Linux – Console user locked out – pam problems

linuxpamssh

I am trying to enable AD authentication for Debian stable servers to enable users to logon via ssh authenticating against Windows AD. It all works fine and I can ssh to the server using my Windows credentials but I have noticed this message on remote ssh logon when logging on as root:

Your account has been locked. Please contact your System administrator
Your account has been locked. Please contact your System administrator
Your account has been locked. Please contact your System administrator
Last login: Sat Jun 13 14:15:14 2009 from workstation1
server1:~#

I have checked if I can login via local console as root and oops, I cannot. Same error pops up. This could kick me painfully in the future. At the same time I have tried the same setup for RedfHat and I don't have this problem. I believe the problem is somewhere in my pam configuration but can't see where.googling for error does not get me anywhere either.

Below are details for corresponding pam files on Debian and redhat…

Debian Version

common-account

account sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
account sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
account sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
account required    pam_unix.so

common-auth

auth    sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
auth    sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
auth    sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
auth    required    pam_unix.so nullok_secure

common-session

session required        pam_mkhomedir.so skel=/etc/skel/ umask=0022
session sufficient      pam_winbind.so  require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX 
session sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXXX
session sufficient      pam_winbind.so require_membership_of=S-1-5-21-602162358-1844823847-725345543-XXXXX
session required    pam_unix.so

RedHat system-auth file:

auth        required      pam_env.so
auth        sufficient    pam_unix.so nullok try_first_pass
auth        sufficient    pam_winbind.so use_first_pass
auth        requisite     pam_succeed_if.so uid >= 500 quiet
auth        required      pam_deny.so

account     required      pam_unix.so
account     sufficient    pam_succeed_if.so uid < 500 quiet
account     sufficient    pam_winbind.so use_first_pass
account     required      pam_permit.so

password    requisite     pam_cracklib.so try_first_pass retry=3
password    sufficient    pam_unix.so md5 shadow nullok try_first_pass use_authtok
password    sufficient    pam_winbind.so use_first_pass
password    required      pam_deny.so

session     optional      pam_keyinit.so revoke
session     required      pam_limits.so
session     required      pam_winbind.so    use_first_pass
session     [success=1 default=ignore] pam_succeed_if.so service in crond quiet use_uid
session     required      pam_unix.so
session     optional      pam_mkhomedir.so skel=etc/skel/ umask=0027

/etc/pam.d/sshd

# PAM configuration for the Secure Shell service

# Read environment variables from /etc/environment and
# /etc/security/pam_env.conf.
auth       required     pam_env.so # [1]
# In Debian 4.0 (etch), locale-related environment variables were moved to
# /etc/default/locale, so read that as well.
auth       required     pam_env.so envfile=/etc/default/locale

# Standard Un*x authentication.
@include common-auth

# Disallow non-root logins when /etc/nologin exists.
account    required     pam_nologin.so

# Uncomment and edit /etc/security/access.conf if you need to set complex
# access limits that are hard to express in sshd_config.
# account  required     pam_access.so

# Standard Un*x authorization.
@include common-account

# Standard Un*x session setup and teardown.
@include common-session

# Print the message of the day upon successful login.
session    optional     pam_motd.so # [1]

# Print the status of the user's mailbox upon successful login.
session    optional     pam_mail.so standard noenv # [1]

# Set up user limits from /etc/security/limits.conf.
session    required     pam_limits.so

# Set up SELinux capabilities (need modified pam)
# session  required     pam_selinux.so multiple

# Standard Un*x password updating.
@include common-password

Best Answer

For the love of ${Diety}, don't adjust the common-* parts of the PAM stack when experimenting with a new authentication setup. It is the fastest, easiest way to Hole Hawg yourself. You could potentially lock yourself out of the system permanently because of a chicken-and-egg scenario: you are locked out of the system, but you need to log into the system to make the changes needed to prevent you from being locked out.

Consider experimenting on a single service, like SSH (assuming you have console access nearby). Once you have the service prototyped/configured to your exact requirements, don't apply it right away to the common-* files, instead, consider what impact it will have on other system services. Remember, common-* acts as a "catch-all" for most configurations and a single mistake here means a visit to the rescue CD to get it unlocked again. Once you have a good handle on how the config will interact with different services that depend on the system's default(s), then apply it.

Another point to consider is that if you are making this change to common-* to facilitate SSO for all services on the box, it will not catch every service, some services have their own authentication setup and you'll need to check those as well.

As far as the console messages are concerned, what has happened is that winbind is contacting your AD controller, which is seeing excessive failed login attempts. After 15 attempts (which I believe is the out-of-box number MS uses) the account is locked for a period of time, unless an administrator unlocks the account. This is why you're getting "account locked" messages when you log in - the winbind portion of your stack is failing the authentication attempts, and the process "falls through" to the next step in the stack.

I would look hard at your winbind settings to determine that the authentication is truly succeeding in the first place. If you're submitting credentials from a domain member that the AD controller doesn't like, it doesn't matter if the password is correct or not - sooner or later, the account will lock because the request is originating from what is perceived as a non-domain member. The first thing to check would be winbind's join to the domain, as this will affect if the credentials are even looked at. I would also look at how your administrative account is handled by winbind - I seem to recall there were one or two additional settings that were required to ensure proper behavior (I'll dig them out and re-edit when I have them...)

I would also recommend setting up a secondary password on the local linux box, using /etc/passwd, so that you have "fail-though" athentication. Should the winbind service fail to authenticate (and it has in this case) /etc/passwd will pick up the slack and allow you in. The fact that you're able to still get in seems to indicate that you've already done this by setting the local password the same as the AD password for the account your using.

Also consider installing another safety valve in the form of a sudo entry, so that a single, specific account will allow you to switch into root via sudo su.

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