So I wish to be able to access my Raspberry Pi (which I keep at home behind a firewall) remotely. One option is to use a static IP address, but as a poor student I don't want to fork out for one, and most of the free options are a bit messier (require regular maintenance etc.). As I understand it, another option is to set up a remote SSH tunnel to a server outside my firewall, which will forward connections to a specified localhost port (say 9999) on the server onwards to port 22 on my Raspberry Pi (through said remote SSH tunnel). Broadly I would be following the steps from Raspberry Pi: Phoning Home Using a Reverse Remote Ssh Tunnel, except for a different purpose.
As it happens my university has a student Linux server which I have a shell account on, so setting all that up should be fine. My question is this: given that the student server is shared, will any user with a shell account be able to use the tunnel to my Pi if they happen upon whichever localhost port I've selected (9999 in the above example)? Or will it only allow me to use that port? Is it possible to create such a restriction?
Obviously I'm not that keen on relying upon security by obscurity to protect the connection and would rather that it is only available to me.