Configuring Kerberos Clients

Kerberos clients include any host, that is not a KDC server, on the network that needs to use Kerberos services. This section provides procedures for installing a Kerberos client, as well as specific information about using root authentication to mount NFS file systems.

Configuring Kerberos Clients (Task Map)

The following task map includes all of the procedures associated with setting up Kerberos clients. Each row includes a task identifier, a description of why you would want to do that task, followed by a link to the task.

How to Create a Kerberos Client Installation Profile

This procedure creates a kclient profile that can be used when you install a Kerberos client. By using the kclient profile, you reduce the likelihood of typing errors. Also, using the profile reduces user intervention as compared to the interactive process.

1. Become superuser.

2. Create a kclient installation profile.

   A sample kclient profile could look similar to the following:

   client# cat /net/denver.example.com/export/install/profile REALM EXAMPLE.COM KDC kdc1.example.com ADMIN clntconfig FILEPATH /net/denver.example.com/export/install/krb5.conf NFS 1 DNSLOOKUP none

How to Automatically Configure a Kerberos Client

Before You Begin

This procedure uses an installation profile. See How to Create a Kerberos Client Installation Profile.

1. Become superuser.

2. Run the kclient installation script.

   You need to provide the password for the clntconfig principal to complete the process.

   client# /usr/sbin/kclient -p /net/denver.example.com/export/install/profile Starting client setup --------------------------------------------------- kdc1.example.com Setting up /etc/krb5/krb5.conf. Obtaining TGT for clntconfig/admin ... Password for clntconfig/admin@EXAMPLE.COM: <Type the password> nfs/client.example.com entry ADDED to KDC database. nfs/client.example.com entry ADDED to keytab. host/client.example.com entry ADDED to KDC database. host/client.example.com entry ADDED to keytab. Copied /net/denver.example.com/export/install/krb5.conf. --------------------------------------------------- Setup COMPLETE. client#

Example 23–7 Automatically Configuring a Kerberos Client With Command-Line Overrides

The following example overrides the DNSARG and the KDC parameters that are set in the installation profile.

# /usr/sbin/kclient -p /net/denver.example.com/export/install/profile\
-d dns_fallback -k kdc2.example.com

Starting client setup
---------------------------------------------------

kdc1.example.com

Setting up /etc/krb5/krb5.conf.

Obtaining TGT for clntconfig/admin ...
Password for clntconfig/admin@EXAMPLE.COM: <Type the password>

nfs/client.example.com entry ADDED to KDC database.
nfs/client.example.com entry ADDED to keytab.

host/client.example.com entry ADDED to KDC database.
host/client.example.com entry ADDED to keytab.

Copied /net/denver.example.com/export/install/krb5.conf.

---------------------------------------------------
Setup COMPLETE.

client#

How to Interactively Configure a Kerberos Client

This procedure uses the kclient installation utility without a installation profile.

1. Become superuser.

2. Run the kclient installation script.

   You need to provide the following information:

   • Kerberos realm name

   • KDC master host name

   • Administrative principal name

   • Password for the administrative principal

Example 23–8 Running the kclient Installation Utility

The following output shows the results of running the kclient command.

client# /usr/sbin/kclient

Starting client setup
---------------------------------------------------

Do you want to use DNS for kerberos lookups ? [y/n]: n
        No action performed.
Enter the Kerberos realm: EXAMPLE.COM
Specify the KDC hostname for the above realm: kdc1.example.com

Setting up /etc/krb5/krb5.conf.

Enter the krb5 administrative principal to be used: clntconfig/admin
Obtaining TGT for clntconfig/admin ...
Password for clntconfig/admin@EXAMPLE.COM: <Type the password>
Do you plan on doing Kerberized nfs ? [y/n]: n

host/client.example.com entry ADDED to KDC database.
host/client.example.com entry ADDED to keytab.

Do you want to copy over the master krb5.conf file ? [y/n]: y
Enter the pathname of the file to be copied: \
/net/denver.example.com/export/install/krb5.conf

Copied /net/denver.example.com/export/install/krb5.conf.

---------------------------------------------------
Setup COMPLETE !
#

How to Manually Configure a Kerberos Client

In this procedure, the following configuration parameters are used:

• Realm name = EXAMPLE.COM

• DNS domain name = example.com

• Master KDC = kdc1.example.com

• Slave KDC = kdc2.example.com

• NFS server = denver.example.com

• Client = client.example.com

• admin principal = kws/admin

• User principal = mre

• Online help URL = http://denver:8888/ab2/coll.384.1/SEAM/@AB2PageView/6956

  ---

  Note –

  Adjust the URL to point to the “Graphical Kerberos Administration Tool” section, as described in the Online Help URL in the Graphical Kerberos Administration Tool.

  ---

1. Become superuser.

2. Edit the Kerberos configuration file (krb5.conf).

   To change the file from the Kerberos default version, you need to change the realm names and the server names. You also need to identify the path to the help files for gkadmin.

   kdc1 # cat /etc/krb5/krb5.conf [libdefaults] default_realm = EXAMPLE.COM [realms] EXAMPLE.COM = { kdc = kdc1.example.com kdc = kdc2.example.com admin_server = kdc1.example.com } [domain_realm] .example.com = EXAMPLE.COM # # if the domain name and realm name are equivalent, # this entry is not needed # [logging] default = FILE:/var/krb5/kdc.log kdc = FILE:/var/krb5/kdc.log [appdefaults] gkadmin = { help_url = http://denver:8888/ab2/coll.384.1/SEAM/@AB2PageView/6956

   ---

   Note –

   If you want to restrict the encryption types, you can set the default_tkt_enctypes or default_tgs_enctypes lines. Refer to Using Kerberos Encryption Types for a description of the issues involved with restricting the encryption types.

   ---

3. (Optional) Change the process used to locate the KDCs.

   Starting with the Solaris 10 5/08release, by default the Kerberos realm to KDC mapping is determined in the following order:

   • The definition in the realms section in krb5.conf.

   • By looking up SRV records in DNS.

   You can change this behavior by adding dns_lookup_kdc or dns_fallback to the libdefaults section of the krb5.conf file. See the krb5.conf(4) man page for more information. Note that referrals are always tried first.

4. (Optional) Change the process used to determine the realm for a host.

   Starting with the Solaris 10 5/08release, by default the host to realm mapping is determined in the following order:

   • If the KDC supports referrals, then the KDC may inform the client which realm the host belongs to.

   • By the definition of domain_realm in the krb5.conf file.

   • The DNS domainname of the host.

   • The default realm.

   You can change this behavior by adding dns_lookup_kdc or dns_fallback to the libdefaults section of the krb5.conffile. See the krb5.conf(4) man page for more information. Note that referrals will always be tried first.

5. (Optional) Synchronize the client's clock with the master KDC's clock by using NTP or another clock synchronization mechanism.

   Installing and using the Network Time Protocol (NTP) is not required. However, every clock must be synchronized with the time on the KDC server within a maximum difference defined in the clockskew relation in the krb5.conf file for authentication to succeed. See Synchronizing Clocks Between KDCs and Kerberos Clients for information about NTP.

6. Start kadmin.

   You can use the Graphical Kerberos Administration Tool to add a principal, as explained in How to Create a New Kerberos Principal. To do so, you must log in with one of the admin principal names that you created when you configured the master KDC. However, the following example shows how to add the required principals by using the command line.

   denver # /usr/sbin/kadmin -p kws/admin Enter password: <Type kws/admin password> kadmin:

   1. (Optional) Create a user principal if a user principal does not already exist.

      You need to create a user principal only if the user associated with this host does not already have a principal assigned to him or her.

      kadmin: addprinc mre Enter password for principal mre@EXAMPLE.COM: <Type the password> Re-enter password for principal mre@EXAMPLE.COM: <Type it again> kadmin:

   2. (Optional) Create a root principal and add the principal to the server's keytab file.

      This step is required so that the client can have root access to file systems mounted using the NFS service. This step is also required if non-interactive root access is needed, such as running cron jobs as root.

      If the client does not require root access to a remote file system which is mounted using the NFS service, then you can skip this step. The root principal should be a two component principal with the second component the host name of the Kerberos client system to avoid the creation of a realm wide root principal. Note that when the principal instance is a host name, the FQDN must be specified in lowercase letters, regardless of the case of the domain name in the /etc/resolv.conf file.

      kadmin: addprinc -randkey root/client.example.com Principal "root/client.example.com" created. kadmin: ktadd root/client.example.com Entry for principal root/client.example.com with kvno 3, encryption type AES-256 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type AES-128 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 added to keytab WRFILE:/etc/krb5/krb5.keytab. kadmin:

   3. Create a host principal and add the principal to the server's keytab file.

      The host principal is used by remote access services to provide authentication. The principal allows root to acquire a credential, if there is not one already in the keytab file.

      kadmin: addprinc -randkey host/denver.example.com Principal "host/denver.example.com@EXAMPLE.COM" created. kadmin: ktadd host/denver.example.com Entry for principal host/denver.example.com with kvno 3, encryption type AES-256 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal host/denver.example.com with kvno 3, encryption type AES-128 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal host/denver.example.com with kvno 3, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal host/denver.example.com with kvno 3, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal host/denver.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 added to keytab WRFILE:/etc/krb5/krb5.keytab. kadmin:

   4. (Optional) Add the server's NFS service principal to the server's keytab file.

      This step is only required if the client needs to access NFS file systems using Kerberos authentication.

      kadmin: ktadd nfs/denver.example.com Entry for principal nfs/denver.example.com with kvno 3, encryption type AES-256 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal nfs/denver.example.com with kvno 3, encryption type AES-128 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal nfs/denver.example.com with kvno 3, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal nfs/denver.example.com with kvno 3, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal nfs/denver.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 added to keytab WRFILE:/etc/krb5/krb5.keytab. kadmin:

   5. Quit kadmin.

      kadmin: quit

7. (Optional) Enable Kerberos with NFS.

   1. Enable Kerberos security modes in the /etc/nfssec.conf file.

      Edit the /etc/nfssec.conf file and remove the “#” that is placed in front of the Kerberos security modes.

      # cat /etc/nfssec.conf . . # # Uncomment the following lines to use Kerberos V5 with NFS # krb5 390003 kerberos_v5 default - # RPCSEC_GSS krb5i 390004 kerberos_v5 default integrity # RPCSEC_GSS krb5p 390005 kerberos_v5 default privacy # RPCSEC_GSS

   2. Enable DNS.

      If the /etc/resolv.conf file has not already been created, then create this file as the service principal canonicalization is dependent upon DNS to do this. See the resolv.conf(4) man page for more information.

   3. Restart the gssd service.

      After the /etc/resolv.conf file has been created or modified you must then restart the gssd daemon to reread any changes.

      # svcadm restart network/rpc/gss

8. If you want the client to automatically renew the TGT or to warn users about Kerberos ticket expiration, create an entry in the /etc/krb5/warn.conf file.

   See the warn.conf(4) man page for more information.

Example 23–9 Setting Up a Kerberos Client Using a Non-Solaris KDC

A Kerberos client can be set up to work with a non-Solaris KDC. In this case, a line must be included in the /etc/krb5/krb5.conf file in the realms section. This line changes the protocol that is used when the client is communicating with the Kerberos password-changing server. The format of this line follows.

[realms]
                EXAMPLE.COM = {
                kdc = kdc1.example.com
                kdc = kdc2.example.com
                admin_server = kdc1.example.com
                kpasswd_protocol = SET_CHANGE
        }

Example 23–10 DNS TXT Records for the Mapping of Host and Domain Name to Kerberos Realm

@ IN SOA kdc1.example.com root.kdc1.example.com (
                                1989020501   ;serial
                                10800        ;refresh
                                3600         ;retry
                                3600000      ;expire
                                86400 )      ;minimum

                        IN      NS      kdc1.example.com.
kdc1                    IN      A       192.146.86.20
kdc2                    IN      A       192.146.86.21

_kerberos.example.com.             IN      TXT     "EXAMPLE.COM"
_kerberos.kdc1.example.com.        IN      TXT     "EXAMPLE.COM"
_kerberos.kdc2.example.com.        IN      TXT     "EXAMPLE.COM"

Example 23–11 DNS SRV Records for Kerberos Server Locations

This example defines the records for the location of the KDCs, the admin server, and the kpasswd server, respectively.

@ IN SOA kdc1.example.com root.kdc1.example.com (
                                1989020501   ;serial
                                10800        ;refresh
                                3600         ;retry
                                3600000      ;expire
                                86400 )      ;minimum

                                   IN      NS      kdc1.example.com.
kdc1                               IN      A       192.146.86.20
kdc2                               IN      A       192.146.86.21

_kerberos._udp.EXAMPLE.COM         IN      SRV 0 0 88  kdc2.example.com
_kerberos._tcp.EXAMPLE.COM         IN      SRV 0 0 88  kdc2.example.com
_kerberos._udp.EXAMPLE.COM         IN      SRV 1 0 88  kdc1.example.com
_kerberos._tcp.EXAMPLE.COM         IN      SRV 1 0 88  kdc1.example.com
_kerberos-adm._tcp.EXAMPLE.COM     IN      SRV 0 0 749 kdc1.example.com
_kpasswd._udp.EXAMPLE.COM          IN      SRV 0 0 749 kdc1.example.com

How to Disable Verification of the Ticket Granting Ticket (TGT)

This procedure disables the security check that checks that the KDC of the host principal stored in the local /etc/krb5/krb5.keytab file is the same KDC that issued the Ticket Granting Ticket. This check prevents DNS spoofing attacks. However, for some client configurations, the host principal may not be available, so this check would need to be disabled to allow the client to function. These are the configurations that require that this check is disabled:

• The client IP address is dynamically assigned. For instance, a DHCP client.

• The client is not configured to host any services, so no host principal was created.

• The host key is not stored on the client.

1. Become superuser.

2. Change the krb5.conf file.

   If the verify_ap_req_nofail option is set to false, the TGT verification process is not enabled. See the krb5.conf(4) man page for more information about this option.

   client # cat /etc/krb5/krb5.conf [libdefaults] default_realm = EXAMPLE.COM verify_ap_req_nofail = false ...

   ---

   Note –

   The verify_ap_req_nofail option can be entered in either the [libdefaults] or the [realms] section of the krb5.conf file. If the option is in the [libdefaults]section, the setting is used for all realms. If the option is in the [realms]section, the setting only applies to the defined realm.

   ---

How to Access a Kerberos Protected NFS File System as the root User

This procedure allows a client to access a NFS file system that requires Kerberos authentication with the root ID privilege. In particular, when the NFS file system is shared with options like: -o sec=krb5,root=client1.sun.com.

1. Become superuser.

2. Start kadmin.

   You can use the Graphical Kerberos Administration Tool to add a principal, as explained in How to Create a New Kerberos Principal. To do so, you must log in with one of the admin principal names that you created when you configured the master KDC. However, the following example shows how to add the required principals by using the command line.

   denver # /usr/sbin/kadmin -p kws/admin Enter password: <Type kws/admin password> kadmin:

   1. Create a root principal for the NFS client.

      This principal is used to provide root equivalent access to NFS mounted file systems that require Kerberos authentication. The root principal should be a two component principal with the second component the host name of the Kerberos client system to avoid the creation of a realm wide root principal. Note that when the principal instance is a host name, the FQDN must be specified in lowercase letters, regardless of the case of the domain name in the /etc/resolv.conf file.

      kadmin: addprinc -randkey root/client.example.com Principal "root/client.example.com" created. kadmin:

   2. Add the root principal to the server's keytab file.

      This step is required if you added a root principal so that the client can have root access to file systems mounted using the NFS service. This step is also required if non-interactive root access is needed, such as running cron jobs as root.

      kadmin: ktadd root/client.example.com Entry for principal root/client.example.com with kvno 3, encryption type AES-256 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type AES-128 CTS mode with 96-bit SHA-1 HMAC added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type Triple DES cbc mode with HMAC/sha1 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type ArcFour with HMAC/md5 added to keytab WRFILE:/etc/krb5/krb5.keytab. Entry for principal root/client.example.com with kvno 3, encryption type DES cbc mode with RSA-MD5 added to keytab WRFILE:/etc/krb5/krb5.keytab. kadmin:

   3. Quit kadmin.

      kadmin: quit

How to Configure Automatic Migration of Users in a Kerberos Realm

Users, who do not have a Kerberos principal, can be automatically migrated to an existing Kerberos realm. The migration is achieved by using the PAM framework for the service in use by stacking the pam_krb5_migrate module in the service's authentication stack in /etc/pam.conf.

In this example, the dtlogin and other PAM service names are configured to use the automatic migration. The following configuration parameters are used:

• Realm name = EXAMPLE.COM

• Master KDC = kdc1.example.com

• Machine hosting the migration service = server1.example.com

• Migration service principal = host/server1.example.com

Before You Begin

Setup server1 as a Kerberos client of the realm EXAMPLE.COM. See Configuring Kerberos Clients for more information.

1. Check to see if a host service principal for server1 exists.

   The host service principal in the keytab file of server1 is used to authenticate the server to the master KDC.

   server1 # klist -k Keytab name: FILE:/etc/krb5/krb5.keytab KVNO Principal ---- ------------------------------------------------ 3 host/server1.example.com@EXAMPLE.COM 3 host/server1.example.com@EXAMPLE.COM 3 host/server1.example.com@EXAMPLE.COM 3 host/server1.example.com@EXAMPLE.COM

2. Make changes to the PAM configuration file.

   1. Add entries for the dtlogin service.

      # cat /etc/pam.conf . . # # dtlogin service (explicit because of pam_krb5_migrate) # dtlogin auth requisite pam_authtok_get.so.1 dtlogin auth required pam_dhkeys.so.1 dtlogin auth required pam_unix_cred.so.1 dtlogin auth sufficient pam_krb5.so.1 dtlogin auth requisite pam_unix_auth.so.1 dtlogin auth optional pam_krb5_migrate.so.1

   2. (Optional) Force an immediate password change, if needed.

      The newly created Kerberos accounts can have their password expiration time set to the current time (now), in order to force an immediate Kerberos password change. To set the expiration time to now, add the expire_pw option to the lines which use the pam_krb5_migrate module. See the pam_krb5_migrate(5) man page for more information.

      # cat /etc/pam.conf . . dtlogin auth optional pam_krb5_migrate.so.1 expire_pw

   3. Add the pam_krb5 module to the account stack.

      This addition allows for password expiration in Kerberos to block access.

      # cat /etc/pam.conf . . # # Default definition for Account management # Used when service name is not explicitly mentioned for account management # other account requisite pam_roles.so.1 other account required pam_krb5.so.1 other account required pam_unix_account.so.1

   4. Add the pam_krb5 module to the password stack.

      This addition allows for passwords to be updated when the password expire.

      # cat /etc/pam.conf . . # # Default definition for Password management # Used when service name is not explicitly mentioned for password management # other password required pam_dhkeys.so.1 other password requisite pam_authtok_get.so.1 other password requisite pam_authtok_check.so.1 other password sufficient pam_krb5.so.1 other password required pam_authtok_store.so.1

3. On the master KDC, update the access control file.

   The following entries grant migrate and inquire privileges to the host/server1.example.com service principal for all users, excepting the root user. It is important that users who should not be migrated are listed in the kadm5.acl file using the U privilege. These entries need to be before the permit all or ui entry. See the kadm5.acl(4) man page for more information.

   kdc1 # cat /etc/krb5/kadm5.acl host/server1.example.com@EXAMPLE.COM U root host/server1.example.com@EXAMPLE.COM ui * */admin@EXAMPLE.COM *

4. On the master KDC, restart the Kerberos administration daemon.

   This step allows the kadmind daemon to use the new kadm5.acl entries.

   kdc1 # svcadm restart network/security/kadmin

5. On the master KDC, add entries to the pam.conf file.

   The following entries enable the kadmind daemon to use the k5migrate PAM service, to validate UNIX user password for accounts that require migration.

   # grep k5migrate /etc/pam.conf k5migrate auth required pam_unix_auth.so.1 k5migrate account required pam_unix_account.so.1