SUDOers LDAP container¶

The sudoers configuration is contained in the ou=SUDOers LDAP container.

Sudo first looks for the cn=default entry in the SUDOers container. If found, the multi-valued sudoOption attribute is parsed in the same manner as a global Defaults line in /etc/sudoers. In the following example, the SSH_AUTH_SOCK variable will be preserved in the environment for all users.

dn: cn=defaults,ou=SUDOers,dc=example,dc=com
objectClass: top
objectClass: sudoRole
cn: defaults
description: Default sudoOption's go here
sudoOption: env_keep+=SSH_AUTH_SOCK

The equivalent of a sudoer in LDAP is a sudoRole. It consists of the following attributes:

sudoUser

A user name, user ID (prefixed with ‘#’), Unix group (prefixed with ‘%’), Unix group ID (prefixed with ‘%#’), or user netgroup (prefixed with ‘+’).

sudoHost

A host name, IP address, IP network, or host netgroup (prefixed with a ‘+’). The special value ALL will match any host.

sudoCommand

A Unix command with optional command line arguments, potentially including globbing characters (aka wild cards). The special value ALL will match any command. If a command is prefixed with an exclamation point ‘!’, the user will be prohibited from running that command.

sudoOption

Identical in function to the global options described above, but specific to the sudoRole in which it resides.

sudoRunAsUser

A user name or uid (prefixed with ‘#’) that commands may be run as or a Unix group (prefixed with a ‘%’) or user netgroup (prefixed with a ‘+’) that contains a list of users that commands may be run as. The special value ALL will match any user.

The sudoRunAsUser attribute is only available in sudo versions 1.7.0 and higher. Older versions of sudo use the sudoRunAs attribute instead.

sudoRunAsGroup

A Unix group or gid (prefixed with ‘#’) that commands may be run as. The special value ALL will match any group.

The sudoRunAsGroup attribute is only available in sudo versions 1.7.0 and higher.

sudoNotBefore

A timestamp in the form yyyymmddHHMMSSZ that can be used to provide a start date/time for when the sudoRole will be valid. If multiple sudoNotBefore entries are present, the earliest is used. Note that timestamps must be in Coordinated Universal Time (UTC), not the local timezone. The minute and seconds portions are optional, but some LDAP servers require that they be present (contrary to the RFC).

The sudoNotBefore attribute is only available in sudo versions 1.7.5 and higher and must be explicitly enabled via the SUDOERS_TIMED option in /etc/sudo-ldap.conf.

sudoNotAfter

A timestamp in the form yyyymmddHHMMSSZ that indicates an expiration date/time, after which the sudoRole will no longer be valid. If multiple sudoNotAfter entries are present, the last one is used. Note that timestamps must be in Coordinated Universal Time (UTC), not the local timezone. The minute and seconds portions are optional, but some LDAP servers require that they be present (contrary to the RFC).

The sudoNotAfter attribute is only available in sudo versions 1.7.5 and higher and must be explicitly enabled via the SUDOERS_TIMED option in /etc/sudo-ldap.conf.

sudoOrder

The sudoRole entries retrieved from the LDAP directory have no inherent order. The sudoOrder attribute is an integer (or floating point value for LDAP servers that support it) that is used to sort the matching entries. This allows LDAP-based sudoers entries to more closely mimic the behaviour of the sudoers file, where the order of the entries influences the result. If multiple entries match, the entry with the highest sudoOrder attribute is chosen. This corresponds to the “last match” behavior of the sudoers file. If the sudoOrder attribute is not present, a value of 0 is assumed.

The sudoOrder attribute is only available in sudo versions 1.7.5 and higher.

Each attribute listed above should contain a single value, but there may be multiple instances of each attribute type. A sudoRole must contain at least one sudoUser, sudoHost and sudoCommand.

The following example allows users in group wheel to run any command on any host via sudo:

dn: cn=%wheel,ou=SUDOers,dc=example,dc=com
objectClass: top
objectClass: sudoRole
cn: %wheel
sudoUser: %wheel
sudoHost: ALL
sudoCommand: ALL

Anatomy of LDAP sudoers lookup¶

When looking up a sudoer using LDAP there are only two or three LDAP queries per invocation. The first query is to parse the global options. The second is to match against the user's name and the groups that the user belongs to. (The special ALL tag is matched in this query too.) If no match is returned for the user's name and groups, a third query returns all entries containing user netgroups and checks to see if the user belongs to any of them.

If timed entries are enabled with the SUDOERS_TIMED configuration directive, the LDAP queries include a subfilter that limits retrieval to entries that satisfy the time constraints, if any.

Differences between LDAP and non-LDAP sudoers¶

There are some subtle differences in the way sudoers is handled once in LDAP. Probably the biggest is that according to the RFC, LDAP ordering is arbitrary and you cannot expect that Attributes and Entries are returned in any specific order.

The order in which different entries are applied can be controlled using the sudoOrder attribute, but there is no way to guarantee the order of attributes within a specific entry. If there are conflicting command rules in 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 ignored. For example, the following attributes do not behave the way one might expect.

# 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

Sudoers schema¶

In order to use sudo's LDAP support, the sudo schema must be installed on your LDAP server. In addition, be sure to index the sudoUser attribute.

Three versions of the schema: one for OpenLDAP servers (schema.OpenLDAP), one for Netscape-derived servers (schema.iPlanet), and one for Microsoft Active Directory (schema.ActiveDirectory) may be found in the sudo distribution.

The schema for sudo in OpenLDAP form is also included in the EXAMPLES section.

Configuring ldap.conf¶

Sudo reads the /etc/sudo-ldap.conf file for LDAP-specific configuration. Typically, this file is shared amongst different LDAP-aware clients. As such, most of the settings are not sudo-specific. Note that sudo parses /etc/sudo-ldap.conf itself and may support options that differ from those described in the system's ldap.conf(8) manual.

Also note that on systems using the OpenLDAP libraries, default values specified in /etc/openldap/ldap.conf or the user's .ldaprc files are not used.

Only those options explicitly listed in /etc/sudo-ldap.conf as being supported by sudo are honored. Configuration options are listed below in upper case but are parsed in a case-independent manner.

URI ldap[s]://[hostname[:port]] ...

Specifies a whitespace-delimited list of one or more URIs describing the LDAP server(s) to connect to. The protocol may be either ldap ldaps, the latter being for servers that support TLS (SSL) encryption. If no port is specified, the default is port 389 for ldap:// or port 636 for ldaps://. If no hostname is specified, sudo will connect to localhost. Multiple URI lines are treated identically to a URI line containing multiple entries. Only systems using the OpenSSL libraries support the mixing of ldap:// and ldaps:// URIs. Both the Netscape-derived and Tivoli LDAP libraries used on most commercial versions of Unix are only capable of supporting one or the other.

HOST name[:port] ...

If no URI is specified, the HOST parameter specifies a whitespace-delimited list of LDAP servers to connect to. Each host may include an optional port separated by a colon (‘:’). The HOST parameter is deprecated in favor of the URI specification and is included for backwards compatibility.

PORT port_number

If no URI is specified, the PORT parameter specifies the default port to connect to on the LDAP server if a HOST parameter does not specify the port itself. If no PORT parameter is used, the default is port 389 for LDAP and port 636 for LDAP over TLS (SSL). The PORT parameter is deprecated in favor of the URI specification and is included for backwards compatibility.

BIND_TIMELIMIT seconds

The BIND_TIMELIMIT parameter specifies the amount of time, in seconds, to wait while trying to connect to an LDAP server. If multiple URIs or HOSTs are specified, this is the amount of time to wait before trying the next one in the list.

NETWORK_TIMEOUT seconds

An alias for BIND_TIMELIMIT for OpenLDAP compatibility.

TIMELIMIT seconds

The TIMELIMIT parameter specifies the amount of time, in seconds, to wait for a response to an LDAP query.

TIMEOUT seconds

The TIMEOUT parameter specifies the amount of time, in seconds, to wait for a response from the various LDAP APIs.

SUDOERS_BASE base

The base DN to use when performing sudo LDAP queries. Typically this is of the form ou=SUDOers,dc=example,dc=com for the domain example.com. Multiple SUDOERS_BASE lines may be specified, in which case they are queried in the order specified.

SUDOERS_SEARCH_FILTER ldap_filter

An LDAP filter which is used to restrict the set of records returned when performing a sudo LDAP query. Typically, this is of the form attribute=value or (&(attribute=value)(attribute2=value2)).

SUDOERS_TIMED on/true/yes/off/false/no

Whether or not to evaluate the sudoNotBefore and sudoNotAfter attributes that implement time-dependent sudoers entries.

SUDOERS_DEBUG debug_level

This sets the debug level for sudo LDAP queries. Debugging information is printed to the standard error. A value of 1 results in a moderate amount of debugging information. A value of 2 shows the results of the matches themselves. This parameter should not be set in a production environment as the extra information is likely to confuse users.

BINDDN DN

The BINDDN parameter specifies the identity, in the form of a Distinguished Name (DN), to use when performing LDAP operations. If not specified, LDAP operations are performed with an anonymous identity. By default, most LDAP servers will allow anonymous access.

BINDPW secret

The BINDPW parameter specifies the password to use when performing LDAP operations. This is typically used in conjunction with the BINDDN parameter.

ROOTBINDDN DN

The ROOTBINDDN parameter specifies the identity, in the form of a Distinguished Name (DN), to use when performing privileged LDAP operations, such as sudoers queries. The password corresponding to the identity should be stored in /etc/ldap.secret. If not specified, the BINDDN identity is used (if any).

LDAP_VERSION number

The version of the LDAP protocol to use when connecting to the server. The default value is protocol version 3.

SSL on/true/yes/off/false/no

If the SSL parameter is set to on, true or yes, TLS (SSL) encryption is always used when communicating with the LDAP server. Typically, this involves connecting to the server on port 636 (ldaps).

SSL start_tls

If the SSL parameter is set to start_tls, the LDAP server connection is initiated normally and TLS encryption is begun before the bind credentials are sent. This has the advantage of not requiring a dedicated port for encrypted communications. This parameter is only supported by LDAP servers that honor the start_tls extension, such as the OpenLDAP and Tivoli Directory servers.

TLS_CHECKPEER on/true/yes/off/false/no

If enabled, TLS_CHECKPEER will cause the LDAP server's TLS certificated to be verified. If the server's TLS certificate cannot be verified (usually because it is signed by an unknown certificate authority), sudo will be unable to connect to it. If TLS_CHECKPEER is disabled, no check is made. Note that disabling the check creates an opportunity for man-in-the-middle attacks since the server's identity will not be authenticated. If possible, the CA's certificate should be installed locally so it can be verified. This option is not supported by the Tivoli Directory Server LDAP libraries.

TLS_CACERT file name

An alias for TLS_CACERTFILE for OpenLDAP compatibility.

TLS_CACERTFILE file name

The path to a certificate authority bundle which contains the certificates for all the Certificate Authorities the client knows to be valid, e.g. /etc/ssl/ca-bundle.pem. This option is only supported by the OpenLDAP libraries. Netscape-derived LDAP libraries use the same certificate database for CA and client certificates (see TLS_CERT).

TLS_CACERTDIR directory

Similar to TLS_CACERTFILE but instead of a file, it is a directory containing individual Certificate Authority certificates, e.g. /etc/ssl/certs. The directory specified by TLS_CACERTDIR is checked after TLS_CACERTFILE. This option is only supported by the OpenLDAP libraries.

TLS_CERT file name

The path to a file containing the client certificate which can be used to authenticate the client to the LDAP server. The certificate type depends on the LDAP libraries used.

OpenLDAP:

tls_cert /etc/ssl/client_cert.pem

Netscape-derived:

tls_cert /var/ldap/cert7.db

Tivoli Directory Server:

Unused, the key database specified by TLS_KEY contains both keys and certificates.

When using Netscape-derived libraries, this file may also contain Certificate Authority certificates.

TLS_KEY file name

The path to a file containing the private key which matches the certificate specified by TLS_CERT. The private key must not be password-protected. The key type depends on the LDAP libraries used.

OpenLDAP:

tls_key /etc/ssl/client_key.pem

Netscape-derived:

tls_key /var/ldap/key3.db

Tivoli Directory Server:

tls_cert /usr/ldap/ldapkey.kdb

When using Tivoli LDAP libraries, this file may also contain Certificate Authority and client certificates and may be encrypted.

TLS_KEYPW secret

The TLS_KEYPW contains the password used to decrypt the key database on clients using the Tivoli Directory Server LDAP library. If no TLS_KEYPW is specified, a stash file will be used if it exists. The stash file must have the same path as the file specified by TLS_KEY, but use a .sth file extension instead of .kdb, e.g. ldapkey.sth. The default ldapkey.kdb that ships with Tivoli Directory Server is encrypted with the password ssl_password. This option is only supported by the Tivoli LDAP libraries.

TLS_RANDFILE file name

The TLS_RANDFILE parameter specifies the path to an entropy source for systems that lack a random device. It is generally used in conjunction with prngd or egd. This option is only supported by the OpenLDAP libraries.

TLS_CIPHERS cipher list

The TLS_CIPHERS parameter allows the administer to restrict which encryption algorithms may be used for TLS (SSL) connections. See the OpenLDAP or Tivoli Directory Server manual for a list of valid ciphers. This option is not supported by Netscape-derived libraries.

USE_SASL on/true/yes/off/false/no

Enable USE_SASL for LDAP servers that support SASL authentication.

SASL_AUTH_ID identity

The SASL user name to use when connecting to the LDAP server. By default, sudo will use an anonymous connection.

ROOTUSE_SASL on/true/yes/off/false/no

Enable ROOTUSE_SASL to enable SASL authentication when connecting to an LDAP server from a privileged process, such as sudo.

ROOTSASL_AUTH_ID identity

The SASL user name to use when ROOTUSE_SASL is enabled.

SASL_SECPROPS none/properties

SASL security properties or none for no properties. See the SASL programmer's manual for details.

KRB5_CCNAME file name

The path to the Kerberos 5 credential cache to use when authenticating with the remote server.

DEREF never/searching/finding/always

How alias dereferencing is to be performed when searching. See the ldap.conf(8) manual for a full description of this option.

See the ldap.conf entry in the EXAMPLES section.

Configuring nsswitch.conf¶

Unless it is disabled at build time, sudo consults the Name Service Switch file, /etc/nsswitch.conf, to specify the sudoers search order. Sudo looks for a line beginning with sudoers: and uses this to determine the search order. Note that sudo does not stop searching after the first match and later matches take precedence over earlier ones. The following sources are recognized:

In addition, the entry [NOTFOUND=return] will short-circuit the search if the user was not found in the preceding source.

To consult LDAP first followed by the local sudoers file (if it exists), use:

sudoers: ldap files

The local sudoers file can be ignored completely by using:

sudoers: ldap

If the /etc/nsswitch.conf file is not present or there is no sudoers line, the following default is assumed:

sudoers: files

Note that /etc/nsswitch.conf is supported even when the underlying operating system does not use an nsswitch.conf file, except on AIX (see below).

Configuring netsvc.conf¶

On AIX systems, the /etc/netsvc.conf file is consulted instead of /etc/nsswitch.conf. sudo simply treats netsvc.conf as a variant of nsswitch.conf; information in the previous section unrelated to the file format itself still applies.

To consult LDAP first followed by the local sudoers file (if it exists), use:

sudoers = ldap, files

The local sudoers file can be ignored completely by using:

sudoers = ldap

To treat LDAP as authoratative and only use the local sudoers file if the user is not present in LDAP, use:

sudoers = ldap = auth, files

Note that in the above example, the auth qualfier only affects user lookups; both LDAP and sudoers will be queried for Defaults entries.

If the /etc/netsvc.conf file is not present or there is no sudoers line, the following default is assumed:

sudoers = files

Example ldap.conf¶

# Either specify one or more URIs or one or more host:port pairs.
# If neither is specified sudo will default to localhost, port 389.
#
#host          ldapserver
#host          ldapserver1 ldapserver2:390
#
# Default port if host is specified without one, defaults to 389.
#port          389
#
# URI will override the host and port settings.
uri            ldap://ldapserver
#uri            ldaps://secureldapserver
#uri            ldaps://secureldapserver ldap://ldapserver
#
# The amount of time, in seconds, to wait while trying to connect to
# an LDAP server.
bind_timelimit 30
#
# The amount of time, in seconds, to wait while performing an LDAP query.
timelimit 30
#
# Must be set or sudo will ignore LDAP; may be specified multiple times.
sudoers_base   ou=SUDOers,dc=example,dc=com
#
# verbose sudoers matching from ldap
#sudoers_debug 2
#
# Enable support for time-based entries in sudoers.
#sudoers_timed yes
#
# optional proxy credentials
#binddn        <who to search as>
#bindpw        <password>
#rootbinddn    <who to search as, uses /etc/ldap.secret for bindpw>
#
# LDAP protocol version, defaults to 3
#ldap_version 3
#
# Define if you want to use an encrypted LDAP connection.
# Typically, you must also set the port to 636 (ldaps).
#ssl on
#
# Define if you want to use port 389 and switch to
# encryption before the bind credentials are sent.
# Only supported by LDAP servers that support the start_tls
# extension such as OpenLDAP.
#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.  Only supported when using OpenLDAP.
#
#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.
# Only supported when using OpenLDAP.
#
#tls_randfile /etc/egd-pool
#
# You may restrict which ciphers are used.  Consult your SSL
# documentation for which options go here.
# Only supported when using OpenLDAP.
#
#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.
#
# For OpenLDAP:
#tls_cert /etc/certs/client_cert.pem
#tls_key  /etc/certs/client_key.pem
#
# For SunONE or iPlanet LDAP, tls_cert and tls_key may specify either
# a directory, in which case the files in the directory must have the
# default names (e.g. cert8.db and key4.db), or the path to the cert
# and key files themselves.  However, a bug in version 5.0 of the LDAP
# SDK will prevent specific file names from working.  For this reason
# it is suggested that tls_cert and tls_key be set to a directory,
# not a file name.
#
# The certificate database specified by tls_cert may contain CA certs
# and/or the client's cert.  If the client's cert is included, tls_key
# should be specified as well.
# For backward compatibility, "sslpath" may be used in place of tls_cert.
#tls_cert /var/ldap
#tls_key /var/ldap
#
# If using SASL authentication for LDAP (OpenSSL)
# use_sasl yes
# sasl_auth_id <SASL user name>
# rootuse_sasl yes
# rootsasl_auth_id <SASL user name for root access>
# sasl_secprops none
# krb5_ccname /etc/.ldapcache

Sudo schema for OpenLDAP¶

The following schema, in OpenLDAP format, is included with sudo source and binary distributions as schema.OpenLDAP. Simply copy it to the schema directory (e.g. /etc/openldap/schema), add the proper include line in slapd.conf and restart slapd.

attributetype ( 1.3.6.1.4.1.15953.9.1.1
   NAME 'sudoUser'
   DESC 'User(s) who may  run sudo'
   EQUALITY caseExactIA5Match
   SUBSTR caseExactIA5SubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.2
   NAME 'sudoHost'
   DESC 'Host(s) who may run sudo'
   EQUALITY caseExactIA5Match
   SUBSTR caseExactIA5SubstringsMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.3
   NAME 'sudoCommand'
   DESC 'Command(s) to be executed by sudo'
   EQUALITY caseExactIA5Match
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.4
   NAME 'sudoRunAs'
   DESC 'User(s) impersonated by sudo'
   EQUALITY caseExactIA5Match
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.5
   NAME 'sudoOption'
   DESC 'Options(s) followed by sudo'
   EQUALITY caseExactIA5Match
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.6
   NAME 'sudoRunAsUser'
   DESC 'User(s) impersonated by sudo'
   EQUALITY caseExactIA5Match
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.7
   NAME 'sudoRunAsGroup'
   DESC 'Group(s) impersonated by sudo'
   EQUALITY caseExactIA5Match
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.26 )

attributetype ( 1.3.6.1.4.1.15953.9.1.8
   NAME 'sudoNotBefore'
   DESC 'Start of time interval for which the entry is valid'
   EQUALITY generalizedTimeMatch
   ORDERING generalizedTimeOrderingMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )

attributetype ( 1.3.6.1.4.1.15953.9.1.9
   NAME 'sudoNotAfter'
   DESC 'End of time interval for which the entry is valid'
   EQUALITY generalizedTimeMatch
   ORDERING generalizedTimeOrderingMatch
   SYNTAX 1.3.6.1.4.1.1466.115.121.1.24 )

attributeTypes ( 1.3.6.1.4.1.15953.9.1.10
    NAME 'sudoOrder'
    DESC 'an integer to order the sudoRole entries'
    EQUALITY integerMatch
    ORDERING integerOrderingMatch
    SYNTAX 1.3.6.1.4.1.1466.115.121.1.27 )

objectclass ( 1.3.6.1.4.1.15953.9.2.1 NAME 'sudoRole' SUP top STRUCTURAL
   DESC 'Sudoer Entries'
   MUST ( cn )
   MAY ( sudoUser $ sudoHost $ sudoCommand $ sudoRunAs $ sudoRunAsUser $
	 sudoRunAsGroup $ sudoOption $ sudoNotBefore $ sudoNotAfter $
	 sudoOrder $ description )
   )