Additional validation of receipts (#16327)

Reject invalid receipts with a reasonable error message &
expands tests for receipts.

changelog.d/16327.bugfix

@@ -0,0 +1 @@
+Fix a long-standing bug where invalid receipts would be accepted.

synapse/handlers/receipts.py

@@ -37,6 +37,8 @@ def __init__(self, hs: "HomeServer"):
         self.server_name = hs.config.server.server_name
         self.store = hs.get_datastores().main
         self.event_auth_handler = hs.get_event_auth_handler()
+        self.event_handler = hs.get_event_handler()
+        self._storage_controllers = hs.get_storage_controllers()
 
         self.hs = hs
 
@@ -81,6 +83,20 @@ async def _received_remote_receipt(self, origin: str, content: JsonDict) -> None
                 )
                 continue
 
+            # Let's check that the origin server is in the room before accepting the receipt.
+            # We don't want to block waiting on a partial state so take an
+            # approximation if needed.
+            domains = await self._storage_controllers.state.get_current_hosts_in_room_or_partial_state_approximation(
+                room_id
+            )
+            if origin not in domains:
+                logger.info(
+                    "Ignoring receipt for room %r from server %s as they're not in the room",
+                    room_id,
+                    origin,
+                )
+                continue
+
             for receipt_type, users in room_values.items():
                 for user_id, user_values in users.items():
                     if get_domain_from_id(user_id) != origin:
@@ -158,17 +174,23 @@ async def received_client_receipt(
         self,
         room_id: str,
         receipt_type: str,
-        user_id: str,
+        user_id: UserID,
         event_id: str,
         thread_id: Optional[str],
     ) -> None:
         """Called when a client tells us a local user has read up to the given
         event_id in the room.
         """
+
+        # Ensure the room/event exists, this will raise an error if the user
+        # cannot view the event.
+        if not await self.event_handler.get_event(user_id, room_id, event_id):
+            return
+
         receipt = ReadReceipt(
             room_id=room_id,
             receipt_type=receipt_type,
-            user_id=user_id,
+            user_id=user_id.to_string(),
             event_ids=[event_id],
             thread_id=thread_id,
             data={"ts": int(self.clock.time_msec())},

synapse/rest/client/read_marker.py

@@ -84,7 +84,7 @@ async def on_POST(
                 await self.receipts_handler.received_client_receipt(
                     room_id,
                     receipt_type,
-                    user_id=requester.user.to_string(),
+                    user_id=requester.user,
                     event_id=event_id,
                     # Setting the thread ID is not possible with the /read_markers endpoint.
                     thread_id=None,

synapse/rest/client/receipts.py

@@ -108,7 +108,7 @@ async def on_POST(
             await self.receipts_handler.received_client_receipt(
                 room_id,
                 receipt_type,
-                user_id=requester.user.to_string(),
+                user_id=requester.user,
                 event_id=event_id,
                 thread_id=thread_id,
             )

tests/rest/client/test_receipts.py

@@ -11,11 +11,16 @@
 # 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 http import HTTPStatus
+from typing import Optional
+
 from twisted.test.proto_helpers import MemoryReactor
 
 import synapse.rest.admin
-from synapse.rest.client import login, receipts, register
+from synapse.api.constants import EduTypes, EventTypes, HistoryVisibility, ReceiptTypes
+from synapse.rest.client import login, receipts, room, sync
 from synapse.server import HomeServer
+from synapse.types import JsonDict
 from synapse.util import Clock
 
 from tests import unittest
@@ -24,30 +29,113 @@
 class ReceiptsTestCase(unittest.HomeserverTestCase):
     servlets = [
         login.register_servlets,
-        register.register_servlets,
         receipts.register_servlets,
         synapse.rest.admin.register_servlets,
+        room.register_servlets,
+        sync.register_servlets,
     ]
 
     def prepare(self, reactor: MemoryReactor, clock: Clock, hs: HomeServer) -> None:
-        self.owner = self.register_user("owner", "pass")
-        self.owner_tok = self.login("owner", "pass")
+        self.url = "/sync?since=%s"
+        self.next_batch = "s0"
+
+        # Register the first user
+        self.user_id = self.register_user("kermit", "monkey")
+        self.tok = self.login("kermit", "monkey")
+
+        # Create the room
+        self.room_id = self.helper.create_room_as(self.user_id, tok=self.tok)
+
+        # Register the second user
+        self.user2 = self.register_user("kermit2", "monkey")
+        self.tok2 = self.login("kermit2", "monkey")
+
+        # Join the second user
+        self.helper.join(room=self.room_id, user=self.user2, tok=self.tok2)
 
     def test_send_receipt(self) -> None:
+        # Send a message.
+        res = self.helper.send(self.room_id, body="hello", tok=self.tok)
+
+        # Send a read receipt
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertNotEqual(self._get_read_receipt(), None)
+
+    def test_send_receipt_unknown_event(self) -> None:
+        """Receipts sent for unknown events are ignored to not break message retention."""
+        # Attempt to send a receipt to an unknown room.
         channel = self.make_request(
             "POST",
             "/rooms/!abc:beep/receipt/m.read/$def",
             content={},
-            access_token=self.owner_tok,
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200, channel.result)
+        self.assertIsNone(self._get_read_receipt())
+
+        # Attempt to send a receipt to an unknown event.
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/m.read/$def",
+            content={},
+            access_token=self.tok2,
         )
         self.assertEqual(channel.code, 200, channel.result)
+        self.assertIsNone(self._get_read_receipt())
+
+    def test_send_receipt_unviewable_event(self) -> None:
+        """Receipts sent for unviewable events are errors."""
+        # Create a room where new users can't see events from before their join
+        # & send events into it.
+        room_id = self.helper.create_room_as(
+            self.user_id,
+            tok=self.tok,
+            extra_content={
+                "preset": "private_chat",
+                "initial_state": [
+                    {
+                        "content": {"history_visibility": HistoryVisibility.JOINED},
+                        "state_key": "",
+                        "type": EventTypes.RoomHistoryVisibility,
+                    }
+                ],
+            },
+        )
+        res = self.helper.send(room_id, body="hello", tok=self.tok)
+
+        # Attempt to send a receipt from the wrong user.
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{room_id}/receipt/{ReceiptTypes.READ}/{res['event_id']}",
+            content={},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 403, channel.result)
+
+        # Join the user to the room, but they still can't see the event.
+        self.helper.invite(room_id, self.user_id, self.user2, tok=self.tok)
+        self.helper.join(room=room_id, user=self.user2, tok=self.tok2)
+
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{room_id}/receipt/{ReceiptTypes.READ}/{res['event_id']}",
+            content={},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 403, channel.result)
 
     def test_send_receipt_invalid_room_id(self) -> None:
         channel = self.make_request(
             "POST",
             "/rooms/not-a-room-id/receipt/m.read/$def",
             content={},
-            access_token=self.owner_tok,
+            access_token=self.tok,
         )
         self.assertEqual(channel.code, 400, channel.result)
         self.assertEqual(
@@ -59,7 +147,7 @@ def test_send_receipt_invalid_event_id(self) -> None:
             "POST",
             "/rooms/!abc:beep/receipt/m.read/not-an-event-id",
             content={},
-            access_token=self.owner_tok,
+            access_token=self.tok,
         )
         self.assertEqual(channel.code, 400, channel.result)
         self.assertEqual(
@@ -71,6 +159,123 @@ def test_send_receipt_invalid_receipt_type(self) -> None:
             "POST",
             "/rooms/!abc:beep/receipt/invalid-receipt-type/$def",
             content={},
-            access_token=self.owner_tok,
+            access_token=self.tok,
         )
         self.assertEqual(channel.code, 400, channel.result)
+
+    def test_private_read_receipts(self) -> None:
+        # Send a message as the first user
+        res = self.helper.send(self.room_id, body="hello", tok=self.tok)
+
+        # Send a private read receipt to tell the server the first user's message was read
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ_PRIVATE}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+
+        # Test that the first user can't see the other user's private read receipt
+        self.assertIsNone(self._get_read_receipt())
+
+    def test_public_receipt_can_override_private(self) -> None:
+        """
+        Sending a public read receipt to the same event which has a private read
+        receipt should cause that receipt to become public.
+        """
+        # Send a message as the first user
+        res = self.helper.send(self.room_id, body="hello", tok=self.tok)
+
+        # Send a private read receipt
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ_PRIVATE}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertIsNone(self._get_read_receipt())
+
+        # Send a public read receipt
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+
+        # Test that we did override the private read receipt
+        self.assertNotEqual(self._get_read_receipt(), None)
+
+    def test_private_receipt_cannot_override_public(self) -> None:
+        """
+        Sending a private read receipt to the same event which has a public read
+        receipt should cause no change.
+        """
+        # Send a message as the first user
+        res = self.helper.send(self.room_id, body="hello", tok=self.tok)
+
+        # Send a public read receipt
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+        self.assertNotEqual(self._get_read_receipt(), None)
+
+        # Send a private read receipt
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/{ReceiptTypes.READ_PRIVATE}/{res['event_id']}",
+            {},
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, 200)
+
+        # Test that we didn't override the public read receipt
+        self.assertIsNone(self._get_read_receipt())
+
+    def test_read_receipt_with_empty_body_is_rejected(self) -> None:
+        # Send a message as the first user
+        res = self.helper.send(self.room_id, body="hello", tok=self.tok)
+
+        # Send a read receipt for this message with an empty body
+        channel = self.make_request(
+            "POST",
+            f"/rooms/{self.room_id}/receipt/m.read/{res['event_id']}",
+            access_token=self.tok2,
+        )
+        self.assertEqual(channel.code, HTTPStatus.BAD_REQUEST)
+        self.assertEqual(channel.json_body["errcode"], "M_NOT_JSON", channel.json_body)
+
+    def _get_read_receipt(self) -> Optional[JsonDict]:
+        """Syncs and returns the read receipt."""
+
+        # Checks if event is a read receipt
+        def is_read_receipt(event: JsonDict) -> bool:
+            return event["type"] == EduTypes.RECEIPT
+
+        # Sync
+        channel = self.make_request(
+            "GET",
+            self.url % self.next_batch,
+            access_token=self.tok,
+        )
+        self.assertEqual(channel.code, 200)
+
+        # Store the next batch for the next request.
+        self.next_batch = channel.json_body["next_batch"]
+
+        if channel.json_body.get("rooms", None) is None:
+            return None
+
+        # Return the read receipt
+        ephemeral_events = channel.json_body["rooms"]["join"][self.room_id][
+            "ephemeral"
+        ]["events"]
+        receipt_event = filter(is_read_receipt, ephemeral_events)
+        return next(receipt_event, None)