Bug 484322

Consider the following PAM rules for the auth service:

auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        required      pam_deny.so

This works as expected.

Now consider the following rules:

auth        required      pam_env.so
auth        sufficient    pam_krb5.so use_first_pass
auth        required      pam_deny.so

This also works as expected; if Kerberos is correctly configured, authentication will succeed.

But it is undesirable to authenticate system accounts (e.g., root, apache) against Kerberos.  We therefore want to select pam_unix authentication for accounts 0 <= uid <= 1000 (our local account range) and 61000 <= uid <= 61999 (our fedora-usermgmt range).

We can use pam_succeed_if to do this:

auth        required      pam_env.so
auth        [default=ignore success=2] pam_succeed_if.so uid <= 1000 quiet
auth        [default=3 success=ignore] pam_succeed_if.so uid >= 61000 quiet
auth        [default=2 success=ignore] pam_succeed_if.so uid <= 61999 quiet
auth        sufficient    pam_unix.so nullok try_first_pass
auth        required      pam_deny.so
auth        sufficient    pam_krb5.so use_first_pass
auth        required      pam_deny.so

And, indeed, this appears to work: system accounts will hit the pam_unix rule; all other accounts will hit the pam_krb5 rule.

However, I've encountered an unexpected failure: when connecting remotely via ssh using keyboard-interactive, sshd unexpectedly dies:

2009-02-05T19:56:24.136406-05:00 example sshd[15644]: pam_krb5[15644]: authentication succeeds for 'joeuser' (joeuser)
2009-02-05T19:56:24.142610-05:00 example sshd[15642]: Accepted keyboard-interactive/pam for joeuser from 10.0.0.3 port 38559 ssh2
2009-02-05T19:56:24.207110-05:00 example sshd[15642]: fatal: PAM: pam_setcred(): The return value should be ignored by PAM dispatch

When this happens, the client gets a "Connection reset by peer" error, as the server basically just closes the TCP connection and exits; it doesn't bother to perform an orderly shutdown of the ssh session.

This failure occurs ONLY with keyboard-interactive; using "password" or "gssapi-with-mic" authentication works perfectly.

The problem is, "keyboard-interactive" is preferred over "password" for virtually all ssh clients.

I cannot make any sense of the error message, and I cannot see what (if anything) is wrong with the construct I wrote. Furthermore, I can't find any other service that bombs out with these PAM rules.

Are the PAM rules I wrote bogus, or is this a bug in pam (or possibly pam_krb5, or sshd)?