Allow use of different ratelimits for admin redactions.

This is useful to allow room admins to quickly deal with a large number
of abusive messages.

synapse/config/ratelimiting.py

@@ -80,6 +80,12 @@ class RatelimitConfig(Config):
             "federation_rr_transactions_per_room_per_second", 50
         )
 
+        rc_admin_redaction = config.get("rc_admin_redaction")
+        if rc_admin_redaction:
+            self.rc_admin_redaction = RateLimitConfig(rc_admin_redaction)
+        else:
+            self.rc_admin_redaction = None
+
     def generate_config_section(self, **kwargs):
         return """\
         ## Ratelimiting ##
@@ -102,6 +108,9 @@ class RatelimitConfig(Config):
         #   - one for login that ratelimits login requests based on the account the
         #     client is attempting to log into, based on the amount of failed login
         #     attempts for this account.
+        #   - one for ratelimiting redactions by room admins. If this is not explicitly
+        #     set then it uses the same ratelimiting as per rc_message. This is useful
+        #     to allow room admins to quickly deal with abuse quickly.
         #
         # The defaults are as shown below.
         #
@@ -123,6 +132,10 @@ class RatelimitConfig(Config):
         #  failed_attempts:
         #    per_second: 0.17
         #    burst_count: 3
+        #
+        #rc_admin_redaction:
+        #  per_second: 1
+        #  burst_count: 50
 
 
         # Ratelimiting settings for incoming federation

synapse/handlers/_base.py

@@ -45,6 +45,7 @@ class BaseHandler(object):
         self.state_handler = hs.get_state_handler()
         self.distributor = hs.get_distributor()
         self.ratelimiter = hs.get_ratelimiter()
+        self.admin_redaction_ratelimiter = hs.get_admin_redaction_ratelimiter()
         self.clock = hs.get_clock()
         self.hs = hs
 
@@ -53,7 +54,7 @@ class BaseHandler(object):
         self.event_builder_factory = hs.get_event_builder_factory()
 
     @defer.inlineCallbacks
-    def ratelimit(self, requester, update=True):
+    def ratelimit(self, requester, update=True, is_admin_redaction=False):
         """Ratelimits requests.
 
         Args:
@@ -62,6 +63,9 @@ class BaseHandler(object):
                 Set to False when doing multiple checks for one request (e.g.
                 to check up front if we would reject the request), and set to
                 True for the last call for a given request.
+            is_admin_redaction (bool): Whether this is a room admin/moderator
+                redacting an event. If so then we may apply different
+                ratelimits depending on config.
 
         Raises:
             LimitExceededError if the request should be ratelimited
@@ -90,16 +94,33 @@ class BaseHandler(object):
             messages_per_second = override.messages_per_second
             burst_count = override.burst_count
         else:
-            messages_per_second = self.hs.config.rc_message.per_second
-            burst_count = self.hs.config.rc_message.burst_count
+            # We default to different values if this is an admin redaction and
+            # the config is set
+            if is_admin_redaction and self.hs.config.rc_admin_redaction:
+                messages_per_second = self.hs.config.rc_admin_redaction.per_second
+                burst_count = self.hs.config.rc_admin_redaction.burst_count
+            else:
+                messages_per_second = self.hs.config.rc_message.per_second
+                burst_count = self.hs.config.rc_message.burst_count
 
-        allowed, time_allowed = self.ratelimiter.can_do_action(
-            user_id,
-            time_now,
-            rate_hz=messages_per_second,
-            burst_count=burst_count,
-            update=update,
-        )
+        if is_admin_redaction and self.hs.config.rc_admin_redaction:
+            # If we have separate config for admin redactions we use a separate
+            # ratelimiter.
+            allowed, time_allowed = self.admin_redaction_ratelimiter.can_do_action(
+                user_id,
+                time_now,
+                rate_hz=messages_per_second,
+                burst_count=burst_count,
+                update=update,
+            )
+        else:
+            allowed, time_allowed = self.ratelimiter.can_do_action(
+                user_id,
+                time_now,
+                rate_hz=messages_per_second,
+                burst_count=burst_count,
+                update=update,
+            )
         if not allowed:
             raise LimitExceededError(
                 retry_after_ms=int(1000 * (time_allowed - time_now))

synapse/handlers/message.py

@@ -729,7 +729,13 @@ class EventCreationHandler(object):
         assert not self.config.worker_app
 
         if ratelimit:
-            yield self.base_handler.ratelimit(requester)
+            is_admin_redaction = (
+                event.type == EventTypes.Redaction
+                and event.sender != requester.user.to_string()
+            )
+            yield self.base_handler.ratelimit(
+                requester, is_admin_redaction=is_admin_redaction
+            )
 
         yield self.base_handler.maybe_kick_guest_users(event, context)
 

synapse/server.py

@@ -221,6 +221,7 @@ class HomeServer(object):
         self.clock = Clock(reactor)
         self.distributor = Distributor()
         self.ratelimiter = Ratelimiter()
+        self.admin_redaction_ratelimiter = Ratelimiter()
         self.registration_ratelimiter = Ratelimiter()
 
         self.datastore = None
@@ -279,6 +280,9 @@ class HomeServer(object):
     def get_registration_ratelimiter(self):
         return self.registration_ratelimiter
 
+    def get_admin_redaction_ratelimiter(self):
+        return self.admin_redaction_ratelimiter
+
     def build_federation_client(self):
         return FederationClient(self)