NAME
ckpasswd - nnrpd password authenticator
SYNOPSIS
ckpasswd [-gs] [-d database] [-f filename] [-u username -p password]
DESCRIPTION
ckpasswd is the basic password authenticator for nnrpd, suitable for
being run from an auth stanza in readers.conf. See readers.conf(5) for
more information on how to configure an nnrpd authenticator.
ckpasswd accepts a username and password from nnrpd and tells nnrpd(8)
whether that’s the correct password for that username. By default,
when given no arguments, it tries to check the password using PAM if
support for PAM was found when INN was built. Failing that, it tries
to check the password against the password field returned by
getpwnam(3). Note that these days most systems no longer make real
passwords available via getpwnam(3) (some still do if and only if the
program calling getpwnam(3) is running as root).
When using PAM, ckpasswd identifies itself as "nnrpd", not as
"ckpasswd", and the PAM configuration must be set up accordingly. The
details of PAM configuration are different on different operating
systems (and even different Linux distributions); see EXAMPLES below
for help getting started, and look for a pam(7) or pam.conf(4) manual
page on your system.
When using any method other than PAM, ckpasswd expects all passwords to
be stored encrypted by the system crypt(3) function and calls crypt(3)
on the supplied password before comparing it to the expected password.
If you’re using a different password hash scheme (like MD5), you must
use PAM.
OPTIONS
-d database
Read passwords from a database (ndbm or dbm format depending on
what your system has) rather than by using getpwnam(3). ckpasswd
expects database.dir and database.pag to exist and to be a database
keyed by username with the encrypted passwords as the values.
While INN doesn’t come with a program intended specifically to
create such databases, on most systems it’s fairly easy to write a
Perl script to do so. Something like:
#!/usr/bin/perl
use NDBM_File;
use Fcntl;
tie (%db, 'NDBM_File', '/path/to/database', O_RDWR|O_CREAT, 0640)
or die "Cannot open /path/to/database: $!\n";
$| = 1;
print "Username: ";
my $user = <STDIN>;
chomp $user;
print "Password: ";
my $passwd = <STDIN>;
chomp $passwd;
my @alphabet = ('.', '/', 0..9, 'A'..'Z', 'a'..'z');
my $salt = join '', @alphabet[rand 64, rand 64];
$db{$user} = crypt ($passwd, $salt);
untie %db;
Note that this will echo back the password when typed; there are
obvious improvements that could be made to this, but it should be a
reasonable start. Sometimes a program like this will be available
with the name dbmpasswd.
This option will not be available on systems without dbm or ndbm
libraries.
-f filename
Read passwords from the given file rather than using getpwnam(3).
The file is expected to be formatted like a system password file,
at least vaguely. That means each line should look something like:
username:pdIh9NCNslkq6
(and each line may have an additional colon after the encrypted
password and additional data; that data will be ignored by
ckpasswd). Lines starting with a number sign ("#") are ignored.
INN does not come with a utility to create the encrypted passwords,
but htpasswd (which comes with Apache) can do so and it’s a quick
job with Perl (see the example script under -d). If using Apache’s
htpasswd program, be sure to give it the -d option so that it will
use crypt(3).
-g Attempt to look up system group corresponding to username and
return a string like "user@group" to be matched against in
readers.conf. This option is incompatible with the -d and -f
options.
-p password
Use password as the password for authentication rather than reading
a password using the nnrpd authenticator protocol. This option is
useful only for testing your authentication system (particularly
since it involves putting a password on the command line), and does
not work when ckpasswd is run by nnrpd. If this option is given,
-u must also be given.
-s Check passwords against the result of getspnam(3) instead of
getpwnam(3). This function, on those systems that supports it,
reads from /etc/shadow or similar more restricted files. If you
want to check passwords supplied to nnrpd(8) against system account
passwords, you will probably have to use this option on most
systems.
Most systems require special privileges to call getspnam(3), so in
order to use this option you may need to make ckpasswd setgid to
some group (like group "shadow") or even setuid root. ckpasswd has
not been specifically audited for such uses! It is, however, a
very small program that you should be able to check by hand for
security.
This configuration is not recommended if it can be avoided, for
serious security reasons. See "SECURITY CONSIDERATIONS" in
readers.conf(5) for discussion.
-u username
Authenticate as username. This option is useful only for testing
(so that you can test your authentication system easily) and does
not work when ckpasswd is run by nnrpd. If this option is given,
-p must also be given.
EXAMPLES
See readers.conf(5) for examples of nnrpd(8) authentication
configuration that uses ckpasswd to check passwords.
An example PAM configuration for /etc/pam.conf that tells ckpasswd to
check usernames and passwords against system accounts is:
nnrpd auth required pam_unix.so
nnrpd account required pam_unix.so
Your system may want you to instead create a file named nnrpd in
/etc/pam.d with lines like:
auth required pam_unix.so
account required pam_unix.so
This is only the simplest configuration. You may be able to include
common shared files, and you may want to stack other modules, either to
allow different authentication methods or to apply restrictions like
lists of users who can’t authenticate using ckpasswd. The best guide
is the documentation for your system and the other PAM configurations
you’re already using.
To test to make sure that ckpasswd is working correctly, you can run it
manually and then give it the username (prefixed with
"ClientAuthname:") and password (prefixed with "ClientPassword:") on
standard input. For example:
(echo 'ClientAuthname: test' ; echo 'ClientPassword: testing') \
| ckpasswd -f /path/to/passwd/file
will check a username of "test" and a password of "testing" against the
username and passwords stored in /path/to/passwd/file. On success,
ckpasswd will print "User:test" and exit with status 0. On failure, it
will print some sort of error message and exit a non-zero status.
HISTORY
Written by Russ Allbery <rra@stanford.edu> for InterNetNews.
$Id: ckpasswd.pod 7674 2007-09-15 21:49:08Z iulius $
SEE ALSO
crypt(3), nnrpd(8), pam(7), readers.conf(5).
Linux users who want to use PAM should read the Linux-PAM System
Administrator’s Guide at
<http://www.kernel.org/pub/linux/libs/pam/Linux-PAM-html/Linux-PAM_SAG.html>.