Replicas aren't allowed to run the replicaof command

src/replication.c

@@ -2038,6 +2038,14 @@ void replicaofCommand(client *c) {
     } else {
         long port;
 
+        if (c->flags & CLIENT_SLAVE)
+        {
+            /* If a client is already a replica they cannot run this command,
+	     * because it involves flushing all replicas (including this client) */
+            addReplyError(c, "Command is not valid when client is a replica.");
+            return;
+        }
+
         if ((getLongFromObjectOrReply(c, c->argv[2], &port, NULL) != C_OK))
             return;