bin/89770: pam_krb5 'authentication token failure' in passwd and a patch for it

Toby Karyadi toby at
Wed Nov 30 19:20:22 GMT 2005

>Number:         89770
>Category:       bin
>Synopsis:       pam_krb5 'authentication token failure' in passwd and a patch for it
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Nov 30 19:20:02 GMT 2005
>Originator:     Toby Karyadi
>Release:        6.0-RELEASE
FreeBSD myhost 6.0-RELEASE FreeBSD 6.0-RELEASE #0: Thu Nov  3 09:36:13 UTC 2005
     root at x64.samsco.home:/usr/obj/usr/src/sys/GENERIC  i386              
/usr/bin/passwd spits out the following error message:

myhost% passwd
Changing local password for moi
Old password: 
passwd: pam_chauthtok(): authentication token failure

This only happens when the pam configuration is specified to use, for example like in the following /etc/pam.d/passwd file:

# PAM configuration for the "passwd" service

# passwd(1) does not use the auth, account or session services.

# password
password        required             no_warn try_first_pass
password        required             try_first_pass              
Please read problem description for repro steps. Note, I assume that kerberos, (Heimdal, to be specific) has been setup properly, i.e. all of the k* tools works right and that kdc, kadmindd, kpasswdd all are up and running.
The problem is because the function pam_sm_chauthtok() in src/lib/libpam/modules/pam_krb5/pam_krb5.c does not handle the case where the PAM_PRELIM_CHECK is set. In comparison, pam_unix.c handles it by asking for the old password and return PAM_SUCCESS only if the old password is correct. The fix is simply to return PAM_SUCCESS when the PAM_PRELIM_CHECK is set above the code that checks if the PAM_UPDATE_AUTHTOK is set.

Also look at src/contrib/openpam/lib/pam_chauthtok.c to see the calling sequence into pam_sm_chauthtok() of the pam modules.

Below is the patch. 

For those who're not familier with patching (otherwise skip this section):
1. Copy the text from --- until the end of this message into a file, call it pam_krb5.c.patch
2. Put the file in /usr/src/lib/libpam/modules/pam_krb5/ and cd into that dir.
3. yourhost% patch < pam_krb5.c.patch
4. make clean
5. make
6. make install


--- pam_krb5.c.orig     Thu Jul  7 14:16:38 2005
+++ pam_krb5.c  Tue Nov 29 16:12:41 2005
@@ -666,6 +666,9 @@
        const void *user;
        char *princ_name, *passdup;

+       if (flags & PAM_PRELIM_CHECK)
+               return PAM_SUCCESS;
        if (!(flags & PAM_UPDATE_AUTHTOK))
                return (PAM_AUTHTOK_ERR);


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