Land rapid7#7490, xml importer fingerprinting fixed

Author: sgonzalez-r7

lib/msf/core/db_manager/import.rb

@@ -86,12 +86,21 @@ def emit(sym,data,&block)
   # is unknown.
   def import(args={}, &block)
     wspace = args[:wspace] || args['wspace'] || workspace
+    preserve_hosts = args[:task].options["DS_PRESERVE_HOSTS"] if args[:task].present? && args[:task].options.present?
     wspace.update_attribute(:import_fingerprint, true)
+    existing_host_ids = wspace.hosts.map(&:id)
     data = args[:data] || args['data']
     ftype = import_filetype_detect(data)
     yield(:filetype, @import_filedata[:type]) if block
     self.send "import_#{ftype}".to_sym, args, &block
-    wspace.hosts.each(&:normalize_os)
+    if preserve_hosts
+      new_host_ids = Mdm::Host.where(workspace: wspace).map(&:id)
+      (new_host_ids - existing_host_ids).each do |id|
+        Mdm::Host.where(id: id).first.normalize_os
+      end
+    else
+      Mdm::Host.where(workspace: wspace).each(&:normalize_os)
+    end
     wspace.update_attribute(:import_fingerprint, false)
   end