6.16. pam_listfile - deny or allow services based on an arbitrary file
pam_listfile.so item=[tty|user|rhost|ruser|group|shell] sense=[allow|deny] file=/path/filename onerr=[succeed|fail] [ apply=[user|@group] ] [ quiet ]
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 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=. filenamefilename contains one line per item listed. If the item is found, then if sense=, PAM_SUCCESS is returned, causing the authorization request to succeed; else if allowsense=, PAM_AUTH_ERR is returned, causing the authorization request to fail.deny
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=) or a given group (usernameapply=). This added restriction is only meaningful when used with the tty, rhost and shell items.@groupname
Besides this last one, all arguments should be specified; do not count on any default behavior.
No credentials are awarded by this module.
-
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 found in 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 foritem=[tty|rhost|shell]it have a meaning. -
quiet -
Do not treat service refusals or missing list files as errors that need to be logged.
- PAM_AUTH_ERR
-
Authentication failure.
- PAM_BUF_ERR
-
Memory buffer error.
- PAM_IGNORE
-
The rule does not apply to the
applyoption. - PAM_SERVICE_ERR
-
Error in service module.
- PAM_SUCCESS
-
Success.
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.