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} [dir=/path/to/tally-directory] [even_deny_root] [deny=n]
[fail_interval=n] [unlock_time=n] [root_unlock_time=n] [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, succeded. 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.
dir=/path/to/tally-directory
The directory where the user files with the failure records are kept. The default is /var/run/faillock.
audit
Will log the user name into the system log if the user is not found.
silent
Don't print informative messages. This option is implicite in the authfail and authsucc functions.
no_log_info
Don't log informative messages via syslog(3).
deny=n
Deny access if the number of consecutive authentication failures for this user during the recent interval
exceeds n. The default is 3.
fail_interval=n
target of denial of service attack unless the usernames are random and kept secret to potential attackers.
even_deny_root
Root account can become locked as well as regular accounts.
root_unlock_time=n
This option implies even_deny_root option. Allow access after n seconds to root account after the account
is locked. In case the option is not specified the value is the same as of the unlock_time option.
MODULE TYPES PROVIDED
The auth and account module types are provided.
RETURN VALUES
PAM_AUTH_ERR
A 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_SUCCESS
Everything was successful.
PAM_IGNORE
User not present in passwd database.
NOTES
pam_faillock setup in the PAM stack is different from the pam_tally2 module setup.
The 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 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
nonexisting 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 blocking by pam_faillock. The preauth call can be added to tell the user that his login is
blocked by the module and also to abort the authentication without even asking for password in such case.
auth required pam_securetty.so
auth required pam_env.so
auth required pam_nologin.so
# optionally call: auth requisite pam_faillock.so preauth deny=4 even_deny_root unlock_time=1200
# to display the message about account being locked
auth [success=1 default=bad] pam_unix.so
auth [default=die] pam_faillock.so authfail deny=4 even_deny_root unlock_time=1200
auth sufficient pam_faillock.so authsucc deny=4 even_deny_root unlock_time=1200
auth required pam_deny.so
account required pam_unix.so
auth required pam_nologin.so
auth required pam_faillock.so preauth silent deny=4 even_deny_root unlock_time=1200
# optionally use requisite above if you do not want to prompt for the password
# on locked accounts, possibly with removing the silent option as well
auth sufficient pam_unix.so
auth [default=die] pam_faillock.so authfail deny=4 even_deny_root unlock_time=1200
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
SEE ALSO
faillock(8), pam.conf(5), pam.d(5), pam(8)
AUTHOR
pam_faillock was written by Tomas Mraz.
Linux-PAM Manual 11/05/2016 PAM_FAILLOCK(8)
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