fix(matrix): bind and bound SAS requests

nanobot/channels/matrix/runtime.py

@@ -80,6 +80,7 @@ _MSGTYPE_MAP = {"m.image": "image", "m.audio": "audio", "m.video": "video", "m.f
 _SAS_METHOD = "m.sas.v1"
 _SAS_REQUEST_MAX_AGE_MS = 10 * 60 * 1000
 _SAS_REQUEST_MAX_FUTURE_MS = 5 * 60 * 1000
+_SAS_REQUEST_MAX_PENDING = 256
 
 MATRIX_MEDIA_EVENT_FILTER = (RoomMessageMedia, RoomEncryptedMedia)
 MatrixMediaEvent: TypeAlias = RoomMessageMedia | RoomEncryptedMedia
@@ -759,6 +760,16 @@ class MatrixChannel(BaseChannel):
             if request.timestamp_ms >= oldest_allowed
         }
 
+    def _remember_sas_verification_request(
+        self,
+        transaction_id: str,
+        request: _SasVerificationRequest,
+    ) -> None:
+        self._sas_verification_requests[transaction_id] = request
+        while len(self._sas_verification_requests) > _SAS_REQUEST_MAX_PENDING:
+            oldest_transaction_id = next(iter(self._sas_verification_requests))
+            self._sas_verification_requests.pop(oldest_transaction_id)
+
     async def _send_sas_control_message(
         self,
         *,
@@ -849,7 +860,7 @@ class MatrixChannel(BaseChannel):
                 },
             )
             if sent:
-                self._sas_verification_requests[transaction_id] = request
+                self._remember_sas_verification_request(transaction_id, request)
             return
 
         if event_type == "m.key.verification.done":
@@ -882,6 +893,16 @@ class MatrixChannel(BaseChannel):
             return
 
         if isinstance(event, KeyVerificationStart):
+            request = self._sas_verification_requests.get(transaction_id)
+            from_device = str(getattr(event, "from_device", "") or "")
+            if request is not None and (
+                request.sender != sender or request.device_id != from_device
+            ):
+                self.logger.warning(
+                    "Ignoring Matrix SAS start for transaction {} from unexpected device",
+                    transaction_id,
+                )
+                return
             if "emoji" not in (getattr(event, "short_authentication_string", None) or []):
                 self.logger.info(
                     "Ignoring Matrix SAS verification from {} without emoji support",

nanobot/channels/matrix/tests/test_matrix_channel.py

@@ -241,10 +241,12 @@ class _FakeKeyVerificationStart:
         *,
         sender: str = "@alice:matrix.org",
         transaction_id: str = "tx1",
+        from_device: str = "ALICEDEVICE",
         short_authentication_string: list[str] | None = None,
     ) -> None:
         self.sender = sender
         self.transaction_id = transaction_id
+        self.from_device = from_device
         self.short_authentication_string = short_authentication_string or ["emoji"]
 
 
@@ -477,6 +479,65 @@ async def test_sas_verification_request_sends_ready_to_allowed_device(monkeypatc
     assert channel._sas_verification_requests["tx1"].device_id == "ALICEDEVICE"
 
 
+@pytest.mark.asyncio
+async def test_sas_verification_requests_are_bounded(monkeypatch) -> None:
+    monkeypatch.setattr(matrix_module.time, "time", lambda: 1_000.0)
+    channel = MatrixChannel(
+        _make_config(
+            allow_from=["@alice:matrix.org"],
+            e2ee_enabled=True,
+            sas_verification=True,
+        ),
+        MessageBus(),
+    )
+    client = _FakeAsyncClient("", "", "", None)
+    client.device_id = "BOTDEVICE"
+    channel.client = client
+
+    for index in range(matrix_module._SAS_REQUEST_MAX_PENDING + 1):
+        await channel._handle_key_verification_event(_unknown_verification_event(
+            "m.key.verification.request",
+            transaction_id=f"tx-{index}",
+            from_device="ALICEDEVICE",
+            methods=["m.sas.v1"],
+            timestamp=1_000_000,
+        ))
+
+    assert len(channel._sas_verification_requests) == matrix_module._SAS_REQUEST_MAX_PENDING
+    assert "tx-0" not in channel._sas_verification_requests
+    assert f"tx-{matrix_module._SAS_REQUEST_MAX_PENDING}" in channel._sas_verification_requests
+
+
+@pytest.mark.asyncio
+async def test_sas_verification_start_must_match_requested_device(monkeypatch) -> None:
+    _patch_key_verification_events(monkeypatch)
+    monkeypatch.setattr(matrix_module.time, "time", lambda: 1_000.0)
+    channel = MatrixChannel(
+        _make_config(
+            allow_from=["@alice:matrix.org"],
+            e2ee_enabled=True,
+            sas_verification=True,
+        ),
+        MessageBus(),
+    )
+    client = _FakeAsyncClient("", "", "", None)
+    client.device_id = "BOTDEVICE"
+    channel.client = client
+
+    await channel._handle_key_verification_event(_unknown_verification_event(
+        "m.key.verification.request",
+        from_device="ALICEDEVICE",
+        methods=["m.sas.v1"],
+        timestamp=1_000_000,
+    ))
+    await channel._handle_key_verification_event(
+        _FakeKeyVerificationStart(from_device="OTHERDEVICE")
+    )
+
+    assert client.accept_key_verification_calls == []
+    assert channel._sas_verification_requests["tx1"].device_id == "ALICEDEVICE"
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     ("sender", "methods", "timestamp"),