Standards, Environments, and Macros pam_krb5(5)
NAME
pam_krb5 - authentication, account, session, and password
management PAM modules for Kerberos V5SYNOPSIS
/usr/lib/security/pam_krb5.so.1
DESCRIPTION
The Kerberos V5 service module for PAM provides functional-
ity for all four PAM modules: authentication, account management, session management, 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 functionsto verify the identity of a user, pam_sm_authenticate(), and
to manage the Kerberos credentials cache, pam_sm_setcred().
pam_sm_authenticate() authenticates a user principal through
the Kerberos authentication service. If the authentication request is successful, the authentication service sends aticket-granting ticket (TGT) back to the service module,
which then verifies that the TGT came from a valid Key Dis-
tribution 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/hostname.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 can optionally disable this "strict" verifi-
cation by setting "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.If pam_sm_authenticate() is called and the pkinit module
option is set, the Kerberos V5 authentication module tries to do PKINIT authentication, assuming that both the systemand the KDC are configured to support this type of authenti-
cation. This form of authentication uses a user's certifi-
cate and private key to acquire the user's initial Kerberos credential (TGT). One of the keystore formats supported is PKCS11 which supports use of any PKCS11 compatible keystore capable of storing the required credential and private key needed for PKINIT authentication (PKCS11 compatibleSunOS 5.11 Last change: 12 Apr 2010 1
Standards, Environments, and Macros pam_krb5(5)
smartcards are an example). See krb5.conf(4) for more details on PKINIT configuration. This form of authentication is typically useful for services where the system on which the auth stack is being processed has access to the user's certificate and private key.If pam_sm_authenticate() is called and the pkinit module
option is not set then the Kerberos V5 authentication module does password based authentication.In either case, if the PAM_AUTHTOK password item has been
set when pam_sm_authenticate() is called, which is the case
when pam_krb5 is stacked after pam_authtok_get in the auth
stack, the Kerberos V5 authentication module uses thatPAM_AUTHTOK password for either PKINIT or password based
Kerberos authentication.If the PAM_USER item is not set pam_krb5 with the pkinit
option prompts for and set that item.If the PAM_AUTHTOK password item has not been set when
pam_sm_authenticate() is called, which is the case when
pam_krb5 is stacked before pam_authtok_get in the auth
stack, and the pkinit option is present the Kerberos V5 authentication module allows the Kerberos pkinit preauthplugin to prompt for whatever information is needed to per-
form PKINIT (typically this is for the user's PIN). No PAM items are set by way of this prompting. See krb5.conf(4) for more information on PKINIT configuration options.If it is desirable to initially have the Kerberos V5 authen-
tication module try PKINIT Kerberos authentication and fall back to password based Kerberos authentication then either the sufficient or optional control flags must be providedfor the instance of pam_krb5 with the pkinit module option
set and another instance of pam_krb5 without the pkinit
module option must be stacked below pam_authtok_get. If
there are PAM modules other than pam_krb5 that must be
evaluated below pam_authtok_get then the control flag should
be set to optional for the instance of pam_krb5 with the
pkinit module option set otherwise the control flag should be set to sufficient.Only two instances of pam_krb5 are supported in a auth
stack.SunOS 5.11 Last change: 12 Apr 2010 2
Standards, Environments, and Macros pam_krb5(5)
pam_sm_authenticate(3PAM) can be passed the following flag:
PAM_DISALLOW_NULL_AUTHTOK
This flag is ignored. The Kerberos authentication mechanism does 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 Kerberos network applications. The following flags can 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 credentialcache so that the user can access Kerberos network ser-
vices. If a successful authentication pass was made, the new credentials are stored in the credential cache,overwriting any existing credentials that were previ-
ously stored. If an unsuccessful authentication pass wasmade, PAM_CRED_UNAVAIL is returned.
PAM_DELETE_CRED
This flag has no effect on the credential cache andalways 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 can 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
Does not require a previous authentication pass, but if a successful one is made, the new credentials are storedSunOS 5.11 Last change: 12 Apr 2010 3
Standards, Environments, and Macros pam_krb5(5)
in the credential cache. If a previous authentication pass was not made or was unsuccessful, an attempt to renew the existing credentials is made. This function fails if the user's renewable ticket lifetime is expired. The following options can be passed to the Kerberos V5 authentication module: debug Provides syslog(3C) debugging information atLOG_DEBUG level.
nowarn Turns off warning messages. pkinit Indicates that the Kerberos V5 authentication module should try Kerberos PKINIT authentication instead of the default password based Kerberos authentication. Kerberos V5 Account Management ModuleThe Kerberos account management component provides a func-
tion 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 fol-
lowing options can be passed in to the Kerberos V5 account management module: debug Provides syslog(3C) debugging information atLOG_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 ModuleThe Kerberos V5 session management component provides func-
tions to initiate pam_sm_open_session() and terminate
pam_sm_close_session() Kerberos 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 afunction to change passwords, pam_sm_chauthtok(), in the Key
Distribution Center (KDC) database.SunOS 5.11 Last change: 12 Apr 2010 4
Standards, Environments, and Macros pam_krb5(5)
If the Kerberos V5 authentication module used PKINIT authen-
tication in the auth stack then the Kerberos V5 passwordmanagement module returns PAM_IGNORE in the following cases:
o The new password is NULL. o The old password is NULL. o Verification of the old password fails. The rationale behind this is that the KDC can not allow a PKINIT user to change/set a password since the user can be expected to use PKINIT only. If all of the cases above are false the Kerberos V5 password management module tries to change the user's password in the KDC database.If the KDC only supports PKINIT authentication then the Ker-
beros V5 password management module should not be present in any password stacks. Related to PKINIT the Kerberos V5 password management module does not support changing the key store PIN used to access a user's private key and certificate.The following flags can be passed to pam_sm_chauthtok(3PAM):
PAM_CHANGE_EXPIRED_AUTHTOK
The password service should only update the user's Ker-
beros password if it is expired. Otherwise, this func-
tion 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_IGNORE.
PAM_UPDATE_AUTHTOK
This flag is necessary to change the user's Kerberospassword. If this flag is not set, pam_krb5 returns
PAM_SYSTEM_ERR.
SunOS 5.11 Last change: 12 Apr 2010 5
Standards, Environments, and Macros pam_krb5(5)
The following option can be passed to the Kerberos V5 pass-
word module: debug Provides syslog(3C) debugging information atLOG_DEBUG level.
ERRORS
The following error codes are returned forpam_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 creden-
tials .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 creden-
tial cache.SunOS 5.11 Last change: 12 Apr 2010 6
Standards, Environments, and Macros pam_krb5(5)
The following error codes are returned forpam_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 forpam_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 forpam_sm_chauthtok():
PAM_AUTH_ERR Authentication failure.
PAM_IGNORE The user has not been authenticated
by Kerberos service modulepam_sm_authenticate(), or the user
is "root" and the root key exists in the default keytab.SunOS 5.11 Last change: 12 Apr 2010 7
Standards, Environments, and Macros pam_krb5(5)
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 Ker-
beros password.EXAMPLES
Example 1 Authenticating Users Through Kerberos as FirstChoice Using Password-based Authentication
The following is an excerpt of a sample pam.conf configura-
tion 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 fewnon-Kerberos type user accounts, such as root. The service
illustrated below is for gdm.gdm auth requisite pam_authtok_get.so.1
gdm auth required pam_dhkeys.so.1
gdm auth required pam_unix_cred.so.1
gdm auth sufficient pam_krb5.so.1
gdm auth required pam_unix_auth.so.1
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.SunOS 5.11 Last change: 12 Apr 2010 8
Standards, Environments, and Macros pam_krb5(5)
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, usekpasswd(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 Authenticating Users Through Kerberos Only UsingPassword-based Authentication
The following example allows authentication only to usersthat have Kerberos-based accounts.
gdm auth requisite pam_authtok_get.so.1
gdm auth required pam_dhkeys.so.1
gdm auth required pam_unix_cred.so.1
gdm auth binding pam_krb5.so.1
gdm auth required pam_unix_auth.so.1
Typically, you would have another service specified in thepam.conf file that would allow local users, such as data-
base, web server, system administrator accounts, to log in to the host machine. For example, the service name "login" could be used for these users. These users should not belong to any roles.SunOS 5.11 Last change: 12 Apr 2010 9
Standards, Environments, and Macros pam_krb5(5)
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 importantthat 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 pass-
words; 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 Authenticating Through Kerberos Optionally UsingPassword-based Authentication
This configuration is helpful when the majority of users arenon-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 successfully logged in:gdm auth requisite pam_authtok_get.so.1
gdm auth required pam_dhkeys.so.1
gdm auth required pam_unix_cred.so.1
gdm auth required pam_unix_auth.so.1
gdm auth optional pam_krb5.so.1
The rest of the configuration is as follows:SunOS 5.11 Last change: 12 Apr 2010 10
Standards, Environments, and Macros pam_krb5(5)
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 reposi-
tories by using the -r option when changing their password
with the passwd(1) command. Example 4 Authenticating Users Through Kerberos PKINIT as First ChoiceThe following is an excerpt of a sample pam.conf configura-
tion file that authenticates users through the Kerberos authentication service and authenticates through the Unix login only if the Kerberos authentication (using PKINIT) fails. This arrangement is helpful when a majority of the users are networked by means of Kerberos and when there areonly a few non-Kerberos type user accounts, such as root.
The service illustrated below is for login. The user isprompted once for the PIN by pam_krb5.
login auth required pam_unix_cred.so.1
login auth sufficient pam_krb5.so.1 pkinit
login auth requisite pam_authtok_get.so.1
login auth required pam_dhkeys.so.1
login auth required pam_unix_auth.so.1
Example 5 Authenticating Users Through Kerberos PKINIT Only The following example allows authentication only to usersthat have kerberos-based accounts requiring PKINIT authenti-
cation.login auth required pam_unix_cred.so.1
login auth required pam_krb5.so.1 pkinit
SunOS 5.11 Last change: 12 Apr 2010 11
Standards, Environments, and Macros pam_krb5(5)
Example 6 Authenticating Users Through Kerberos PKINIT Optionally The following example allows users to acquire a Kerberoscredential using PKINIT authentication if they have a Ker-
beros account. Whether pam_krb5 succeeds or fails the user
must provide their Unix password to login.login auth required pam_unix_cred.so.1
login auth optional pam_krb5.so.1 pkinit
login auth requisite pam_authtok_get.so.1
login auth required pam_unix_auth.so.1
Example 7 Authenticating Users Through Kerberos PKINIT as a RequirementThe following example allows users to login if pam_krb5 is
able to acquire a Kerberos credential using PKINT authenti-
cation and in addition must provide their Unix password topam_unix_auth.
login auth required pam_unix_cred.so.1
login auth required pam_krb5.so.1 pkinit
login auth requisite pam_authtok_get.so.1
login auth required pam_unix_auth.so.1
Example 8 Authenticating Users Through Kerberos PKINIT as a Requirement The following example allows users to login using theirPAM_AUTHTOK password acquired by pam_authtok_get. This
password is used by pam_krb5 to try PKINIT authentication
and is also used by pam_unix_auth to authenticate the user
using the user's Unix account. If PKINIT requires apassword/PIN that differs from the user's Unix password then
pam_krb5 must be stacked above pam_authtok_get.
login auth required pam_unix_cred.so.1
login auth requisite pam_authtok_get.so.1
login auth required pam_krb5.so.1 pkinit
login auth required pam_unix_auth.so.1
SunOS 5.11 Last change: 12 Apr 2010 12
Standards, Environments, and Macros pam_krb5(5)
Example 9 Authenticating Users Through Kerberos PKINIT witha Fall Back to Password-based krb auth
The following example allows users to acquire a Kerberos credential using PKINIT authentication or using password based authentication if PKINIT fails. If PKINIT succeedsthe user is not prompted for their password. If pam_krb5
PKINIT succeeds, the second instance of pam_krb5 does not
try password authentication and returns success. If PKINIT fails the user is prompted for their Kerberos password.login auth required pam_unix_cred.so.1
login auth sufficient pam_krb5.so.1 pkinit
login auth requisite pam_authtok_get.so.1
login auth required pam_krb5.so.1
Example 10 Authenticating Users Through Kerberos Requiring Users to Authenticate Either through Kerberos PKINIT or FallBack to Password-based krb auth
The following example allows users to acquire a Kerberos credential using PKINIT authentication or using passwordbased authentication if PKINIT fails. If pam_krb5 PKINIT
succeeds, the second instance of pam_krb5 does not try pass-
word authentication and returns ignore. If pam_krb5 PKINIT
fails the second instance of pam_krb5 tries password based
authentication and return success or failure.login auth required pam_unix_cred.so.1
login auth optional pam_krb5.so.1 pkinit
login auth requisite pam_authtok_get.so.1
login auth required pam_krb5.so.1
login auth required pam_dhkeys.so.1
login auth required pam_unix_auth.so.1
Example 11 Authenticating Users Through Kerberos Requiring Users to Authenticate Either through Kerberos PKINIT or FallBack to pam_pkcs11
The following example allows users to acquire a Kerberos credential using PKINIT authentication or if that fails usepam_pkcs11 to validate the user's PIN using their certifi-
cate and private key.SunOS 5.11 Last change: 12 Apr 2010 13
Standards, Environments, and Macros pam_krb5(5)
login auth required pam_unix_cred.so.1
login auth sufficient pam_krb5.so.1 pkinit
login auth sufficient pam_pkcs11.so.1
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
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_authenticate(3PAM),
pam_sm_chauthtok(3PAM), pam_sm_close_session(3PAM),
pam_sm_open_session(3PAM), pam_sm_setcred(3PAM), syslog(3C),
krb5.conf(4), pam.conf(4), attributes(5), kerberos(5),krb5envvar(5), pam_krb5_migrate(5)
NOTESThe 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) is notified, to alert the
user when the initial credentials are about to expire.SunOS 5.11 Last change: 12 Apr 2010 14