Module Name: pam_tally Author[s]: Tim Baverstock Maintainer: Management groups provided: auth; account Cryptographically sensitive: Security rating: Clean code base: System dependencies: A faillog file (default location /var/log/faillog) Network aware: Overview of module

This module maintains a count of attempted accesses, can reset count on success, can deny access if too many attempts fail.

pam_tally comes in two parts: pam_tally.so and pam_tally. The former is the PAM module and the latter, a stand-alone program. pam_tally is an (optional) application which can be used to interrogate and manipulate the counter file. It can display users' counts, set individual counts, or clear all counts. Setting artificially high counts may be useful for blocking users without changing their passwords. For example, one might find it useful to clear all counts every midnight from a cron job.

The counts file is organized as a binary-word array, indexed by uid. You can probably make sense of it with od, if you don't want to use the supplied appliction.

Note, there are some outstanding issues with this module: pam_tally is very dependant on getpw*() - a database of usernames would be much more flexible; the `keep a count of current logins' bit has been #ifdef'd out and you can only reset the counter on successful authentication, for now. Generic options accepted by both components

onerr=(succeed|fail): if something weird happens, such as unable to open the file, how should the module react? file=/where/to/keep/counts: specify the file location for the counts. The default location is /var/log/faillog. Authentication component

Recognized arguments: onerr=(succeed|fail); file=/where/to/keep/counts; no_magic_root Description:

The authentication component of this module increments the attempted login counter.

Examples/suggested usage:

The module argument no_magic_root is used to indicate that if the module is invoked by a user with uid=0, then the counter is incremented. The sys-admin should use this for daemon-launched services, like telnet/rsh/login. For user launched services, like su, this argument should be omitted.

By way of more explanation, when a process already running as root tries to access some service, the access is magic, and bypasses pam_tally's checks: this is handy for suing from root into an account otherwise blocked. However, for services like telnet or login, which always effectively run from the root account, root (ie everyone) shouldn't be granted this magic status, and the flag `no_magic_root' should be set in this situation, as noted in the summary above. Account component

Recognized arguments: onerr=(succeed|fail); file=/where/to/keep/counts; deny=n; no_magic_root; even_deny_root_account; reset; no_reset; per_user; no_lock_time Description:

The account component can deny access and/or reset the attempts counter. It also checks to make sure that the counts file is a plain file and not world writable. Examples/suggested usage:

The deny=n option is used to deny access if tally for this user exceeds n. The presence of deny=n changes the default for reset/no_reset to reset, unless the user trying to gain access is root and the no_magic_root option has NOT been specified.

The no_magic_root option ensures that access attempts by root DON'T ignore deny. Use this for daemon-based stuff, like telnet/rsh/login.

The even_deny_root_account option is used to ensure that the root account can become unavailable. Note that magic root trying to gain root bypasses this, but normal users can be locked out.

The reset option instructs the module to reset count to 0 on successful entry, even for magic root. The no_reset option is used to instruct the module to not reset the count on successful entry. This is the default unless deny exists and the user attempting access is NOT magic root.

If /var/log/faillog contains a non-zero .fail_max field for this user then the per_user module argument will ensure that the module uses this value and not the global deny=n parameter.

The no_lock_time option is for ensuring that the module does not use the .fail_locktime field in /var/log/faillog for this user.

Normally, failed attempts to access 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. If you really want root to be blocked for some given service, use even_deny_root_account.