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.
To enable PAM support,
include the following lines in the /etc/ssh2/sshd2_config file on the server:
AllowedAuthentications keyboard-interactive
...
AuthKbdInt.Optional pam
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Include the following line in the /etc/ssh2/ssh2_config file on the client:
AllowedAuthentications keyboard-interactive
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The PAM configuration settings are located either in
/etc/pam.conf or in /etc/pam.d/sshd2. The modules
are usually either in the /lib/security directory or in the
/usr/lib/security directory. Currently, SSH Tectia Server supports PAM on
Linux and on Solaris 2.6 or later.
There must be at least one auth, one account, and one
session module in the configuration file. Otherwise the
connection will be refused. Also, modules which require PAM_TTY
will not work because TTY allocation is done in SSH Tectia Server after the
authentication.
See Section Keyboard-Interactive Authentication for more information on Keyboard-Interactive
authentication.
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 different PAM configurations.
PAM on Red Hat Linux
The /etc/pam.d/sshd2 file on Red Hat Linux:
auth required /lib/security/pam_pwdb.so shadow nullok
auth required /lib/security/pam_nologin.so
account required /lib/security/pam_pwdb.so
password required /lib/security/pam_cracklib.so
password required /lib/security/pam_pwdb.so shadow nullok use_authtok
session required /lib/security/pam_pwdb.so
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On SUSE LINUX, the configuration is otherwise the same but
pam_unix.so is used instead of pam_pwdb.so.
PAM on Sun Solaris
The /etc/pam.conf entry on Solaris:
sshd2 auth required /usr/lib/security/pam_unix.so debug
sshd2 account required /usr/lib/security/pam_unix.so debug
sshd2 password required /usr/lib/security/pam_unix.so debug
sshd2 session required /usr/lib/security/pam_unix.so debug
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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 9 machine. Before trying this setup, verify
that PAM works for local accounts.
In the file /etc/pam.d/sshd2, add the following:
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
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In the file /etc/nsswitch.conf, add the following:
passwd: files ldap
shadow: files ldap
group: files ldap
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In the file /etc/ldap.conf, add the following:
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
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This is just an example and needs to be modified according to your LDAP
server configuration.
PAM Account Management and Session Logging
Normally account management and session logging are done as a part of PAM
authentication when it is used (keyboard-interactive with the submethod
pam). This feature allows limited account management and session
logging by PAM to be used for all authentication methods.
Provided that the feature is enabled (see configuration options below) and
that full PAM authentication was not used successfully, the PAM account
management functions will be called after successful authentication.
Access is denied if pam_acct_mgmt() returns an error. After
pam_acct_mgmt() has approved the connection,
pam_open_session() will be called, followed by
pam_close_session() after the connection has been closed.
Note that if full PAM authentication has been performed, this feature will
not be used, as an account management function has been called as a part of
normal PAM authentication. This means that if more than one authentcation
method is required, PAM account management can be done either after all
authentications (separate PAM account management) or before some other
authentications (as a part of PAM authentication).
Configuration Options
-
AlwaysUsePAMAccountManagement If PAM authentication was not used, still use the PAM function
pam_acct_mgmt to check login restrictions as configured in the
account group of the system's PAM configuration. Even if this
option is disabled, the account management will be called if PAM
authentication was used. The argument must be yes or no.
The default is no.
-
AlwaysUsePAMSessionLogging If PAM authentication was not used, still use PAM functions
pam_open_session and pam_close_session to log session
data as configured in the session group of the system's PAM
configuration. Even if this option is disabled, the account management
will be called if PAM authentication was used. The argument must be
yes or no. The default is no.
-
ForcedPAMAccountManagementPasswordChange If PAM account management is used and it requires an authentication token
change (pam_acct_mgmt returns PAM_NEW_AUTHOK_REQD) and
the used authentication method also requires a password change, allow this
connection as it can only be used to change the password. The user login
shell will be replaced with the passwd command and the user is
disconnected afterwards. Note that if AlwaysUsePAMSessionLogging
is enabled, the pam_open_session will be called on connection
before the password has been changed. Disabling this option will cause
the server to disconnect the client with an error message stating that
password change is needed and that the user should connect again using the
keyboard- interactive authentication method. This option does not affect
normal PAM authentication which will still prompt for a new password event
if this option has been disabled. The argument must be yes or
no. The default is no.
