We assign tasks to someone who suppose to pick up needed files from parent tasks. The only available permissions now in Redmine are:

All Issues¶

All non-private issues¶

Issues created by or assigned to the user¶

I need something between item #2 and #3 so an assignee be able to see only parent task of an assigned task.
It also could be like this: see the parent/child tasks but not be able to edit them. This way s/he can see the tasks but is not able to edit them and this need would be fulfilled.