so, it seems that what i need is a telnet server running on my CentOS box that, instead of calling /bin/login when someone connects, instead starts up a serial session (i'd prefer something more transparent than minicom, if possible). anyone have any good ideas on how to do this? i had been thinking of creating a user for this purpose whose shell was /usr/bin/minicom, but i'm open to other suggestions.
Assuming the network you're on is at least sort of secure, what about a netcat listener connected to /bin/cu ? If you wanted authentication on it as well, perhaps a small C program that netcat is connected to can do the authentication then spawn /bin/cu.
As in: nc -l -p 23 -t -e /bin/cu -l <line> -s <speed>
Just noticed my RHEL3 box doesn't have cu installed, but I'm betting it'd be in a uucp package somewhere.
Change the port, change the line, speed, etc to match whatever you have running. Could always place netcat behind inetd and tcp_wrappers to secure down the inbound to a certain ip/subnet. Also, it looks like GNU Netcat actually has the ability to specify the source that's allowed.