Control what users can su into
Hi guys, I'm currently in the midst of doing a bit of network admin, in preparation to go live in the near future. In the process, a good portion of that is hardening the server.
My question is: currently I have a user, ssh, that is the only user that can be sshed into. Idea being, it will be more secure. I want to set up this account with NO permissions, other than read/write from its home directory, and su to rootl1. The rootl1 account will be able to access the web server root directory, with read/write permissions, but cannot delete anything. This can su into rootl2, which can delete stuff, but everything is backed up before modifications. This can su into rootl3, and, well, you get the idea.
My question is, how can I make it so that accounts can only su into certain other accounts, and no others? So ssh can su into rootl1, but can only get to rootl2 by going through rootl1 (the idea being that if someone can get into ssh, they would need a bunch more passwords to be able to do anything bad).