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PAM Authentication without Apache

• /etc/pam.d/twiki

auth include system

• /root/bin/checkpassword-pam.sh

#!/bin/sh
exec /usr/local/bin/checkpassword-pam "$@" 3<&0

• /usr/local/etc/sudoers

%www ALL = (root) NOPASSWD: /root/bin/checkpassword-pam.sh

• twiki/lib/TWiki/Users/PAM.pm

package TWiki::Users::PAM;

use Assert;
use strict;
use TWiki::Users::Password;
use Error qw( :try );

use base qw( TWiki::Users::Password );

sub checkPassword {
    my( $this, $login, $passU ) = @_;
    ASSERT( $login ) if DEBUG;

    if($login =~ /([^']+)/){
        $login = $1;
    }else{
        return 0;
    }
    if($passU =~ /([^']+)/){
        $passU = $1;
    }else{
        return 0;
    }
    if(`id -u '$login'` == 0){
        return 0;
    }
    my $res=`/usr/bin/printf '%s\\0%s\\0time\\0' '$login' '$passU'|/usr/local/bin/sudo /root/checkpassword-pam.sh -s twiki echo 'SUCCESS'`;
    warn "$login - $res";
    if($res =~ /SUCCESS/){
        return 1;
    }else{
        return 0;
    }
}
1;

• twiki/lib/LocalSite.cfg

$TWiki::cfg{PasswordManager} = 'TWiki::Users::PAM';

-- Contributor: AndrewPantyukhin - 11 Dec 2007

Comments & Questions about this Supplemental Document Topic

I am a little concerned that:

my $res=`/usr/bin/printf '%s\\0%s\\0time\\0' '$login' '$passU'...

exposes the password (in $passU) in the arguments to printf where it can be seen by anybody running ps(1).

I am not quite sure what is in $passU, but that looks dangerous. Better would be something along the lines of:

  open(CHECKPASS, '|/usr/local/bin/sudo /root/checkpassword-pam.sh -s twiki /bin/sh -c "exit 0" ');

  print CHECKPASS "$login\000$passU\000time\000";

  $exitval = close(CHECKPASS);

  if ( $exitval != 0 ) {
    return 1;
  } else {
    return 0;
  }

so that the magic string sent to checkpasswd-pam doesn't show up on a command line anywhere. (Note you need to catch SIGPIPE in case the open fails and add some error checking (like the return status of open for example)). Then use the exit status of the command to determine pass/fail. You could use the original method with a call to one of the IPC::open functions to allow reading from and writing to the checkpasswd-pam subprocess.

• You're right, of course -- AndrewPantyukhin - 27 Dec 2007

• Fixed, thanks -- AndrewPantyukhin - 27 Dec 2007

nice one!

Is there a reason not to use one of the CPAN Pam modules rather than shelling out? like Authen::PAM or Authen::Simple::PAM ?

-- SvenDowideit - 12 Dec 2007

They still need to be run under root (through sudo or a simple setuid wrapper). So it's either you fork perl or shell with a tiny C program (or, of course, a persistent service, which is a bit more complicated to implement). Since authentication is rarely a performance concern (except under DoS), it's just a matter of taste.

-- AndrewPantyukhin - 27 Dec 2007