Edit: /usr/share/doc/pam/txts/README.pam_faillock (6062B)
pam_faillock -- Module counting authentication failures during a specified
interval
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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.
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.
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
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.
/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 gives the authenticating user message 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
AUTHOR
pam_faillock was written by Tomas Mraz.