Possible bug in PAM pam-0.99.8.1 regarding password changing

[Tomas Mraz]

On Sun, 2007-10-14 at 21:41 +0200, decoder wrote:
> Hello all,
> 
> 
> I ran into problems when using the "requisite" keyword with password
> changing modules. I reduced my problem to a very simple stack which only
> involves 2 instances of pam_debug, to make it easier to understand:
> 
> password   requisite   pam_debug.so prechauthtok=success
> chauthtok=authtok_err
> password   sufficient  pam_debug.so prechauthtok=success chauthtok=success
> 
> This accurately describes the current situation I am having with two pam
> modules (pam_krb5 and pam_smbpass). The first module is failing in the
> change phase because the new password does not satisfy a given policy
> (similar to cracklib policies). Nevertheless, the output for `passwd` as
> a user is:
> 
> decoder at myserver ~ $ passwd
> prechauthtok=success
> prechauthtok=success
> chauthtok=authtok_err
> chauthtok=success
> passwd: Authentication token manipulation error
> 
> 
> As you can see, the second chauthtok is still returning success here,
> although it shouldn't even get called at all! (because of requisite).
> This essentially causes my password databases to go out of sync because
> PAM does not stop although it is told to stop on failure with the
> requisite keyword.
> 
> System Information:
> 
> OS: Gentoo Linux
> Installed PAM version: pam-0.99.8.1-r1 provided by Gentoo portage
> 
> If anyone could verify this behavior, and, if this is not a problem on
> my side, tell me if this is supposed to happen or not, that would help
> me a lot.
> 

This behavior is right. The order of module stack evaluation is frozen
in the first pass (prechauthtok) and because both modules are successful
in the first pass both must be called in the second pass regardless of
requisite keyword. The pam_krb5 module should check the policy in the
prechauthtok pass so the failures in the chauthtok pass would happen
only on special circumstances like a network failure and so on.

-- 
Tomas Mraz
No matter how far down the wrong road you've gone, turn back.
                                              Turkish proverb