ProFTPD module mod_ldap


This module is contained in the mod_ldap.c file for ProFTPD 1.2.x/1.3.x, and is not compiled by default. Installation instructions are discussed here.

The most current version of mod_ldap is distributed with the ProFTPD source code.

Author

Please contact John Morrissey <jwm at horde.net> with any questions, concerns, or suggestions regarding this module.

Directives

LDAPAliasDereference

Syntax: LDAPAliasDereference never|always|search|find
Default: None
Context: server config, <VirtualHost>, <Global>
Module: mod_ldap
Compatibility: 1.2.7rc1 and later

The LDAPAliasDereference directive configures how aliases are handled. The possible values have the following behaviors:

The default is "never", e.g.: 

  <IfModule mod_ldap.c>
    LDAPAliasDeference never
  </IfModule>

LDAPAttr

Syntax: LDAPAttr old-attr-name new-attr-name
Default: None
Context: server config, <VirtualHost>, <Global>
Module: mod_ldap
Compatibility: 1.2.7rc1 and later

The LDAPAttr directive is used to map, or to associate, a standard attribute name to a non-standard attribute name. If, for example, your LDAP directory schema used different names for some of the attributes used by mod_ldap, you would use this directive to tell mod_ldap what new attribute names to use.

The following LDAP attributes can be renamed in this manner:

LDAPAuthBinds

Syntax: LDAPAuthBinds on|off
Default: LDAPAuthBinds on
Context: server config, <VirtualHost>, <Global>
Module: mod_ldap
Compatibility: 1.2.7rc1 and later

By default, the DN specified by the LDAPBindDN will be used to bind to the LDAP server to obtain user information, including the userPassword attribute. If LDAPAuthBinds is set to on, the DN specified by LDAPDNInfo will be used to fetch all user information except the userPassword attribute. Then, the mod_ldap module will bind to the LDAP server as the user who is logging in via FTP with the user-supplied password. If this bind succeeds, the user is considered authenticated and is allowed to log in. This method of LDAP authentication has the added benefit of supporting any password encryption scheme that your LDAP server supports.

In versions of mod_ldap up to 2.7.6, the default for LDAPAuthBinds was off. After mod_ldap 2.8, the default value for LDAPAuthBinds is on.

LDAPBindDN

Syntax: LDAPBindDN dn password
Default: None
Context: server config, <VirtualHost>, <Global>
Module: mod_ldap
Compatibility: 1.3.5rc1 and later

The LDAPBindDN directive configures the DN and the password that mod_ldap will use when binding to the LDAP directory. If this configuration directive is missing, then anonymous binds are used.

The default is: 

  <IfModule mod_ldap.c>
    # Use anonymous binds
    LDAPBindDN "" ""
  </IfModule>

See also: LDAPServer, LDAPUseSASL

LDAPDefaultAuthScheme

Syntax: LDAPDefaultAuthScheme "crypt"|"clear"
Default: crypt
Context: server config, <VirtualHost>, <Global>
Module: mod_ldap
Compatibility: 1.2.7rc1 and later

The LDAPDefaultAuthScheme directive specifies the authentication scheme used for passwords which have no "{hashname}" prefix in the LDAP directory. For example, if you have: 

  userPassword mypass
in your directory, you would want to set LDAPDefaultAuthScheme to "clear", e.g.: 
  LDAPDefaultAuthScheme clear




The default value is "crypt".






LDAPDefaultGID

Syntax: LDAPDefaultGID gid

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPDefaultGID directive sets the default GID to be used
for users when no gidNumber attribute is found for that user.



This directive is useful primarily in virtual user environments common in
large-scale ISPs and hosting organizations.  If a user does not have an LDAP
gidNumber attribute, the LDAPDefaultGID is used.
This allows one to have a large number of users in an LDAP directory without
gidNumber attributes; setting this configuration directive will
automatically assign those users a single GID.



See also: LDAPDefaultUID






LDAPDefaultQuota

Syntax: LDAPDefaultQuota default-quota

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.3.5rc1 and later



The LDAPDefaultQuota directive configures a default-quota
to use if a user does not have an ftpQuota attribute.  This
parameter is formatted the same way as the ftpQuota LDAP attribute.






LDAPDefaultUID

Syntax: LDAPDefaultUID uid

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPDefaultUID directive sets the default UID to be used
for users when no uidNumber attribute is found for that user.



This directive is useful primarily in virtual user environments common in
large-scale ISPs and hosting organizations.  If a user does not have an LDAP
uidNumber attribute, the LDAPDefaultGID is used.
This allows one to have a large number of users in an LDAP directory without
uidNumber attributes; setting this configuration directive will
automatically assign those users a single UID.



See also: LDAPDefaultGID

DoAuth


By default, the search filter template used is:

  (&(uid=%v)(objectclass=posixAccount))


The uid for the the search filter is taken from the
LDAPAttr directive.  Search filter templates are only supported
in versions of mod_ldap 2.7 and later.



See also: LDAPAttr






LDAPForceDefaultGID

Syntax: LDAPForceDefaultGID on|off

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



Even when a LDAPDefaultGID is
configured, the mod_ldap module will allow individual users to
have gidNumber attributes that will override this default GID.
With LDAPForceDefaultGID directive configured to be on,
all LDAP-authenticated users are given the default GID; GIDs may not be
overridden by gidNumber attributes.






LDAPForceDefaultUID

Syntax: LDAPForceDefaultUID on|off

Default: None

Context: server config

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



Even when a LDAPDefaultUID is
configured, the mod_ldap module will allow individual users to
have uidNumber attributes that will override this default UID.
With LDAPForceDefaultUID directive configured to be on,
all LDAP-authenticated users are given the default UID; UIDs may not be
overridden by uidNumber attributes.






LDAPForceGeneratedHomedir

Syntax: LDAPForceGeneratedHomedir off|on

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



When no homeDirectory attribute is found, the mod_ldap
module can be configured to generate a home directory using the
LDAPGenerateHomedir directive.
If there is a homeDirectory attribute present, however,
the mod_ldap module will use that attribute value as the home
directory.



However, there may be cases where the administrator wishes to override
the homeDirectory attribute, and thus to always use the
home directory value that mod_ldap would generate.  The
LDAPForceGeneratedHomedir directive is used in such cases.



For example, assume that the user logging in is named "tj", and has an
LDAP object whose homeDirectory attribute value is "/home/tj".
To force the use of mod_ldap's generated home directory
instead of that homeDirectory value, the configuration might
look like:

  LDAPForceGeneratedHomedir on
  LDAPGenerateHomedir on
  LDAPGenerateHomedirPrefix /var/ftp


Using the above configuration, the home directory that the
mod_ldap module would use is /var/ftp/tj, despite
what homeDirectory attribute may be in the LDAP directory.



Note that if LDAPForceGeneratedHomedir is enabled, then
LDAPGenerateHomedir must also be enabled.  It is an error
to enable LDAPForceGeneratedHomedir without also enabling
LDAPGenerateHomdir.



See also: LDAPGenerateHomedir, LDAPGenerateHomedirPrefix, LDAPGenerateHomedirPrefixNoUsername






LDAPGenerateHomedir

Syntax: LDAPGenerateHomedir on|off

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



By default, the mod_ldap module uses the homeDirectory
attribute to determine what home directory to use for the session.  Sometimes,
however, an administrator will want to use a different home directory
for these FTP/SFTP sessions, something other than the path in the
homeDirectory attribute.  The LDAPGenerateHomedir
directive is used for situations like this.



The LDAPGenerateHomedir directive configures the
mod_ldap module to "generate" a new home directory value,
overriding the value from the homeDirectory attribute.
The generated home directory value requires that a starting point
for the new home directory, a "prefix", also be provided using the
LDAPGenerateHomedirPrefix
directive.



The LDAPGenerateHomedir directives does not cause the
new home directory to be created on the filesystem.  It only changes
the home directory value that the mod_ldap module provides to
the ProFTPD engine.  The creation of the home directory, if it does
not already exist, is done using the
CreateHome directive.



See also: LDAPGenerateHomedirPrefix, LDAPGenerateHomedirPrefixNoUsername






LDAPGenerateHomedirPrefix

Syntax: LDAPGenerateHomedirPrefix prefix

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPGenerateHomedirPrefix directive is used when
LDAPGenerateHomedir is enabled, causing the mod_ldap
module to generate a default home directory, when the
homeDirectory attribute value is not present.  The generated home
directory value like this:

  prefix/username


The configured prefix string has the username (from the
uid attribute) appended to generate the home directory value for
the user.



For example:

  LDAPGenerateHomedir on
  LDAPGenerateHomedirPrefix /var/ftp


Using the above configuration, and assuming a user name of "tj", the home
directory that the mod_ldap module would use is
/var/ftp/tj, no matter what the homeDirectory
attribute may be in the LDAP directory.



See also: LDAPForceGeneratedHomedir, LDAPGenerateHomedir, LDAPGenerateHomedirPrefixNoUsername






LDAPGenerateHomedirPrefixNoUsername

Syntax: LDAPGenerateHomedirPrefixNoUsername on|off

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



When the LDAPGenerateHomedir
and LDAPGenerateHomedirPrefix directives are used, the generated home directory value for
the session is:

  prefix/username


However, there may be cases where the administrator does not want
the username automatically appended to the generated value, and instead wishes
to use just the prefix as the home directory.  For these use cases,
use the LDAPGenerateHomedirPrefixNoUsername directive.



For example:

  LDAPGenerateHomedir on
  LDAPGenerateHomedirPrefix /var/ftp
  LDAPGenerateHomedirPrefixNoUsername on


Using the above configuration, and assuming a user name of "tj", the home
directory that the mod_ldap module would use is
/var/ftp, no matter what the homeDirectory attribute
may be in the LDAP directory.



See also: LDAPGenerateHomedir, LDAPGenerateHomedirPrefix






LDAPGroups

Syntax: LDAPGroups base-dn cn-filter-template gid-number-filter-template member-uid-filter-template

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.3.5rc1 and later



The LDAPGroups directive activates LDAP GID-to-name lookups for
directory listings.  The first parameter to this directive is the LDAP
base DN to use for GID-to-name lookups.  The second through fourth
optional parameters are templates to be used for the search filter;
%v will be replaced with the GID that is being looked up.



By default, the CN filter template look like this:

  (&(LDAPAttr_cn=%v)(objectclass=posixGroup))


The gidNumber filter template is:

  (&(LDAPAttr_gidNumber=%v)(objectclass=posixGroup))


and the memberUid filter template used is:

  (&(LDAPAttr_memberUid=%v)(objectclass=posixGroup))


Note that filter templates are only supported in mod_ldap
version 2.8.3 and later.



The attribute names used in the default search filters are taken from the
LDAPAttr directive.






LDAPLog

Syntax: LDAPLog file|"none"

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.3.5rc4 and later



The LDAPLog directive is used to specify a log file for
mod_ldap's reporting on a per-server basis.  The file
parameter given must be the full path to the file to use for logging.



Note that this path must not be to a world-writable directory and,
unless AllowLogSymlinks is explicitly set to on
(generally a bad idea), the path must not be a symbolic link.






LDAPProtocolVersion

Syntax: LDAPProtocolVersion 2|3

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPProtocolVersion directive configures the version of
the LDAP protocol that mod_ldap will use when talking to the
LDAP servers.  The default protocol version used is 3.






LDAPQueryTimeout

Syntax: LDAPQueryTimeout secs

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPQueryTimeout directive configures the timeout value,
in seconds, that will be used for LDAP directory queries.  The default timeout
value is determined by your LDAP API.






LDAPSearchScope

Syntax: LDAPSearchScope base|onelevel|subtree

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPSearchScope directive is used to set the scope used for
LDAP searches.  The default setting, subtree, searches for all entries
in the tree from the current level down.  Setting this directive to
onelevel searches only one level deep in the LDAP tree.



Note that the LDAPSearchScope directive cannot be
used when the LDAP URL syntax, rather than hostname/port, is used for your
LDAPServer configuration.  Why not?
The search scope can be specified as part of the URL itself.  This, combined
with the fact that the LDAPServer directive can take
multiple hosts/URLs, makes it clear to include the search scope in the
URLs as needed.



If you are not using the LDAP URL syntax, then the following will
use the subtree search scope:

  LDAPServer ldap.example.com


or, to make it explicit in your configuration:

  LDAPServer ldap.example.com
  LDAPSearchScope subtree


On the other hand, if you are using LDAP URLs, then you specify the
search scope as part of the URL:

  LDAPServer ldap://ldap.example.com/??sub


It is important that the "/" after the hostname/port be part of your
LDAP URL when specifying the search scope.  That is, using:

  LDAPServer ldap://ldap.example.com??sub


will not work as expected; see
RFC 2255, Section 3.  LDAP
URL parameters are not like HTTP URL query parameters; LDAP URL
parameters are order-specific.  And the "/" before any of the
optional parameters is required.






LDAPServer

Syntax: LDAPServer url1|host1:port1 url2|host2:port2 [ssl-ca:<path>] [ssl-cert:<path>] [ssl-key:<path>] [ssl-ciphers:<list>] [ssl-verify:boolean]

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPServer directive allows you to to specify the hostname(s)
and port(s) of the LDAP server(s) to use for LDAP authentication. If no
LDAPServer configuration directive is present, the default LDAP
servers specified by your LDAP library will be used.  Note that the LDAP
URL syntax may also be used.



To specify multiple LDAP servers, you can configure the entire list of servers
on one line:

  # Using just hostname/port
  LDAPServer host1:port1 host2:port2


or:

  # Using the URL syntax
  LDAPServer url1 url2


In ProFTPD 1.3.7rc4 and later, you can also use multiple LDAPServer
directives as well, e.g.:

  LDAPServer host1:port1
  LDAPServer url1
  LDAPServer host2
  LDAPServer url2





The default search scope for LDAP URLs is "base" (unless a scope is explicitly
provided in the URL). This behavior differs from the
LDAPSearchScope directive, which
defaults to "subtree".



Note that to use LDAPS (LDAP over SSL), you must use the
URL format, e.g.:

  LDAPServer ldaps://host1:port1 ldaps://host2:port2





However, LDAPS is deprecated.  Instead, LDAP prefers the
STARTTLS mechanism. To
enable use of STARTTLS for your LDAP connections, use the
LDAPUseTLS directive, e.g.:

  LDAPServer ldap://host1:port1 ldap://host2:port2
  LDAPUseTLS on





In ProFTPD 1.3.7rc4 and later, it is possible to configure SSL/TLS parameters
for a given connection.  Most of the time, all that is needed for the SSL
session is the CA (Certificate Authority) to use, for verifying the
certificate presented by the LDAP server, using the ssl-ca: parameter.
Thus:

  LDAPServer ... ssl-ca:/path/to/cacert.pem


If your LDAP server is configured to require SSL/TLS mutual authentication
(also called "client auth"), you may need the ssl-cert: and
ssl-key: parameters as well:

  LDAPServer ... ssl-ca:/path/to/cacert.pem \
    ssl-cert:/path/to/client-cert.pem \
    ssl-key:/path/to/client-key.pem


Finally, you may want to configure the specific SSL/TLS ciphersuites that
should be used; the ssl-ciphers: parameter can be used for this:

  LDAPServer ... ssl-ca:/path/to/cacert.pem \
    ssl-cert:/path/to/client-cert.pem \
    ssl-key:/path/to/client-key.pem \
    ssl-ciphers:DEFAULT:!EXPORT:!DES





If there is an issue with the server certificate presented by your LDAP
server, but you need to create the SSL/TLS session anyway, you can
relax the certificate verification requirements using the ssl-verify:
parameter, e.g.:

  LDAPServer ... ssl-ca:/path/to/cacert.pem \
    ssl-verify:off








LDAPUsers

Syntax: LDAPUsers base-dn [name-filter-template [uid-filter-template]]

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.3.5rc1 and later



The LDAPUsers directive activates LDAP UID-to-name lookups
for directory listings.  The first parameter to this directive is the LDAP
base DN to use for UID-to-name lookups.  The optional second parameter
is a template to be used for the search filter for the username; %v
will be replaced with the UID that is being looked up.  Similarly, an optional
third parameter is also a template, to be used for the search filter for
the UID.



By default, the name search filter template looks like this:

  (&(uid=%v)(objectclass=posixAccount))


and the UID search filter template looks like this:

  (&(LDAPAttr_uidNumber=%v)(objectclass=posixGroup))


The uidNumber attribute name used in the search filter comes from
the LDAPAttr directive.
Note that filter templates are only supported in mod_ldap
version 2.7 and later.






LDAPUseSASL

Syntax: LDAPUseSASL mech1 ...

Default: None

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.3.7rc4 and later



The LDAPUseSASL directive tells the mod_ldap module
to use the configured space-separated list of
SASL (Simple Authentication and
Security Layer) mechanisms, when using the
LDAPBindDN to talk to the LDAP server.
By default, simple binds are done to the LDAP server.



The currently supported mechanisms are:


The order in which the mechanisms are configured matters; the first one
selected by the LDAP server wins.



Note that a SASL mechanism configured here may still be rejected by
the LDAP server, if the server-side policies for authentication are not met.
Indeed, some SASL mechanisms may only be allowed by the server if used
in conjunction with SSL/TLS; this is a common requirement for using the
LOGIN and PLAIN mechanisms.



Thus a good default configuration, using TLS and SASL, might be:

  <IfModule mod_ldap.c>
    LDAPServer ldap.example.com
    LDAPBindDN CN=readonly,DC=example,DC=com ...
    LDAPUseSASL SCRAM-SHA-1 DIGEST-MD5
    LDAPUseTLS on
  </IfModule>








LDAPUseTLS

Syntax: LDAPUseTLS on|off

Default: off

Context: server config, <VirtualHost>, <Global>

Module: mod_ldap

Compatibility: 1.2.7rc1 and later



The LDAPUseTLS directive configures whether mod_ldap
will use SSL/TLS via STARTTLS to protect the connections made to the configured LDAP servers.



By default, the mod_ldap module connects to the LDAP server via 
non-encrypted connections.  Enabling this option causes mod_ldap
to use an encrypted (TLS/SSL) connection to the LDAP server. If a secure
connection to the LDAP server fails, mod_ldap will not
authenticate users; mod_ldap will not fall back to an
unsecure connection.






Installation

Follow the normal steps for using third-party modules in ProFTPD:

  $ ./configure --with-modules=mod_ldap
  $ make
  $ make install


You may need to specify the location of the OpenLDAP header and library files
in your configure command, e.g.:

 $ ./configure --with-modules=mod_ldap \
    --with-includes=/usr/local/openldap/include \
    --with-libraries=/usr/local/openldap/lib








Usage




One mod_ldap user submitted the following configuration for
allowing mod_ldap to communicate to a Windows Active Directory
server.  Note that this configuration has not been tested; if it works for
you (or not), please let us know:

  <IfModule mod_ldap.c>
    LDAPServer ldaps://dc.example.org:3268
    LDAPUseTLS on
    LDAPAuthBinds on
    LDAPBindDN "cn=SRV_ACC_SVN_AUTH,ou=special accounts,ou=Sales,dc=example,dc=org" ******************

    LDAPUsers ou=Users,ou=Sales,dc=example,dc=org "(&(sAMAccountName=%u)(objectclass=user)(memberOf=cn=Linux Admins,ou=Groups,ou=Sales,dc=example,dc=com))"
    LDAPSearchScope subtree

    # Assign default IDs
    LDAPDefaultUID 106
    LDAPDefaultGID 65534

    # Create the home directory
    LDAPGenerateHomedir on
    LDAPGenerateHomedirPrefix /home

    # Use different attribute names where necessary
    LDAPAttr uid sAMAccountName
    LDAPAttr gidNumber primaryGroupID
  </IfModule>





Logging

The mod_ldap module supports trace logging, via the module-specific log channels:


Thus for trace logging, to aid in debugging, you would use the following in
your proftpd.conf:

  TraceLog /path/to/ftpd/trace.log
  Trace ldap:20


This trace logging can generate large files; it is intended for debugging use
only, and should be removed from any production configuration.



Frequently Asked Questions




Question: Why is mod_ldap using a "base"
scope by default, rather than "subtree"?  I configured:

  LDAPSearchScope subtree


but it is not working; I see the following in my LDAP server logs:

  slapd[31709]: conn=20239 op=1 SRCH base="ou=people,dc=example,dc=com" scope=0 deref=0 filter="(&(uid=tj)(objectClass=posixAccount))"


Answer: The use of the "base" scope for searches, in
spite of any LDAPSearchScope directive, happens when a URL, rather
than hostname/port, are used in the LDAPServer directive. RFC 2255, Section 3 specifies that the default scope is "base".



Thus instead of:

  LDAPServer ldap://ldap.example.com


you will need to use:

  LDAPServer ldap://ldap.example.com/??sub


See the LDAPSearchScope
documentation for more details.



Question: How do I use LDAPGenerateHomedir
and CreateHome together successfully?  Can I use just
LDAPGenerateHomedir?

Answer: If you want to have home directories for your
LDAP users automatically created, you do need to use the
CreateHome directive.
Whether you need to use the LDAPGenerateHomedir directive is a different (but related) question.



The LDAPGenerateHomedir directive (and its relative LDAPForceGeneratedHomedir) should be
used when you want to users to have a different home directory than is
configured for them in LDAP.  They are not used for creating these
directories, just generating the paths to use.



Thus to generate a different home directory for your LDAP-defined users,
and to have these different home directories created, you
might use something like this:

  <IfModule mod_ldap.c>
    ...
    LDAPGenerateHomedir on
    LDAPGenerateHomedirPrefix /data
    LDAPForceGeneratedHomedir on

    # And make sure these home directories are created
    CreateHome on 0770 skel /opt/ProFTPD/etc/skel
    ...
  </IfModule>





Question: In my LDAP server logs, I see ProFTPD make
multiple binds for the same client logging in:

  slapd[31709]: conn=20239 op=0 BIND dn="cn=admin,dc=example,dc=com" method=128
  slapd[31709]: conn=20239 op=0 BIND dn="cn=admin,dc=example,dc=com" mech=SIMPLE ssf=0


I was expecting just one bind.  Is this a bug, or is it expected
behavior?

Answer: Yes, this is the expected behavior.
See the LDAPAuthBinds directive
for details.



Note that you may see additional binds when other modules, such
as mod_ifsession, are present in your proftpd build.






© Copyright 2013-2020 TJ Saunders

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