From 346476df211a36d008d23990fc53fffc34a1a0d9 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
Date: Thu, 16 Jul 2020 15:17:31 +0100
Subject: [PATCH] Reject attempts to join empty rooms over federation (#7859)
We shouldn't allow others to make_join through us if we've left the room;
reject such attempts with a 404.
Fixes #7835. Fixes #6958.
---
changelog.d/7859.bugfix | 1 +
synapse/handlers/federation.py | 15 +++++++++++++--
2 files changed, 14 insertions(+), 2 deletions(-)
create mode 100644 changelog.d/7859.bugfix
diff --git a/changelog.d/7859.bugfix b/changelog.d/7859.bugfix
new file mode 100644
index 0000000000..19cff4b061
--- /dev/null
+++ b/changelog.d/7859.bugfix
@@ -0,0 +1 @@
+Fix a bug which allowed empty rooms to be rejoined over federation.
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index e43bccd721..df885e45e8 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -44,6 +44,7 @@ from synapse.api.errors import (
FederationDeniedError,
FederationError,
HttpResponseException,
+ NotFoundError,
RequestSendFailed,
SynapseError,
)
@@ -1439,10 +1440,20 @@ class FederationHandler(BaseHandler):
)
raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
- event_content = {"membership": Membership.JOIN}
-
+ # checking the room version will check that we've actually heard of the room
+ # (and return a 404 otherwise)
room_version = await self.store.get_room_version_id(room_id)
+ # now check that we are *still* in the room
+ is_in_room = await self.auth.check_host_in_room(room_id, self.server_name)
+ if not is_in_room:
+ logger.info(
+ "Got /make_join request for room %s we are no longer in", room_id,
+ )
+ raise NotFoundError("Not an active room on this server")
+
+ event_content = {"membership": Membership.JOIN}
+
builder = self.event_builder_factory.new(
room_version,
{
--
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