Don't MAU limit AS ghost users

changelog.d/8962.bugfix

@@ -0,0 +1 @@
+Fix bug where application services couldn't register new ghost users if the server had reached its MAU limit.

synapse/api/auth_blocking.py

@@ -36,6 +36,7 @@ def __init__(self, hs):
         self._limit_usage_by_mau = hs.config.limit_usage_by_mau
         self._mau_limits_reserved_threepids = hs.config.mau_limits_reserved_threepids
         self._server_name = hs.hostname
+        self._track_appservice_user_ips = hs.config.appservice.track_appservice_user_ips
 
     async def check_auth_blocking(
         self,
@@ -76,6 +77,12 @@ async def check_auth_blocking(
                 # We never block the server from doing actions on behalf of
                 # users.
                 return
+            elif requester.app_service and not self._track_appservice_user_ips:
+                # If we're authenticated as an appservice then we only block
+                # auth if `track_appservice_user_ips` is set, as that option
+                # implicitly means that application services are part of MAU
+                # limits.
+                return
 
         # Never fail an auth check for the server notices users or support user
         # This can be a problem where event creation is prohibited due to blocking

synapse/handlers/auth.py

@@ -709,6 +709,7 @@ async def get_access_token_for_user_id(
         device_id: Optional[str],
         valid_until_ms: Optional[int],
         puppets_user_id: Optional[str] = None,
+        is_appservice_ghost: bool = False,
     ) -> str:
         """
         Creates a new access token for the user with the given user ID.
@@ -725,6 +726,7 @@ async def get_access_token_for_user_id(
                we should always have a device ID)
             valid_until_ms: when the token is valid until. None for
                 no expiry.
+            is_appservice_ghost: Whether the user is an application ghost user
         Returns:
               The access token for the user's session.
         Raises:
@@ -745,7 +747,11 @@ async def get_access_token_for_user_id(
                 "Logging in user %s on device %s%s", user_id, device_id, fmt_expiry
             )
 
-        await self.auth.check_auth_blocking(user_id)
+        if (
+            not is_appservice_ghost
+            or self.hs.config.appservice.track_appservice_user_ips
+        ):
+            await self.auth.check_auth_blocking(user_id)
 
         access_token = self.macaroon_gen.generate_access_token(user_id)
         await self.store.add_access_token_to_user(

synapse/handlers/register.py

@@ -630,6 +630,7 @@ async def register_device(
         device_id: Optional[str],
         initial_display_name: Optional[str],
         is_guest: bool = False,
+        is_appservice_ghost: bool = False,
     ) -> Tuple[str, str]:
         """Register a device for a user and generate an access token.
 
@@ -651,6 +652,7 @@ async def register_device(
                 device_id=device_id,
                 initial_display_name=initial_display_name,
                 is_guest=is_guest,
+                is_appservice_ghost=is_appservice_ghost,
             )
             return r["device_id"], r["access_token"]
 
@@ -672,7 +674,10 @@ async def register_device(
             )
         else:
             access_token = await self._auth_handler.get_access_token_for_user_id(
-                user_id, device_id=registered_device_id, valid_until_ms=valid_until_ms
+                user_id,
+                device_id=registered_device_id,
+                valid_until_ms=valid_until_ms,
+                is_appservice_ghost=is_appservice_ghost,
             )
 
         return (registered_device_id, access_token)

synapse/replication/http/login.py

@@ -36,7 +36,9 @@ def __init__(self, hs):
         self.registration_handler = hs.get_registration_handler()
 
     @staticmethod
-    async def _serialize_payload(user_id, device_id, initial_display_name, is_guest):
+    async def _serialize_payload(
+        user_id, device_id, initial_display_name, is_guest, is_appservice_ghost
+    ):
         """
         Args:
             device_id (str|None): Device ID to use, if None a new one is
@@ -48,6 +50,7 @@ async def _serialize_payload(user_id, device_id, initial_display_name, is_guest)
             "device_id": device_id,
             "initial_display_name": initial_display_name,
             "is_guest": is_guest,
+            "is_appservice_ghost": is_appservice_ghost,
         }
 
     async def _handle_request(self, request, user_id):
@@ -56,9 +59,14 @@ async def _handle_request(self, request, user_id):
         device_id = content["device_id"]
         initial_display_name = content["initial_display_name"]
         is_guest = content["is_guest"]
+        is_appservice_ghost = content["is_appservice_ghost"]
 
         device_id, access_token = await self.registration_handler.register_device(
-            user_id, device_id, initial_display_name, is_guest
+            user_id,
+            device_id,
+            initial_display_name,
+            is_guest,
+            is_appservice_ghost=is_appservice_ghost,
         )
 
         return 200, {"device_id": device_id, "access_token": access_token}

synapse/rest/client/v2_alpha/register.py

@@ -655,9 +655,13 @@ async def _do_appservice_registration(self, username, as_token, body):
         user_id = await self.registration_handler.appservice_register(
             username, as_token
         )
-        return await self._create_registration_details(user_id, body)
+        return await self._create_registration_details(
+            user_id, body, is_appservice_ghost=True,
+        )
 
-    async def _create_registration_details(self, user_id, params):
+    async def _create_registration_details(
+        self, user_id, params, is_appservice_ghost=False
+    ):
         """Complete registration of newly-registered user
 
         Allocates device_id if one was not given; also creates access_token.
@@ -674,7 +678,11 @@ async def _create_registration_details(self, user_id, params):
             device_id = params.get("device_id")
             initial_display_name = params.get("initial_device_display_name")
             device_id, access_token = await self.registration_handler.register_device(
-                user_id, device_id, initial_display_name, is_guest=False
+                user_id,
+                device_id,
+                initial_display_name,
+                is_guest=False,
+                is_appservice_ghost=is_appservice_ghost,
             )
 
             result.update({"access_token": access_token, "device_id": device_id})

tests/test_mau.py

@@ -19,6 +19,7 @@
 
 from synapse.api.constants import LoginType
 from synapse.api.errors import Codes, HttpResponseException, SynapseError
+from synapse.appservice import ApplicationService
 from synapse.rest.client.v2_alpha import register, sync
 
 from tests import unittest
@@ -75,6 +76,44 @@ def test_simple_deny_mau(self):
         self.assertEqual(e.code, 403)
         self.assertEqual(e.errcode, Codes.RESOURCE_LIMIT_EXCEEDED)
 
+    def test_as_ignores_mau(self):
+        """Test that application services can still create users when the MAU
+        limit has been reached.
+        """
+
+        # Create and sync so that the MAU counts get updated
+        token1 = self.create_user("kermit1")
+        self.do_sync_for_user(token1)
+        token2 = self.create_user("kermit2")
+        self.do_sync_for_user(token2)
+
+        # check we're testing what we think we are: there should be two active users
+        self.assertEqual(self.get_success(self.store.get_monthly_active_count()), 2)
+
+        # We've created and activated two users, we shouldn't be able to
+        # register new users
+        with self.assertRaises(SynapseError) as cm:
+            self.create_user("kermit3")
+
+        e = cm.exception
+        self.assertEqual(e.code, 403)
+        self.assertEqual(e.errcode, Codes.RESOURCE_LIMIT_EXCEEDED)
+
+        # Cheekily add an application service that we use to register a new user
+        # with.
+        as_token = "foobartoken"
+        self.store.services_cache.append(
+            ApplicationService(
+                token=as_token,
+                hostname=self.hs.hostname,
+                id="SomeASID",
+                sender="@as_sender:test",
+                namespaces={"users": [{"regex": "@as_*", "exclusive": True}]},
+            )
+        )
+
+        self.create_user("as_kermit4", token=as_token)
+
     def test_allowed_after_a_month_mau(self):
         # Create and sync so that the MAU counts get updated
         token1 = self.create_user("kermit1")
@@ -192,7 +231,7 @@ def test_tracked_but_not_limited(self):
         self.reactor.advance(100)
         self.assertEqual(2, self.successResultOf(count))
 
-    def create_user(self, localpart):
+    def create_user(self, localpart, token=None):
         request_data = json.dumps(
             {
                 "username": localpart,
@@ -201,7 +240,9 @@ def create_user(self, localpart):
             }
         )
 
-        request, channel = self.make_request("POST", "/register", request_data)
+        request, channel = self.make_request(
+            "POST", "/register", request_data, access_token=token
+        )
 
         if channel.code != 200:
             raise HttpResponseException(