pam_krb5(5) Standards, Environments, and Macros pam_krb5(5)
NAME
pam_krb5 - authentication, account, session, and password management PAM modules for Kerberos V5
SYNOPSIS
/usr/lib/security/pam_krb5.so.1
DESCRIPTION
The Kerberos V5 service module for PAM provides functionality for all four PAM modules: authentication, account management, session manage-
ment, and password management. The service module is a shared object that can be dynamically loaded to provide the necessary functionality
upon demand. Its path is specified in the PAM configuration file.
Kerberos Authentication Module
The Kerberos V5 authentication component provides functions to verify the identity of a user, pam_sm_authenticate(), and to manage the Ker-
beros credentials cache, pam_sm_setcred().
pam_sm_authenticate() authenticates a user principal through the Kerberos authentication service. If the authentication request is success-
ful, the authentication service sends a ticket-granting ticket (TGT) back to the service module, which then verifies that the TGT came from
a valid Key Distribution Center (KDC) by attempting to get a service ticket for the local host service. For this to succeed, the local
host's keytab file (/etc/krb5/krb5.keytab) must contain the entry for the local host service. For example, in the file host/host-
name.com@REALM, hostname.com is the fully qualified local hostname and REALM is the default realm of the local host as defined in
/etc/krb5/krb5.conf. If the host entry is not found in the keytab file, the authentication fails. Administrators may optionally disable
this "strict" verification by setting the "verify_ap_req_nofail = false" in /etc/krb5/krb5.conf. See krb5.conf(4) for more details on this
option. This allows TGT verification to succeed in the absence of a keytab host principal entry.
pam_sm_authenticate(3PAM) may be passed the following flag:
PAM_DISALLOW_NULL_AUTHTOK
This flag is ignored. The Kerberos authentication mechanism will not allow an empty password string by default.
pam_sm_setcred() creates and modifies the user's credential cache. This function initializes the user's credential cache, if it does not
already exist, and stores the initial credentials for later use by Kerberized network applications. The following flags may be set in the
flags field. They are best described by their effect on the user's credential cache.
PAM_ESTABLISH_CRED
Stores the initial credentials in the user's credential cache so that the user may access Kerberos network services. If the credential
cache exists, then this function is functionally equivalent to using the PAM_REFRESH_CRED flag. That is, the user's credentials are
refreshed. If the credential cache does not exist, then it is created, and new credentials are stored in it.
PAM_DELETE_CRED
This flag has no effect on the credential cache and always returns PAM_SUCCESS. The credential cache is not deleted because there is no
accurate method to determine if the credentials are needed by another process. The credential cache may be deleted with the kdestroy(1)
command.
PAM_REINITIALIZE_CRED
Deletes the user's existing credential cache, if it exists, and creates a new credential cache. The new credentials are stored in the
new cache and the user's ticket lifetime and renewable life time values are reset.
PAM_REFRESH_CRED
Extends lifetime of user's credentials. Does not wipe out the credentials cache, but instead just extends the lifetime of the user's
TGT. Notice that this function fails if the user's renewable ticket lifetime has expired.
The following options can be passed to the Kerberos V5 authentication module:
debug Provides syslog(3C) debugging information at LOG_DEBUG level.
nowarn Turns off warning messages.
Kerberos V5 Account Management Module
The Kerberos account management component provides a function to perform account management, pam_sm_acct_mgmt(). This function checks to
see if the pam_krb5 authentication module has noted that the user's password has not expired. The following options may be passed in to the
Kerberos V5 account management module:
debug Provides syslog(3C) debugging information at LOG_DEBUG level
nowarn Turns off warning messages. Also, does not query KDC for impending password expiration information used to warn the user.
Kerberos V5 Session Management Module
The Kerberos V5 session management component provides functions to initiate pam_sm_open_session() and terminate pam_sm_close_session() Ker-
beros sessions. For Kerberos V5, both pam_sm_open_session and pam_sm_close_session() are null functions, returning PAM_IGNORE.
Kerberos V5 Password Management Module
The Kerberos V5 password management component provides a function to change passwords, pam_sm_chauthtok(), in the Key Distribution Center
(KDC) database. The following flags may be passed to pam_sm_chauthtok(3PAM):
PAM_CHANGE_EXPIRED_AUTHTOK
The password service should only update the user's Kerberos password if it is expired. Otherwise, this function returns PAM_IGNORE. The
default behaviour is to always change the user's Kerberos password.
PAM_PRELIM_CHECK
This is a null function that always returns PAM_SUCCESS.
PAM_UPDATE_AUTHTOK
This flag is necessary to change the user's Kerberos password. If this flag is not set, pam_krb5 returns PAM_SYSTEM_ERR.
The following option can be passed to the Kerberos V5 password module:
debug Provides syslog(3C) debugging information at LOG_DEBUG level.
ERRORS
The following error codes are returned for pam_sm_authenticate():
PAM_AUTH_ERR
Authentication failure
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The user is "root" and the root key exists in the default keytab.
PAM_SUCCESS
Successfully obtained Kerberos credentials .
PAM_SYSTEM_ERR
System error.
PAM_USER_UNKNOWN
An unknown Kerberos principal was requested.
The following error codes are returned for pam_sm_setcred():
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_IGNORE
The user is "root" and the root key exists in the default keytab.
PAM_SYSTEM_ERR
System error.
PAM_SUCCESS
Successfully modified the Kerberos credential cache.
The following error codes are returned for pam_sm_acct_mgmt():
PAM_AUTH_ERR
Authentication failure.
PAM_IGNORE
Kerberos service module pam_sm_authenticate() was never called, or the user is "root" and the root key exists in the default keytab.
PAM_NEW_AUTHTOK_REQD
Obtain new authentication token from the user.
PAM_SERVICE_ERR
Error in underlying service module.
PAM_SUCCESS
Kerberos principal account is valid.
PAM_SYSTEM_ERR
System error.
PAM_USER_UNKNOWN
An unknown Kerberos principal was requested.
The following error code is returned for pam_sm_open_session() and pam_sm_close_session():
PAM_IGNORE
These two functions are null functions in pam_krb5:
The following error codes are returned for pam_sm_chauthtok():
PAM_AUTH_ERR
Authentication failure.
PAM_IGNORE
The user has not been authenticated by Kerberos service module pam_sm_authenticate(), or the user is "root" and the root key exists in
the default keytab.
PAM_NEW_AUTHTOK_REQD
User's Kerberos password has expired.
PAM_SERVICE_ERR
Error in module. At least one input parameter is missing.
PAM_SYSTEM_ERR
System error.
PAM_USER_UNKNOWN
An unknown Kerberos principal was requested.
PAM_SUCCESS
Successfully changed the user's Kerberos password.
EXAMPLES
Example 1: Authenticate Users Through Kerberos as First Choice
The following is an excerpt of a sample pam.conf configuration file that authenticates users through the Kerberos authentication service
and authenticates through the Unix login only if the Kerberos authentication fails. This arrangement is helpful when a majority of the
users are networked by means of Kerberos and when there are only a few non-Kerberos type user accounts, such as root. The service illus-
trated below is for dtlogin.
dtlogin auth requisite pam_smartcard.so.1
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 required pam_unix_auth.so.1
Note that these changes should not be made to the existing krlogin, krsh, and ktelnet service entries. Those services require Kerberos
authentication, so using a seemingly sufficient control flag would not provide the necessary functionality for privacy and integrity. There
should be no need to change those entries.
The following entries check for password expiration when dealing with Kerberos and Unix password aging policies:
other account requisite pam_roles.so.1
other account required pam_unix_account.so.1
other account required pam_krb5.so.1
The following entries would change the Kerberos password of the user and continue to change the Unix login password only if the Kerberos
password change had failed:
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
When changing Kerberos based user's password, use kpasswd(1). When changing a non-Kerberos user's password, it is recommended that the
repository is specified (-r) with the passwd(1) command.
Example 2: Authenticate Users Through Kerberos Only
The following example allows authentication only to users that have Kerberos-based accounts.
dtlogin auth requisite pam_smartcard.so.1
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 binding pam_krb5.so.1
dtlogin auth required pam_unix_auth.so.1
Typically, you would have another service specified in the pam.conf file that would allow local users, such as database, web server, system
administrator accounts, to log in to the host machine. For example, the "login" service name could be used for these users. Note that these
users should not belong to any roles.
The rest of the module types look similar to that shown in the previous example:
other account requisite pam_roles.so.1
other account required pam_unix_account.so.1
other account required pam_krb5.so.1
With binding specified in the following, it is important that non-Kerberos users specify the repository in which they reside using the -r
option with the passwd(1) command. This configuration is also based on the assumptions that:
o Kerberos users maintain only their Kerberos passwords;
o changing their Unix password is not necessary, given that they are authenticated only through their Kerberos passwords when logging
in.
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 binding pam_krb5.so.1
other password required pam_authtok_store.so.1
Example 3: Authenticate Through Kerberos Optionally
This configuration is helpful when the majority of users are non-Kerberos users and would like to authenticate through Kerberos if they
happened to exist in the Kerberos database. The effect of this is similar to users voluntarily executing kinit(1) after they have success-
fully logged in:
dtlogin auth requisite pam_smartcard.so.1
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 required pam_unix_auth.so.1
dtlogin auth optional pam_krb5.so.1
The rest of the configuration is as follows:
other account requisite pam_roles.so.1
other account required pam_unix_account.so.1
other account required pam_krb5.so.1
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 required pam_authtok_store.so.1
other password optional pam_krb5.so.1
Non-Kerberos users should specify their respective repositories by using the -r option when changing their password with the passwd(1) com-
mand.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Evolving |
+-----------------------------+-----------------------------+
SEE ALSO
kdestroy(1), kinit(1), kpasswd(1), passwd(1), ktkt_warnd(1M), libpam(3LIB), pam(3PAM), pam_sm(3PAM), pam_sm_acct_mgmt(3PAM), pam_sm_authen-
ticate(3PAM), pam_sm_chauthtok(3PAM), pam_sm_close_session(3PAM), pam_sm_open_session(3PAM), pam_sm_setcred(3PAM), syslog(3C), pam.conf(4),
attributes(5), krb5envvar(5), SEAM(5)
NOTES
The interfaces in libpam(3LIB) are MT-Safe only if each thread within the multi-threaded application uses its own PAM handle.
On successful acquisition of initial credentials (ticket-granting ticket), ktkt_warnd(1M) will be notified, to alert the user when the ini-
tial credentials are about to expire.
SunOS 5.10 22 Apr 2004 pam_krb5(5)