Fix failing federation tests

clientapi/routing/sendevent.go

@@ -15,6 +15,7 @@
 package routing
 
 import (
+	"context"
 	"net/http"
 	"sync"
 
@@ -80,6 +81,12 @@ func SendEvent(
 		return *resErr
 	}
 
+	if e.Type() == gomatrixserverlib.MRoomPowerLevels {
+		if ok, plErr := checkPowerLevels(req.Context(), roomID, rsAPI, e); !ok {
+			return *plErr
+		}
+	}
+
 	var txnAndSessionID *api.TransactionID
 	if txnID != nil {
 		txnAndSessionID = &api.TransactionID{
@@ -120,6 +127,46 @@ func SendEvent(
 	return res
 }
 
+func checkPowerLevels(
+	ctx context.Context,
+	roomID string,
+	rsAPI api.RoomserverInternalAPI,
+	event *gomatrixserverlib.Event,
+) (ok bool, response *util.JSONResponse) {
+	req := api.QueryLatestEventsAndStateRequest{RoomID: roomID}
+	res := api.QueryLatestEventsAndStateResponse{}
+	if err := rsAPI.QueryLatestEventsAndState(ctx, &req, &res); err != nil {
+		return false, &util.JSONResponse{
+			Code: http.StatusInternalServerError,
+			JSON: err.Error(),
+		}
+	}
+
+	var creator string
+	for _, v := range res.StateEvents {
+		pl, _ := v.PowerLevels() // we only care about the existence of power levels, so ignore any errors
+		if pl != nil {
+			return true, nil
+		}
+		if v.Type() == gomatrixserverlib.MRoomCreate {
+			creator = v.Sender()
+		}
+	}
+
+	if creator != "" && event.Sender() != creator {
+		logrus.WithFields(logrus.Fields{
+			"creator": creator,
+			"sender":  event.Sender(),
+		}).Warnf("rejecting request to set initial powerlevel, no powerlevels defined and sender != creator")
+		return false, &util.JSONResponse{
+			Code: http.StatusForbidden,
+			JSON: jsonerror.Forbidden("non room creator is not allowed to set initial powerlevels"),
+		}
+	}
+
+	return true, nil
+}
+
 func generateSendEvent(
 	req *http.Request,
 	device *userapi.Device,

roomserver/internal/input/input_events.go

@@ -77,6 +77,12 @@ func (r *Inputer) processRoomEvent(
 		isRejected = true
 	}
 
+	var isPLRejected bool
+	var isPLRejectedErr error
+	if event.Type() == gomatrixserverlib.MRoomPowerLevels {
+		isPLRejected, isPLRejectedErr = r.checkPowerLevels(ctx, event)
+	}
+
 	var softfail bool
 	if input.Kind == api.KindNew {
 		// Check that the event passes authentication checks based on the
@@ -149,7 +155,10 @@ func (r *Inputer) processRoomEvent(
 	}
 
 	// We stop here if the event is rejected: We've stored it but won't update forward extremities or notify anyone about it.
-	if isRejected || softfail {
+	if isRejected || isPLRejected || softfail {
+		if rejectionErr == nil {
+			rejectionErr = isPLRejectedErr
+		}
 		logrus.WithFields(logrus.Fields{
 			"event_id":  event.EventID(),
 			"type":      event.Type(),
@@ -210,6 +219,34 @@ func (r *Inputer) processRoomEvent(
 	return event.EventID(), nil
 }
 
+func (r *Inputer) checkPowerLevels(
+	ctx context.Context, event gomatrixserverlib.Event,
+) (isRejected bool, err error) {
+	req := &api.QueryLatestEventsAndStateRequest{RoomID: event.RoomID()}
+	resp := &api.QueryLatestEventsAndStateResponse{}
+	if err := helpers.QueryLatestEventsAndState(ctx, r.DB, req, resp); err != nil {
+		logrus.WithError(err).Error("helpers.QueryLatestEventsAndState failed to get latest events and state")
+		return true, err
+	}
+	var creator string
+	for _, v := range resp.StateEvents {
+		if v.Type() == gomatrixserverlib.MRoomCreate {
+			creator = v.Sender()
+			break
+		}
+	}
+	if event.Sender() != creator && r.ServerName != event.Origin() {
+		logrus.WithFields(logrus.Fields{
+			"event_id":   event.EventID(),
+			"origin":     event.Origin(),
+			"servername": r.ServerName,
+		}).Error("remote server is not allowed to set powerlevels, rejecting event")
+
+		return true, &gomatrixserverlib.NotAllowed{Message: "remote server is not allowed to set powerlevels"}
+	}
+	return false, nil
+}
+
 func (r *Inputer) calculateAndSetState(
 	ctx context.Context,
 	input *api.InputRoomEvent,

sytest-whitelist

@@ -496,3 +496,5 @@ Forgotten room messages cannot be paginated
 Forgetting room does not show up in v2 /sync
 Can forget room you've been kicked from
 Can re-join room if re-invited
+Remote servers should reject attempts by non-creators to set the power levels
+Remote servers cannot set power levels in rooms without existing powerlevels