From 0a65450d044fb580d789013dcdac48b10c930761 Mon Sep 17 00:00:00 2001
From: Richard van der Hoff <richard@matrix.org>
Date: Thu, 2 Aug 2018 11:53:52 +0100
Subject: [PATCH] Validation for events/rooms in fed requests

When we get a federation request which refers to an event id, make sure that
said event is in the room the caller claims it is in.

(patch supplied by @turt2live)
---
 synapse/federation/federation_server.py |  1 +
 synapse/handlers/federation.py          | 35 ++++++++++++++++++++++++-
 synapse/storage/event_federation.py     | 29 ++++++++++++++++++++
 3 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/synapse/federation/federation_server.py b/synapse/federation/federation_server.py
index 48f26db67..10e71c78c 100644
--- a/synapse/federation/federation_server.py
+++ b/synapse/federation/federation_server.py
@@ -425,6 +425,7 @@ class FederationServer(FederationBase):
             ret = yield self.handler.on_query_auth(
                 origin,
                 event_id,
+                room_id,
                 signed_auth,
                 content.get("rejects", []),
                 content.get("missing", []),
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index 20fb46fc8..12eeb7c4c 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -1349,6 +1349,9 @@ class FederationHandler(BaseHandler):
     def get_state_for_pdu(self, room_id, event_id):
         """Returns the state at the event. i.e. not including said event.
         """
+
+        yield self._verify_events_in_room([event_id], room_id)
+
         state_groups = yield self.store.get_state_groups(
             room_id, [event_id]
         )
@@ -1391,6 +1394,9 @@ class FederationHandler(BaseHandler):
     def get_state_ids_for_pdu(self, room_id, event_id):
         """Returns the state at the event. i.e. not including said event.
         """
+
+        yield self._verify_events_in_room([event_id], room_id)
+
         state_groups = yield self.store.get_state_groups_ids(
             room_id, [event_id]
         )
@@ -1420,6 +1426,8 @@ class FederationHandler(BaseHandler):
         if not in_room:
             raise AuthError(403, "Host not in room.")
 
+        yield self._verify_events_in_room(pdu_list, room_id)
+
         events = yield self.store.get_backfill_events(
             room_id,
             pdu_list,
@@ -1706,8 +1714,17 @@ class FederationHandler(BaseHandler):
         defer.returnValue(context)
 
     @defer.inlineCallbacks
-    def on_query_auth(self, origin, event_id, remote_auth_chain, rejects,
+    def on_query_auth(self, origin, event_id, room_id, remote_auth_chain, rejects,
                       missing):
+        in_room = yield self.auth.check_host_in_room(
+            room_id,
+            origin
+        )
+        if not in_room:
+            raise AuthError(403, "Host not in room.")
+
+        yield self._verify_events_in_room([event_id], room_id)
+
         # Just go through and process each event in `remote_auth_chain`. We
         # don't want to fall into the trap of `missing` being wrong.
         for e in remote_auth_chain:
@@ -2368,3 +2385,19 @@ class FederationHandler(BaseHandler):
             )
         if "valid" not in response or not response["valid"]:
             raise AuthError(403, "Third party certificate was invalid")
+
+    @defer.inlineCallbacks
+    def _verify_events_in_room(self, pdu_ids, room_id):
+        """Checks whether the given PDU IDs are in the given room or not.
+
+        Args:
+            pdu_ids (list): list of PDU IDs
+            room_id (str): the room ID that the PDUs should be in
+
+        Raises:
+            AuthError: if one or more of the PDUs does not belong to the
+                given room.
+        """
+        room_ids = yield self.store.get_room_ids_for_events(pdu_ids)
+        if len(room_ids) != 1 or room_ids[0] != room_id:
+            raise AuthError(403, "Events must belong to the given room")
diff --git a/synapse/storage/event_federation.py b/synapse/storage/event_federation.py
index 8d366d1b9..e860fe1a1 100644
--- a/synapse/storage/event_federation.py
+++ b/synapse/storage/event_federation.py
@@ -295,6 +295,35 @@ class EventFederationWorkerStore(EventsWorkerStore, SignatureWorkerStore,
             get_forward_extremeties_for_room_txn
         )
 
+    def get_room_ids_for_events(self, event_ids):
+        """Get a list of room IDs for which the given events belong.
+
+        Args:
+            event_ids (list): the events to look up the room of
+
+        Returns:
+            list, the room IDs for the events
+        """
+        return self.runInteraction(
+            "get_room_ids_for_events",
+            self._get_room_ids_for_events, event_ids
+        )
+
+    def _get_room_ids_for_events(self, txn, event_ids):
+        logger.debug("_get_room_ids_for_events: %s", repr(event_ids))
+
+        base_sql = (
+            "SELECT DISTINCT room_id FROM events"
+            " WHERE event_id IN (%s)"
+        )
+
+        txn.execute(
+            base_sql % (",".join(["?"] * len(event_ids)),),
+            event_ids
+        )
+
+        return [r[0] for r in txn]
+
     def get_backfill_events(self, room_id, event_list, limit):
         """Get a list of Events for a given topic that occurred before (and
         including) the events in event_list. Return a list of max size `limit`