase): format_version = EventFormatVersions.V1 # All events of this type are V1 diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py index 1535cc5339..77fbd3f68a 100644 --- a/synapse/events/third_party_rules.py +++ b/synapse/events/third_party_rules.py @@ -12,7 +12,8 @@ # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License. -from typing import Callable + +from typing import Callable, Union from synapse.events import EventBase from synapse.events.snapshot import EventContext @@ -44,15 +45,20 @@ class ThirdPartyEventRules: async def check_event_allowed( self, event: EventBase, context: EventContext - ) -> bool: + ) -> Union[bool, dict]: """Check if a provided event should be allowed in the given context. + The module can return: + * True: the event is allowed. + * False: the event is not allowed, and should be rejected with M_FORBIDDEN. + * a dict: replacement event data. + Args: event: The event to be checked. context: The context of the event. Returns: - True if the event should be allowed, False if not. + The result from the ThirdPartyRules module, as above """ if self.third_party_rules is None: return True @@ -63,9 +69,10 @@ class ThirdPartyEventRules: events = await self.store.get_events(prev_state_ids.values()) state_events = {(ev.type, ev.state_key): ev for ev in events.values()} - # The module can modify the event slightly if it wants, but caution should be - # exercised, and it's likely to go very wrong if applied to events received over - # federation. + # Ensure that the event is frozen, to make sure that the module is not tempted + # to try to modify it. Any attempt to modify it at this point will invalidate + # the hashes and signatures. + event.freeze() return await self.third_party_rules.check_event_allowed(event, state_events) diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py index 455acd7669..fde8f00531 100644 --- a/synapse/handlers/federation.py +++ b/synapse/handlers/federation.py @@ -1507,18 +1507,9 @@ class FederationHandler(BaseHandler): event, context = await self.event_creation_handler.create_new_client_event( builder=builder ) - except AuthError as e: + except SynapseError as e: logger.warning("Failed to create join to %s because %s", room_id, e) - raise e - - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.info("Creation of join %s forbidden by third-party rules", event) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) + raise # The remote hasn't signed it yet, obviously. We'll do the full checks # when we get the event back in `on_send_join_request` @@ -1567,15 +1558,6 @@ class FederationHandler(BaseHandler): context = await self._handle_new_event(origin, event) - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.info("Sending of join %s forbidden by third-party rules", event) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) - logger.debug( "on_send_join_request: After _handle_new_event: %s, sigs: %s", event.event_id, @@ -1748,15 +1730,6 @@ class FederationHandler(BaseHandler): builder=builder ) - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.warning("Creation of leave %s forbidden by third-party rules", event) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) - try: # The remote hasn't signed it yet, obviously. We'll do the full checks # when we get the event back in `on_send_leave_request` @@ -1789,16 +1762,7 @@ class FederationHandler(BaseHandler): event.internal_metadata.outlier = False - context = await self._handle_new_event(origin, event) - - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.info("Sending of leave %s forbidden by third-party rules", event) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) + await self._handle_new_event(origin, event) logger.debug( "on_send_leave_request: After _handle_new_event: %s, sigs: %s", @@ -2694,18 +2658,6 @@ class FederationHandler(BaseHandler): builder=builder ) - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.info( - "Creation of threepid invite %s forbidden by third-party rules", - event, - ) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) - event, context = await self.add_display_name_to_third_party_invite( room_version, event_dict, event, context ) @@ -2756,18 +2708,6 @@ class FederationHandler(BaseHandler): event, context = await self.event_creation_handler.create_new_client_event( builder=builder ) - - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - logger.warning( - "Exchange of threepid invite %s forbidden by third-party rules", event - ) - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) - event, context = await self.add_display_name_to_third_party_invite( room_version, event_dict, event, context ) diff --git a/synapse/handlers/message.py b/synapse/handlers/message.py index f18f882596..7f00805a91 100644 --- a/synapse/handlers/message.py +++ b/synapse/handlers/message.py @@ -811,6 +811,23 @@ class EventCreationHandler: if requester: context.app_service = requester.app_service + third_party_result = await self.third_party_event_rules.check_event_allowed( + event, context + ) + if not third_party_result: + logger.info( + "Event %s forbidden by third-party rules", event, + ) + raise SynapseError( + 403, "This event is not allowed in this context", Codes.FORBIDDEN + ) + elif isinstance(third_party_result, dict): + # the third-party rules want to replace the event. We'll need to build a new + # event. + event, context = await self._rebuild_event_after_third_party_rules( + third_party_result, event + ) + self.validator.validate_new(event, self.config) # If this event is an annotation then we check that that the sender @@ -897,14 +914,6 @@ class EventCreationHandler: else: room_version = await self.store.get_room_version_id(event.room_id) - event_allowed = await self.third_party_event_rules.check_event_allowed( - event, context - ) - if not event_allowed: - raise SynapseError( - 403, "This event is not allowed in this context", Codes.FORBIDDEN - ) - if event.internal_metadata.is_out_of_band_membership(): # the only sort of out-of-band-membership events we expect to see here # are invite rejections we have generated ourselves. @@ -1307,3 +1316,57 @@ class EventCreationHandler: room_id, ) del self._rooms_to_exclude_from_dummy_event_insertion[room_id] + + async def _rebuild_event_after_third_party_rules( + self, third_party_result: dict, original_event: EventBase + ) -> Tuple[EventBase, EventContext]: + # the third_party_event_rules want to replace the event. + # we do some basic checks, and then return the replacement event and context. + + # Construct a new EventBuilder and validate it, which helps with the + # rest of these checks. + try: + builder = self.event_builder_factory.for_room_version( + original_event.room_version, third_party_result + ) + self.validator.validate_builder(builder) + except SynapseError as e: + raise Exception( + "Third party rules module created an invalid event: " + e.msg, + ) + + immutable_fields = [ + # changing the room is going to break things: we've already checked that the + # room exists, and are holding a concurrency limiter token for that room. + # Also, we might need to use a different room version. + "room_id", + # changing the type or state key might work, but we'd need to check that the + # calling functions aren't making assumptions about them. + "type", + "state_key", + ] + + for k in immutable_fields: + if getattr(builder, k, None) != original_event.get(k): + raise Exception( + "Third party rules module created an invalid event: " + "cannot change field " + k + ) + + # check that the new sender belongs to this HS + if not self.hs.is_mine_id(builder.sender): + raise Exception( + "Third party rules module created an invalid event: " + "invalid sender " + builder.sender + ) + + # copy over the original internal metadata + for k, v in original_event.internal_metadata.get_dict().items(): + setattr(builder.internal_metadata, k, v) + + event = await builder.build(prev_event_ids=original_event.prev_event_ids()) + + # we rebuild the event context, to be on the safe side. If nothing else, + # delta_ids might need an update. + context = await self.state.compute_event_context(event) + return event, context diff --git a/tests/rest/client/test_third_party_rules.py b/tests/rest/client/test_third_party_rules.py index b737625e33..0048bea54a 100644 --- a/tests/rest/client/test_third_party_rules.py +++ b/tests/rest/client/test_third_party_rules.py @@ -114,10 +114,10 @@ class ThirdPartyRulesTestCase(unittest.HomeserverTestCase): self.render(request) self.assertEquals(channel.result["code"], b"403", channel.result) - def test_modify_event(self): - """Tests that the module can successfully tweak an event before it is persisted. - """ - # first patch the event checker so that it will modify the event + def test_cannot_modify_event(self): + """cannot accidentally modify an event before it is persisted""" + + # first patch the event checker so that it will try to modify the event async def check(ev: EventBase, state): ev.content = {"x": "y"} return True @@ -132,6 +132,26 @@ class ThirdPartyRulesTestCase(unittest.HomeserverTestCase): access_token=self.tok, ) self.render(request) + self.assertEqual(channel.result["code"], b"500", channel.result) + + def test_modify_event(self): + """The module can return a modified version of the event""" + # first patch the event checker so that it will modify the event + async def check(ev: EventBase, state): + d = ev.get_dict() + d["content"] = {"x": "y"} + return d + + current_rules_module().check_event_allowed = check + + # now send the event + request, channel = self.make_request( + "PUT", + "/_matrix/client/r0/rooms/%s/send/modifyme/1" % self.room_id, + {"x": "x"}, + access_token=self.tok, + ) + self.render(request) self.assertEqual(channel.result["code"], b"200", channel.result) event_id = channel.json_body["event_id"] |