pam_listfile — deny or allow services based on an arbitrary file

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

DESCRIPTION

pam_listfile is a PAM module which provides a way to deny or allow services
based on an arbitrary file.

The module gets the item of the type specified -- user specifies the username, 
PAM_USER; tty specifies the name of the terminal (if any) over which the
request has been made, PAM_TTY; rhost specifies the name of the remote host (if
any) from which the request was made, PAM_RHOST; and ruser specifies the name
of the remote user (if available) who made the request, PAM_RUSER -- and looks
for an instance of that item in the file=filename. filename contains one line
per item listed. If the item is found, then if sense=allow, PAM_SUCCESS is
returned, causing the authorization request to succeed; else if sense=deny, 
PAM_AUTH_ERR is returned, causing the authorization request to fail.

If an error is encountered (for instance, if filename does not exist, or a
poorly-constructed argument is encountered), then if onerr=succeed, PAM_SUCCESS
is returned, otherwise if onerr=fail, PAM_AUTH_ERR or PAM_SERVICE_ERR (as
appropriate) will be returned.

An additional argument, apply=, can be used to restrict the application of the
above to a specific user (apply=username) or a given group (apply=@groupname).
This added restriction is only meaningful when used with the tty, rhost and 
shell items.

Besides this last one, all arguments should be specified; do not count on any
default behavior.

No credentials are awarded by this module.

OPTIONS

item=[tty|user|rhost|ruser|group|shell]

    What is listed in the file and should be checked for.

sense=[allow|deny]

    Action to take if the item is found in the file. If the item is NOT found
    in the file, then the opposite action is requested.

file=/path/filename

    File containing one item per line. The file needs to be a plain file and
    not world writable.

onerr=[succeed|fail]

    What to do if something weird happens like being unable to open the file.

apply=[user|@group]

    Restrict the user class for which the restriction apply. Note that with
    item=[user|ruser|group] this does not make sense, but for item=[tty|rhost|
    shell] it has a meaning.

quiet

    Do not treat service refusals or missing list files as errors that need to
    be logged.

EXAMPLES

Classic 'ftpusers' authentication can be implemented with this entry in /etc/
pam.d/ftpd:

#
# deny ftp-access to users listed in the /etc/ftpusers file
#
auth    required       pam_listfile.so \
        onerr=succeed item=user sense=deny file=/etc/ftpusers


Note, users listed in /etc/ftpusers file are (counterintuitively) not allowed
access to the ftp service.

To allow login access only for certain users, you can use a /etc/pam.d/login
entry like this:

#
# permit login to users listed in /etc/loginusers
#
auth    required       pam_listfile.so \
        onerr=fail item=user sense=allow file=/etc/loginusers


For this example to work, all users who are allowed to use the login service
should be listed in the file /etc/loginusers. Unless you are explicitly trying
to lock out root, make sure that when you do this, you leave a way for root to
log in, either by listing root in /etc/loginusers, or by listing a user who is
able to su to the root account.

AUTHOR

pam_listfile was written by Michael K. Johnson <johnsonm@redhat.com> and Elliot
Lee <sopwith@cuc.edu>.

