Pam unix vs. pam ldap
From Brandonhutchinson.com
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* The entered password is not sent to the LDAP server. | * The entered password is not sent to the LDAP server. | ||
* The default ''/etc/pam.conf'' file is configured for ''pam_unix'' (at least on Solaris 8). | * The default ''/etc/pam.conf'' file is configured for ''pam_unix'' (at least on Solaris 8). | ||
| + | * ''pam_unix'' will not support the LDAP server's password policy controls (e.g., password syntax checking, account lockout, forced password change after reset, etc.). | ||
Given the severe limitation of '''ldaplist -l password''' returning all password hashes, ''pam_ldap'' should be used if possible. | Given the severe limitation of '''ldaplist -l password''' returning all password hashes, ''pam_ldap'' should be used if possible. | ||
Revision as of 15:49, 17 December 2007
Contents |
Overview
The following notes list some differences between pam_unix and pam_ldap authentication.
pam_unix
With pam_unix:
- The userPassword attribute must be non-null.
- Passwords must be stored in {crypt} format on the LDAP server.
- The proxy agent (e.g., cn=proxyagent,ou=profile,dc=example,dc=com) must have read and search privileges for the userPassword attribute.
- ldaplist -l passwd will return all password hashes, similar to ypcat passwd in a NIS environment.
- The entered password is not sent to the LDAP server.
- The default /etc/pam.conf file is configured for pam_unix (at least on Solaris 8).
- pam_unix will not support the LDAP server's password policy controls (e.g., password syntax checking, account lockout, forced password change after reset, etc.).
Given the severe limitation of ldaplist -l password returning all password hashes, pam_ldap should be used if possible.
pam_ldap
With pam_ldap:
- The proxy agent (e.g., cn=proxyagent,ou=profile,dc=example,dc=com) does not need read and search privileges for the userPassword attribute.
- If the LDAP server is properly configured, ldaplist -l passwd will not return all user password hashes.
- The entered password is sent to the LDAP server, so encryption (e.g., TLS:Simple) should be used.
- The default /etc/pam.conf will have to be modified.
Authentication walk-through
A user attempts to login to a host using ssh and is prompted for a password:
$ ssh user@host Password:
What happens next?
pam_unix
With pam_unix:
- An LDAP search is performed in the ou=people container for an entry that contains objectClass=shadowAccount and uid=user. The search base is the value of NS_LDAP_SEARCH_BASEDN from /var/ldap/ldap_client_file.
- If an entry is found, the password specified on the command line is hashed with crypt() and compared with the userPassword attribute. If the values match, the user is authenticated.
pam_ldap
With pam_ldap:
- An LDAP search is performed in the ou=people container for an entry that contains object=posixAccount and uid=user. The search base is the value of NS_LDAP_SEARCH_BASEDN from /var/ldap/ldap_client_file.
- If an entry is found, the client attempts to bind to the LDAP server using the Distinguished Name (DN) (e.g., uid=user,ou=people,dc=example,dc=com) and password specified on the command line. If the client is able to bind, the user is authenticated.
