48 KiB
48 KiB
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
1. Introduction
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.
1.1. Overview
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.
1.2. Candy
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.
1.3. Disclaimer
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.
1.4. New versions
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>.
1.5. Translations
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.
1.6. Feedback
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
1.7. Copyright and trademarks
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".
1.8. Acknowledgments and Thanks
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.
2. Requirements
2.1. Knowledge
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.
2.2. Software
Installed on your server, you will need at least:
· Samba;
· Iptables;
· A scripting language;
3. Linux box setup
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.
3.1. Basic system setup
Generally any basic system setup from the common Linux distributions
will fit in this gateway example. Just check if you have Samba and
IPTABLES.
3.2. Additional directory hierarchy
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.
3.3. Firewall setup
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!
3.4. SAMBA setup
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.
3.4.1. Basic SAMBA setup.
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.
3.4.2. The "logon script"
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.
3.4.3. The netlogon and the tracking shares
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
4. An alternative solution
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/>
5. SSH setup
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.
5.1. Important
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.
5.2. Key pair generation
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
5.3. SSH enabled logon script
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.
6. Windows workstation setup
6.1. Introduction
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.
6.2. Network protocols
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?
6.3. DHCP setup
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.
6.4. Join your Linux server domain
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.
6.4.1. Windows fo workgroups
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
6.4.2. Windows 95/98/ME
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
6.4.3. Windows NT
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
6.4.4. Windows 2000
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
6.4.5. Windows XP
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
6.5. Policy editor
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.
7. User management
7.1. Adding users
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.
7.2. Password management
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.
7.3. Granting or denying access to users
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.
8. Group management
8.1. Creating groups
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.
8.2. Group policy
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.
9. Bibliography
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
10. GNU Free Documentation License
GNU Free Documentation License Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple
Place, Suite 330, Boston, MA 02111-1307 USA Everyone is permitted to
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0. PREAMBLE
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Copyright (c) YEAR YOUR NAME. Permission is granted to copy,
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Documentation License, Version 1.2 or any later version published by
the Free Software Foundation; with no Invariant Sections, no Front-
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permit their use in free software.
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
1. Introduction
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.
1.1. Overview
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.
1.2. Candy
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.
1.3. Disclaimer
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.
1.4. New versions
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>.
1.5. Translations
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.
1.6. Feedback
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
1.7. Copyright and trademarks
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".
1.8. Acknowledgments and Thanks
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.
2. Requirements
2.1. Knowledge
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.
2.2. Software
Installed on your server, you will need at least:
· Samba;
· Iptables;
· A scripting language;
3. Linux box setup
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.
3.1. Basic system setup
Generally any basic system setup from the common Linux distributions
will fit in this gateway example. Just check if you have Samba and
IPTABLES.
3.2. Additional directory hierarchy
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.
3.3. Firewall setup
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!
3.4. SAMBA setup
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.
3.4.1. Basic SAMBA setup.
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.
3.4.2. The "logon script"
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.
3.4.3. The netlogon and the tracking shares
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
4. An alternative solution
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/>
5. SSH setup
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.
5.1. Important
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.
5.2. Key pair generation
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
5.3. SSH enabled logon script
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.
6. Windows workstation setup
6.1. Introduction
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.
6.2. Network protocols
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?
6.3. DHCP setup
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.
6.4. Join your Linux server domain
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.
6.4.1. Windows fo workgroups
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
6.4.2. Windows 95/98/ME
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
6.4.3. Windows NT
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
6.4.4. Windows 2000
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
6.4.5. Windows XP
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
6.5. Policy editor
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.
7. User management
7.1. Adding users
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.
7.2. Password management
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.
7.3. Granting or denying access to users
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.
8. Group management
8.1. Creating groups
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.
8.2. Group policy
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.
9. Bibliography
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
10. GNU Free Documentation License
GNU Free Documentation License Version 1.2, November 2002
Copyright (C) 2000,2001,2002 Free Software Foundation, Inc. 59 Temple
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Make the same adjustment to the section titles in the list of
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In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications". You must delete all sections
Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the rules
of this License for verbatim copying of each of the documents in all
other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert a
copy of this License into the extracted document, and follow this
License in all other respects regarding verbatim copying of that
document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
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8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
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original versions of these Invariant Sections. You may include a
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of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided for under this License. Any other attempt
to copy, modify, sublicense or distribute the Document is void, and
will automatically terminate your rights under this License. However,
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License will not have their licenses terminated so long as such
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10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the
GNU Free Documentation License from time to time. Such new versions
will be similar in spirit to the present version, but may differ in
detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.
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as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:
Copyright (c) YEAR YOUR NAME. 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".
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-
Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
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If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.