Setting up OpenBSD as a ssh gateway

[dbach]

I'm setting up OpenBSD machine as an ssh gateway, (so have to first gain access to this machine before you can get to mail, dns and web servers). Anyone have any suggestions for set. I've been reading a lot but I want to ensure I haven't forgot anything. Also does OpenBSD use PF in place of stand hosts.deny?

Thanks,
Darryl

[jggimi]

I would use authpf(8), it was designed for just this purpose, and you should see if it meets your needs. In brief, a user authenticates with an ssh session, as long as that session is active, a set of rules associated with that user are anchored into your PF ruleset. When that session ends, so do those rules.

There was an interesting discussion in the misc@ mailing list about authpf this week regarding its limitations -- how someone on a NATted network who authenticates would authorize their entire NATted network; and some other possible "tailgating" attacks. I recommend a review of the thread, which began here:

http://marc.info/?l=openbsd-misc&m=131556113701941&w=2

While hosts.deny(5) is an available service, I don't use it, as PF does all I need without the caveats, booby traps, and other problems inherent in the hosts access control language. PF also has the ability to automatically add attackers to block lists, which I prefer.

[dbach]

man page says to set shell to authpf, however in /etc/shells there isn't a selection for authpf, and no such entry in /bin. Do I just add /bin/authpf to /etc/shells and it will allow to create a user with that shell, doesn't seem logical to me.

Just added /bin/authpf to /etc/shells then tried useradd and got to shell selection with the following response:
Enter your default shell: csh ksh nologin sh [ksh]: authpf
authpf: is not allowed

So not sure how to set shell to authpf.

Thanks guys

[jggimi]

The AuthPF shell is a pseudo-shell. The authenticating user does not get anything other than a text message on their ssh terminal session, and keyboard entry is ignored. The shells(5) configuration file need not be altered, since that is to restrict end users to a list of authorized shells when they change shells on their own.

If you have a shell user who will -also- need authentication via AuthPF, that user will need two accounts.

Please see the AuthPF chapter of the PF Users Guide.

[jggimi]

I just saw your update. You are using adduser, a script which builds a configuration file the first time it is used. Check /etc/adduser.conf.

[dbach]

There is no adduser.conf in /etc, is it better to use useradd, or is this just 6 of one 1/2 dozen of another?

Thanks again,
Darryl

[jggimi]

Sorry, I read your update too quickly. I use adduser, rather than useradd, and pointed you to the wrong configuration file. User admin tools are a matter of personal preference. The latter tool uses a different configuration file, usermgmt.conf.

Userid management tools are a matter of personal preference. In this situation, you have yet another choice -- create a "normal" userid and then use vipw(8) to set the shell.