Pass-through proxy?

Forgive me if I'm using incorrect terminology...

I would like to allow some external MS clients to query an internal
MSSQL database via a proxy service on a Linux machine. This would
ideally just pass through select queries and block
update/insert/delete, etc., only allow certain IP's. It should look
like a client to the server and a server to the clients.

It seems like this would be relatively simple since it's speaking TDS
on both ends, is that right? Is there anything out there that does
this? If not, would you recommend against my writing something to do
that using the FreeTDS library?

Thanks for any suggestions.

-Steve