  Samba Authenticated Gateway HOWTO
  Ricardo Alexandre Mattar
  v1.3, 2005-01-06

  This document intends to show how to build a Firewall/Gateway with
  rules set on user basis having the users authenticated by a Samba Pri-
  mary Domain Controller

  [1m1.  Introduction[0m

  As you can see by the poorness of my language, English is not my
  native language. I am writing this document in English for the sake of
  the Linux community. So, please, excuse me for my poor English.  And,
  please, if you speak Portuguese, address me in this language.


  This document intends to enlighten you (and myself) in the process of
  building a Linux Gateway or Firewall, which modify rules on demand
  when users log in or out from their Windows workstations.


  In this document, I will try to show how to build a gateway to NAT or
  MASQUERADE Windows workstations. Use your imagination to modify it to
  get any level of network management. You may use it to grant or deny
  access to services, servers or entire subnetworks on your network.


  Imagine that you have to build a gateway to let Windows workstation
  access the Internet and that you need to authenticate each user before
  letting them access the external networks. The first solution you
  think about is Squid. It's indeed a great solution, when http and ftp
  access is enough for your users. When it comes to let them access
  other services like pop, smtp, ssh, a database server or whatever
  else, you immediately think about NAT or MASQUERADE. But what happens
  to the user authentication?


  Well, this is my solution. It gives you user authentication and fine
  grain control over their access to the external networks.


  [1m1.1.  Overview[0m

  We know that SAMBA can act as a Domain Controller and so it can
  authenticate users on Windows boxes. As a PDC, SAMBA can push netlogon
  scripts to the Windows workstations. We can use this netlogon scripts
  to force the Windows workstations mounting a given share from our
  Linux PDC. This "forced" share shall have preexec and postexec scripts
  which shall be triggered when the user logs in or out. There is a
  program named smbstatus which lists the shares being used, giving us
  also the username and ip address of the workstation. We just need to
  grep this information from smbstatus output and update our firewall
  rules.


  [1m1.2.  Candy[0m

  If you are impatient and don't like to read, go to
  http://sourceforge.net/projects/smbgate/
  <http://sourceforge.net/projects/smbgate/>, but in the end you may
  find yourself coming back here to read.



  [1m1.3.  Disclaimer[0m

  No liability for the contents of this document can be accepted.  Use
  the concepts, examples and other content at your own risk. As this is
  a new edition of this document, there may be errors and inaccuracies,
  that may of course be damaging to your system. Proceed with caution,
  and although this is highly unlikely, the author(s) do not take any
  responsibility for that.


  All copyrights are held by their respective owners, unless
  specifically noted otherwise. Use of a term in this document should
  not be regarded as affecting the validity of any trademark or service
  mark.


  Naming of particular products or brands should not be seen as
  endorsements.


  [1m1.4.  New versions[0m

  The newest release of this document can be found at http://ram.eti.br
  <http://ram.eti.br> or at http://www.tldp.org <http://www.tldp.org>


  Related HOWTOs can be found at the Linux Documentation Project
  homepage at http://tldp.org <http://tldp.org>.


  [1m1.5.  Translations[0m

  A Portuguese version is available.


  A French translation by Guillaume Lelarge is available
  athttp://www.traduc.org
  <http://www.traduc.org/docs/HOWTO/lecture/Samba-Authenticated-Gateway-
  HOWTO.html>


  A Hungarian translation is available at http://tldp.fsf.hu
  <http://tldp.fsf.hu/HOWTO/Samba-Authenticated-Gateway-HOWTO-hu/Samba-
  Authenticated-Gateway-HOWTO-hu.html>


  If you want to contribute with a translation, please do.


  [1m1.6.  Feedback[0m

  Contributions and criticism are both welcome.


  Corrections to my English are also very welcome!


  If you find any bugs in the scripts included, please tell me.


  You can find me at ricardo@ram.eti.br or at ricardo.mattar@bol.com.br



  [1m1.7.  Copyright and trademarks[0m

  Copyright (c) 2002-2003 Ricardo Alexandre Mattar


  Permission is granted to copy, distribute and/or modify this document
  under the terms of the GNU Free Documentation License, Version 1.2 or
  any later version published by the Free Software Foundation; with no
  Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
  copy of the license is included in the section entitled "GNU Free
  Documentation License".


  [1m1.8.  Acknowledgments and Thanks[0m

  Thanks to Carlos Alberto Reis Ribeiro for introducing me to Linux.


  Thanks to Cesar Bremer Pinheiro for motivating me to write this
  document.


  Thanks to Guillaume Lelarge for the (continuous) help with the
  revision.


  Thanks to Erik Esplund for further language corrections.


  Thanks to Albert Teixidr code improvements.


  Thanks to Felipe Cordeiro Caetano for helping on my main testing site.


  Thanks to the secure communications company RASEAC
  <http://www.raseac.com.br> for sponsoring my work.


  [1m2.  Requirements[0m

  [1m2.1.  Knowledge[0m

  This document is target at the seasoned systems administrator.


  You must have a fair knowledge about (at least know what these are):



  · TCP/IP;

  · Linux netfilter;

  · A scripting language (bash?);

  · SAMBA and Windows networking and domain controllers;

  Fortunately, there is plenty of documentation on these topics on the
  Internet.


  [1m2.2.  Software[0m

  Installed on your server, you will need at least:

  · Samba;

  · Iptables;

  · A scripting language;

  [1m3.  Linux box setup[0m

  This Howto assumes you have a kernel from the 2.4 series as it uses
  iptables. Other than that, there are no known issues why this should
  not work on a 2.2 kernel box with the scripts adapted to ipchains.


  Of course, you need to install the iptables userland tools, an apache
  http server if you want to run a CGI tool to change passwords and
  SAMBA. And you will need a kernel compiled with iptables modules.


  You may wish to use DHCP. If so, it is easy to set up. Remember to
  configure the dhcp server to give the nameserver IP address and the
  gateway IP address as well. The Windows machines will make good use of
  this information.


  [1m3.1.  Basic system setup[0m

  Generally any basic system setup from the common Linux distributions
  will fit in this gateway example. Just check if you have Samba and
  IPTABLES.


  [1m3.2.  Additional directory hierarchy[0m

  The additional directory hierarchy will be required to accomplish the
  example of this howto:


  This is used to keep track of the users and IP addresses:



  /var/run/smbgate/



  This is where I place user specific scripts:



  /etc/smbgate/users/



  And group specific scripts:



  /etc/smbgate/groups/



  Directory for the netlogon share:



  /home/samba/netlogon/



  Directory for the tracking share:



  /home/samba/samba/



  These hierarchies are required by some of the scripts and daemons of
  the example.


  [1m3.3.  Firewall setup[0m

  Its very unlikely that your distribution's kernel won't be compiled
  with Iptables and the userland tools won't be installed either.
  Anyway, if you don't have it, refer to http://www.netfilter.org
  <http://www.netfilter.org> or http://www.iptables.org
  <http://www.iptables.org> to get the software and the documentation.


  You will need a basic firewall setup in order to get the gateway
  working. Take a look at the iptables tutorial at IPTABLES TUTORIAL
  <http://www.netfilter.org/documentation/tutorials/blueflux/iptables-
  tutorial.html>. It's an interesting reading. Anyway, if you have no
  time to spend, the following code is somewhat (very) loose but it may
  fit your needs:



  #!/bin/sh
  IPTABLES=/usr/sbin/iptables
  /sbin/depmod -a
  /sbin/insmod ip_tables
  /sbin/insmod ip_conntrack
  /sbin/insmod ip_conntrack_ftp
  /sbin/insmod ip_conntrack_irc
  /sbin/insmod iptable_nat
  /sbin/insmod ip_nat_ftp
  echo "1" > /proc/sys/net/ipv4/ip_forward
  echo "1" > /proc/sys/net/ipv4/ip_dynaddr
  $IPTABLES -P INPUT ACCEPT
  $IPTABLES -F INPUT
  $IPTABLES -P OUTPUT ACCEPT
  $IPTABLES -F OUTPUT
  $IPTABLES -P FORWARD ACCEPT
  $IPTABLES -F FORWARD
  $IPTABLES -t nat -F



  You will notice that this code actually does nothing, but load the
  kernel modules related to nat and firewalling and turns the packet
  routing on. You can (and should) place any rules there to give your
  gateway a standard behavior, but the big magic will be done by scripts
  called by the SAMBA daemon.


  Please, remember that this code doesn't have the least bit of
  security! Don't use these examples in production environments. This
  example intends only to be educational. You have to add a firewall
  configuration that suits your systems.
  You have been warned!


  [1m3.4.  SAMBA setup[0m

  Check if you have Samba installed. If your distribution doesn't come
  with Samba pre-packaged then refer to http://www.samba.org
  <http://www.samba.org> to get the packages and for documentation on
  how to install Samba. Brows around their web site and learn about it.
  The site has plenty of documentation and maybe your LINUX distribution
  also has plenty of SAMBA documentation.


  We will need to setup SAMBA as a Primary Domain Controller. I will
  give an example configuration file here, but you should read the Samba
  HOWTO Collection <http://www.samba.org/samba/docs/man/Samba-HOWTO-
  Collection.html> and learn all you can about a PDC.


  [1m3.4.1.  Basic SAMBA setup.[0m

  Since I do not intend to rewrite the SAMBA documentation, here goes a
  sample smb.conf file:



  # Global parameters
  [global]
  workgroup = DOMAIN
  netbios name = LINUX
  server string = Linux PDC
  encrypt passwords = Yes
  map to guest = Bad Password
  passwd program = /usr/bin/passwd
  unix password sync = Yes
  max log size = 50
  time server = Yes
  socket options = TCP_NODELAY SO_RCVBUF=8192 SO_SNDBUF=8192
  add user script = /usr/sbin/useradd -d /dev/null -g 100 -s /bin/false -M %u
  logon script = %a.bat
  domain logons = Yes
  os level = 64
  lm announce = True
  preferred master = True
  domain master = True
  dns proxy = No
  printing = lprng
  [homes]
  comment = Home Directories
  path = /home/%u
  read only = No
  [printers]
  comment = All Printers
  path = /var/spool/samba
  printable = Yes
  browseable = No
  available = No
  [netlogon]
  comment = NetLogon ShARE
  path = /home/samba/netlogon
  guest account =
  [samba]
  comment = login tracking share
  path = /home/samba/samba
  browseable = No
  root preexec = /usr/local/bin/netlogon.sh %u %I
  root postexec = /usr/local/bin/netlogoff.sh %u



  You will have to do with it or read the SAMBA documentation if you
  really want to control your server and network.


  [1m3.4.2.  The "logon script"[0m

  Using "logon script = %a.bat" makes samba evaluate the guest os and
  call an appropriated logon script. If you want a static script, just
  change to "logon script = netlogon.bat". Actually you can do anything
  here and even generate any script during the logon.


  [1m3.4.3.  The netlogon and the tracking shares[0m

  The netlogon share is where the Windows workstations download the
  logon script from. We need this share in order to place there a logon
  script, which will tell the workstation to mount a share that will be
  used to track the users ip addresses.


  As you can see, there must be a line like the following in your
  smb.conf
  logon script = netlogon.bat



  This line will tell your Windows client to download and execute the
  script named netlogon.bat. This script must be placed at the netlogon
  share. So, we will also need a netlogon.bat script to your Windows
  workstations. You can use the following example and place it at the
  netlogon share, in this case: /home/samba/netlogon/NETLOGON.BAT.



  REM NETLOGON.BAT
  net use z: \\linux\samba /yes



  This script will tell the Windows workstation to mount the specified
  share, and so we will be able to keep track of the user and
  workstation through the output of the smbstatus program.


  Quite simple! But not enough...


  As you could see, we will need also a tracking share which, in this
  example, I named samba. You can see the tracking share configuration
  in smb.conf:



  [samba]
  comment = login tracking share
  path = /home/samba/samba
  browseable = No
  root preexec = /usr/local/bin/netlogon.sh %u %I
  root postexec = /usr/local/bin/netlogoff.sh %u



  As you can guess or know if you read the SAMBA documentation, the root
  preexec and the root postexec lines tell SAMBA to run the indicated
  scripts when a user mounts or unmounts the share. In this case, we are
  passing the username to the script as a parameter. Note the %u at the
  end of the lines. These scripts are the beasts which will call a
  script or program to modify our gateway's packet filtering rules.


  Note that the netlogon.sh script must check if the refered workstation
  has already mounted the tracking share.


  Take a look at the netlogon.sh and netlogoff.sh scripts:



  #!/bin/sh
  #
  # netlogon.sh
  #
  # usage:
  # netlogon.sh <username>
  #
  if [ -f /var/run/smbgate/$1 ] ; then
      exit 0
  fi
  echo $2 > /var/run/smbgate/$1
  IPTABLES='/usr/sbin/iptables'
  EXTIF='eth0'
  COMMAND='-A'
  ADDRESS=`cat /var/run/smbgate/$1`
  GROUP=`groups $1 | gawk '// { print $3 }'`
  if [ -f /etc/smbgate/users/$1 ] ; then
      /etc/smbgate/users/$1 $COMMAND $ADDRESS $EXTIF
  else
      if [ -f /etc/smbgate/groups/$GROUP ] ; then
          /etc/smbgate/groups/$GROUP $COMMAND $ADDRESS $EXTIF
      else
          /etc/smbgate/users/default.sh $COMMAND $ADDRESS $EXTIF
      fi
  fi



  This script (netlogon.sh) is intended to run when the user logs in and
  will select the which scripts will be executed based on the user name
  and to which group the user belongs. The user's ip address will be
  written to a file at /var/run/smbgate for tracking purposes.  The file
  will take the user's name and will be later used when the user log
  off. The IP address will be passed as an argument to a script with the
  users' name which will finally update the firewall.


  Notice that this netlogon.sh script tries a user script, then if it
  can't find the user script it tries a group script, and finally if it
  can't find the group script it tries the default.sh script.  You can
  modify this logic and behavior as you wish and need, just remember to
  modify the others accordingly.


  Chances are if the user belong to more than one that these scripts
  will fail. I did not have time to write a better code.



  #!/bin/sh
  #
  # netlogoff.sh
  #
  # usage:
  # netlogoff.sh <username>
  #
  IPTABLES='/usr/sbin/iptables'
  EXTIF='ppp0'
  COMMAND='-D'
  TRACKSHARE="samba"
  ADDRESS=`cat /var/run/smbgate/$1`
  GROUP=`groups $1 | gawk '// { print $3 }'`
  NM=`smbstatus -u $1 | grep $TRACKSHARE | wc -l`
  if [ $NM -gt 0 ]; then
      exit
  fi
  if [ -f /etc/smbgate/users/$1 ] ; then
      /etc/smbgate/users/$1 $COMMAND $ADDRESS $EXTIF
  else
      if [ -f /etc/smbgate/groups/$GROUP ] ; then
          /etc/smbgate/groups/$GROUP $COMMAND $ADDRESS $EXTIF
      else
          /etc/smbgate/users/default.sh $COMMAND $ADDRESS $EXTIF
      fi
  fi
  rm -f /var/run/smbgate/$1



  This script (netlogoff.sh) is intended to run when the user logs off
  and will get the address from the /var/run/smbgate/user file which
  will be passed as an argument to the /etc/smbgate/users/user script
  which will update the firewall to the state desired when the user is
  not logged in.


  Some versions of Windows, such as Windows 2000, mount the tracking
  share more than once per login. This may cause problems with the
  netlogon.sh and netlogoff.sh, triggering the scripts more the once.
  This can make a real mess. So, you may prefer to use a logout checking
  script at cron instead of a netlogoff.sh script triggered by SAMBA.
  Here is an example:



  #!/bin/sh
  # checklogout.sh
  #
  # usage:
  # intended to run at cron (maybe each 10 minutes)

  TRACKDIR="/var/run/smbgate"
  DIRLENGTH=${#TRACKDIR}
  TRACKSHARE="samba"
  EXTIF='eth0'
  COMMAND='-D'
  if [ -d $TRACKDIR ]; then
    for n in $TRACKDIR/*; do
      [ -d $n ] && continue;
      if [ -f $n ] ; then
        IPADDRESS=`cat $n`
        USERNAME=${n:$DIRLENGTH+1}
        NMS=`smbstatus -u $USERNAME | grep $TRACKSHARE | grep $IPADDRESS | grep -v grep | wc -l`
        if [ $NMS == 0 ] ; then
          rm -f $n
          GROUP=`groups $USERNAME | gawk '// { print $3 }'`
          if [ -f /etc/smbgate/users/$USERNAME ] ; then
            /etc/smbgate/users/$USERNAME $COMMAND $IPADDRESS $EXTIF
          else
            if [ -f /etc/smbgate/groups/$GROUP ] ; then
              /etc/smbgate/groups/$GROUP $COMMAND $IPADDRESS $EXTIF
            else
              /etc/smbgate/users/default.sh $COMMAND $IPADDRESS $EXTIF
            fi
          fi
        fi
      else
        exit 0
      fi
    done
  fi



  In that case you should remove the root postexec clause from the
  tracking share on smb.conf:



  root postexec = /usr/local/bin/netlogoff.sh %u



  The following is a standard /etc/smbgate/users/user script. This is
  the one which will actually modify the firewall rules.



  #!/bin/sh
  #
  COMMAND=$1
  ADDRESS=$2
  EXTIF=$3
  IPTABLES='/usr/sbin/iptables'
  $IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF -j MASQUERADE



  We should also have a default.sh script at /etc/smbgate/users/ to give
  the gateway a default behavior.

  #!/bin/sh
  #
  # default.sh
  COMMAND=$1
  ADDRESS=$2
  EXTIF=$3
  IPTABLES='/usr/sbin/iptables'
  #$IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF -j MASQUERADE
  exit 0



  [1m4.  An alternative solution[0m

  The whole scheme of mounting a tracking share and triggering scripts
  to update the firewall and waiting for them to be triggered again on
  unmounting to reset the firewall rule may be too confusing and loose.
  It may become even obsolete as the Samba project release new features.


  The latest Samba release has the capability of listing the logged
  users. I used this feature in a script to track the users and update
  the firewall as they log in and out. This script does not require all
  the work described on this text. It is very easy to use actually.


  You can download the code from the project site at
  http://sourceforge.net/projects/smbgate/
  <http://sourceforge.net/projects/smbgate/>


  [1m5.  SSH setup[0m

  You may want to run your PDC on one box and have another box as a
  managed gateway for any reason. If so you must setup your gateway to
  accept rsa authenticated logins without passwords from the PDC.


  Take a look at www.openssh.org <http://www.openssh.org/manual.html>
  for information on how to properly setup your ssh server and client
  for this.


  [1m5.1.  Important[0m

  You should read the ssh documentation and make shure that you fully
  understand what you are doing when you setup rsa or any other kind of
  cryptographic authentication.


  If security isn't an issue, just use my example and go on.


  [1m5.2.  Key pair generation[0m

  To create a key pair issue the following commands on the manchine
  meant to be the PDC:



  pdc:~# ssh-keygen -t rsa



  Answer the questions and copy the resulting public key to the gateway
  it self. Usually the public key goes to "~.ssh/id_rsa.pub"
  pdc:~# cd .ssh
  pdc:~# scp id_rsa.pub root@gateway:/root/.ssh/authorized_keys2



  [1m5.3.  SSH enabled logon script[0m

  The following is a standard /etc/smbgate/users/user script modified to
  use the ssh cryptographic authentication.



  #!/bin/sh
  #
  COMMAND=$1
  ADDRESS=$2
  EXTIF=$3
  IPTABLES='/sbin/iptables'
  ssh root@gateway $IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF -j MASQUERADE



  Note that the iptables binary in called through ssh at the "gateway".
  Again, make sure that you read the ssh server documentation.


  [1m6.  Windows workstation setup[0m

  [1m6.1.  Introduction[0m

  We will stick to setting up the network, user management and policies
  on the Windows workstations.


  I will not go through all those steps, naming each dialog box.  I will
  presume that if you can read and understand this document you can find
  your way through that mess.


  [1m6.2.  Network protocols[0m

  First, unless you really need, remove all network protocols but
  TCP/IP. Even without their own protocol, Windows machines like to
  broadcast a lot, and this doesn't please anyone. Anyway, with TCP/IP
  who needs anything else?


  [1m6.3.  DHCP setup[0m

  If you setup a DHCP server on your Linux box, remember that Windows
  workstations can get the nameservers and gateway's address besides its
  own IP address from it. So, you don't need to set all these items on
  each workstation.


  [1m6.4.  Join your Linux server domain[0m

  Configure the Windows workstation to log in a Domain, and give the
  domain name of your Linux server. This is essential to the gateway
  work.


  You must know that in order to join some versions of Windows to a
  SAMBA domain controller, you must create machine accounts in your
  Linux PDC. Check the SAMBA documentation on how to setup your PDC to
  the specific version of Windows which you have.
  [1m6.4.1.  Windows fo workgroups[0m

  This version seems to need no special configuration to join the Linux
  PDC domain.


  The netlogon script shall be named "WfWg.bat" so when %a is translated
  the right script is chosen.


  Example:



  REM WFWG.BAT
  net use z: \\linux\samba /yes



  [1m6.4.2.  Windows 95/98/ME[0m

  These versions also seems to need no special configuration to join the
  Linux PDC domain.


  The netlogon script shall be named "Win95.bat" so when %a is
  translated the right script is chosen.


  Example:



  REM WIN95.BAT
  net use z: \\linux\samba /yes



  [1m6.4.3.  Windows NT[0m

  This version requires machine accounts at the Linux box. Check the
  SAMBA documentation.


  The netlogon script shall be named "WinNT.bat" so when %a is
  translated the right script is chosen.


  Example:



  REM WINNT.BAT
  net use z: \\linux\samba /yes /persistent:no



  [1m6.4.4.  Windows 2000[0m

  This version requires machine accounts at the Linux box. Again, check
  the SAMBA documentation.


  The netlogon script shall be named "Win2K.bat" so when %a is
  translated the right script is chosen.

  Example:



  REM WIN2K.BAT
  net use z: \\linux\samba /yes /persistent:no



  [1m6.4.5.  Windows XP[0m

  This version needs a machine account at the Linux box and a tweak at
  the registry, as follows.


  Locate the key
  "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters\RequireSignOrSeal".
  The default value is 1. Set it to 0 and it will no more complain about
  joining the domain.


  If you have many workstation to configure create a file named
  anything.reg with the following content and use it to modify the
  "faulty" registry.



  Windows Registry Editor Version 5.00

  [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Netlogon\Parameters]
  "requiresignorseal"=dword:00000000



  This version also needs an adjust at the logon script. Sometimes it
  insists on making the mounting persistent. The netlogon script shall
  be named "WinXP.bat" so when %a is translated the right script is
  chosen.


  Example:



  REM WINXP.BAT
  net use z: \\linux\samba /yes /persistent:no



  [1m6.5.  Policy editor[0m

  There is a utility named policy editor bundled on the Windows CD. The
  file name is poledit.exe. This tool, as the name suggest, allows to
  create a user and system policy file.


  Unfortunately, this tool does not generate a plain text configuration
  file, so I can't place an example here.


  Use the policy editor to create a policy to your workstations and
  users. You should disable the local password cache and domain cache in
  order to get some security. Save the policy file as config.pol and
  place it at the netlogon share of your Linux server. In this way, your
  Windows workstations will download and use the config.pol file to set
  their policy. Of course this task must be done on a Windows machine.
  If you don't use a config.pol file, your Windows workstations will
  annoy you asking for a Windows password and you will become nuts
  trying to synchronize and manage your Domain and Windows passwords.
  It seems that the OS doesn't know that it joined a domain. You must
  tell it and then you have to slap it in the face so it will believe
  you.


  [1m7.  User management[0m

  [1m7.1.  Adding users[0m

  Adding a Linux user by usual means and setting a samba password using
  smbpasswd will work. If you have any doubt, just refer to the SAMBA
  documentation. This is not a difficult issue.


  [1m7.2.  Password management[0m

  I am issuing this a major topic because I couldn't learn yet how to
  manage users and users' passwords from a Windows workstation without
  using a web interface. I couldn't find and didn't know how to build
  integrated tools to solve this problem. So, I am using a CGI program
  to get it done.


  Try the package at http://changepassword.sourceforge.net
  <http://changepassword.sourceforge.net>, it seems to be a good choice.


  [1m7.3.  Granting or denying access to users[0m

  As you could see in a previous section of this howto, the SAMBA daemon
  will call a netlogon.sh script every time the tracking share is
  mounted. This netlogon.sh script will call a script with the user's
  name giving this script the ip address of the refered workstation as a
  parameter. This user script will apply the desired rules.


  For example if you want to give the user full access to internet:



  #!/bin/sh
  #
  COMMAND=$1
  ADDRESS=$2
  EXTIF=$3
  IPTABLES='/usr/sbin/iptables'
  $IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF -j MASQUERADE



  If you don't want to change anything to a particular user, just give
  him an empty script:



  #/bin/sh
  #
  exit 0



  Or just don't create any script for the less privileged users, letting
  them have the default.sh script, which would be empty as the previous
  or just give limited access as follows:



  #!/bin/sh
  #
  COMMAND=$1
  ADDRESS=$2
  EXTIF=$3
  EXTIFADDRESS=$4
  IPTABLES='/usr/sbin/iptables'
  $IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF --dport 25 -j SNAT --to-source $EXTIFADDRESS
  $IPTABLES $COMMAND POSTROUTING -t nat -s $ADDRESS -o $EXTIF --dport 110 -j SNAT --to-source $EXTIFADDRESS



  Remember that this script requires you to modify all the previous
  scripts to include the extra parameter ou just modify the script
  script. And remember that you will go nowhere whis this howto if you
  don't understand iptables.


  [1m8.  Group management[0m

  [1m8.1.  Creating groups[0m

  Just create your user groups in the Linux PDC and add the users to the
  groups. This is it.


  Remember that the example scripts in this howto will probably fail if
  you have users belonging to more than one group. If you need this,
  remember to adjust the scripts.


  [1m8.2.  Group policy[0m

  You will need to define group specific scripts and place them in the
  directory "/etc/smbgate/groups/". Remember that the script must be
  named as the group, at least if you want to follow the examples in
  this howto.


  The default scheme of this howto is to check for a user script, then
  for a group script and finally for the default script. If you want to
  modify this behavior remember to adapt the netlogon.sh, netlogoff.sh
  (or the checklogout.sh) scripts. The whole logic is in these scripts.


  [1m9.  Bibliography[0m

  IPTABLES TUTORIAL
  <http://www.netfilter.org/documentation/tutorials/blueflux/iptables-
  tutorial.html> by Oskar Andreasson


  Samba HOWTO Collection <http://www.samba.org/samba/docs/man/Samba-
  HOWTO-Collection.html> by the SAMBA Team


  [1m10.  GNU Free Documentation License[0m

  GNU Free Documentation License Version 1.2, November 2002



  Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple
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