[debian/sudo] / README.LDAP

This file explains how to use the optional LDAP functionality of SUDO to
store /etc/sudoers information.  This feature is distinct from LDAP passwords.

LDAP philosophy
===============
As times change and servers become cheap, an enterprise can easily have 500+
UNIX servers.  Using LDAP to synchronize Users, Groups, Hosts, Mounts, and
others across an enterprise can greatly reduce the administrative overhead.

Sudo in the past has only used a single local configuration file /etc/sudoers.
Some have attempted to workaround this by synchronizing changes via
RCS/CVS/RSYNC/RDIST/RCP/SCP and even NFS.  Many have asked for a Hesiod, NIS,
or LDAP patch for sudo, so here is my attempt at LDAP'izing sudo.

For information on OpenLDAP, please see http://www.openldap.org/.

Definitions
===========
Many times the word 'Directory' is used in the document to refer to the LDAP
server, structure and contents.

Many times 'options' are used in this document to refer to sudoer 'defaults'.
They are one and the same.

Design Features
===============

  * Sudo no longer needs to read sudoers in its entirety.  Parsing of
    /etc/sudoers requires the entire file to be read.  The LDAP feature of sudo
    uses two (sometimes three) LDAP queries per invocation.  It never reads all
    the sudoer entries in the LDAP store.  This makes it especially fast and
    particularly usable in LDAP environments.  The first query is to parse
    default options (see below).  The second is to match against the username or
    groups a user belongs to.  (The special ALL tag is matched in this query
    too.) If no match is made against the username, the third query pulls the
    entries that match against user netgroups to compare back to the user.

  * Sudo no longer blows up if there is a typo.  Parsing of /etc/sudoers can
    still blow up when sudo is invoked.  However when using the LDAP feature of
    sudo, LDAP syntax rules are applied before the data is uploaded into the
    LDAP server, so proper syntax is always guaranteed!  One can of course still
    insert a bogus hostname or username, but sudo will not care.

  * Options inside of entries now override global default options.
    /etc/sudoers allowed for only default options and limited options associated
    with user/host/command aliases.  The syntax can be difficult for the newbie.
    The LDAP feature attempts to simplify this and yet still provide maximum
    flexibility.

    Sudo first looks for an entry called 'cn=default' in the SUDOers container.
    If found, the multi-valued sudoOption attribute is parsed the same way the
    global 'Defaults' line in /etc/sudoers is parsed.

    If on the second or third query, a response contains a sudoRole which
    matches against the user, host, and command, then the matched object is
    scanned for a additional options to override the top-level defaults.  See
    the example LDAP content below for more information.

  * Visudo is no longer needed.  Visudo provides locking and syntax checking
    against the /etc/sudoers file.  Since LDAP updates are atomic, locking is no
    longer necessary.  Because syntax is checked when the data is inserted into
    LDAP, the sudoers syntax check becomes unnecessary.

  * Aliases are no longer needed.  User, Host, and Command Aliases were setup
    to allow simplification and readability of the sudoers files.  Since the
    LDAP sudoer entry allows multiple values for each of its attributes and
    since most LDAP browsers are graphical and easy to work with, original
    aliases are no longer needed.

    If you want to specify lots of users into an entry or want to have similar
    entries with identical users, then use either groups or user netgroups.
    Thats what groups and netgroups are for and Sudo handles this well.
    Alternately, one can just paste them all into the LDAP record.

    If you want to specify lots of hosts into an entry, use netgroups or IP
    address matches (10.2.3.4/255.255.0.0).  Thats what netgroups are for and
    Sudo handles this well.  Or just past them all into the LDAP record.

    If you want to specify lots of commands, use directories or wildcards, or
    just paste them all into LDAP.  That's what it's for.

  * The /etc/sudoers file can be disabled.  Paranoid security administrators
    can now disallow parsing of any local /etc/sudoers file by an LDAP
    sudoOption 'ignore_local_sudoers'.  This way all sudoers can be controlled
    and audited in one place because local entries are not allowed.
    In fact, if this option is included in the cn=defaults object of LDAP,
    sudo won't even look for a /etc/sudoers file.

  * The sudo binary compiled with LDAP support should be totally backward
    compatible and be syntactically and source code equivalent to its non
    LDAP-enabled build.


Build instructions
==================
The most simplest way to build sudo with LDAP support is to include the
'--with-ldap' option.

  $ ./configure --with-ldap

If your ldap libraries and headers are in a non-standard place, you will need
to specify them at configure time.  E.g.

  $ ./configure --with-ldap=/usr/local/ldapsdk

Sudo is developed using OpenLDAP.  Other LDAP implementations may
require adding '-lldif' to SUDO_LIBS in the Makefile.

Your Mileage may vary.  Please let the sudo workers mailing list
<sudo-workers@sudo.ws> know what combinations worked best for your
OS and LDAP Combinations so we can improve sudo.

More Build Notes:
HP-UX 11.23 (gcc3) Galen Johnson <Galen.Johnson@sas.com>
  CFLAGS="-D__10_10_compat_code" LDFLAGS="-L/opt/ldapux/lib"

Schema Changes
==============
Add the appropriate schema to your LDAP server so that it may contain
sudoers content.

For OpenLDAP, simply copy schema.OpenLDAP to the schema directory
(e.g. /etc/openldap/schema) and 'include' it in your slapd.conf and
restart slapd.  For other LDAP servers, provide this to your LDAP
Administrator.  Make sure to index the attribute 'sudoUser'.

For the SunONE or iPlanet LDAP server, use the schema.iPlanet file.

Importing /etc/sudoers to LDAP
==============================
Importing is a two step process.

Step 1:
Ask your LDAP Administrator where to create the ou=SUDOers container.

For instance, if using OpenLDAP:

  dn: ou=SUDOers,dc=example,dc=com
  objectClass: top
  objectClass: organizationalUnit
  ou: SUDOers

(An example location is shown below).  Then use the provided script to convert
your sudoers file into LDIF format.  The script will also convert any default
options.

  # SUDOERS_BASE=ou=SUDOers,dc=example,dc=com
  # export SUDOERS_BASE
  # ./sudoers2ldif /etc/sudoers > /tmp/sudoers.ldif

Step 2:
Import into your directory server.  If you are using OpenLDAP, do the following
if you are using another directory, provide the LDIF file to your LDAP
Administrator.  An example is shown below.

  # ldapadd -f /tmp/sudoers.ldif -h ldapserver \
  > -D cn=Manager,dc=example,dc=com -W -x

Example sudoers Entries in LDAP
===============================
The equivalent of a sudoer in LDAP is a 'sudoRole'.  It contains sudoUser(s),
sudoHost, sudoCommand and optional sudoOption(s) and sudoRunAs(s).
<put an example here>

Managing LDAP entries
=====================
Doing a one-time bulk load of your ldap entries is fine.  However what if you
need to make minor changes on a daily basis?  It doesn't make sense to delete
and re-add objects.  (You can, but this is tedious).

I recommend using any of the following LDAP browsers to administer your SUDOers.
  * GQ - The gentleman's LDAP client - Open Source - I use this a lot on Linux
    and since it is Schema aware, I don't need to create a sudoRole template.
        http://biot.com/gq/

  * LDAP Browser/Editor - by Jarek Gawor - I use this a lot on Windows
    and Solaris.  It runs anywhere in a Java Virtual Machine including
    web pages.  You have to make a template from an existing sudoRole entry.
        http://www.iit.edu/~gawojar/ldap
        http://www.mcs.anl.gov/~gawor/ldap
        http://ldapmanager.com

  There are dozens of others, some open source, some free, some not.


Configure your /etc/ldap.conf
=============================
The /etc/ldap.conf file is meant to be shared between sudo, pam_ldap, nss_ldap
and other ldap applications and modules.  IBM Secureway unfortunately uses
the same filename but has a different syntax.  If you need to rename where
this file is stored, recompile SUDO with the -DLDAP_CONFIG compile option.

Make sure you sudoers_base matches exactly with the location you specified
when you imported the sudoers.  Below is an example /etc/ldap.conf

  # Either specify a uri or host & port
  #host          ldapserver
  #port          389
  #
  # URI will override host & port settings
  # but only works with LDAP SDK's that support
  # ldap_initialize() such as OpenLDAP
  uri            ldap://ldapserver
  #uri            ldaps://secureldapserver
  #
  # must be set or sudo will ignore LDAP
  sudoers_base   ou=SUDOers,dc=example,dc=com
  #
  # verbose sudoers matching from ldap
  #sudoers_debug 2
  #
  # optional proxy credentials
  #binddn        <who to search as>
  #bindpw        <password>
  #rootbinddn    <who to search as, uses /etc/ldap.passwd for bindpw>
  #
  # LDAP Protocol Version defaults to 3
  #ldap_version 3
  #
  # Define if you want to use port 389 and switch to
  # encryption before the bind credentials are sent
  #ssl start_tls
  #
  # Additional TLS options follow that allow tweaking
  # of the SSL/TLS connection
  #
  #tls_checkpeer yes # verify server SSL certificate
  #tls_checkpeer no  # ignore server SSL certificate
  #
  # If you enable tls_checkpeer, specify either tls_cacertfile
  # or tls_cacertdir.
  #
  #tls_cacertfile /etc/certs/trusted_signers.pem
  #tls_cacertdir  /etc/certs
  #
  # For systems that don't have /dev/random
  # use this along with PRNGD or EGD.pl to seed the
  # random number pool to generate cryptographic session keys.
  #
  #tls_randfile /etc/egd-pool
  #
  # You may restrict which ciphers are used.  Consult your SSL
  # documentation for which options go here.
  #
  #tls_ciphers <cipher-list>
  #
  # Sudo can provide a client certificate when communicating to
  # the LDAP server.
  # Tips:
  #   * Enable both lines at the same time.
  #   * Do not password protect the key file.
  #   * Ensure the keyfile is only readable by root.
  #
  #tls_cert /etc/certs/client_cert.pem
  #tls_key  /etc/certs/client_key.pem
  #

Debugging your LDAP configuration
=================================
Enable debugging if you believe sudo is not parsing LDAP the way you think it
it should.  A value of 1 shows moderate debugging.  A value of 2 shows the
results of the matches themselves.  Make sure to set the value back to zero
so that other users don't get confused by the debugging messages.  This value
is 'sudoers_debug' in the /etc/ldap.conf.

Parsing Differences between /etc/sudoers and LDAP
=================================================
There are some subtle differences in the way sudoers is handled once in LDAP.
Probably the biggest is that according to the RFC, LDAP's ordering is
arbitrary and you cannot expect that Attributes & Entries are returned in
any order.  If there are conflicting command rules on an entry, the negative
takes precedence.  This is called paranoid behavior (not necessarily the
most specific match).

Here is an example:

  # /etc/sudoers:
  # Allow all commands except shell
  johnny  ALL=(root) ALL,!/bin/sh
  # Always allows all commands because ALL is matched last
  puddles ALL=(root) !/bin/sh,ALL

  # LDAP equivalent of Johnny
  # Allows all commands except shell
  dn: cn=role1,ou=Sudoers,dc=my-domain,dc=com
  objectClass: sudoRole
  objectClass: top
  cn: role1
  sudoUser: johnny
  sudoHost: ALL
  sudoCommand: ALL
  sudoCommand: !/bin/sh

  # LDAP equivalent of Puddles
  # Notice that even though ALL comes last, it still behaves like
  # role1 since the LDAP code assumes the more paranoid configuration
  dn: cn=role2,ou=Sudoers,dc=my-domain,dc=com
  objectClass: sudoRole
  objectClass: top
  cn: role2
  sudoUser: puddles
  sudoHost: ALL
  sudoCommand: !/bin/sh
  sudoCommand: ALL

Another difference is that negations on the Host, User or Runas are
currently ignorred.  For example, these attributes do not work how they first
seem.  If you desperately want this to be changed, contact Aaron Spangler
(aaron@spangler.ods.org).

  # does not match all but joe
  # rather, does not match anyone
  sudoUser: !joe

  # does not match all but joe
  # rather, matches everyone including Joe
  sudoUser: ALL
  sudoUser: !joe

  # does not match all but web01
  # rather, matches all hosts including web01
  sudoHost: ALL
  sudoHost: !web01


Configure your /etc/nsswitch.conf
=================================
At the time of this writing, sudo does not consult nsswitch.conf for the
search order.  But if it did, it would look like this:
This might be implemented in the future.  For now just skip this step.

  sudoers: files ldap