Add rate-limiting on registration (#4735)

* Rate-limiting for registration

* Add unit test for registration rate limiting

* Add config parameters for rate limiting on auth endpoints

* Doc

* Fix doc of rate limiting function

Co-Authored-By: babolivier <contact@brendanabolivier.com>

* Incorporate review

* Fix config parsing

* Fix linting errors

* Set default config for auth rate limiting

* Fix tests

* Add changelog

* Advance reactor instead of mocked clock

* Move parameters to registration specific config and give them more sensible default values

* Remove unused config options

* Don't mock the rate limiter un MAU tests

* Rename _register_with_store into register_with_store

* Make CI happy

* Remove unused import

* Update sample config

* Fix ratelimiting test for py2

* Add non-guest test

synapse/rest/client/v2_alpha/register.py

@@ -25,7 +25,12 @@ from twisted.internet import defer
 import synapse
 import synapse.types
 from synapse.api.constants import LoginType
-from synapse.api.errors import Codes, SynapseError, UnrecognizedRequestError
+from synapse.api.errors import (
+    Codes,
+    LimitExceededError,
+    SynapseError,
+    UnrecognizedRequestError,
+)
 from synapse.config.server import is_threepid_reserved
 from synapse.http.servlet import (
     RestServlet,
@@ -191,18 +196,36 @@ class RegisterRestServlet(RestServlet):
         self.identity_handler = hs.get_handlers().identity_handler
         self.room_member_handler = hs.get_room_member_handler()
         self.macaroon_gen = hs.get_macaroon_generator()
+        self.ratelimiter = hs.get_ratelimiter()
+        self.clock = hs.get_clock()
 
     @interactive_auth_handler
     @defer.inlineCallbacks
     def on_POST(self, request):
         body = parse_json_object_from_request(request)
 
+        client_addr = request.getClientIP()
+
+        time_now = self.clock.time()
+
+        allowed, time_allowed = self.ratelimiter.can_do_action(
+            client_addr, time_now_s=time_now,
+            rate_hz=self.hs.config.rc_registration_requests_per_second,
+            burst_count=self.hs.config.rc_registration_request_burst_count,
+            update=False,
+        )
+
+        if not allowed:
+            raise LimitExceededError(
+                retry_after_ms=int(1000 * (time_allowed - time_now)),
+            )
+
         kind = b"user"
         if b"kind" in request.args:
             kind = request.args[b"kind"][0]
 
         if kind == b"guest":
-            ret = yield self._do_guest_registration(body)
+            ret = yield self._do_guest_registration(body, address=client_addr)
             defer.returnValue(ret)
             return
         elif kind != b"user":
@@ -411,6 +434,7 @@ class RegisterRestServlet(RestServlet):
                 guest_access_token=guest_access_token,
                 generate_token=False,
                 threepid=threepid,
+                address=client_addr,
             )
             # Necessary due to auth checks prior to the threepid being
             # written to the db
@@ -522,12 +546,13 @@ class RegisterRestServlet(RestServlet):
         defer.returnValue(result)
 
     @defer.inlineCallbacks
-    def _do_guest_registration(self, params):
+    def _do_guest_registration(self, params, address=None):
         if not self.hs.config.allow_guest_access:
             raise SynapseError(403, "Guest access is disabled")
         user_id, _ = yield self.registration_handler.register(
             generate_token=False,
-            make_guest=True
+            make_guest=True,
+            address=address,
         )
 
         # we don't allow guests to specify their own device_id, because