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<sect1>The login counter (tallying) module

<sect2>Synopsis

<p>
<descrip>

<tag><bf>Module Name:</bf></tag>
pam_tally

<tag><bf>Author[s]:</bf></tag>
Tim Baverstock

<tag><bf>Maintainer:</bf></tag>

<tag><bf>Management groups provided:</bf></tag>
auth; account

<tag><bf>Cryptographically sensitive:</bf></tag>
	
<tag><bf>Security rating:</bf></tag>

<tag><bf>Clean code base:</bf></tag>

<tag><bf>System dependencies:</bf></tag>
A faillog file (default location /var/log/faillog)

<tag><bf>Network aware:</bf></tag>

</descrip>

<sect2>Overview of module

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

<p>
pam_tally comes in two parts: <tt>pam_tally.so</tt> and
<tt>pam_tally</tt>. The former is the PAM module and the latter, a
stand-alone program. <tt>pam_tally</tt> 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.

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

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

<sect3>Generic options accepted by both components
<p>
<itemize>
<item> <tt>onerr=</tt>(<tt>succeed</tt>|<tt>fail</tt>):
   if something weird happens, such as unable to open the file, how
   should the module react?
<item> <tt>file=</tt><em>/where/to/keep/counts</em>:
   specify the file location for the counts.
   The default location is <tt>/var/log/faillog</tt>.
</itemize>

<sect2>Authentication component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>
<tt>onerr=</tt>(<tt>succeed</tt>|<tt>fail</tt>);
<tt>file=</tt>/where/to/keep/counts;
<tt>no_magic_root</tt>

<tag><bf>Description:</bf></tag>

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

<p>
<tag><bf>Examples/suggested usage:</bf></tag>

<p>
The module argument <tt>no_magic_root</tt> 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 <tt>telnet</tt>/<tt>rsh</tt>/<tt>login</tt>. For user
launched services, like <tt>su</tt>, this argument should be omitted.

<p>
By way of more explanation, when a process already running as root
tries to access some service, the access is <em>magic</em>, and
bypasses <tt>pam_tally</tt>'s checks: this is handy for <tt>su</tt>ing
from root into an account otherwise blocked. However, for services
like <tt>telnet</tt> or <tt>login</tt>, 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.

</descrip>

<sect2>Account component

<p>
<descrip>

<tag><bf>Recognized arguments:</bf></tag>
<tt>onerr=</tt>(<tt>succeed</tt>|<tt>fail</tt>);
<tt>file=</tt>/where/to/keep/counts;
<tt>deny=</tt><em>n</em>;
<tt>no_magic_root</tt>;
<tt>even_deny_root_account</tt>;
<tt>reset</tt>;
<tt>no_reset</tt>;
<tt>per_user</tt>;
<tt>no_lock_time</tt>

<tag><bf>Description:</bf></tag>

<p>
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.

<tag><bf>Examples/suggested usage:</bf></tag>

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

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

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

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

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

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

<p>
Normally, failed attempts to access root will <bf>NOT</bf> 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
<tt>su</tt> or at the machine console (not
<tt>telnet</tt>/<tt>rsh</tt>, etc), this is safe. If you really want
root to be blocked for some given service, use
<tt>even_deny_root_account</tt>.

</descrip>

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