12. Overlays
Overlays are software components that provide hooks to functions analogous to those provided by backends, which can be stacked on top of the backend calls and as callbacks on top of backend responses to alter their behavior.
Overlays may be compiled statically into slapd, or when module support is enabled, they may be dynamically loaded. Most of the overlays are only allowed to be configured on individual databases.
Some can be stacked on the frontend as well, for global use. This means that they can be executed after a request is parsed and validated, but right before the appropriate database is selected. The main purpose is to affect operations regardless of the database they will be handled by, and, in some cases, to influence the selection of the database by massaging the request DN.
Essentially, overlays represent a means to:
- customize the behavior of existing backends without changing the backend code and without requiring one to write a new custom backend with complete functionality
- write functionality of general usefulness that can be applied to different backend types
When using slapd.conf(5), overlays that are configured before any other databases are considered global, as mentioned above. In fact they are implicitly stacked on top of the frontend database. They can also be explicitly configured as such:
database frontend
overlay <overlay name>
Overlays are usually documented by separate specific man pages in section 5; the naming convention is
slapo-<overlay name>
All distributed core overlays have a man page. Feel free to contribute to any, if you think there is anything missing in describing the behavior of the component and the implications of all the related configuration directives.
Official overlays are located in
servers/slapd/overlays/
That directory also contains the file slapover.txt, which describes the rationale of the overlay implementation, and may serve as a guideline for the development of custom overlays.
Contribware overlays are located in
contrib/slapd-modules/<overlay name>/
along with other types of run-time loadable components; they are officially distributed, but not maintained by the project.
All the current overlays in OpenLDAP are listed and described in detail in the following sections.
12.1. Access Logging
12.1.1. Overview
This overlay can record accesses to a given backend database on another database.
This allows all of the activity on a given database to be reviewed using arbitrary LDAP queries, instead of just logging to local flat text files. Configuration options are available for selecting a subset of operation types to log, and to automatically prune older log records from the logging database. Log records are stored with audit schema to assure their readability whether viewed as LDIF or in raw form.
It is also used for
Note: An accesslog database is unique to a given provider. It should never be replicated.
12.1.2. Access Logging Configuration
The following is a basic example that implements Access Logging:
database mdb
suffix dc=example,dc=com
...
overlay accesslog
logdb cn=log
logops writes reads
logold (objectclass=person)
database mdb
suffix cn=log
...
index reqStart eq
access to *
by dn.base="cn=admin,dc=example,dc=com" read
The following is an example used for
database mdb
suffix cn=accesslog
directory /usr/local/var/openldap-accesslog
rootdn cn=accesslog
index default eq
index entryCSN,objectClass,reqEnd,reqResult,reqStart,reqDN
Accesslog overlay definitions for the primary db
database mdb
suffix dc=example,dc=com
...
overlay accesslog
logdb cn=accesslog
logops writes
logsuccess TRUE
# scan the accesslog DB every day, and purge entries older than 7 days
logpurge 07+00:00 01+00:00
An example search result against cn=accesslog might look like:
[ghenry@suretec ghenry]# ldapsearch -x -b cn=accesslog
# extended LDIF
#
# LDAPv3
# base <cn=accesslog> with scope subtree
# filter: (objectclass=*)
# requesting: ALL
#
# accesslog
dn: cn=accesslog
objectClass: auditContainer
cn: accesslog
# 20080110163829.000004Z, accesslog
dn: reqStart=20080110163829.000004Z,cn=accesslog
objectClass: auditModify
reqStart: 20080110163829.000004Z
reqEnd: 20080110163829.000005Z
reqType: modify
reqSession: 196696
reqAuthzID: cn=admin,dc=suretecsystems,dc=com
reqDN: uid=suretec-46022f8$,ou=Users,dc=suretecsystems,dc=com
reqResult: 0
reqMod: sambaPwdCanChange:- ###CENSORED###
reqMod: sambaPwdCanChange:+ ###CENSORED###
reqMod: sambaNTPassword:- ###CENSORED###
reqMod: sambaNTPassword:+ ###CENSORED###
reqMod: sambaPwdLastSet:- ###CENSORED###
reqMod: sambaPwdLastSet:+ ###CENSORED###
reqMod: entryCSN:= 20080110163829.095157Z#000000#000#000000
reqMod: modifiersName:= cn=admin,dc=suretecsystems,dc=com
reqMod: modifyTimestamp:= 20080110163829Z
# search result
search: 2
result: 0 Success
# numResponses: 3
# numEntries: 2
12.1.3. Further Information
slapo-accesslog(5) and the
12.2. Audit Logging
The Audit Logging overlay can be used to record all changes on a given backend database to a specified log file.
12.2.1. Overview
If the need arises whereby changes need to be logged as standard LDIF, then the auditlog overlay slapo-auditlog (5) can be used. Full examples are available in the man page slapo-auditlog (5)
12.2.2. Audit Logging Configuration
If the directory is running vi slapd.d, then the following LDIF could be used to add the overlay to the overlay list in cn=config and set what file the
dn: olcOverlay=auditlog,olcDatabase={1}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcAuditLogConfig
olcOverlay: auditlog
olcAuditlogFile: /tmp/auditlog.ldif
In this example for testing, we are logging changes to /tmp/auditlog.ldif
A typical
# add 1196797576 dc=suretecsystems,dc=com cn=admin,dc=suretecsystems,dc=com
dn: dc=suretecsystems,dc=com
changetype: add
objectClass: dcObject
objectClass: organization
dc: suretecsystems
o: Suretec Systems Ltd.
structuralObjectClass: organization
entryUUID: 1606f8f8-f06e-1029-8289-f0cc9d81e81a
creatorsName: cn=admin,dc=suretecsystems,dc=com
modifiersName: cn=admin,dc=suretecsystems,dc=com
createTimestamp: 20051123130912Z
modifyTimestamp: 20051123130912Z
entryCSN: 20051123130912.000000Z#000001#000#000000
auditContext: cn=accesslog
# end add 1196797576
# add 1196797577 dc=suretecsystems,dc=com cn=admin,dc=suretecsystems,dc=com
dn: ou=Groups,dc=suretecsystems,dc=com
changetype: add
objectClass: top
objectClass: organizationalUnit
ou: Groups
structuralObjectClass: organizationalUnit
entryUUID: 160aaa2a-f06e-1029-828a-f0cc9d81e81a
creatorsName: cn=admin,dc=suretecsystems,dc=com
modifiersName: cn=admin,dc=suretecsystems,dc=com
createTimestamp: 20051123130912Z
modifyTimestamp: 20051123130912Z
entryCSN: 20051123130912.000000Z#000002#000#000000
# end add 1196797577
12.2.3. Further Information
slapo-auditlog(5)
12.3. Chaining
12.3.1. Overview
The chain overlay provides basic chaining capability to the underlying database.
What is chaining? It indicates the capability of a DSA to follow referrals on behalf of the client, so that distributed systems are viewed as a single virtual DSA by clients that are otherwise unable to "chase" (i.e. follow) referrals by themselves.
The chain overlay is built on top of the ldap backend; it is compiled by default when --enable-ldap.
12.3.2. Chaining Configuration
In order to demonstrate how this overlay works, we shall discuss a typical scenario which might be one provider server and three Syncrepl replicas.
On each replica, add this near the top of the slapd.conf(5) file (global), before any database definitions:
overlay chain
chain-uri "ldap://ldapprovider.example.com"
chain-idassert-bind bindmethod="simple"
binddn="cn=Manager,dc=example,dc=com"
credentials="<secret>"
mode="self"
chain-tls start
chain-return-error TRUE
Add this below your syncrepl statement:
updateref "ldap://ldapprovider.example.com/"
The chain-tls statement enables TLS from the replica to the ldap provider. The DITs are exactly the same between these machines, therefore whatever user bound to the replica will also exist on the provider. If that DN does not have update privileges on the provider, nothing will happen.
You will need to restart the replica after these slapd.conf changes. Then, if you are using loglevel stats (256), you can monitor an ldapmodify on the replica and the provider. (If you're using cn=config no restart is required.)
Now start an ldapmodify on the replica and watch the logs. You should expect something like:
Sep 6 09:27:25 replica1 slapd[29274]: conn=11 fd=31 ACCEPT from IP=143.199.102.216:45181 (IP=143.199.102.216:389)
Sep 6 09:27:25 replica1 slapd[29274]: conn=11 op=0 STARTTLS
Sep 6 09:27:25 replica1 slapd[29274]: conn=11 op=0 RESULT oid= err=0 text=
Sep 6 09:27:25 replica1 slapd[29274]: conn=11 fd=31 TLS established tls_ssf=256 ssf=256
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=people,dc=example,dc=com" method=128
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=1 BIND dn="uid=user1,ou=People,dc=example,dc=com" mech=SIMPLE ssf=0
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=1 RESULT tag=97 err=0 text=
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=2 MOD dn="uid=user1,ou=People,dc=example,dc=com"
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=2 MOD attr=mail
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=2 RESULT tag=103 err=0 text=
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 op=3 UNBIND
Sep 6 09:27:28 replica1 slapd[29274]: conn=11 fd=31 closed
Sep 6 09:27:28 replica1 slapd[29274]: syncrepl_entry: LDAP_RES_SEARCH_ENTRY(LDAP_SYNC_MODIFY)
Sep 6 09:27:28 replica1 slapd[29274]: syncrepl_entry: be_search (0)
Sep 6 09:27:28 replica1 slapd[29274]: syncrepl_entry: uid=user1,ou=People,dc=example,dc=com
Sep 6 09:27:28 replica1 slapd[29274]: syncrepl_entry: be_modify (0)
And on the provider you will see this:
Sep 6 09:23:57 ldapprovider slapd[2961]: conn=55902 op=3 PROXYAUTHZ dn="uid=user1,ou=people,dc=example,dc=com"
Sep 6 09:23:57 ldapprovider slapd[2961]: conn=55902 op=3 MOD dn="uid=user1,ou=People,dc=example,dc=com"
Sep 6 09:23:57 ldapprovider slapd[2961]: conn=55902 op=3 MOD attr=mail
Sep 6 09:23:57 ldapprovider slapd[2961]: conn=55902 op=3 RESULT tag=103 err=0 text=
Note: You can clearly see the PROXYAUTHZ line on the provider, indicating the proper identity assertion for the update on the provider. Also note the replica immediately receiving the Syncrepl update from the provider.
12.3.3. Handling Chaining Errors
By default, if chaining fails, the original referral is returned to the client under the assumption that the client might want to try and follow the referral.
With the following directive however, if the chaining fails at the provider side, the actual error is returned to the client.
chain-return-error TRUE
12.3.4. Read-Back of Chained Modifications
Occasionally, applications want to read back the data that they just wrote. If a modification requested to a shadow server was silently chained to its provider, an immediate read could result in receiving data not yet synchronized. In those cases, clients should use the dontusecopy control to ensure they are directed to the authoritative source for that piece of data.
This control usually causes a referral to the actual source of the data to be returned. However, when the slapo-chain(5) overlay is used, it intercepts the referral being returned in response to the dontusecopy control, and tries to fetch the requested data.
12.3.5. Further Information
slapo-chain(5)
12.4. Constraints
12.4.1. Overview
This overlay enforces a regular expression constraint on all values of specified attributes during an LDAP modify request that contains add or modify commands. It is used to enforce a more rigorous syntax when the underlying attribute syntax is too general.
12.4.2. Constraint Configuration
Configuration via slapd.conf(5) would look like:
overlay constraint
constraint_attribute mail regex ^[[:alnum:]]+@mydomain.com$
constraint_attribute title uri
ldap:///dc=catalog,dc=example,dc=com?title?sub?(objectClass=titleCatalog)
A specification like the above would reject any mail attribute which did not look like <alphanumeric string>@mydomain.com.
It would also reject any title attribute whose values were not listed in the title attribute of any titleCatalog entries in the given scope.
An example for use with cn=config:
dn: olcOverlay=constraint,olcDatabase={1}mdb,cn=config
changetype: add
objectClass: olcOverlayConfig
objectClass: olcConstraintConfig
olcOverlay: constraint
olcConstraintAttribute: mail regex ^[[:alnum:]]+@mydomain.com$
olcConstraintAttribute: title uri ldap:///dc=catalog,dc=example,dc=com?title?sub?(objectClass=titleCatalog)
12.4.3. Further Information
slapo-constraint(5)
12.5. Dynamic Directory Services
12.5.1. Overview
The dds overlay to slapd(8) implements dynamic objects as per RFC2589. The name dds stands for Dynamic Directory Services. It allows to define dynamic objects, characterized by the dynamicObject objectClass.
Dynamic objects have a limited lifetime, determined by a time-to-live (TTL) that can be refreshed by means of a specific refresh extended operation. This operation allows to set the Client Refresh Period (CRP), namely the period between refreshes that is required to preserve the dynamic object from expiration. The expiration time is computed by adding the requested TTL to the current time. When dynamic objects reach the end of their lifetime without being further refreshed, they are automatically deleted. There is no guarantee of immediate deletion, so clients should not count on it.
12.5.2. Dynamic Directory Service Configuration
A usage of dynamic objects might be to implement dynamic meetings; in this case, all the participants to the meeting are allowed to refresh the meeting object, but only the creator can delete it (otherwise it will be deleted when the TTL expires).
If we add the overlay to an example database, specifying a Max TTL of 1 day, a min of 10 seconds, with a default TTL of 1 hour. We'll also specify an interval of 120 (less than 60s might be too small) seconds between expiration checks and a tolerance of 5 second (lifetime of a dynamic object will be entryTtl + tolerance).
overlay dds
dds-max-ttl 1d
dds-min-ttl 10s
dds-default-ttl 1h
dds-interval 120s
dds-tolerance 5s
and add an index:
entryExpireTimestamp
Creating a meeting is as simple as adding the following:
dn: cn=OpenLDAP Documentation Meeting,ou=Meetings,dc=example,dc=com
objectClass: groupOfNames
objectClass: dynamicObject
cn: OpenLDAP Documentation Meeting
member: uid=ghenry,ou=People,dc=example,dc=com
member: uid=hyc,ou=People,dc=example,dc=com
12.5.2.1. Dynamic Directory Service ACLs
Allow users to start a meeting and to join it; restrict refresh to the member; restrict delete to the creator:
access to attrs=userPassword
by self write
by * read
access to dn.base="ou=Meetings,dc=example,dc=com"
attrs=children
by users write
access to dn.onelevel="ou=Meetings,dc=example,dc=com"
attrs=entry
by dnattr=creatorsName write
by * read
access to dn.onelevel="ou=Meetings,dc=example,dc=com"
attrs=participant
by dnattr=creatorsName write
by users selfwrite
by * read
access to dn.onelevel="ou=Meetings,dc=example,dc=com"
attrs=entryTtl
by dnattr=member manage
by * read
In simple terms, the user who created the OpenLDAP Documentation Meeting can add new attendees, refresh the meeting using (basically complete control):
ldapexop -x -H ldap://ldaphost "refresh" "cn=OpenLDAP Documentation Meeting,ou=Meetings,dc=example,dc=com" "120" -D "uid=ghenry,ou=People,dc=example,dc=com" -W
Any user can join the meeting, but not add another attendee, but they can refresh the meeting. The ACLs above are quite straight forward to understand.
12.5.3. Further Information
slapo-dds(5)
12.6. Dynamic Groups
12.6.1. Overview
This overlay extends the Compare operation to detect members of a dynamic group. This overlay is now deprecated as all of its functions are available using the Dynamic Lists overlay.
12.6.2. Dynamic Group Configuration
12.7. Dynamic Lists
12.7.1. Overview
This overlay allows expansion of dynamic groups and lists. Instead of having the group members or list attributes hard coded, this overlay allows us to define an LDAP search whose results will make up the group or list.
12.7.2. Dynamic List Configuration
This module can behave both as a dynamic list and dynamic group, depending on the configuration. The syntax is as follows:
overlay dynlist
dynlist-attrset <group-oc> <URL-ad> [member-ad]
The parameters to the dynlist-attrset directive have the following meaning:
- <group-oc>: specifies which object class triggers the subsequent LDAP search. Whenever an entry with this object class is retrieved, the search is performed.
- <URL-ad>: is the name of the attribute which holds the search URI. It has to be a subtype of labeledURI. The attributes and values present in the search result are added to the entry unless member-ad is used (see below).
- member-ad: if present, changes the overlay behavior into a dynamic group. Instead of inserting the results of the search in the entry, the distinguished name of the results are added as values of this attribute.
Here is an example which will allow us to have an email alias which automatically expands to all user's emails according to our LDAP filter:
In slapd.conf(5):
overlay dynlist
dynlist-attrset nisMailAlias labeledURI
This means that whenever an entry which has the nisMailAlias object class is retrieved, the search specified in the labeledURI attribute is performed.
Let's say we have this entry in our directory:
cn=all,ou=aliases,dc=example,dc=com
cn: all
objectClass: nisMailAlias
labeledURI: ldap:///ou=People,dc=example,dc=com?mail?one?(objectClass=inetOrgPerson)
If this entry is retrieved, the search specified in labeledURI will be performed and the results will be added to the entry just as if they have always been there. In this case, the search filter selects all entries directly under ou=People that have the inetOrgPerson object class and retrieves the mail attribute, if it exists.
This is what gets added to the entry when we have two users under ou=People that match the filter:
Figure X.Y: Dynamic List for all emails
The configuration for a dynamic group is similar. Let's see an example which would automatically populate an allusers group with all the user accounts in the directory.
In slapd.conf(5):
include /path/to/dyngroup.schema
...
overlay dynlist
dynlist-attrset groupOfURLs labeledURI member
Note: We must include the dyngroup.schema file that defines the groupOfURLs objectClass used in this example.
Let's apply it to the following entry:
cn=allusers,ou=group,dc=example,dc=com
cn: all
objectClass: groupOfURLs
labeledURI: ldap:///ou=people,dc=example,dc=com??one?(objectClass=inetOrgPerson)
The behavior is similar to the dynamic list configuration we had before: whenever an entry with the groupOfURLs object class is retrieved, the search specified in the labeledURI attribute is performed. But this time, only the distinguished names of the results are added, and as values of the member attribute.
This is what we get:
Figure X.Y: Dynamic Group for all users
Note that a side effect of this scheme of dynamic groups is that the members need to be specified as full DNs. So, if you are planning in using this for posixGroups, be sure to use RFC2307bis and some attribute which can hold distinguished names. The memberUid attribute used in the posixGroup object class can hold only names, not DNs, and is therefore not suitable for dynamic groups.
12.7.3. Further Information
slapo-dynlist(5)
12.8. Reverse Group Membership Maintenance
12.8.1. Overview
In some scenarios, it may be desirable for a client to be able to determine which groups an entry is a member of, without performing an additional search. Examples of this are applications using the
The memberof overlay updates an attribute (by default memberOf) whenever changes occur to the membership attribute (by default member) of entries of the objectclass (by default groupOfNames) configured to trigger updates.
Thus, it provides maintenance of the list of groups an entry is a member of, when usual maintenance of groups is done by modifying the members on the group entry.
12.8.2. Member Of Configuration
The typical use of this overlay requires just enabling the overlay for a specific database. For example, with the following minimal slapd.conf:
include /usr/share/openldap/schema/core.schema
include /usr/share/openldap/schema/cosine.schema
authz-regexp "gidNumber=0\\\+uidNumber=0,cn=peercred,cn=external,cn=auth"
"cn=Manager,dc=example,dc=com"
database mdb
suffix "dc=example,dc=com"
rootdn "cn=Manager,dc=example,dc=com"
rootpw secret
directory /var/lib/ldap2.5
checkpoint 256 5
index objectClass eq
index uid eq,sub
overlay memberof
adding the following ldif:
cat memberof.ldif
dn: dc=example,dc=com
objectclass: domain
dc: example
dn: ou=Group,dc=example,dc=com
objectclass: organizationalUnit
ou: Group
dn: ou=People,dc=example,dc=com
objectclass: organizationalUnit
ou: People
dn: uid=test1,ou=People,dc=example,dc=com
objectclass: account
uid: test1
dn: cn=testgroup,ou=Group,dc=example,dc=com
objectclass: groupOfNames
cn: testgroup
member: uid=test1,ou=People,dc=example,dc=com
Results in the following output from a search on the test1 user:
# ldapsearch -LL -Y EXTERNAL -H ldapi:/// "(uid=test1)" -b dc=example,dc=com memberOf SASL/EXTERNAL authentication started SASL username: gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth SASL SSF: 0 version: 1 dn: uid=test1,ou=People,dc=example,dc=com memberOf: cn=testgroup,ou=Group,dc=example,dc=com
Note that the memberOf attribute is an operational attribute, so it must be requested explicitly.
12.8.3. Further Information
slapo-memberof(5)
12.9. The Proxy Cache Engine
12.9.1. Overview
The proxy cache extension of slapd is designed to improve the responsiveness of the ldap and meta backends. It handles a search request (query) by first determining whether it is contained in any cached search filter. Contained requests are answered from the proxy cache's local database. Other requests are passed on to the underlying ldap or meta backend and processed as usual.
E.g. (shoesize>=9) is contained in (shoesize>=8) and (sn=Richardson) is contained in (sn=Richards*)
Correct matching rules and syntaxes are used while comparing assertions for query containment. To simplify the query containment problem, a list of cacheable "templates" (defined below) is specified at configuration time. A query is cached or answered only if it belongs to one of these templates. The entries corresponding to cached queries are stored in the proxy cache local database while its associated meta information (filter, scope, base, attributes) is stored in main memory.
A template is a prototype for generating LDAP search requests. Templates are described by a prototype search filter and a list of attributes which are required in queries generated from the template. The representation for prototype filter is similar to RFC4515, except that the assertion values are missing. Examples of prototype filters are: (sn=),(&(sn=)(givenname=)) which are instantiated by search filters (sn=Doe) and (&(sn=Doe)(givenname=John)) respectively.
The cache replacement policy removes the least recently used (LRU) query and entries belonging to only that query. Queries are allowed a maximum time to live (TTL) in the cache thus providing weak consistency. A background task periodically checks the cache for expired queries and removes them.
The Proxy Cache paper (http://www.openldap.org/pub/kapurva/proxycaching.pdf) provides design and implementation details.
12.9.2. Proxy Cache Configuration
The cache configuration specific directives described below must appear after a overlay pcache directive within a "database meta" or "database ldap" section of the server's slapd.conf(5) file.
12.9.2.1. Setting cache parameters
pcache <DB> <maxentries> <nattrsets> <entrylimit> <period>
This directive enables proxy caching and sets general cache parameters. The <DB> parameter specifies which underlying database is to be used to hold cached entries. It should be set to mdb. The <maxentries> parameter specifies the total number of entries which may be held in the cache. The <nattrsets> parameter specifies the total number of attribute sets (as specified by the pcacheAttrset directive) that may be defined. The <entrylimit> parameter specifies the maximum number of entries in a cacheable query. The <period> specifies the consistency check period (in seconds). In each period, queries with expired TTLs are removed.
12.9.2.2. Defining attribute sets
pcacheAttrset <index> <attrs...>
Used to associate a set of attributes to an index. Each attribute set is associated with an index number from 0 to <numattrsets>-1. These indices are used by the pcacheTemplate directive to define cacheable templates.
12.9.2.3. Specifying cacheable templates
pcacheTemplate <prototype_string> <attrset_index> <TTL>
Specifies a cacheable template and the "time to live" (in sec) <TTL> for queries belonging to the template. A template is described by its prototype filter string and set of required attributes identified by <attrset_index>.
12.9.2.4. Example for slapd.conf
An example slapd.conf(5) database section for a caching server which proxies for the "dc=example,dc=com" subtree held at server ldap.example.com.
database ldap
suffix "dc=example,dc=com"
rootdn "dc=example,dc=com"
uri ldap://ldap.example.com/
overlay pcache
pcache mdb 100000 1 1000 100
pcacheAttrset 0 mail postaladdress telephonenumber
pcacheTemplate (sn=) 0 3600
pcacheTemplate (&(sn=)(givenName=)) 0 3600
pcacheTemplate (&(departmentNumber=)(secretary=*)) 0 3600
directory ./testrun/db.2.a
maxsize 1073741824
index objectClass eq
index cn,sn,uid,mail pres,eq,sub
12.9.2.5. Example for slapd-config
The same example as a LDIF file for back-config for a caching server which proxies for the "dc=example,dc=com" subtree held at server ldap.example.com.
dn: olcDatabase={2}ldap,cn=config
objectClass: olcDatabaseConfig
objectClass: olcLDAPConfig
olcDatabase: {2}ldap
olcSuffix: dc=example,dc=com
olcRootDN: dc=example,dc=com
olcDbURI: "ldap://ldap.example.com"
dn: olcOverlay={0}pcache,olcDatabase={2}ldap,cn=config
objectClass: olcOverlayConfig
objectClass: olcPcacheConfig
olcOverlay: {0}pcache
olcPcache: mdb 100000 1 1000 100
olcPcacheAttrset: 0 mail postalAddress telephoneNumber
olcPcacheTemplate: "(sn=)" 0 3600 0 0 0
olcPcacheTemplate: "(&(sn=)(givenName=))" 0 3600 0 0 0
olcPcacheTemplate: "(&(departmentNumber=)(secretary=))" 0 3600
dn: olcDatabase={0}mdb,olcOverlay={0}pcache,olcDatabase={2}ldap,cn=config
objectClass: olcMdbConfig
objectClass: olcPcacheDatabase
olcDatabase: {0}mdb
olcDbDirectory: ./testrun/db.2.a
olcDbMaxSize: 1073741824
olcDbIndex: objectClass eq
olcDbIndex: cn,sn,uid,mail pres,eq,sub
12.9.2.5.1. Cacheable Queries
A LDAP search query is cacheable when its filter matches one of the templates as defined in the "pcacheTemplate" statements and when it references only the attributes specified in the corresponding attribute set. In the example above the attribute set number 0 defines that only the attributes: mail postaladdress telephonenumber are cached for the following pcacheTemplates.
12.9.2.5.2. Examples:
Filter: (&(sn=Richard*)(givenName=jack))
Attrs: mail telephoneNumber
is cacheable, because it matches the template (&(sn=)(givenName=)) and its attributes are contained in pcacheAttrset 0.
Filter: (&(sn=Richard*)(telephoneNumber))
Attrs: givenName
is not cacheable, because the filter does not match the template, nor is the attribute givenName stored in the cache
Filter: (|(sn=Richard*)(givenName=jack))
Attrs: mail telephoneNumber
is not cacheable, because the filter does not match the template ( logical OR "|" condition instead of logical AND "&" )
12.9.3. Further Information
slapo-pcache(5)
12.10. Password Policies
12.10.1. Overview
This overlay follows the specifications contained in the draft RFC titled draft-behera-ldap-password-policy-09. While the draft itself is expired, it has been implemented in several directory servers, including slapd. Nonetheless, it is important to note that it is a draft, meaning that it is subject to change and is a work-in-progress.
The key abilities of the password policy overlay are as follows:
- Enforce a minimum length for new passwords
- Make sure passwords are not changed too frequently
- Cause passwords to expire, provide warnings before they need to be changed, and allow a fixed number of 'grace' logins to allow them to be changed after they have expired
- Maintain a history of passwords to prevent password re-use
- Prevent password guessing by locking a password for a specified period of time after repeated authentication failures
- Force a password to be changed at the next authentication
- Set an administrative lock on an account
- Support multiple password policies on a default or a per-object basis.
- Perform arbitrary quality checks using an external loadable module. This is a non-standard extension of the draft RFC.
12.10.2. Password Policy Configuration
Instantiate the module in the database where it will be used, after adding the new ppolicy schema and loading the ppolicy module. The following example shows the ppolicy module being added to the database that handles the naming context "dc=example,dc=com". In this example we are also specifying the DN of a policy object to use if none other is specified in a user's object.
database mdb
suffix "dc=example,dc=com"
[...additional database configuration directives go here...]
overlay ppolicy
ppolicy_default "cn=default,ou=policies,dc=example,dc=com"
Now we need a container for the policy objects. In our example the password policy objects are going to be placed in a section of the tree called "ou=policies,dc=example,dc=com":
dn: ou=policies,dc=example,dc=com
objectClass: organizationalUnit
objectClass: top
ou: policies
The default policy object that we are creating defines the following policies:
- The user is allowed to change his own password. Note that the directory ACLs for this attribute can also affect this ability (pwdAllowUserChange: TRUE).
- The name of the password attribute is "userPassword" (pwdAttribute: userPassword). Note that this is the only value that is accepted by OpenLDAP for this attribute.
- The server will check the syntax of the password. If the server is unable to check the syntax (i.e., it was hashed or otherwise encoded by the client) it will return an error refusing the password (pwdCheckQuality: 2).
- When a client includes the Password Policy Request control with a bind request, the server will respond with a password expiration warning if it is going to expire in ten minutes or less (pwdExpireWarning: 600). The warnings themselves are returned in a Password Policy Response control.
- When the password for a DN has expired, the server will allow five additional "grace" logins (pwdGraceAuthNLimit: 5).
- The server will maintain a history of the last five passwords that were used for a DN (pwdInHistory: 5).
- The server will lock the account after the maximum number of failed bind attempts has been exceeded (pwdLockout: TRUE).
- When the server has locked an account, the server will keep it locked until an administrator unlocks it (pwdLockoutDuration: 0)
- The server will reset its failed bind count after a period of 30 seconds.
- Passwords will not expire (pwdMaxAge: 0).
- Passwords can be changed as often as desired (pwdMinAge: 0).
- Passwords must be at least 5 characters in length (pwdMinLength: 5).
- The password does not need to be changed at the first bind or when the administrator has reset the password (pwdMustChange: FALSE)
- The current password does not need to be included with password change requests (pwdSafeModify: FALSE)
- The server will only allow five failed binds in a row for a particular DN (pwdMaxFailure: 5).
The actual policy would be:
dn: cn=default,ou=policies,dc=example,dc=com
cn: default
objectClass: pwdPolicy
objectClass: namedPolicy
objectClass: top
pwdAllowUserChange: TRUE
pwdAttribute: userPassword
pwdCheckQuality: 2
pwdExpireWarning: 600
pwdFailureCountInterval: 30
pwdGraceAuthNLimit: 5
pwdInHistory: 5
pwdLockout: TRUE
pwdLockoutDuration: 0
pwdMaxAge: 0
pwdMaxFailure: 5
pwdMinAge: 0
pwdMinLength: 5
pwdMustChange: FALSE
pwdSafeModify: FALSE
You can create additional policy objects as needed.
The namedPolicy object class is present because the policy entry requires a structural object class.
There are two ways password policy can be applied to individual objects:
1. The pwdPolicySubentry in a user's object - If a user's object has a pwdPolicySubEntry attribute specifying the DN of a policy object, then the policy defined by that object is applied.
2. Default password policy - If there is no specific pwdPolicySubentry set for an object, and the password policy module was configured with the DN of a default policy object and if that object exists, then the policy defined in that object is applied.
Please see slapo-ppolicy(5) for a complete explanation of its features.
A guiding philosophy for OpenLDAP and directory servers in general has been that they always hand back exactly what they were given, without modification. For example, if the cn attribute of an object was set to fOObaR, the server will return that exact string during a search. Values of attributes of a sensitive nature, such as userPassword, are often hashed to conceal their values. Since the userPassword values are used internally by the directory server to authenticate users, any hash algorithm that is applied to the value must be compatible with the directory server. Historically this problem has been solved by making the LDAP client application be able to hash the userPassword attribute value in a way that is compatible with the directory server, but this solution has the obvious drawback of requiring tight coupling between the LDAP client and server, and limits the choices of usable hashing algorithms to those that are accommodated by both. This is clearly a sub-optimal solution.
In 2001 RFC 3062 became a standard that specified an LDAP extended operation for cases like this. Extended operations are not bound by the return-what-you-are-given philosophy and so are free to do things to attribute values that the add and modify operations cannot. The change password extended operation accepts a plaintext password and hashes it based on a specification that is contained in the server. This allows the server to be in control of the hashing algorithm which, in turn, ensures that any hashes applied to userPassword attribute values will not prevent users from being authenticated.
The password policy module's ppolicy_hash_cleartext flag addresses this problem by intercepting LDAP modify operations that include the userPassword attribute and converting them to change password extended operations so they can be hashed according to the specification contained in slapd's configuration. When this flag is set, LDAP applications that modify the userPassword attribute can send the password in cleartext form to the server using a standard LDAP modify command and the server will hash the value according to the password-hash directive before storing it. It goes without saying that steps need to be taken to protect the cleartext password in transit, such as using SSL, TLS, or some other link encryption method.
The following example shows the ppolicy module configured to hash cleartext passwords:
database mdb
suffix "dc=example,dc=com"
[...additional database configuration directives go here...]
overlay ppolicy
ppolicy_default "cn=default,ou=policies,dc=example,dc=com"
ppolicy_hash_cleartext
12.10.3. Further Information
slapo-ppolicy(5)
12.11. Referential Integrity
12.11.1. Overview
This overlay can be used with a backend database such as slapd-mdb(5) to maintain the cohesiveness of a schema which utilizes reference attributes.
Whenever a modrdn or delete is performed, that is, when an entry's DN is renamed or an entry is removed, the server will search the directory for references to this DN (in selected attributes: see below) and update them accordingly. If it was a delete operation, the reference is deleted. If it was a modrdn operation, then the reference is updated with the new DN.
For example, a very common administration task is to maintain group membership lists, specially when users are removed from the directory. When an user account is deleted or renamed, all groups this user is a member of have to be updated. LDAP administrators usually have scripts for that. But we can use the refint overlay to automate this task. In this example, if the user is removed from the directory, the overlay will take care to remove the user from all the groups he/she was a member of. No more scripting for this.
12.11.2. Referential Integrity Configuration
The configuration for this overlay is as follows:
overlay refint
refint_attributes <attribute [attribute ...]>
refint_nothing <string>
- refint_attributes: this parameter specifies a space separated list of attributes which will have the referential integrity maintained. When an entry is removed or has its DN renamed, the server will do an internal search for any of the refint_attributes that point to the affected DN and update them accordingly. IMPORTANT: the attributes listed here must have the distinguishedName syntax, that is, hold DNs as values.
- refint_nothing: some times, while trying to maintain the referential integrity, the server has to remove the last attribute of its kind from an entry. This may be prohibited by the schema: for example, the groupOfNames object class requires at least one member. In these cases, the server will add the attribute value specified in refint_nothing to the entry.
To illustrate this overlay, we will use the group membership scenario.
In slapd.conf:
overlay refint
refint_attributes member
refint_nothing "cn=admin,dc=example,dc=com"
This configuration tells the overlay to maintain the referential integrity of the member attribute. This attribute is used in the groupOfNames object class which always needs a member, so we add the refint_nothing directive to fill in the group with a standard member should all the members vanish.
If we have the following group membership, the refint overlay will automatically remove john from the group if his entry is removed from the directory:
Figure X.Y: Maintaining referential integrity in groups
Notice that if we rename (modrdn) the john entry to, say, jsmith, the refint overlay will also rename the reference in the member attribute, so the group membership stays correct.
If we removed all users from the directory who are a member of this group, then the end result would be a single member in the group: cn=admin,dc=example,dc=com. This is the refint_nothing parameter kicking into action so that the schema is not violated.
The rootdn must be set for the database as refint runs as the rootdn to gain access to make its updates. The rootpw does not need to be set.
12.11.3. Further Information
slapo-refint(5)
12.12. Return Code
12.12.1. Overview
This overlay is useful to test the behavior of clients when server-generated erroneous and/or unusual responses occur, for example; error codes, referrals, excessive response times and so on.
This would be classed as a debugging tool whilst developing client software or additional Overlays.
For detailed information, please see the slapo-retcode(5) man page.
12.12.2. Return Code Configuration
The retcode overlay utilizes the "return code" schema described in the man page. This schema is specifically designed for use with this overlay and is not intended to be used otherwise.
Note: The necessary schema is loaded automatically by the overlay.
An example configuration might be:
overlay retcode
retcode-parent "ou=RetCodes,dc=example,dc=com"
include ./retcode.conf
retcode-item "cn=Unsolicited" 0x00 unsolicited="0"
retcode-item "cn=Notice of Disconnect" 0x00 unsolicited="1.3.6.1.4.1.1466.20036"
retcode-item "cn=Pre-disconnect" 0x34 flags="pre-disconnect"
retcode-item "cn=Post-disconnect" 0x34 flags="post-disconnect"
Note: retcode.conf can be found in the openldap source at: tests/data/retcode.conf
An excerpt of a retcode.conf would be something like:
retcode-item "cn=success" 0x00
retcode-item "cn=success w/ delay" 0x00 sleeptime=2
retcode-item "cn=operationsError" 0x01
retcode-item "cn=protocolError" 0x02
retcode-item "cn=timeLimitExceeded" 0x03 op=search
retcode-item "cn=sizeLimitExceeded" 0x04 op=search
retcode-item "cn=compareFalse" 0x05 op=compare
retcode-item "cn=compareTrue" 0x06 op=compare
retcode-item "cn=authMethodNotSupported" 0x07
retcode-item "cn=strongAuthNotSupported" 0x07 text="same as authMethodNotSupported"
retcode-item "cn=strongAuthRequired" 0x08
retcode-item "cn=strongerAuthRequired" 0x08 text="same as strongAuthRequired"
Please see tests/data/retcode.conf for a complete retcode.conf
12.12.3. Further Information
slapo-retcode(5)
12.13. Rewrite/Remap
12.13.1. Overview
It performs basic DN/data rewrite and objectClass/attributeType mapping. Its usage is mostly intended to provide virtual views of existing data either remotely, in conjunction with the proxy backend described in slapd-ldap(5), or locally, in conjunction with the relay backend described in slapd-relay(5).
This overlay is extremely configurable and advanced, therefore recommended reading is the slapo-rwm(5) man page.
12.13.2. Rewrite/Remap Configuration
12.13.3. Further Information
slapo-rwm(5)
12.14. Sync Provider
12.14.1. Overview
This overlay implements the provider-side support for the LDAP Content Synchronization (RFC4533) as well as syncrepl replication support, including persistent search functionality.
12.14.2. Sync Provider Configuration
There is very little configuration needed for this overlay, in fact for many situations merely loading the overlay will suffice.
However, because the overlay creates a contextCSN attribute in the root entry of the database which is updated for every write operation performed against the database and only updated in memory, it is recommended to configure a checkpoint so that the contextCSN is written into the underlying database to minimize recovery time after an unclean shutdown:
overlay syncprov
syncprov-checkpoint 100 10
For every 100 operations or 10 minutes, which ever is sooner, the contextCSN will be checkpointed.
The four configuration directives available are syncprov-checkpoint, syncprov-sessionlog, syncprov-nopresent and syncprov-reloadhint which are covered in the man page discussing various other scenarios where this overlay can be used.
12.14.3. Further Information
The slapo-syncprov(5) man page and the Configuring the different replication types section
12.15. Translucent Proxy
12.15.1. Overview
This overlay can be used with a backend database such as slapd-mdb(5) to create a "translucent proxy".
Entries retrieved from a remote LDAP server may have some or all attributes overridden, or new attributes added, by entries in the local database before being presented to the client.
A search operation is first populated with entries from the remote LDAP server, the attributes of which are then overridden with any attributes defined in the local database. Local overrides may be populated with the add, modify, and modrdn operations, the use of which is restricted to the root user of the translucent local database.
A compare operation will perform a comparison with attributes defined in the local database record (if any) before any comparison is made with data in the remote database.
12.15.2. Translucent Proxy Configuration
There are various options available with this overlay, but for this example we will demonstrate adding new attributes to a remote entry and also searching against these newly added local attributes. For more information about overriding remote entries and search configuration, please see slapo-translucent(5)
Note: The Translucent Proxy overlay will disable schema checking in the local database, so that an entry consisting of overlay attributes need not adhere to the complete schema.
First we configure the overlay in the normal manner:
include /usr/local/etc/openldap/schema/core.schema
include /usr/local/etc/openldap/schema/cosine.schema
include /usr/local/etc/openldap/schema/nis.schema
include /usr/local/etc/openldap/schema/inetorgperson.schema
pidfile ./slapd.pid
argsfile ./slapd.args
database mdb
suffix "dc=suretecsystems,dc=com"
rootdn "cn=trans,dc=suretecsystems,dc=com"
rootpw secret
directory ./openldap-data
index objectClass eq
overlay translucent
translucent_local carLicense
uri ldap://192.168.X.X:389
lastmod off
acl-bind binddn="cn=admin,dc=suretecsystems,dc=com" credentials="blahblah"
You will notice the overlay directive and a directive to say what attribute we want to be able to search against in the local database. We must also load the ldap backend which will connect to the remote directory server.
Now we take an example LDAP group:
# itsupport, Groups, suretecsystems.com
dn: cn=itsupport,ou=Groups,dc=suretecsystems,dc=com
objectClass: posixGroup
objectClass: sambaGroupMapping
cn: itsupport
gidNumber: 1000
sambaSID: S-1-5-21-XXX
sambaGroupType: 2
displayName: itsupport
memberUid: ghenry
memberUid: joebloggs
and create an LDIF file we can use to add our data to the local database, using some pretty strange choices of new attributes for demonstration purposes:
[ghenry@suretec test_configs]$ cat test-translucent-add.ldif
dn: cn=itsupport,ou=Groups,dc=suretecsystems,dc=com
businessCategory: frontend-override
carLicense: LIVID
employeeType: special
departmentNumber: 9999999
roomNumber: 41L-535
Searching against the proxy gives:
[ghenry@suretec test_configs]$ ldapsearch -x -H ldap://127.0.0.1:9001 "(cn=itsupport)"
# itsupport, Groups, OxObjects, suretecsystems.com
dn: cn=itsupport,ou=Groups,ou=OxObjects,dc=suretecsystems,dc=com
objectClass: posixGroup
objectClass: sambaGroupMapping
cn: itsupport
gidNumber: 1003
SAMBASID: S-1-5-21-XXX
SAMBAGROUPTYPE: 2
displayName: itsupport
memberUid: ghenry
memberUid: joebloggs
roomNumber: 41L-535
departmentNumber: 9999999
employeeType: special
carLicense: LIVID
businessCategory: frontend-override
Here we can see that the 5 new attributes are added to the remote entry before being returned to the our client.
Because we have configured a local attribute to search against:
overlay translucent
translucent_local carLicense
we can also search for that to return the completely fabricated entry:
ldapsearch -x -H ldap://127.0.0.1:9001 (carLicense=LIVID)
This is an extremely useful feature because you can then extend a remote directory server locally and also search against the local entries.
Note: Because the translucent overlay does not perform any DN rewrites, the local and remote database instances must have the same suffix. Other configurations will probably fail with No Such Object and other errors
12.15.3. Further Information
slapo-translucent(5)
12.16. Attribute Uniqueness
12.16.1. Overview
This overlay can be used with a backend database such as slapd-mdb(5) to enforce the uniqueness of some or all attributes within a subtree.
12.16.2. Attribute Uniqueness Configuration
This overlay is only effective on new data from the point the overlay is enabled. To check uniqueness for existing data, you can export and import your data again via the LDAP Add operation, which will not be suitable for large amounts of data, unlike slapcat.
For the following example, if uniqueness were enforced for the mail attribute, the subtree would be searched for any other records which also have a mail attribute containing the same value presented with an add, modify or modrdn operation which are unique within the configured scope. If any are found, the request is rejected.
Note: If no attributes are specified, for example ldap:///??sub?, then the URI applies to all non-operational attributes. However, the keyword ignore can be specified to exclude certain non-operational attributes.
To search at the base dn of the current backend database ensuring uniqueness of the mail attribute, we simply add the following configuration:
overlay unique
unique_uri ldap:///?mail?sub?
For an existing entry of:
dn: cn=gavin,dc=suretecsystems,dc=com
objectClass: top
objectClass: inetorgperson
cn: gavin
sn: henry
mail: ghenry@suretecsystems.com
and we then try to add a new entry of:
dn: cn=robert,dc=suretecsystems,dc=com
objectClass: top
objectClass: inetorgperson
cn: robert
sn: jones
mail: ghenry@suretecsystems.com
would result in an error like so:
adding new entry "cn=robert,dc=example,dc=com"
ldap_add: Constraint violation (19)
additional info: some attributes not unique
The overlay can have multiple URIs specified within a domain, allowing complex selections of objects and also have multiple unique_uri statements or olcUniqueURI attributes which will create independent domains.
For more information and details about the strict and ignore keywords, please see the slapo-unique(5) man page.
12.16.3. Further Information
slapo-unique(5)
12.17. Value Sorting
12.17.1. Overview
The Value Sorting overlay can be used with a backend database to sort the values of specific multi-valued attributes within a subtree. The sorting occurs whenever the attributes are returned in a search response.
12.17.2. Value Sorting Configuration
Sorting can be specified in ascending or descending order, using either numeric or alphanumeric sort methods. Additionally, a "weighted" sort can be specified, which uses a numeric weight prepended to the attribute values.
The weighted sort is always performed in ascending order, but may be combined with the other methods for values that all have equal weights. The weight is specified by prepending an integer weight {<weight>} in front of each value of the attribute for which weighted sorting is desired. This weighting factor is stripped off and never returned in search results.
Here are a few examples:
loglevel sync stats
database mdb
suffix "dc=suretecsystems,dc=com"
directory /usr/local/var/openldap-data
......
overlay valsort
valsort-attr memberUid ou=Groups,dc=suretecsystems,dc=com alpha-ascend
For example, ascend:
# sharedemail, Groups, suretecsystems.com
dn: cn=sharedemail,ou=Groups,dc=suretecsystems,dc=com
objectClass: posixGroup
objectClass: top
cn: sharedemail
gidNumber: 517
memberUid: admin
memberUid: dovecot
memberUid: laura
memberUid: suretec
For weighted, we change our data to:
# sharedemail, Groups, suretecsystems.com
dn: cn=sharedemail,ou=Groups,dc=suretecsystems,dc=com
objectClass: posixGroup
objectClass: top
cn: sharedemail
gidNumber: 517
memberUid: {4}admin
memberUid: {2}dovecot
memberUid: {1}laura
memberUid: {3}suretec
and change the config to:
overlay valsort
valsort-attr memberUid ou=Groups,dc=suretecsystems,dc=com weighted
Searching now results in:
# sharedemail, Groups, OxObjects, suretecsystems.com
dn: cn=sharedemail,ou=Groups,ou=OxObjects,dc=suretecsystems,dc=com
objectClass: posixGroup
objectClass: top
cn: sharedemail
gidNumber: 517
memberUid: laura
memberUid: dovecot
memberUid: suretec
memberUid: admin
12.17.3. Further Information
slapo-valsort(5)
12.18. Overlay Stacking
12.18.1. Overview
Overlays can be stacked, which means that more than one overlay can be instantiated for each database, or for the frontend. As a consequence, each overlays function is called, if defined, when overlay execution is invoked. Multiple overlays are executed in reverse order (as a stack) with respect to their definition in slapd.conf (5), or with respect to their ordering in the config database, as documented in slapd-config (5).