Description of problem:

(Description from customer)
The option "validate" is used for pam_krb5's auth module. When a user logs in
with an expired passwd, pam_krb5 will request a ticket for kadmin/changepw
instead of krbtgt. The ticket from kadmin/changepw can't be used to request a
service ticket for a local host to verify the local host identity. As a result,
the user authentication failed.  Turning off "validate" works, but will decrease
the security.

The proper behavior should be:
When pam_sm_authenticate request ticket for kadmin/changepw, it should not
validate the local host identity. Then it should return PAM_NEW_AUTHTOK_REQD.
When pam_sm_chauthtok is called, it should change the pwd, and use the new pwd
to validate the local host.

Version-Release number of selected component (if applicable):
pam_krb5-1.79-1

How reproducible:
Always

Steps to Reproduce:

1) Build a RHEL 3 U9 box and make sure you are using the latest pam_krb5-1.79-1
package (behavior also occurs with older versions as well).

2) Add host key to kdc and add the generated key to the client's keytab file.

addprinc -randkey host/hostname
ktadd -k /etc/krb5.keytab host/hostname

3) Setup system-auth to do auth and password sections using pam_krb5. Add the
'validate' option to the auth section of the pam_krb5 module in system-auth.

4) Expire the user's password on the kdc. (modprinc -pwexpire "01/01" user03)

5) Try to log into the client, you will hit the condition in pam_krb5afs.c:2059:

krc = krb5_verify_init_creds(context,
                            &stash->v5_creds,
                            NULL,
                            NULL,
                            NULL,
                            NULL);
if (krc == KRB5_SUCCESS) {
   INFO("TGT for %s successfully verified", user);
} else {
   CRIT("TGT verification failed for `%s'");
}

krb5_verify_init_creds will fail with the password changing credentials and the
user will never be prompted for a password change.

Actual results:
Authentication failure

Expected results:
Authentication succeed after tgt validation.

Additional info:
Patch attached and fixing the issue, written by Paul Batkowski
<pbatkowski>