As has been pointed out, it is actually a libc problem. The pam_unix_....so
modules use libc, so these modules will exhibit this unfortunate behavior.
Admins should beware that if libc has a hand in the process of changing a
user's password the corresponding UID entry in /etc/passwd will be
explicitly reset to 0.
Fortunately, pam_pwdb (a plug-in replacement for pam_unix_..), which does
not use libc for any authentication related actions, does not suffer from
this problem. So Linux-PAM based systems can be made resistant to this
"administrative problem" by putting pam_pwdb in all the places that their
pam configuration refers to pam_unix_...
PS. I'd really like to hear from anyone that _can_ break Linux-PAM in any
way... [Use the "source" (Luke ;^)]
Cheers
Andrew
--
Linux-PAM, libpwdb, Orange-Linux and Linux-GSS
http://parc.power.net/morgan/index.html