Rate limiting invites per issuer (#13125)

Co-authored-by: reivilibre <oliverw@matrix.org>

3 files changed, 24 insertions, 2 deletions

diff --git a/changelog.d/13125.feature b/changelog.d/13125.feature
new file mode 100644

index 0000000000..9b0f609541
--- /dev/null
+++ b/changelog.d/13125.feature
@@ -0,0 +1 @@
+Add a rate limit for local users sending invites.
\ No newline at end of file
diff --git a/synapse/config/ratelimiting.py b/synapse/config/ratelimiting.py

index d4090a1f9a..4fc1784efe 100644
--- a/synapse/config/ratelimiting.py
+++ b/synapse/config/ratelimiting.py
@@ -136,6 +136,11 @@ class RatelimitConfig(Config):
             defaults={"per_second": 0.003, "burst_count": 5},
         )
 
+        self.rc_invites_per_issuer = RateLimitConfig(
+            config.get("rc_invites", {}).get("per_issuer", {}),
+            defaults={"per_second": 0.3, "burst_count": 10},
+        )
+
         self.rc_third_party_invite = RateLimitConfig(
             config.get("rc_third_party_invite", {}),
             defaults={
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py

index bf6bae1232..5648ab4bf4 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -101,19 +101,33 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             burst_count=hs.config.ratelimiting.rc_joins_remote.burst_count,
         )
 
+        # Ratelimiter for invites, keyed by room (across all issuers, all
+        # recipients).
         self._invites_per_room_limiter = Ratelimiter(
             store=self.store,
             clock=self.clock,
             rate_hz=hs.config.ratelimiting.rc_invites_per_room.per_second,
             burst_count=hs.config.ratelimiting.rc_invites_per_room.burst_count,
         )
-        self._invites_per_user_limiter = Ratelimiter(
+
+        # Ratelimiter for invites, keyed by recipient (across all rooms, all
+        # issuers).
+        self._invites_per_recipient_limiter = Ratelimiter(
             store=self.store,
             clock=self.clock,
             rate_hz=hs.config.ratelimiting.rc_invites_per_user.per_second,
             burst_count=hs.config.ratelimiting.rc_invites_per_user.burst_count,
         )
 
+        # Ratelimiter for invites, keyed by issuer (across all rooms, all
+        # recipients).
+        self._invites_per_issuer_limiter = Ratelimiter(
+            store=self.store,
+            clock=self.clock,
+            rate_hz=hs.config.ratelimiting.rc_invites_per_issuer.per_second,
+            burst_count=hs.config.ratelimiting.rc_invites_per_issuer.burst_count,
+        )
+
         self._third_party_invite_limiter = Ratelimiter(
             store=self.store,
             clock=self.clock,
@@ -258,7 +272,9 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         if room_id:
             await self._invites_per_room_limiter.ratelimit(requester, room_id)
 
-        await self._invites_per_user_limiter.ratelimit(requester, invitee_user_id)
+        await self._invites_per_recipient_limiter.ratelimit(requester, invitee_user_id)
+        if requester is not None:
+            await self._invites_per_issuer_limiter.ratelimit(requester)
 
     async def _local_membership_update(
         self,