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), and slaptest(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. If no access controls are present, the default policy allows anyone and everyone to read anything but restricts updates to rootdn. (e.g., "access to * by * read"). When dealing with an access list, because the global access list is effectively 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
being 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
clause that results in stopping the access control with no access
privileges granted. 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
applies 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
<dnpattern>; 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
(''extended'') regular expression pattern, as detailed in regex(7)
and/or re_format(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 4515. A filter of (objectClass=*) is
implied if no filter form is given.
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. If
no attrs form is given, attrs=@extensibleObject is implied, i.e. all
attributes are addressed.
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
specified. 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,
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. 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
dereferencing 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
different 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
authorization 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
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). It allows the level{<n>} style, where <n> indicates what
ancestor of the DN is to be used in matches. A positive value
indicates 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
submatches 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
children 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
pattern. So, level{1} is equivalent to onelevel, and level{0} is
equivalent to base.
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. 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
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
defaults are groupOfNames and member, respectively. 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/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
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> for IPv4, or IP=[<ipv6>]:<port> for IPv6)
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 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. 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
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 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
moduleload 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
optional <attrname> indicates what attributeType holds the ACI
information 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
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 authorized. The modifier realself refers to the
authenticated 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,
compare, search, read, write, and manage. Each access level implies
all the preceding ones, thus manage grants all access including
administrative access. The write access 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
error.
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
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 m for manage, w
for write, a for add, z for delete, r for read, s for search, c for
compare, x for authentication, and d for disclose. 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). 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
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.
One useful application is to easily grant write privileges to an
updatedn that is different from the rootdn. In this case, since the
updatedn 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
entries. The following summary applies to primary database backends
such as the BDB and HDB backends. 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,
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 delete (=z) privileges on the pseudo-
attribute 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-
attribute 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 required 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)
privileges on the attributes that are defined in the filter. The
resulting entries are finally 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 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
authzTo attribute of the authorizing identity and/or on the authzFrom
attribute 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-bdb(5), and back-hdb(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
expansion, 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 University of Michigan LDAP 3.3 Release.
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