pam_faillock

PAM_FAILLOCK(8)                Linux-PAM Manual                PAM_FAILLOCK(8)

NAME
       pam_faillock - Module counting authentication failures during a
       specified interval

SYNOPSIS
       auth ... pam_faillock.so {preauth|authfail|authsucc}
                                [conf=/path/to/config-file]
                                [dir=/path/to/tally-directory]
                                [even_deny_root] [deny=n] [fail_interval=n]
                                [unlock_time=n] [root_unlock_time=n]
                                [admin_group=name] [audit] [silent]
                                [no_log_info]

       account ... pam_faillock.so [dir=/path/to/tally-directory]
                                   [no_log_info]

DESCRIPTION
       This module maintains a list of failed authentication attempts per user
       during a specified interval and locks the account in case there were
       more than deny consecutive failed authentications.

       Normally, failed attempts to authenticate root will not cause the root
       account to become blocked, to prevent denial-of-service: if your users
       aren't given shell accounts and root may only login via su or at the
       machine console (not telnet/rsh, etc), this is safe.

OPTIONS
       {preauth|authfail|authsucc}
           This argument must be set accordingly to the position of this
           module instance in the PAM stack.

           The preauth argument must be used when the module is called before
           the modules which ask for the user credentials such as the
           password. The module just examines whether the user should be
           blocked from accessing the service in case there were anomalous
           number of failed consecutive authentication attempts recently. This
           call is optional if authsucc is used.

           The authfail argument must be used when the module is called after
           the modules which determine the authentication outcome, failed.
           Unless the user is already blocked due to previous authentication
           failures, the module will record the failure into the appropriate
           user tally file.

           The authsucc argument must be used when the module is called after
           the modules which determine the authentication outcome, succeeded.
           Unless the user is already blocked due to previous authentication
           failures, the module will then clear the record of the failures in
           the respective user tally file. Otherwise it will return
           authentication error. If this call is not done, the pam_faillock
           will not distinguish between consecutive and non-consecutive failed
           authentication attempts. The preauth call must be used in such
           case. Due to complications in the way the PAM stack can be
           configured it is also possible to call pam_faillock as an account
           module. In such configuration the module must be also called in the
           preauth stage.

       conf=/path/to/config-file
           Use another configuration file instead of the default
           /etc/security/faillock.conf.

       The options for configuring the module behavior are described in the
       faillock.conf(5) manual page. The options specified on the module
       command line override the values from the configuration file.

MODULE TYPES PROVIDED
       The auth and account module types are provided.

RETURN VALUES
       PAM_AUTH_ERR
           An invalid option was given, the module was not able to retrieve
           the user name, no valid counter file was found, or too many failed
           logins.

       PAM_BUF_ERR
           Memory buffer error.

       PAM_CONV_ERR
           The conversation method supplied by the application failed to
           obtain the username.

       PAM_INCOMPLETE
           The conversation method supplied by the application returned
           PAM_CONV_AGAIN.

       PAM_SUCCESS
           Everything was successful.

       PAM_IGNORE
           User not present in passwd database.

NOTES
       Configuring options on the module command line is not recommend. The
       /etc/security/faillock.conf should be used instead.

       The setup of pam_faillock in the PAM stack is different from the
       pam_tally2 module setup.

       Individual files with the failure records are created as owned by the
       user. This allows pam_faillock.so module to work correctly when it is
       called from a screensaver.

       Note that using the module in preauth without the silent option
       specified in /etc/security/faillock.conf or with requisite control
       field leaks an information about existence or non-existence of an user
       account in the system because the failures are not recorded for the
       unknown users. The message about the user account being locked is never
       displayed for non-existing user accounts allowing the adversary to
       infer that a particular account is not existing on a system.

EXAMPLES
       Here are two possible configuration examples for /etc/pam.d/login. They
       make pam_faillock to lock the account after 4 consecutive failed logins
       during the default interval of 15 minutes. Root account will be locked
       as well. The accounts will be automatically unlocked after 20 minutes.

       In the first example the module is called only in the auth phase and
       the module does not print any information about the account being
       blocked by pam_faillock. The preauth call can be added to tell users
       that their logins are blocked by the module and also to abort the
       authentication without even asking for password in such case.

       /etc/security/faillock.conf file example:

           deny=4
           unlock_time=1200
           silent

       /etc/pam.d/config file example:

           auth     required       pam_securetty.so
           auth     required       pam_env.so
           auth     required       pam_nologin.so
           # optionally call: auth requisite pam_faillock.so preauth
           # to display the message about account being locked
           auth     [success=1 default=bad] pam_unix.so
           auth     [default=die]  pam_faillock.so authfail
           auth     sufficient     pam_faillock.so authsucc
           auth     required       pam_deny.so
           account  required       pam_unix.so
           password required       pam_unix.so shadow
           session  required       pam_selinux.so close
           session  required       pam_loginuid.so
           session  required       pam_unix.so
           session  required       pam_selinux.so open

       In the second example the module is called both in the auth and account
       phases and the module informs the authenticating user when the account
       is locked if silent option is not specified in the faillock.conf.

           auth     required       pam_securetty.so
           auth     required       pam_env.so
           auth     required       pam_nologin.so
           auth     required       pam_faillock.so preauth
           # optionally use requisite above if you do not want to prompt for the password
           # on locked accounts
           auth     sufficient     pam_unix.so
           auth     [default=die]  pam_faillock.so authfail
           auth     required       pam_deny.so
           account  required       pam_faillock.so
           # if you drop the above call to pam_faillock.so the lock will be done also
           # on non-consecutive authentication failures
           account  required       pam_unix.so
           password required       pam_unix.so shadow
           session  required       pam_selinux.so close
           session  required       pam_loginuid.so
           session  required       pam_unix.so
           session  required       pam_selinux.so open

FILES
       /var/run/faillock/*
           the files logging the authentication failures for users

       /etc/security/faillock.conf
           the config file for pam_faillock options

SEE ALSO
       faillock(8), faillock.conf(5), pam.conf(5), pam.d(5), pam(8)

AUTHOR
       pam_faillock was written by Tomas Mraz.

Linux-PAM Manual                  06/08/2020                   PAM_FAILLOCK(8)