"su" does not work

["massimo s." <devicerandom@gmail.com>]

Hi,
I'm using debian gnu/hurd K14.

I have a problem with "su" being unable to recognize any password (root
or any other user). Login and "sush" work.


I've tried:
"su"
"su -"
"su root"
"su testuser" (where testuser is a user just created for test purpose...)

All of these give "incorrect password".
Login as root, "sush root" etc. all flawlessly works.

I have tried to use "sush" but it has problems with $PATH and I don't
know if it's a suitable replacement. Using "sush" and then issuing bash
from the sush shell does not help that much.

I also tried to enable shadow passwords (shadowconfig on), but with no
effect.

Where can I dig to find the error?

Thanks,
m.