security/unix-selfauth-helper ready for use (screenlockers etc)

Hello everyone,

just a quick notice if you're maintaining a port of some screen locker,
you now *might* want to add security/unix-selfauth-helper as a
RUN_DEPENDS.

Short background is a "special" feature of LinuxPAM that *some* screen
lockers now take for granted: Their pam_unix.so uses a suid-root helper
for the case that you're trying to authenticate as yourself. As a
consequence, a screen locker doesn't need to be suid-root itself (or use
a 3rd-party suid-root helper) in order to use PAM when pam_unix.so might
be used.

I tried to reimplement this feature into our pam_unix.so, which was
rejected, but des@ recommended to use pam_exec.so instead. That's how
unix-selfauth-helper came to be. It must be specifically configured in
the PAM policy used, but it's less intrusive than modifying pam_unix.

To learn how to use it, just have a look at unix-selfauth-helper(8).
You can also look at a review I opened to update xscreensaver to 6.04
(which will need this functionality) as an example here:
<https://reviews.freebsd.org/D35348>.

Best regards, Felix

-- 
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