Add a spamchecker callback to allow or deny room joins (#10910)

Co-authored-by: Erik Johnston <erik@matrix.org>

2 files changed, 33 insertions, 0 deletions

diff --git a/synapse/handlers/room.py b/synapse/handlers/room.py
index 873e08258e..d40dbd761d 100644
--- a/synapse/handlers/room.py
+++ b/synapse/handlers/room.py
@@ -860,6 +860,7 @@ class RoomCreationHandler(BaseHandler):
                     "invite",
                     ratelimit=False,
                     content=content,
+                    new_room=True,
                 )
 
         for invite_3pid in invite_3pid_list:
@@ -962,6 +963,7 @@ class RoomCreationHandler(BaseHandler):
             "join",
             ratelimit=ratelimit,
             content=creator_join_profile,
+            new_room=True,
         )
 
         # We treat the power levels override specially as this needs to be one
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index c8fb24a20c..0b79dbcf8d 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -434,6 +434,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         third_party_signed: Optional[dict] = None,
         ratelimit: bool = True,
         content: Optional[dict] = None,
+        new_room: bool = False,
         require_consent: bool = True,
         outlier: bool = False,
         prev_event_ids: Optional[List[str]] = None,
@@ -451,6 +452,8 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             third_party_signed: Information from a 3PID invite.
             ratelimit: Whether to rate limit the request.
             content: The content of the created event.
+            new_room: Whether the membership update is happening in the context of a room
+                creation.
             require_consent: Whether consent is required.
             outlier: Indicates whether the event is an `outlier`, i.e. if
                 it's from an arbitrary point and floating in the DAG as
@@ -485,6 +488,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                 third_party_signed=third_party_signed,
                 ratelimit=ratelimit,
                 content=content,
+                new_room=new_room,
                 require_consent=require_consent,
                 outlier=outlier,
                 prev_event_ids=prev_event_ids,
@@ -504,6 +508,7 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
         third_party_signed: Optional[dict] = None,
         ratelimit: bool = True,
         content: Optional[dict] = None,
+        new_room: bool = False,
         require_consent: bool = True,
         outlier: bool = False,
         prev_event_ids: Optional[List[str]] = None,
@@ -523,6 +528,8 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
             third_party_signed:
             ratelimit:
             content:
+            new_room: Whether the membership update is happening in the context of a room
+                creation.
             require_consent:
             outlier: Indicates whether the event is an `outlier`, i.e. if
                 it's from an arbitrary point and floating in the DAG as
@@ -726,6 +733,30 @@ class RoomMemberHandler(metaclass=abc.ABCMeta):
                     # so don't really fit into the general auth process.
                     raise AuthError(403, "Guest access not allowed")
 
+            # Figure out whether the user is a server admin to determine whether they
+            # should be able to bypass the spam checker.
+            if (
+                self._server_notices_mxid is not None
+                and requester.user.to_string() == self._server_notices_mxid
+            ):
+                # allow the server notices mxid to join rooms
+                bypass_spam_checker = True
+
+            else:
+                bypass_spam_checker = await self.auth.is_server_admin(requester.user)
+
+            inviter = await self._get_inviter(target.to_string(), room_id)
+            if (
+                not bypass_spam_checker
+                # We assume that if the spam checker allowed the user to create
+                # a room then they're allowed to join it.
+                and not new_room
+                and not await self.spam_checker.user_may_join_room(
+                    target.to_string(), room_id, is_invited=inviter is not None
+                )
+            ):
+                raise SynapseError(403, "Not allowed to join this room")
+
             # Check if a remote join should be performed.
             remote_join, remote_room_hosts = await self._should_perform_remote_join(
                 target.to_string(), room_id, remote_room_hosts, content, is_host_in_room