Improve signature checking on some federation APIs (#6262)

Make sure that we check that events sent over /send_join, /send_leave, and
/invite, are correctly signed and come from the expected servers.

1 files changed, 18 insertions, 2 deletions

diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 4b4c6c15f9..488058fe68 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1222,7 +1222,6 @@ class FederationHandler(BaseHandler):
         Returns:
             Deferred[FrozenEvent]
         """
-
         if get_domain_from_id(user_id) != origin:
             logger.info(
                 "Got /make_join request for user %r from different origin %s, ignoring",
@@ -1280,11 +1279,20 @@ class FederationHandler(BaseHandler):
         event = pdu
 
         logger.debug(
-            "on_send_join_request: Got event: %s, signatures: %s",
+            "on_send_join_request from %s: Got event: %s, signatures: %s",
+            origin,
             event.event_id,
             event.signatures,
         )
 
+        if get_domain_from_id(event.sender) != origin:
+            logger.info(
+                "Got /send_join request for user %r from different origin %s",
+                event.sender,
+                origin,
+            )
+            raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
+
         event.internal_metadata.outlier = False
         # Send this event on behalf of the origin server.
         #
@@ -1503,6 +1511,14 @@ class FederationHandler(BaseHandler):
             event.signatures,
         )
 
+        if get_domain_from_id(event.sender) != origin:
+            logger.info(
+                "Got /send_leave request for user %r from different origin %s",
+                event.sender,
+                origin,
+            )
+            raise SynapseError(403, "User not from origin", Codes.FORBIDDEN)
+
         event.internal_metadata.outlier = False
 
         context = yield self._handle_new_event(origin, event)