Centos – Configure Kerberos/PAM on CentOS 7

I'm trying out Kerberos on two VMs running CentOS 7. One VM acts as the server and the other one as a client host where users are supposed to log in.

My complete setup is shown below. When I create a new user to test my setup, this user can SSH (or directly login) into the client host and he automatically gets a Kerberos TGT (klist). But if I run passwd to change the password, I get an error.

In the log (via journalctl) I see the following messages when authenticating for the password change (with the old password):

unix_chkpwd[8790]: password check failed for user (demouser)
passwd[8788]: pam_unix(passwd:chauthtok): authentication failure; logname= uid=1001 euid=0 tty=pts/2 ruser= rhost=  user=demouser

Then I enter the new password twice and get these additional messages in the log:

unix_chkpwd[8792]: password check failed for user (demouser)
passwd[8788]: pam_unix(passwd:chauthtok): user password changed by another process
passwd[8788]: pam_krb5[8788]: password change failed for demouser@EXAMPLE.COM: Cannot contact any KDC for requested realm
passwd[8788]: PAM 1 more authentication failure; logname= uid=1001 euid=0 tty=pts/2 ruser= rhost=  user=demouser

Then on the console I get this message:

passwd: Authentication token manipulation error

Any idea why the login works but the password change doesn't? And how I can fix this?

Server configuration (VM1)

# collect input
DOMAIN=$(hostname -d)
REALM=$(echo "$DOMAIN" | tr '[:lower:]' '[:upper:]')
read -s -p "Kerberos DB Master Password: " KRB_DBMASTER_PW && echo
read -s -p "Kerberos root/admin Password: " KRB_ROOT_PW && echo

# setup ntp
yum -y install ntp
systemctl start ntpd
systemctl enable ntpd

# install kerberos
yum -y install krb5-server krb5-workstation

# replace realm and domain in krb5.conf
sed -i 's|^\(# Confi\)|#\1|' /etc/krb5.conf
sed -i 's|^#||' /etc/krb5.conf
sed -i "s|EXAMPLE\.COM|$REALM|" /etc/krb5.conf
sed -i "s|kerberos\.example\.com|$(hostname -f)|" /etc/krb5.conf
sed -i "s|example\.com|$DOMAIN|" /etc/krb5.conf

# replace realm in kdc.conf and kadm5.acl
sed -i "s|EXAMPLE\.COM|$REALM|" /var/kerberos/krb5kdc/kdc.conf
sed -i "s|EXAMPLE\.COM|$REALM|" /var/kerberos/krb5kdc/kadm5.acl

# initialize kerberos db
echo -e "${KRB_DBMASTER_PW}\n${KRB_DBMASTER_PW}" | kdb5_util create -s -r $REALM

# start kerberos services
systemctl enable kadmin
systemctl enable krb5kdc
systemctl start kadmin
systemctl start krb5kdc
firewall-cmd --permanent --add-service kerberos
firewall-cmd --reload

# add root/admin principal
cat <<-EOF | kadmin.local
    addprinc root/admin
    $KRB_ROOT_PW
    $KRB_ROOT_PW
    quit
EOF

Client configuration (VM2)

# collect input
DOMAIN=$(hostname -d)
REALM=$(echo "$DOMAIN" | tr '[:lower:]' '[:upper:]')
read -p "Server hostname: " SERVER_HOSTNAME
read -s -p "Kerberos root/admin Password: " KRB_ROOT_PW && echo

# setup ntp
yum -y install ntp
systemctl start ntpd
systemctl enable ntpd

# setup kerberos
yum -y install krb5-workstation pam_krb5

# create host principal for this client on the kerberos server
cat <<-EOF | ssh -t $SERVER_HOSTNAME "sudo kadmin.local ; sudo chown $USER /tmp/$(hostname -s).keytab"
    addprinc -randkey host/$(hostname -f)
    ktadd -k /tmp/$(hostname -s).keytab host/$(hostname -f)
    quit
EOF
scp $SERVER_HOSTNAME:\{/tmp/$(hostname -s).keytab,/etc/krb5.conf\} /tmp

# replace krb5.conf
cp /tmp/krb5.conf /etc

# import host key on client
cat <<-EOF | ktutil
    rkt /tmp/$(hostname -s).keytab
    wkt /etc/krb5.keytab
    quit
EOF

# configure pam
authconfig --enablekrb5 --update

Test with new user

1. Create user principal on the server (VM1)

   kadmin
       addprinc demouser
       quit
   

2. Create local user on the client (VM2)

   useradd -m -s /bin/bash demouser
   

3. Log in and change password (from workstation)

   ssh demouser@krbclient
       passwd