slapd.access - access configuration for slapd, the stand-alone LDAP daemon

/etc/ldap/slapd.conf

The slapd.conf(5) file contains configuration information for the slapd(8) daemon. This configuration file is also used by the slurpd(8) replication daemon and by the SLAPD tools slapadd(8), slapcat(8), and slapindex(8).

The slapd.conf file consists of a series of global configuration options that apply to slapd as a whole (including all backends), followed by zero or more database backend definitions that contain information specific to a backend instance.

The general format of slapd.conf is as follows:

    # comment - these options apply to every database
    <global configuration options>
    # first database definition & configuration options
    database    <backend 1 type>
    <configuration options specific to backend 1>
    # subsequent database definitions & configuration options
    ...

Both the global configuration and each backend-specific section can contain access information. Backend-specific access control directives are used for those entries that belong to the backend, according to their naming context. In case no access control directives are defined for a backend or those which are defined are not applicable, the directives from the global configuration section are then used.

For entries not held in any backend (such as a root DSE), the directives of the first backend (and any global directives) are used.

Arguments that should be replaced by actual text are shown in brackets <>.

The structure of the access control directives is

access to <what> [ by <who> <access> [ <control> ] ]+

Grant access (specified by <access>) to a set of entries and/or attributes (specified by <what>) by one or more requestors (specified by <who>).

The field <what> specifies the entity the access control directive applies to. It can have the forms

	*
	[dn[.<dnstyle>]=<DN>] 
	[filter=<ldapfilter>]
	[attrs=<attrlist>[ val[.<style>]=<attrval>]]

The wildcard * stands for all the entries.

The statement dn=<DN> selects the entries based on their naming context. The pattern is a string representation of the entry's DN. base, the default, or exact (an alias of base) indicates the entry whose DN is equal to the pattern; one (synonym of onelevel) indicates all the entries immediately below the pattern, sub (synonym of subtree) indicates all entries in the subtree at the pattern, children indicates all the entries below (subordinate to) the pattern.

If the <dnstyle> qualifier is regex, then the value is a regular expression pattern, as detailed in regex(7), matching a normalized string representation of the entry's DN. The regex form of the pattern does not (yet) support UTF-8.

The statement filter=<ldapfilter> selects the entries based on a valid LDAP filter as described in RFC 2254.

The statement attrs=<attrlist> selects the attributes the access control rule applies to. It is a comma-separated list of attribute types, plus the special names entry, indicating access to the entry itself, and children, indicating access to the entry's children. ObjectClass names may also be specified in this list, which will affect all the attributes that are required and/or allowed by that objectClass. Actually, names in <attrlist> that are prefixed by @ are directly treated as objectClass names. A name prefixed by ! is also treated as an objectClass, but in this case the access rule affects the attributes that are not required nor allowed by that objectClass.

Using the form attrs=<attr> val[.<style>]=<value> specifies access to a particular value of a single attribute. In this case, only a single attribute type may be given. A value <style> of exact (the default) uses the attribute's equality matching rule to compare the value. If the value <style> is regex, the provided value is used as a regular expression pattern. If the attribute has DN syntax, the value <style> can be any of base, onelevel, subtree or children, resulting in base, onelevel, subtree or children match, respectively.

The dn, filter, and attrs statements are additive; they can be used in sequence to select entities the access rule applies to based on naming context, value and attribute type simultaneously.

The field <who> indicates whom the access rules apply to. Multiple <who> statements can appear in an access control statement, indicating the different access privileges to the same resource that apply to different accessee. It can have the forms

	*
	anonymous
	users
	self

dn[.<dnstyle>[,<modifier>]]=<DN> dnattr=<attrname> group[/<objectclass>[/<attrname>]] [.<groupstyle>]=<group> peername[.<peernamestyle>]=<peername> sockname[.<style>]=<sockname> domain[.<domainstyle>[,<modifier>]]=<domain> sockurl[.<style>]=<sockurl> set[.<setstyle>]=<pattern>

ssf=<n> transport_ssf=<n> tls_ssf=<n> sasl_ssf=<n>

aci=<attrname>

with

	<dnstyle>={{exact|base}|regex|sub(tree)|one(level)|children}
	<groupstyle>={exact|expand}
	<style>={exact|regex|expand}
	<peernamestyle>={<style>|ip|path}
	<domainstyle>={exact|regex|sub(tree)}
	<setstyle>={exact|regex}
	<modifier>={expand}

They may be specified in combination.

The wildcard * refers to everybody.

The keyword anonymous means access is granted to unauthenticated clients; it is mostly used to limit access to authentication resources (e.g. the userPassword attribute) to unauthenticated clients for authentication purposes.

The keyword users means access is granted to authenticated clients.

The keyword self means access to an entry is allowed to the entry itself (e.g. the entry being accessed and the requesting entry must be the same).

The statement dn=<DN> means that access is granted to the matching DN. The optional style qualifier dnstyle allows the same choices of the dn form of the <what> field. In addition, the regex style can exploit substring substitution of submatches in the <what> dn.regex clause by using the form $<digit>, with digit ranging from 1 to 9. The style qualifier allows an optional modifier. At present, the only type allowed is expand, which causes substring substitution of submatches to take place even if dnstyle is not regex. It is perfectly useless to give any access privileges to a DN that exactly matches the rootdn of the database the ACLs apply to, because it implicitly possesses write privileges for the entire tree of that database.

The statement dnattr=<attrname> means that access is granted to requests whose DN is listed in the entry being accessed under the <attrname> attribute.

The statement group=<group> means that access is granted to requests whose DN is listed in the group entry whose DN is given by <group>. The optional parameters <objectclass> and <attrname> define the objectClass and the member attributeType of the group entry. The optional style qualifier <style> can be expand, which means that <group> will be expanded as a replacement string (but not as a regular expression) according to regex (7), and exact, which means that exact match will be used.

For static groups, the specified attributeType must have DistinguishedName or NameAndOptionalUID syntax. For dynamic groups the attributeType must be a subtype of the labeledURI attributeType. Only LDAP URIs of the form ldap:///<base>??<scope>?<filter> will be evaluated in a dynamic group, by searching the local server only.

The statements peername=<peername>, sockname=<sockname>, domain=<domain>, and sockurl=<sockurl> mean that the contacting host IP (in the form IP=<ip>:<port>) or the contacting host named pipe file name (in the form PATH=<path> if connecting through a named pipe) for peername, the named pipe file name for sockname, the contacting host name for domain, and the contacting URL for sockurl are compared against pattern to determine access. The same style rules for pattern match described for the group case apply, plus the regex style, which implies submatch expand and regex(7) match of the corresponding connection parameters. The exact style of the peername clause (the default) implies a case-exact match on the client's IP, including the IP= prefix and the trailing :<port>, or the client's path, including the PATH= prefix if connecting through a named pipe. The special ip style interprets the pattern as <peername>=<ip>[%<mask>][{<n>}], where <ip> and <mask> are dotted digit representations of the IP and the mask, while <n>, delimited by curly brackets, is an optional port. When checking access privileges, the IP portion of the peername is extracted, eliminating the IP= prefix and the :<port> part, and it is compared against the <ip> portion of the pattern after masking with <mask>. As an example, peername.ip=127.0.0.1 alows connections only from localhost, peername.ip=192.168.1.0%255.255.255.0 allows connections from any IP in the 192.168.1 class C domain, and peername.ip=192.168.1.16%255.255.255.240{9009} allows connections from any IP in the 192.168.1.[16-31] range of the same domain, only if port 9009 is used. The special path style eliminates the PATH= prefix from the peername when connecting through a named pipe, and performs an exact match on the given pattern. The domain clause also allows the subtree style, which succeeds when a fully qualified name exactly matches the domain pattern, or its trailing part, after a dot, exactly matches the domain pattern. The expand style is allowed, implying an exact match with submatch expansion; the use of expand as a style modifier is considered more appropriate. As an example, domain.subtree=example.com will match www.example.com, but will not match www.anotherexample.com. The domain of the contacting host is determined by performing a DNS reverse lookup. As this lookup can easily be spoofed, use of the domain statement is strongly discouraged. By default, reverse lookups are disabled. The optional domainstyle qualifier of the domain clause allows a modifier option; the only value currently supported is expand, which causes substring substitution of submatches to take place even if the domainstyle is not regex, much like the analogous usage in dn clause.

The statement set=<pattern> is undocumented yet.

The statement aci=<attrname> means that the access control is determined by the values in the attrname of the entry itself. ACIs are experimental; they must be enabled at compile time.

The statements ssf=<n>, transport_ssf=<n>, tls_ssf=<n>, and sasl_ssf=<n> set the required Security Strength Factor (ssf) required to grant access.

The field <access> ::= [self]{<level>|<priv>} determines the access level or the specific access privileges the who field will have. Its component are defined as

	<level> ::= none|auth|compare|search|read|write
	<priv> ::= {=|+|-}{w|r|s|c|x|0}+

The modifier self allows special operations like having a certain access level or privilege only in case the operation involves the name of the user that's requesting the access. It implies the user that requests access is bound. An example is the selfwrite access to the member attribute of a group, which allows one to add/delete its own DN from the member list of a group, without affecting other members.

The level access model relies on an incremental interpretation of the access privileges. The possible levels are none, auth, compare, search, read, and write. Each access level implies all the preceding ones, thus write access will imply all accesses. While none is trivial, auth access means that one is allowed access to an attribute to perform authentication/authorization operations (e.g. bind) with no other access. This is useful to grant unauthenticated clients the least possible access level to critical resources, like passwords.

The priv access model relies on the explicit setting of access privileges for each clause. The = sign resets previously defined accesses; as a consequence, the final access privileges will be only those defined by the clause. The + and - signs add/remove access privileges to the existing ones. The privileges are w for write, r for read, s for search, c for compare, and x for authentication. More than one of the above privileges can be added in one statement. 0 indicates no privileges and is used only by itself (e.g., +0).

The optional field <control> controls the flow of access rule application. It can have the forms

	stop
	continue
	break

where stop, the default, means access checking stops in case of match. The other two forms are used to keep on processing access clauses. In detail, the continue form allows for other <who> clauses in the same <access> clause to be considered, so that they may result in incrementally altering the privileges, while the break form allows for other <access> clauses that match the same target to be processed. Consider the (silly) example

	access to dn.subtree="dc=example,dc=com" attrs=cn
		by * =cs break

access to dn.subtree="ou=People,dc=example,dc=com" by * +r

which allows search and compare privileges to everybody under the "dc=example,dc=com" tree, with the second rule allowing also read in the "ou=People" subtree, or the (even more silly) example

	access to dn.subtree="dc=example,dc=com" attrs=cn
		by * =cs continue
		by users +r

which grants everybody search and compare privileges, and adds read privileges to authenticated clients.

Operations require different privileges on different portions of entries. The following summary applies to primary database backends such as the LDBM, BDB, and HDB backends. Requirements for other backends may (and often do) differ.

The add operation requires write (=w) privileges on the pseudo-attribute entry of the entry being added, and write (=w) privileges on the pseudo-attribute children of the entry's parent.

The bind operation, when credentials are stored in the directory, requires auth (=x) privileges on the attribute the credentials are stored in (usually userPassword).

The compare operation requires compare (=c) privileges on the attribute that is being compared.

The delete operation requires write (=w) privileges on the pseudo-attribute entry of the entry being deleted, and write (=w) privileges on the children pseudo-attribute of the entry's parent.

The modify operation requires write (=w) privileges on the attibutes being modified.

The modrdn operation requires write (=w) privileges on the pseudo-attribute entry of the entry whose relative DN is being modified, write (=w) privileges on the pseudo-attribute children of the old and new entry's parents, and write (=w) privileges on the attributes that are present in the new relative DN. Write (=w) privileges are also required on the attributes that are present in the old relative DN if deleteoldrdn is set to 1.

The search operation, for each entry, requires search (=s) privileges on the attributes that are defined in the filter. Then, the resulting entries are tested for read (=r) privileges on the pseudo-attribute entry (for read access to the entry itself) and for read (=r) access on each value of each attribute that is requested. Also, for each referral object used in generating continuation references, the operation requires read (=r) access on the pseudo-attribute entry (for read access to the referral object itself), as well as read (=r) access to the attribute holding the referral information (generally the ref attribute).

Some controls require specific access privileges. The proxyAuthz control requires auth (=x) privileges on all the attributes that are present in the search filter of the URI regexp maps (the right-hand side of the sasl-regexp directives). It also requires auth (=x) privileges on the saslAuthzTo attribute of the authorizing identity and/or on the saslAuthzFrom attribute of the authorized identity.

It is strongly recommended to explicitly use the most appropriate <dnstyle>, to avoid possible incorrect specifications of the access rules as well as for performance (avoid unrequired regex matching when an exact match suffices) reasons.

An administrator might create a rule of the form:

	access to dn.regex="dc=example,dc=com"
		by ...

expecting it to match all entries in the subtree "dc=example,dc=com". However, this rule actually matches any DN which contains anywhere the substring "dc=example,dc=com". That is, the rule matches both "uid=joe,dc=example,dc=com" and "dc=example,dc=com,uid=joe".

To match the desired subtree, the rule would be more precisely written:

	access to dn.regex="^(.+,)?dc=example,dc=com$"
		by ...

For performance reasons, it would be better to use the subtree style.

	access to dn.subtree="dc=example,dc=com"
		by ...

When writing submatch rules, it may be convenient to avoid unnecessary regex <dnstyle> use; for instance, to allow access to the subtree of the user that matches the what clause, one could use

	access to dn.regex="^(.+,)?uid=([^,]+),dc=example,dc=com$"
		by dn.regex="^uid=$1,dc=example,dc=com$$" write
		by ...

However, since all that is required in the to clause is substring expansion, a more efficient solution is

	access to dn.regex="^(.+,)?uid=([^,]+),dc=example,dc=com$"
		by dn.exact,expand="uid=$1,dc=example,dc=com" write
		by ...

In fact, while a <dnstyle> of regex implies substring expansion, exact, as well as all the other DN specific <dnstyle> values, does not, so it must be explicitly requested.

/etc/ldap/slapd.conf

default slapd configuration file

slapd(8),

"OpenLDAP Administrator's Guide" (http://www.OpenLDAP.org/doc/admin/)

OpenLDAP is developed and maintained by The OpenLDAP Project (http://www.openldap.org/). OpenLDAP is derived from University of Michigan LDAP 3.3 Release.