Pluggable Authentication Module (PAM) Submethod

Pluggable Authentication Module is an authentication framework used in Unix systems. In SSH Tectia, support for PAM is enabled as a submethod of keyboard-interactive authentication.

When PAM is used, SSH Tectia Server transfers the control of authentication to the PAM library, which will then load the modules specified in the PAM configuration file. Finally, the PAM library tells SSH Tectia Server whether or not the authentication was successful. SSH Tectia Server is not aware of the details of the actual authentication method employed by PAM, only the final result is of interest.

The PAM authentication can be enabled by creating a PAM configuration for the service ssh-server-g3. For information on how to do PAM session and account management irrespective of the authentication methods used, see the configuration element description for pluggable-authentication-modules.

In addition, you can define separate authentication blocks with specific PAM settings (in element <submethod-pam>) which will override the PAM defaults for that particular authentication block.

It is possible to configure the user session management and the authentication to use different services for PAM authentication. This is done by defining different services in the service-name attribute in the pluggable-authentication-modules element and in the submethod-pam element.

SSH Tectia Server expects to find the PAM libraries in the default paths of the supported operating systems. You need to define the PAM libraries in the server configuration only if they are used from non-default locations.

The following configuration example shows the PAM authentication related settings in the ssh-server-config.xml file.

<authentication-methods>
  <authentication action="allow">
    <auth-keyboard-interactive>
      <submethod-pam 
         service-name="sshd2" 
         dll-path="path-to-pam-dll" />
    </auth-keyboard-interactive>
  ...
  </authentication>
</authentication-methods>

	Note
	SSH Communications Security does not provide technical support on how to configure PAM. Our support only covers SSH Tectia applications.

PAM Examples

The following are examples of the PAM configurations on different platforms.

Please note that these are just examples and need to be modified according to the actual server configuration.

PAM on Red Hat Linux

On Red Hat Linux 5, add PAM configuration file /etc/pam.d/ssh-server-g3 with contents:

auth       include      system-auth
account    required     pam_nologin.so
account    include      system-auth
password   include      system-auth
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    required     pam_loginuid.so

When the PAM library is used from the default path, the PAM definitions in the SSH Tectia Server configuration file ssh-server-config.xml can be simply as follows:

<authentication-methods>
  <authentication action="allow">
    <auth-keyboard-interactive >
        <submethod-pam />
   </auth-keyboard-interactive >
  ...
  </authentication>
</authentication-methods>

PAM on SUSE Linux

On SUSE Linux Enterprise Server 10 (both 32- and 64-bit versions) the default configuration settings are suitable for most PAM authentications. You can add file /etc/pam.d/ssh-server-g3 with contents:

auth     include        common-auth
auth     required       pam_nologin.so
account  include        common-account
password include        common-password
session  include        common-session

The following example configuration in ssh-server-config.xml enables PAM session and account management with the service sshd2 (instead of the default ssh-server-g3). The authentication submethod PAM is configured to use service ssh-server-g3. The PAM library is used from the default path.

<params>
  <pluggable-authentication-modules
            service-name="sshd2" 
            pam-calls-with-commands="yes" />
</params>
         <!-- ... -->
<authentication-methods>
  <authentication action="allow" name="allow-default">
    <auth-keyboard-interactive>
      <submethod-pam service-name="ssh-server-g3"/>
    </auth-keyboard-interactive>
  </authentication>
</authentication-methods>

PAM on Sun Solaris

On Solaris version 10, add the /etc/pam.conf entry with contents:

ssh-server-g3   auth requisite          pam_authtok_get.so.1
ssh-server-g3   auth required           pam_dhkeys.so.1
ssh-server-g3   auth required           pam_unix_cred.so.1
ssh-server-g3   auth required           pam_unix_auth.so.1
ssh-server-g3   account requisite       pam_roles.so.1
ssh-server-g3   account required        pam_unix_account.so.1
ssh-server-g3   session required        pam_unix_session.so.1
ssh-server-g3   password required       pam_dhkeys.so.1
ssh-server-g3   password requisite      pam_authtok_get.so.1
ssh-server-g3   password requisite      pam_authtok_check.so.1
ssh-server-g3   password required       pam_authtok_store.so.1

If the PAM library is used from a path different than the operating system default, the path must be specified in the SSH Tectia Server configuration file ssh-server-config.xml both in the pluggable-authentication-modules and in the submethod-pam element with the dll-path attribute. For example:

<params>
  <pluggable-authentication-modules
            dll-path="path-to-pam-dll"
            pam-calls-with-commands="yes" />
</params>
         
<authentication-methods>
  <authentication action="allow" name="allow-default">
    <auth-keyboard-interactive>
      <submethod-pam dll-path="path-to-pam-dll" />
    </auth-keyboard-interactive>
  </authentication>
</authentication-methods>

	Note
	On Solaris, the account lockout setting LOCK_AFTER_RETRIES in `/etc/security/policy.conf` only applies if keyboard interactive authentication is used with PAM. Other types of authentication methods do not increment the retries count.

PAM Used with LDAP on Red Hat Linux

The following is an example on how to configure PAM to use LDAP authentication on a Red Hat Linux machine. Before trying this setup, verify that PAM works for local accounts. Modify the example settings according to your LDAP server configuration.

In file /etc/pam.d/ssh-server-g3, add the following settings:

auth     required /lib/security/pam_ldap.so
account  required /lib/security/pam_ldap.so
password required /lib/security/pam_ldap.so
session  required /lib/security/pam_ldap.so

In file /etc/nsswitch.conf, add the following settings:

passwd: files ldap
shadow: files ldap
group: files ldap

In file /etc/ldap.conf, add the following settings:

host ldapserver.company.com
base dc=company,dc=com
ldap_version 3
port 389
scope one
pam_min_uid 10000
pam_max_uid 20000
nss_base_passwd ou=accounts,dc=company,dc=com?one
nss_base_shadow ou=accounts,dc=company,dc=com?one
nss_base_group ou=groups,dc=company,dc=com?one
ssl no
pam_password md5