SLAPD.ACCESS(5) File Formats Manual SLAPD.ACCESS(5)
NAME
slapd.access - access configuration for slapd, the stand-alone LDAP
daemon
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
The slapd.conf(5) file contains configuration information for the
slapd(8) daemon. This configuration file is also used by the SLAPD
tools slapacl(8), slapadd(8), slapauth(8), slapcat(8), slapdn(8),
slapindex(8), slapmodify(8), and slaptest(8).
The slapd.conf file consists of a series of global configuration op-
tions 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 direc-
tives from the global configuration section are then used.
If no access controls are present, the default policy allows anyone and
everyone to read anything but restricts updates to rootdn. (e.g., "ac-
cess to * by * read").
When dealing with an access list, because the global access list is ef-
fectively appended to each per-database list, if the resulting list is
non-empty then the access list will end with an implicit access to * by
* none directive. If there are no access directives applicable to a
backend, then a default read is used.
Be warned: the rootdn can always read and write EVERYTHING!
For entries not held in any backend (such as a root DSE), the global
directives are used.
Arguments that should be replaced by actual text are shown in brackets
<>.
THE ACCESS DIRECTIVE
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>).
Lists of access directives are evaluated in the order they appear in
slapd.conf. When a <what> clause matches the datum whose access is be-
ing evaluated, its <who> clause list is checked. When a <who> clause
matches the accessor's properties, its <access> and <control> clauses
are evaluated.
Access control checking stops at the first match of the <what> and
<who> clause, unless otherwise dictated by the <control> clause. Each
<who> clause list is implicitly terminated by a
by * none stop
<control> clause. This implicit <control> stops access directive eval-
uation with no more access privileges granted to anyone else. To stop
access directive evaluation only when both <who> and <what> match, add
an explicit
by * break
to the end of the <who> clause list.
Each <what> clause list is implicitly terminated by a
access to *
by * none
clause that results in granting no access privileges to an otherwise
unspecified datum.
THE <WHAT> FIELD
The field <what> specifies the entity the access control directive ap-
plies to. It can have the forms
dn[.<dnstyle>]=<dnpattern>
filter=<ldapfilter>
attrs=<attrlist>[ val[/matchingRule][.<attrstyle>]=<attrval>]
with
<dnstyle>={{exact|base(object)}|regex
|one(level)|sub(tree)|children}
<attrlist>={<attr>|[{!|@}]<objectClass>}[,<attrlist>]
<attrstyle>={{exact|base(object)}|regex
|one(level)|sub(tree)|children}
The statement dn=<dnpattern> selects the entries based on their naming
context. The <dnpattern> is a string representation of the entry's DN.
The wildcard * stands for all the entries, and it is implied if no dn
form is given.
The <dnstyle> is optional; however, it is recommended to specify it to
avoid ambiguities. Base (synonym of baseObject), the default, or exact
(an alias of base) indicates the entry whose DN is equal to the <dnpat-
tern>; one (synonym of onelevel) indicates all the entries immediately
below the <dnpattern>, sub (synonym of subtree) indicates all entries
in the subtree at the <dnpattern>, children indicates all the entries
below (subordinate to) the <dnpattern>.
If the <dnstyle> qualifier is regex, then <dnpattern> is a POSIX (''ex-
tended'') regular expression pattern, as detailed in regex(7) and/or
re_format(7), matching a normalized string representation of the en-
try'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 4515. A filter of (objectClass=*) is
implied if no filter form is given.
The statement attrs=<attrlist> selects the attributes the access con-
trol 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 at-
tributes that are required and/or allowed by that objectClass. Actu-
ally, names in <attrlist> that are prefixed by @ are directly treated
as objectClass names. A name prefixed by ! is also treated as an ob-
jectClass, but in this case the access rule affects the attributes that
are not required nor allowed by that objectClass. If no attrs form is
given, attrs=@extensibleObject is implied, i.e. all attributes are ad-
dressed.
Using the form attrs=<attr> val[/matchingRule][.<attrstyle>]=<attrval>
specifies access to a particular value of a single attribute. In this
case, only a single attribute type may be given. The <attrstyle> exact
(the default) uses the attribute's equality matching rule to compare
the value, unless a different (and compatible) matching rule is speci-
fied. If the <attrstyle> is regex, the provided value is used as a
POSIX (''extended'') regular expression pattern. If the attribute has
DN syntax, the <attrstyle> can be any of base, onelevel, subtree or
children, resulting in base, onelevel, subtree or children match, re-
spectively.
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. Submatches resulting
from regex matching can be dereferenced in the <who> field using the
syntax ${v<n>}, where <n> is the submatch number. The default syntax,
$<n>, is actually an alias for ${d<n>}, that corresponds to dereferenc-
ing submatches from the dnpattern portion of the <what> field.
THE <WHO> FIELD
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 dif-
ferent accessee. It can have the forms
*
anonymous
users
self[.<selfstyle>]
dn[.<dnstyle>[,<modifier>]]=<DN>
dnattr=<attrname>
realanonymous
realusers
realself[.<selfstyle>]
realdn[.<dnstyle>[,<modifier>]]=<DN>
realdnattr=<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>
dynacl/<name>[/<options>][.<dynstyle>][=<pattern>]
with
<style>={exact|regex|expand}
<selfstyle>={level{<n>}}
<dnstyle>={{exact|base(object)}|regex
|one(level)|sub(tree)|children|level{<n>}}
<groupstyle>={exact|expand}
<peernamestyle>={<style>|ip|ipv6|path}
<domainstyle>={exact|regex|sub(tree)}
<setstyle>={exact|expand}
<modifier>={expand}
<name>=aci <pattern>=<attrname>]
They may be specified in combination.
The wildcard * refers to everybody.
The keywords prefixed by real act as their counterparts without prefix;
the checking respectively occurs with the authentication DN and the au-
thorization DN.
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 au-
thentication purposes.
The keyword users means access is granted to authenticated clients.
The keyword self means access to an entry is allowed to the entry it-
self (e.g. the entry being accessed and the requesting entry must be
the same). It allows the level{<n>} style, where <n> indicates what
ancestor of the DN is to be used in matches. A positive value indi-
cates that the <n>-th ancestor of the user's DN is to be considered; a
negative value indicates that the <n>-th ancestor of the target is to
be considered. For example, a "by self.level{1} ..." clause would
match when the object "dc=example,dc=com" is accessed by
"cn=User,dc=example,dc=com". A "by self.level{-1} ..." clause would
match when the same user accesses the object "ou=Address
Book,cn=User,dc=example,dc=com".
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 0 to 9 (where 0
matches the entire string), or the form ${<digit>+}, for submatches
higher than 9. Substring substitution from attribute value can be done
in using the form ${v<digit>+}. Since the dollar character is used to
indicate a substring replacement, the dollar character that is used to
indicate match up to the end of the string must be escaped by a second
dollar character, e.g.
access to dn.regex="^(.+,)?uid=([^,]+),dc=[^,]+,dc=com$"
by dn.regex="^uid=$2,dc=[^,]+,dc=com$$" write
The style qualifier allows an optional modifier. At present, the only
type allowed is expand, which causes substring substitution of sub-
matches to take place even if dnstyle is not regex. Note that the
regex dnstyle in the above example may be of use only if the <by>
clause needs to be a regex; otherwise, if the value of the second (from
the right) dc= portion of the DN in the above example were fixed, the
form
access to dn.regex="^(.+,)?uid=([^,]+),dc=example,dc=com$"
by dn.exact,expand="uid=$2,dc=example,dc=com" write
could be used; if it had to match the value in the <what> clause, the
form
access to dn.regex="^(.+,)?uid=([^,]+),dc=([^,]+),dc=com$"
by dn.exact,expand="uid=$2,dc=$3,dc=com" write
could be used.
Forms of the <what> clause other than regex may provide submatches as
well. The base(object), the sub(tree), the one(level), and the chil-
dren forms provide $0 as the match of the entire string. The
sub(tree), the one(level), and the children forms also provide $1 as
the match of the rightmost part of the DN as defined in the <what>
clause. This may be useful, for instance, to provide access to all the
ancestors of a user by defining
access to dn.subtree="dc=com"
by dn.subtree,expand="$1" read
which means that only access to entries that appear in the DN of the
<by> clause is allowed.
The level{<n>} form is an extension and a generalization of the
onelevel form, which matches all DNs whose <n>-th ancestor is the pat-
tern. So, level{1} is equivalent to onelevel, and level{0} is equiva-
lent to base.
It is perfectly useless to give any access privileges to a DN that ex-
actly matches the rootdn of the database the ACLs apply to, because it
implicitly possesses write privileges for the entire tree of that data-
base. Actually, access control is bypassed for the rootdn, to solve
the intrinsic chicken-and-egg problem.
The statement dnattr=<attrname> means that access is granted to re-
quests whose DN is listed in the entry being accessed under the <attr-
name> 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 object-
Class and the member attributeType of the group entry. The defaults
are groupOfNames and member, respectively. The optional style quali-
fier <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/or re_format(7), and exact, which means that exact match
will be used. If the style of the DN portion of the <what> clause is
regex, the submatches are made available according to regex(7) and/or
re_format(7); other styles provide limited submatches as discussed
above about the DN form of the <by> clause.
For static groups, the specified attributeType must have Distinguished-
Name 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 dy-
namic group, by searching the local server only.
The statements peername=<peername>, sockname=<sockname>, domain=<do-
main>, and sockurl=<sockurl> mean that the contacting host IP (in the
form IP=<ip>:<port> for IPv4, or IP=[<ipv6>]:<port> for IPv6) or the
contacting host named pipe file name (in the form PATH=<path> if con-
necting 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 match of
the corresponding connection parameters. The exact style of the <peer-
name> 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 <peer-
name>=<ip>[%<mask>][{<n>}], where <ip> and <mask> are dotted digit rep-
resentations of the IP and the mask, while <n>, delimited by curly
brackets, is an optional port. The same applies to IPv6 addresses when
the special ipv6 style is used. 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>: ((peername & <mask>) == <ip>). As
an example, peername.ip=127.0.0.1 and peername.ipv6=::1 allow connec-
tions 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 peer-
name.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 sub-
tree 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 re-
verse 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 dynacl/<name>[/<options>][.<dynstyle>][=<pattern>] means
that access checking is delegated to the admin-defined method indicated
by <name>, which can be registered at run-time by means of the mod-
uleload statement. The fields <options>, <dynstyle> and <pattern> are
optional, and are directly passed to the registered parsing routine.
Dynacl is experimental; it must be enabled at compile time.
The statement dynacl/aci[=<attrname>] means that the access control is
determined by the values in the attrname of the entry itself. The op-
tional <attrname> indicates what attributeType holds the ACI informa-
tion in the entry. By default, the OpenLDAPaci operational attribute
is used. 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 minimum required Security Strength Factor (ssf)
needed to grant access. The value should be positive integer.
THE <ACCESS> FIELD
The optional field <access> ::= [[real]self]{<level>|<priv>} determines
the access level or the specific access privileges the who field will
have. Its component are defined as
<level> ::= none|disclose|auth|compare|search|read|{write|add|delete}|manage
<priv> ::= {=|+|-}{0|d|x|c|s|r|{w|a|z}|m}+
The modifier self allows special operations like having a certain ac-
cess level or privilege only in case the operation involves the name of
the user that's requesting the access. It implies the user that re-
quests access is authorized. The modifier realself refers to the au-
thenticated DN as opposed to the authorized DN of the self modifier.
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, while being not allowed to affect other members.
The level access model relies on an incremental interpretation of the
access privileges. The possible levels are none, disclose, auth, com-
pare, search, read, write, and manage. Each access level implies all
the preceding ones, thus manage grants all access including administra-
tive access. This access allows some modifications which would other-
wise be prohibited by the LDAP data model or the directory schema, e.g.
changing the structural objectclass of an entry, or modifying an opera-
tional attribute that is defined as not user modifiable. The write ac-
cess is actually the combination of add and delete, which respectively
restrict the write privilege to add or delete the specified <what>.
The none access level disallows all access including disclosure on er-
ror.
The disclose access level allows disclosure of information on error.
The auth access level 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 privi-
leges for each clause. The = sign resets previously defined accesses;
as a consequence, the final access privileges will be only those de-
fined by the clause. The + and - signs add/remove access privileges to
the existing ones. The privileges are m for manage, w for write, a for
add, z for delete, r for read, s for search, c for compare, x for au-
thentication, and d for disclose. More than one of the above privi-
leges can be added in one statement. 0 indicates no privileges and is
used only by itself (e.g., +0). Note that +az is equivalent to +w.
If no access is given, it defaults to +0.
THE <CONTROL> FIELD
The optional field <control> controls the flow of access rule applica-
tion. 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 incremen-
tally 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.
One useful application is to easily grant write privileges to an updat-
edn that is different from the rootdn. In this case, since the updat-
edn needs write access to (almost) all data, one can use
access to *
by dn.exact="cn=The Update DN,dc=example,dc=com" write
by * break
as the first access rule. As a consequence, unless the operation is
performed with the updatedn identity, control is passed straight to the
subsequent rules.
OPERATION REQUIREMENTS
Operations require different privileges on different portions of en-
tries. The following summary applies to primary MDB database backend.
Requirements for other backends may (and often do) differ.
The add operation requires add (=a) privileges on the pseudo-attribute
entry of the entry being added, and add (=a) privileges on the pseudo-
attribute children of the entry's parent. When adding the suffix entry
of a database, add access to children of the empty DN ("") is required.
Also if Add content ACL checking has been configured on the database
(see the slapd.conf(5) or slapd-config(5) manual page), add (=a) will
be required on all of the attributes being added.
The bind operation, when credentials are stored in the directory, re-
quires 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 delete (=z) privileges on the pseudo-at-
tribute entry of the entry being deleted, and delete (=d) privileges on
the children pseudo-attribute of the entry's parent.
The modify operation requires write (=w) privileges on the attributes
being modified. In detail, add (=a) is required to add new values,
delete (=z) is required to delete existing values, and both delete and
add (=az), or write (=w), are required to replace existing values.
The modrdn operation requires write (=w) privileges on the pseudo-at-
tribute entry of the entry whose relative DN is being modified, delete
(=z) privileges on the pseudo-attribute children of the old entry's
parents, add (=a) privileges on the pseudo-attribute children of the
new entry's parents, and add (=a) privileges on the attributes that are
present in the new relative DN. Delete (=z) privileges are also re-
quired on the attributes that are present in the old relative DN if
deleteoldrdn is set to 1.
The search operation, requires search (=s) privileges on the entry
pseudo-attribute of the searchBase (NOTE: this was introduced with
OpenLDAP 2.4). Then, for each entry, it requires search (=s) privi-
leges on the attributes that are defined in the filter. The resulting
entries are finally tested for read (=r) privileges on the pseudo-at-
tribute 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 internal operations and some controls require specific access
privileges. The authzID mapping and the proxyAuthz control require
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 authz-
regexp directives). Auth (=x) privileges are also required on the au-
thzTo attribute of the authorizing identity and/or on the authzFrom at-
tribute of the authorized identity. In general, when an internal
lookup is performed for authentication or authorization purposes,
search-specific privileges (see the access requirements for the search
operation illustrated above) are relaxed to auth.
Access control to search entries is checked by the frontend, so it is
fully honored by all backends; for all other operations and for the
discovery phase of the search operation, full ACL semantics is only
supported by the primary backends, i.e. back-mdb(5).
Some other backend, like back-sql(5), may fully support them; others
may only support a portion of the described semantics, or even differ
in some aspects. The relevant details are described in the backend-
specific man pages.
CAVEATS
It is strongly recommended to explicitly use the most appropriate
<dnstyle> in <what> and <who> clauses, to avoid possible incorrect
specifications of the access rules as well as for performance (avoid
unnecessary 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=$2,dc=example,dc=com$$" write
by ...
However, since all that is required in the <by> clause is substring ex-
pansion, a more efficient solution is
access to dn.regex="^(.+,)?uid=([^,]+),dc=example,dc=com$"
by dn.exact,expand="uid=$2,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.
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd(8), slapd-*(5), slapacl(8), regex(7), re_format(7)
"OpenLDAP Administrator's Guide" (http://www.OpenLDAP.org/doc/admin/)
ACKNOWLEDGEMENTS
OpenLDAP Software is developed and maintained by The OpenLDAP Project
<http://www.openldap.org/>. OpenLDAP Software is derived from the Uni-
versity of Michigan LDAP 3.3 Release.
OpenLDAP 2.5.13+dfsg-5 2022/07/14 SLAPD.ACCESS(5)
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