I am setting up a Linux server similar to a TCP echo server and am wondering about security issues I should be concerned about. This will be a bare bones Centos/KDE server with no additional files other than my server binary listening on a port of my choice. Assuming I don't have any buffer overflows or similar security flaws in my server and if I configure the server to drop all non-TCP traffic on all ports except for the one my server is listening on, do I have much to worry about? The server runs from user with execute only permissions and I use a STRONG root password. Am I missing anything? Thanks.
You could use xinetd to limit the number of concurrent connections otherwise it will be easy to do a DDOS on you. xinetd also has several other useful features to strengthen things.
Can you restrict access from a certain number of hosts - if so then firewall off the rest of the world for that port.
If you are allowing external ssh access to this system, then move sshd to a non standard port and do not allow root logins. Ideally use ssh keys instead of or with passwords.