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.

2 files changed, 9 insertions, 5 deletions

diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py

index 5a1e23a145..223aace0d9 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -278,9 +278,7 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
             pdu_to_check.sender_domain,
             e.getErrorMessage(),
         )
-        # XX not really sure if these are the right codes, but they are what
-        # we've done for ages
-        raise SynapseError(400, errmsg, Codes.UNAUTHORIZED)
+        raise SynapseError(403, errmsg, Codes.FORBIDDEN)
 
     for p, d in zip(pdus_to_check_sender, more_deferreds):
         d.addErrback(sender_err, p)
@@ -314,8 +312,7 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
                 "event id %s: unable to verify signature for event id domain: %s"
                 % (pdu_to_check.pdu.event_id, e.getErrorMessage())
             )
-            # XX as above: not really sure if these are the right codes
-            raise SynapseError(400, errmsg, Codes.UNAUTHORIZED)
+            raise SynapseError(403, errmsg, Codes.FORBIDDEN)
 
         for p, d in zip(pdus_to_check_event_id, more_deferreds):
             d.addErrback(event_err, p)
diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py

index 21e52c9695..5fc7c1d67b 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -370,6 +370,7 @@ class FederationServer(FederationBase):
         pdu = event_from_pdu_json(content, format_ver)
         origin_host, _ = parse_server_name(origin)
         yield self.check_server_matches_acl(origin_host, pdu.room_id)
+        pdu = yield self._check_sigs_and_hash(room_version, pdu)
         ret_pdu = yield self.handler.on_invite_request(origin, pdu)
         time_now = self._clock.time_msec()
         return {"event": ret_pdu.get_pdu_json(time_now)}
@@ -386,6 +387,9 @@ class FederationServer(FederationBase):
         yield self.check_server_matches_acl(origin_host, pdu.room_id)
 
         logger.debug("on_send_join_request: pdu sigs: %s", pdu.signatures)
+
+        pdu = yield self._check_sigs_and_hash(room_version, pdu)
+
         res_pdus = yield self.handler.on_send_join_request(origin, pdu)
         time_now = self._clock.time_msec()
         return (
@@ -421,6 +425,9 @@ class FederationServer(FederationBase):
         yield self.check_server_matches_acl(origin_host, pdu.room_id)
 
         logger.debug("on_send_leave_request: pdu sigs: %s", pdu.signatures)
+
+        pdu = yield self._check_sigs_and_hash(room_version, pdu)
+
         yield self.handler.on_send_leave_request(origin, pdu)
         return 200, {}