Centralized Logins Using LDAP and Radius
Downloading And Installing The LDAP Packages
Configuring Encrypted LDAP Communication
Common LDAP Administrative Tasks
(c) Peter Harrison, www.linuxhomenetworking.com
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Many centralized database programs have been developed to allow users to log in on multiple computers using a single password. NIS was one of the first, but it doesn't encrypt the password transaction. It also uses the portmapper daemon, which uses an unpredictable range of TCP ports that are difficult for firewalls to track. LDAP (Lightweight Directory Access Protocol) provides an alternative based on the X.500 standard.
The X.500 standard defines how globally referenced directories of people should be structured. X.500 directories are organized under a common root directory in a tree hierarchy with different levels for each category of information, such as country, state, city, organization, organizational unit, and person. Designed to provide a simpler yet robust implementation of X.500, LDAP was originally used as the backbone of Microsoft's Active Directory Service and Novell's Novell Directory Services (NDS) products. LDAP can also interact with other login programs, such as Remote Authentication Dial-in User Service (RADIUS), which the network equipment of many ISPs uses to manage dialup Internet access.
It was later recognized that LDAP had features that could make it a desirable replacement for NIS in some scenarios. For example, it uses a single TCP port (389) for regular communication and another port (636) for encrypted transactions. LDAP also can interact with many login authentication, authorization, and accounting programs external to Linux and UNIX.
This chapter will first show you how to install and use LDAP on Fedora Linux systems, then go on to explain how LDAP interacts with RADIUS.
Like X.500, LDAP directory entries are arranged in a tree structure. Under the root, there are branches that represent countries, organizations, organizational units, and people.
In complicated LDAP deployments, in which you have to exchange information with the LDAP databases of other companies, you may want to get a formal organization number from the Internet Assigned Numbers Authority (IANA) to reduce any data conflicts. In the chapter's example this won't be necessary. Because there will be no data sharing, I'll just make up one.
These concepts are easier to explain when working from an example, so imagine the IT department in a small organization called example.com has many Linux servers it needs to administer.
> The company wants a simple, secure, centralized login scheme for all of the servers.
> It has decided to use the LDAP domain example.com for its LDAP database, in which one domain component (DC) will be example, and the other will be com.
> The database will have only one organizational unit simply called People, which is the LDAP default.
> Each person will have such attributes as a username (User ID or UID), password, Linux home directory, and login shell.
> The Fedora Linux server named bigboy with the IP address 192.168.1.100 will act as the LDAP server containing the database.
> The Fedora Linux server named smallfry will be used to test the system as the LDAP client and has the IP address 192.168.1.102.
> Server bigboy has a special user account named ldapuser that will be used to test the LDAP logins.
Here is how all that is accomplished.
Downloading And Installing The LDAP Packages
Most RedHat and Fedora Linux software products are available in the RPM format. When searching for the file, remember that the FreeRADIUS RPM's filename usually starts with openldap followed by a version number, as in openldap-servers-2.1.22-8.i386.rpm. (For more detail on downloading and installing, see Chapter 6, "Installing Linux Software.")
Make sure these required LDAP Server RPMs are installed on your LDAP server.
You will have to make sure the following packages are installed on your LDAP server.
openldap
openldap-clients
openldap-devel
nss_ldap
openldap-servers
You will have to make sure the following packages are installed on your LDAP client.
openldap
openldap-clients
openldap-devel
nss_ldap
The first stage of the project is to correctly configure the LDAP server. To do so, you must create an LDAP database and into which you import the /etc/passwd file. Take a closer look at the steps:
Fedora LDAP defaults to putting all databases in the /var/lib/ldap directory. For the example, create a dedicated example.com directory owned by the user ldap. (The ldap user is always created during the RPM installation process.)
[root@bigboy tmp]# mkdir /var/lib/ldap/example.com
[root@bigboy tmp]# chown ldap:ldap /var/lib/ldap/example.com
Create an LDAP "root" password
Only the LDAP root user can create, import data, and export data into an LDAP database. This user needs an encrypted password. You can create it with the slappasswd command and use the result in the LDAP configuration file.
[root@bigboy tmp]# slappasswd
New password:
Re-enter new password:
{SSHA}v4qLq/qy01w9my60LLX9BvfNUrRhOjQZ
[root@bigboy tmp]#
The main LDAP server configuration file is the /etc/openldap/slapd.conf file. Update it with:
o A database of the default type ldbm using the domain suffix example.com made up of domain components (DCs) example and com.
o The root user with a common name (CN), or nickname, of Manager who, as expected, is part of the example and com DCs.
o The encrypted version of the LDAP root password as well as the location of the LDAP database.
The configuration file syntax to do this is:
database ldbm
suffix "dc=example,dc=com"
rootdn "cn=Manager,dc=example,dc=com"
rootpw {SSHA}v4qLq/qy01w9my60LLX9BvfNUrRhOjQZ
directory /var/lib/ldap/example.com
The service command uses the options start, stop, and restart to control the LDAP server's operation. Use the start option to load the contents of the slapd.conf file.
[root@bigboy tmp]# service ldap start
Starting slapd: [ OK ]
[root@bigboy tmp]#
Convert the /etc/passwd file to LDIF format
The data on the server's /etc/passwd file now needs to be converted to LDAP Data Interchange Files (LDIF) format before it can be imported into the LDAP database. You don't need to import all of the usernames, just the ones you need.
Create the ldapuser test account
To create the ldapuser account you'll use for testing, type the commands.
[root@bigboy tmp]# useradd -g users ldapuser
[root@bigboy tmp]# passwd ldapuser
Changing password for user ldapuser.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@bigboy tmp]#
Extract the desired records from /etc/passwd
You need to extract the ldapuser information from the /etc/passwd file using the grep command and save it by appending the information to the a file called /etc/openldap/passwd.ldapusers file with the > character.
[root@bigboy tmp]# grep ldapuser /etc/passwd > \
/etc/openldap/passwd.ldapusers
[root@bigboy tmp]#
If this is your first time creating the LDAP database, you will also want to extract the information for the Linux root account from the /etc/passwd file to a brand new file called /etc/openldap/passwd.root.
[root@bigboy tmp]# grep root /etc/passwd > \
/etc/openldap/passwd.root
[root@bigboy tmp]#
The /etc/passwd conversion program is called migrate_passw.pl; you can find it using the locate command. The locate utility updates its database every night and may not be able to find newly installed files. You can use the locate command to do the update ahead of schedule.
[root@bigboy tmp]# locate -u
[root@bigboy tmp]# locate migrate
...
/usr/share/openldap/migration/migrate_passwd.pl
...
[root@bigboy tmp]#
You now need to convert the extracted /etc/passwd data into an LDIF that will then be imported into the database. Give the file used by regular users the name /etc/openldap/ldapuser.ldif and the one for the root user the name /etc/openldap/root.ldif.
[root@bigboy tmp]# /usr/share/openldap/migration/migrate_passwd.pl \
/etc/openldap/passwd.ldapusers /etc/openldap/ldapusers.ldif
[root@bigboy tmp]#
[root@bigboy tmp]# /usr/share/openldap/migration/migrate_passwd.pl \
/etc/openldap/passwd.root /etc/openldap/root.ldif
[root@bigboy tmp]#
With your two new LDIF files, the next step is to import this data into the LDAP database. To prepare for this, you must do some editing and create a new LDIF file that defines the organizational unit.
The Fedora migrate_passwd.pl script creates users that are all part of the organizational unit called People, but everyone belongs to the padl.com domain. You now have to edit both LDIF files and convert the string "padl" to "example" in each record. A text editor is fine for the job. For example, at the vi editor's : prompt, use the command:
%s/padl/example/g
to perform a global substitution of example for padl.
In the slapd.conf file, you gave the root user a common name (CN) of Manager. You now have to add this information to the root LDIF file by inserting this line under the UID line in the file.
cn: Manager
Create an LDIF file for the "example.com" domain
The LDIF files you created from /etc/passwd referred to users only. The attributes of the example.com domain haven't yet been defined, and you also haven't defined the organizational unit called People. This can be done using a third LDIF file called /etc/openldap/example.com.ldif, which should look like this:
dn: dc=example,dc=com
dc: example
description: Root LDAP entry for example.com
objectClass: dcObject
objectClass: organizationalUnit
ou: rootobject
dn: ou=People, dc=example,dc=com
ou: People
description: All people in organisation
objectClass: organizationalUnit
Import the LDIF files into the database
Use the LDAP add command to import all three LDIF files into the database starting with the example.com.ldif file, followed by root.ldif, and lastly by ldapusers.ldif.
Enter the LDAP root password you created when you are prompted.
[root@bigboy tmp]# ldapadd -x -D "cn=Manager,dc=example,dc=com" \
-W -f /etc/openldap/example.com.ldif
[root@bigboy tmp]# ldapadd -x -D "cn=Manager,dc=example,dc=com" \
-W -f /etc/openldap/root.ldif
[root@bigboy tmp]# ldapadd -x -D "cn=Manager,dc=example,dc=com" \
-W -f /etc/openldap/ldapusers.ldif
[root@bigboy tmp]#
You can view all the LDAP database entries all at once with the ldapsearch command; this is a good test to make sure you have all the correct functionality.
[root@bigboy tmp]# ldapsearch -x -b 'dc=example,dc=com' \
'(objectclass=*)'
[root@bigboy tmp]#
Now that the LDAP server is configured properly, you can turn your attention to configuring and testing the clients.
Edit the ldap.conf configuration file
LDAP clients are configured using the /etc/openldap/ldap.conf file. You need to make sure that the file refers to the LDAP server's IP address for the domain example.com. The file should look like this:
HOST 192.168.1.100
BASE dc=example,dc=com
The /etc/nsswitch.conf file defines the order in which the Linux operating system searches login databases for login information.
You want to configure it to first search its /etc/passwd file. If it doesn't find the user password information there, it goes to the LDAP server. The easiest way set this up is to use the /usr/bin/authconfig command:
1. Run /usr/bin/authconfig
2. Select LDAP.
3. Give the LDAP server's IP address, which is 192.168.1.100 in this case.
4. Give the base DN as dc=example,dc=com
5. Do not select TLS.
6. Use MD5 and shadow passwords.
The screen should look like this:
[*] Use Shadow Passwords
[*] Use MD5 Passwords
[*] Use LDAP [ ] Use TLS
Server: 192.168.1.100
Base DN: dc=example,dc=com
When finished, look at the /etc/nsswitch.conf file and make sure it has references to LDAP.
Create Home Directories On The LDAP Client
You previously created a user named ldapuser in the group users on server bigboy. You now need to make sure that this user has a home directory on the LDAP client smallfry. The example in this section creates the directory and makes ldapuser the owner. As you can see, server smallfry correctly gets its user information about ldapuser from bigboy; the chown command doesn't complain about ldapuser not existing in smallfry's /etc/passwd file.
Check if ldapuser is Missing From the /etc/passwd file
You can look for ldapuser by searching the /etc/passwd file with the grep command. There should be no response.
[root@smallfry tmp]# grep ldapuser /etc/passwd
[root@smallfry tmp]#
Create The Home Directory For ldapuser On The LDAP Client
In this phase, you create the home directory, copy a BASH login profile file into it, and modify the ownership of the directory and all the files to user ldapuser.
Note: If the chown command fails, it is probably because of an incorrect LDAP configuration in which the LDAP client cannot read the user information from the LDAP server.
In some cases, you may want to use NFS mounts to provide home directories for your users, which will significantly reduce the need to do this step. The benefits and disadvantages of NFS are covered in Chapter 29, "Remote Disk Access with NFS," and Chapter 30, "Centralized Logins Using NIS," covers using NFS for home directories.
[root@smallfry tmp]# mkdir /home/ldapuser
[root@smallfry tmp]# chmod 700 /home/ldapuser/
[root@smallfry tmp]# chown ldapuser:users /home/ldapuser/
[root@smallfry tmp]# ll /home
total 2
drwx------ 2 ldapuser users 1024 Aug 4 08:05 ldapuser
[root@smallfry tmp]#
[root@smallfry tmp]# cp /etc/skel/.* /home/ldapuser/
cp: omitting directory `/etc/skel/.'
cp: omitting directory `/etc/skel/..'
cp: omitting directory `/etc/skel/.kde'
[root@smallfry tmp]# chown ldapuser:users /home/ldapuser/.*
[root@smallfry tmp]#
You next need to do basic testing. For details, see which is covered in the "Troubleshooting LDAP Logins" section.
Configuring Encrypted LDAP Communication
The secure tunnel (stunnel) utility can be used to intercept regular LDAP communications and encrypt it over an SSL tunnel using the TCP port of your choice. Fortunately, stunnel is installed by default on Fedora Linux, making it even easier to use.
Note: Add the SSL encryption, only after basic LDAP has been proven to work without encryption. This makes troubleshooting much easier.
Here's how to encrypt LDAP with Fedora Linux:
Configuring the stunnel LDAP client
First, you configure the LDAP client to use stunnel.
1. Edit the ldap.conf file. You have to trick the LDAP client into thinking that the LDAP server is actually running locally as a daemon, so you need to set the HOST entry to localhost. You then configure the stunnel utility to intercept this traffic and relay it to the real LDAP server.
HOST localhost
BASE dc=example,dc=com
2. Create an stunnel user with the useradd command.
[root@smallfry tmp]# useradd stunnel
3. Edit the stunnel.conf configuration file in the /etc/stunnel directory, configuring it as shown.
#
# File: /etc/stunnel (LDAP Client)
#
# Configure stunnel to run as user "stunnel" placing temporary
# files in the /usr/var/run/stunnel/ directory
chroot = /home/stunnel
pid = /stunnel.pid
setuid = stunnel
setgid = stunnel
# Configure logging
debug = 7
output = /var/log/messages
# Use it for client mode
client = yes
# Service-level configuration
[ldap]
accept = 389
connect = 192.168.1.100:636
At the very end of the file, notice that traffic on the LDAP TCP port 389 is specifically redirected to the LDAP server on TCP port 636 over the secure tunnel.
4. Start stunnel with the stunnel command.
[root@smallfry tmp]# stunnel
5. Check the log files, especially the last 100 lines of the error log file /var/log/messages, to make sure there are no errors. If there are errors, double check your stunnel configuration file for mistakes.
[root@smallfry tmp]# tail -100 /var/log/messages
6. Make sure stunnel runs on the next reboot. The script /etc/rc.local is run at the end of every boot sequence. Use the locate command to find out where the stunnel program is and then place your stunnel command in /etc/rc.local as shown.
# Run stunnel for LDAP (Fedora file location)
/usr/sbin/stunnel
Configuring the stunnel LDAP server
After you configure the client, you're ready to set up stunnel on the LDAP server.
1. Create an stunnel user using the useradd command.
[root@bigboy tmp]# useradd stunnel
2. Edit the stunnel.conf configuration file located in the /etc/stunnel directory. Configure it as shown.
#
# File: /etc/stunnel (LDAP Server)
#
# Configure stunnel to run as user "stunnel" placing temporary
# files in the /usr/var/run/stunnel/ directory
chroot = /home/stunnel/
pid = /stunnel.pid
setuid = stunnel
setgid = stunnel
# Some debugging stuff
debug = 7
output = /var/log/messages
# Use it for client mode
client = no
cert = /usr/share/ssl/certs/stunnel.pem
key = /usr/share/ssl/certs/stunnel.pem
# Service-level configuration
[ldap]
accept = 636
connect = 389
There are a few differences between the client and server stunnel.conf files. The very bottom of the file shows that all traffic received on the secure LDAP port of 636 is redirected to the application listening on LDAP port 389. The file is configured for server mode and a special SSH certificate has been defined for the encryption process. You'll create the certificates next.
3. Go to the /usr/share/ssl/certs directory and create the certificate using the make command. Use all the defaults when prompted, but make sure you use the server's IP address when prompted for your server's Common Name or hostname.
[root@bigboy tmp]# cd /usr/share/ssl/certs
[root@bigboy certs]# make stunnel.pem
...
Common Name (eg, your name or your server's hostname) []: 192.168.1.100
...
[root@bigboy certs]#
Note: The certificate created only has a 365 day lifetime. Remember to repeat this process next year.
4. Modify certificate file permissions. The certificate needs to be read by root and the stunnel user. Use the chmod and chgrp commands to do this.
[root@bigboy certs]# chmod 640 stunnel.pem
[root@bigboy certs]# chgrp stunnel stunnel.pem
[root@bigboy certs]# ll /usr/share/ssl/certs
-rw-r----- 1 root stunnel 1991 Jul 31 21:50 stunnel.pem
[root@bigboy certs]#
5. Start stunnel with the stunnel command.
[root@bigboy tmp]# stunnel
6. Check the last 100 lines of the error log file /var/log/messages to make sure there are no errors. If you find errors, double check your stunnel configuration file for mistakes.
[root@bigboy tmp]# tail -100 /var/log/messages
The key things to look for are the loading of the certificate, the binding of LDAP to the 636 secure LDAP port, and the creation of the temporary stunnel.pid file.
2004.08.02 08:50:18 LOG7[12102:3210052320]: Certificate: /usr/share/ssl/certs/stunnel.pem
2004.08.02 08:50:18 LOG7[12102:3210052320]: Key file: /usr/share/ssl/certs/stunnel.pem
2004.08.02 08:50:18 LOG7[12102:3210052320]: ldap bound to 0.0.0.0:636
2004.08.02 08:50:18 LOG7[12103:3210052320]: Created pid file /stunnel.pid
7. Make sure stunnel runs on the next reboot. The script /etc/rc.local is run at the end of every boot sequence. Use the locate command to find out where the stunnel program is and then place your stunnel command in /etc/rc.local.
#
# File : /etc/rc.local
#
# Run stunnel for LDAP (Fedora file location)
/usr/sbin/stunnel
The final step of the preparation is to create home directories for each user to use just like in the unencrypted LDAP example before this. After this is complete, you'll need to do some basic testing which is covered in the troubleshooting section.
You can never be certain about the functioning of any application unless you test it. LDAP is fairly complicated to install and should be as thoroughly tested as possible before you deploy it. Here are some steps you can take to help you sleep better at night.
Always run the ldapsearch command on both the LDAP client and server to test your LDAP configuration.
[root@smallfry tmp]# ldapsearch -x -b 'dc=example,dc=com' \
'(objectclass=*)'
When LDAP is configured correctly, the command sends a full database listing to your screen.
Try to log in as user ldapuser to the LDAP client Linux system as an alternative test. If it fails, try restarting SSH on the LDAP client so that the /etc/nsswitch.conf file can be reread with the new LDAP information. This step is not required in all versions of Linux.
If the LDAP configuration files appear correct and LDAP still doesn't work, then you should try using the tcpdump command, outlined in Chapter 4, "Simple Network Troubleshooting," to see whether your systems can correctly communicate with one another. A failure to communicate could be due to poor routing, misconfigured firewalls along the way, or possibly LDAP being turned off on the server.
On the LDAP server, use the tcpdump command to listen for traffic on the secure LDAP port 636 or ldaps. Run the ldapsearch command on the LDAP client and if everything is configured correctly, you should see packet flows such as this one.
[root@bigboy tmp]# tcpdump -n tcp port ldaps
tcpdump: listening on eth0
09:20:02.281257 192.168.1.102.1345 > 192.168.1.100.ldaps: S 1665037104:1665037104(0) win 5840 <mss 1460,sackOK,timestamp 74401362 0,nop,wscale 0> (DF)
09:20:02.281356 192.168.1.100.ldaps > 192.168.1.102.1345: S 1911175072:1911175072(0) ack 1665037105 win 5792 <mss 1460,sackOK,timestamp 20737195 74401362,nop,wscale 0> (DF)
...
...
[root@bigboy tmp]#
On the LDAP server, use the tcpdump command to listen for traffic on the regular LDAP port 389 or ldap. Run the ldapsearch command on the LDAP client.
[root@bigboy tmp]# tcpdump -n tcp port ldap
If everything is configured correctly, you should see LDAP packet flows similar to those in the last section.
The very first step is to use TELNET to determine whether your LDAP server is accessible on TCP port 389 (LDAP) or 636 (LDAPS).
Lack of connectivity could be caused by a firewall in the path between the LDAP server and client or there could be firewall software running on the servers themselves.
Other sources of failure include LDAP not being started at all, the server could be down, or there could be a network related failure.
Troubleshooting with Telnet is covered in Chapter 4 on network troubleshooting.
LDAP works but is not using LDAPS
An LDAPS configuration will default to using regular LDAP if there is an error with the SSL keys. This is usually caused by incorrect permissions and ownerships on the key file.
Stunnel Doesn't Appear To Work
Changes to the stunnel.conf file take effect only after stunnel has been restarted. Unfortunately, there is no stunnel script in the /etc/init.d directory to do this. You have to use the pkill command to stop it and the stunnel command to start it again.
[root@bigboy tmp]# pkill stunnel ; stunnel
[root@bigboy tmp]#
The LDAP bind utility is used for each login and can give failure errors that are usually not very descriptive. Two of the main ones that usually occur when running the ldapadd command are
Can't contact LDAP server (81): This is usually caused by not configuring the correct IP address in the LDAP client's ldap.conf file.
Invalid credentials (49): This is usually caused by incorrect dc= statements in the configuration files or in commands used
Possible stunnel Errors in Fedora Core 2
You may get a cryptonet error when starting stunnel.
Unable to open "/dev/cryptonet"
This is caused by an incompatibility with the hwcrypto RPM used for hardware-, not software-based encryption. You need to uninstall hwcrypto to get stunnel to work correctly.
[root@bigboy tmp]# rpm -e hwcrypto
Common LDAP Administrative Tasks
Here are some explanations of how to do many common LDAP tasks. They are all based on our sample organization with DNs of example and com.
Note: You need to always make sure that there are no entries for regular users in the /etc/passwd files of the LDAP clients. These should only reside on the LDAP server.
You can use the chkconfig command to get ldap configured to start at boot:
[root@bigboy tmp]# chkconfig ldap on
To start, stop, or restart ldap after booting, use
[root@bigboy tmp]# service
ldap start
[root@bigboy tmp]# service ldap stop
[root@bigboy tmp]# service ldap restart
Remember to restart the ldap process every time you make a change to the LDAP database file for the changes to take effect on the running process.
LDAP users changing their own passwords
LDAP users can modify their LDAP passwords using the regular passwd command.
[ldapuser@smallfry ldapuser]$ passwd
Changing password for user ldapuser.
Enter login(LDAP) password:
New password:
Retype new password:
LDAP password information changed for ldapuser
passwd: all authentication tokens updated successfully.
[ldapuser@smallfry ldapuser]$
Modifying LDAP users by user "root"
One easy way for the system administrator to manage LDAP users is to modify the regular Linux users' characteristics on the LDAP server in the regular way and then run a script to automatically modify the LDAP database.
You can use the very simple sample script /usr/local/bin/modifyldapuser to extract a particular user's information from /etc/passwd and import it into your LDAP database.
The script works by using the grep command to extract the /etc/passwd user record to a temporary file. It then runs the migrate_passwd script on this data and outputs the result to a temporary LDIF file. Next, the script replaces the default padl DC with the example DC and exports this to the final LDIF file. Finally, the ldapmodify command does the update, and then the temporary files are deleted.
#!/bin/bash
grep $1 /etc/passwd > /tmp/modifyldapuser.tmp
/usr/share/openldap/migration/migrate_passwd.pl \
/tmp/modifyldapuser.tmp /tmp/modifyldapuser.ldif.tmp
cat /tmp/modifyldapuser.ldif.tmp | sed s/padl/example/ \
> /tmp/modifyldapuser.ldif
ldapmodify -x -D "cn=Manager,dc=example,dc=com" -W -f \
/tmp/modifyldapuser.ldif
rm -f /tmp/modifyldapuser.*
Remember to make the script executable and usable only by user root with the chmod command.
[root@bigboy tmp]# chmod 700 /usr/local/bin/modifyldapuser
[root@bigboy tmp]#
To use the script, modify the Linux user. In this case, modify the password for user ldapuser by running the modifyldapuser script using ldapuser as the argument. You will be prompted for the LDAP root password.
[root@bigboy tmp]# passwd ldapuser
Changing password for user ldapuser.
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[root@bigboy tmp]# modifyldapuser ldapuser
Enter LDAP Password:
modifying entry "uid=ldapuser,ou=People,dc=example,dc=com"
[root@bigboy tmp]#
You can use the short script in this section to add LDAP users to your database. I'll also provide an example of how to use it.
Create an LDAP Add User Script
You can create a /usr/local/bin/addldapuser script based on the modifyldapuser script you created earlier. For example:
#!/bin/bash
grep $1 /etc/passwd > /tmp/changeldappasswd.tmp
/usr/share/openldap/migration/migrate_passwd.pl \
/tmp/changeldappasswd.tmp /tmp/changeldappasswd.ldif.tmp
cat /tmp/changeldappasswd.ldif.tmp | sed s/padl/example/ \
> /tmp/changeldappasswd.ldif
ldapadd -x -D "cn=Manager,dc=example,dc=com" -W -f \
/tmp/changeldappasswd.ldif
rm -f /tmp/changeldappasswd.*
Adding the user to database takes three steps:
1. Create the Linux user on the LDAP server.
2. Run the addldapuser script with the username as the only argument. This example imports a previously created Linux user named ldapuser. The script prompts you for your LDAP root password.
[root@bigboy tmp]# addldapuser ldapuser
Enter LDAP Password:
adding new entry "uid=ldapuser,ou=People,dc=example,dc=com"
[root@bigboy tmp]#
3. Create home directories for the user on all the LDAP client Linux boxes.
Remember that this script adds existing Linux users to the LDAP database. The creation of Linux users still requires the use of the adduser command.
Sometimes you want to get rid of users instead of add them. You can create a /usr/local/bin/deleteldapuser script to delete LDAP users from your database. For example
#!/bin/bash
ldapdelete -x -W -D "cn=Manager,dc=example,dc=com" \
"uid=$1,ou=People,dc=example,dc=com"
To delete the user from the database, run the deleteldapuser script with the username as the only argument. This example below deletes a previously created Linux user named ldapuser. The script prompts you for your LDAP root password.
[root@bigboy tmp]# deleteldapuser ldapuser
Enter LDAP Password:
[root@bigboy tmp]#
LDAP Web Management Tools
Once you understand the principles behind LDAP management, you may want to use a graphical tool to help with further administration. If the tool misbehaves, at least you'll now know how to try to fix it behind the scenes from the command line.
The LDAP Account Manager (LAM), which is available at http://lam.sourceforge.net, is a well known, easy-to-use product. After you feel comfortable enough with the background tasks and concepts outlined in this chapter, you should give it a try.
Many network equipment manufacturers use an authorization scheme called RADIUS to filter the types of activities a user can do. The Linux FreeRADIUS server can be configured to talk to a Linux LDAP server to handle login authentication services. In other words, the user logs into the equipment, which then sends a username/password combination to the RADIUS server, the RADIUS server queries the LDAP server to see if the user is a valid one, and then replies to the network equipment with the desired login privileges if the LDAP query is successful.
You'll have to refer to your manufacturer's manuals on how to configure RADIUS, but fortunately researching how the FreeRADIUS server interacts with the Linux LDAP server is much simpler. Here are the steps.
How To Download and Install The FreeRADIUS Packages
Most RedHat and Fedora Linux software products are available in the RPM format. When searching for the file, remember that the FreeRADIUS RPM's filename usually starts with freeradius followed by a version number, as in freeradius-0.9.1-1.i386.rpm.
Starting and Stopping FreeRADIUS
You can use the chkconfig command to get the FreeRADIUS daemon, radiusd, configured to start at boot:
[root@bigboy tmp]# chkconfig radiusd on
To start, stop, and restart radiusd after booting, use
[root@bigboy tmp]# service
radiusd start
[root@bigboy tmp]# service radiusd stop
[root@bigboy tmp]# service radiusd restart
Remember to restart the radiusd process every time you make a change to the configuration files for the changes to take effect on the running process.
Configuring The /etc/raddb/radiusd.conf File
The /etc/raddb/radiusd.conf file stores the main RADIUS configuration parameters. You'll have to update some of the settings to allow LDAP queries from RADIUS.
1. Activate the use of the LDAP module in the authorize section of the file by uncommenting the word ldap.
authorize {
...
...
#
# The ldap module will set Auth-Type to LDAP if it has not
# already been set
Ldap
...
...
}
2. Activate the use of the LDAP module in the authenticate section by uncommenting the Auth-Type block for LDAP:
Auth-Type LDAP {
ldap
}
3. Define the LDAP domain, LDAP server, and password methods to be used in the ldap block. In the example, the LDAP and RADIUS server is the same machine, so you set the LDAP server IP address to localhost.
ldap {
# Define the LDAP server and the base domain name
server = "localhost"
basedn = "dc=example,dc=com"
# Define which attribute from an LDAP "ldapsearch" query
# is the password. Create a filter to extract the password
# from the "ldapsearch" output
password_attribute = "userPassword"
filter = "(uid=%{Stripped-User-Name:-%{User-Name}})"
# The following are RADIUS defaults
start_tls = no
dictionary_mapping = ${raddbdir}/ldap.attrmap
ldap_connections_number = 5
timeout = 4
timelimit = 3
net_timeout = 1
}
These configuration steps only cover how to configure RADIUS to interact with LDAP. You'll have to define the login attributes and privileges each user will receive and the IP addresses of the varius RADIUS clients. We'll cover these topics next.
Configuring The /etc/raddb/users File
The /etc/raddb/users file defines the types of attributes a user receives upon login. In the case of a router, this may include allowing some user groups to login to a device in a privileged mode, while allowing other only basic access.
One of the first entries in this file is to check the local server's /etc/passwd file. The very next entry should be one referring to your LDAP server with a fall through statement that will allow additional authorizations to be granted to the LDAP user further down the file based on other sets of criteria.
#
# First setup all accounts to be checked against the UNIX /etc/passwd.
#
DEFAULT Auth-Type = System
Fall-Through = 1
#
# Defaults for LDAP
#
DEFAULT Auth-Type := LDAP
Fall-Through = 1
Configuring The /etc/raddb/clients.conf File
You can define a shared secret password key to be used by the RADIUS server and its clients in the /etc/raddb/clients.conf file.
Passwords can be allocated for ranges of IP addresses in each network block using the secret keyword. The next example defines the password testing123 for all queries from localhost, but s3astar for the 192.168.1.0/24 network and shrtp3nc1l for the 172.16.1.0/24 network. All RADIUS clients have to peer with the RADIUS server from these networks using the correct password before logins are correctly accepted.
client 127.0.0.1 {
secret = testing123
shortname = localhost
}
client 192.168.1.0/24 {
secret = s3astar
shortname = home-network
}
client 172.16.1.0/24 {
secret = shrtp3nc1l
shortname = office-network
}
Troubleshooting And Testing RADIUS
You can now test the various elements of the RADIUS setup:
To test the server, run radiusd in debug mode to see verbose messages about the status of the RADIUS queries. These messages are much more informative than those provided in the /var/log/messages and /var/log/radius/radius.log files.
[root@bigboy tmp]# /usr/sbin/radiusd -X -A
After testing is complete, you must start the radiusd daemon in the normal manner using the command service radiusd start.
For Linux clients, you can perform RADIUS queries with the radtest command. The arguments are the LDAP username, the LDAP user's password, the LDAP server IP address, an NAS port value (any value between 1 and 100 will work here), and the RADIUS client-server shared secret password key. Successful queries will show an Access-Accept message.
A successful test from the RADIUS server looks like this.
[root@bigboy tmp]# radtest ldapuser "ldapuser-password" \
localhost 2 testing123
...
rad_recv: Access-Accept packet from host 127.0.0.1:1812, id=99, length=20
...
[root@bigboy tmp]#
A successful test from a Linux RADIUS client looks like this:
[root@smallfry bin]# radtest ldapuser "ldapuser-password" 192.168.1.100 2 s3astar
...
rad_recv: Access-Accept packet from host 192.168.1.100:1812, id=51, length=20
...
[root@smallfry bin]#
In this case, freeradius was installed solely for the purposes of testing the shared secret password key from another network. This is a good troubleshooting tip to verify remote client access before deploying network equipment.
Here is a sample snippet of how to set up a Cisco device to use a RADIUS server. You can find full coverage of Cisco authentication, authorization, and accounting (AAA) setup using RADIUS on Cisco's corporate Web site at www.cisco.com.
aaa new-model
aaa authentication login default radius enable
aaa authentication ppp default radius
aaa authorization network radius
radius-server host 192.168.1.100
radius-server timeout 10
radius-server key shrtp3nc1l
The important thing to note in relation to our setup is that the radius-server statements define the RADIUS server's IP address and the shared secret password key.
The interaction between LDAP and RADIUS on Fedora Core 2 seems to be plagued with a segmentation fault error that you can see on the RADIUS server when running in debug mode. The error looks like this:
ldap_get_conn: Got Id: 0
rlm_ldap: attempting LDAP reconnection
rlm_ldap: (re)connect to localhost:389, authentication 0
rlm_ldap: bind as / to localhost:389
Segmentation fault
The only solution I have found is to install the Fedora Core 1 versions of the RADIUS and LDAP RPMs and to edit the /etc/yum.conf file to prevent them from being automatically updated to newer versions.
LDAP is rapidly becoming a defacto standard for remote authentication and authorization of users, not only in the realm of Linux, but also in that of Windows where it is a key component of Active Directory. Usage of LDAP is also becoming increasingly widespread in wireless networking systems. For example in hot spots, ISPs will sacrifice data security for the sake of convenience by not using encryption, but will use LDAP to restrict access to the Internet to people who have purchased pre-paid access codes with a predefined lifetime.
Chapter 32, "Controlling Web Access with Squid," covers the use of the Linux Squid application to cache Web content, restrict Web access by the time of day and via password prompts. Although it is beyond the scope of this book, you should know that you can use LDAP can to complement the functionality of Squid in larger implementations.
