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Internet-Draft E. Stokes
LDAP Extensions WG B. Blakley
Intended Category: Standards Track Tivoli Systems
Expires: 14 January 2001 D. Rinkevich
IBM
R. Byrne
Sun Microsystems
14 July 2000
Access Control Model for LDAPv3
<draft-ietf-ldapext-acl-model-06.txt>
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full
conformance with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet
Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working
documents as Internet-Drafts. Internet-Drafts are draft
documents valid for a maximum of six months and may be
updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be
accessed at http://www.ietf.org/shadow.html.
Comments and suggestions on this document are encouraged.
Comments on this document should be sent to the LDAPEXT
working group discussion list:
ietf-ldapext@netscape.com
COPYRIGHT NOTICE
Copyright (C) The Internet Society (2000). All Rights
Reserved.
ABSTRACT
This document describes the access control model for the
Lightweight Directory Application Protocol V3 (LDAPv3)
directory service. It includes a description of the model,
the LDAP controls, and the extended operations to the LDAP
protocol. The current LDAP APIs are sufficient for most
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access control operations. An API (in a separate document)
is needed for the extended operation getEffectiveAccess. A
separate requirements document for access control exists
[REQTS]. The access control model used the requirements
documents as a guideline for the development of this
specification and are reflected in this specification to the
extent that the working group could agree on an access
control model.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", and
"MAY" used in this document are to be interpreted as
described in [Bradner97].
1. Introduction
The ability to securely access (replicate and distribute)
directory information throughout the network is necessary
for successful deployment. LDAP's acceptance as an access
protocol for directory information is driving the need to
provide an access control model definition for LDAP
directory content among servers within an enterprise and the
Internet. Currently LDAP does not define an access control
model, but one is needed to ensure consistent secure access,
replication, and management across heterogeneous LDAP
implementations. The major objective is to provide a simple,
usable, and implementable, but secure and efficient access
control model for LDAP while also providing the appropriate
flexibility to meet the needs of both the Internet and
enterprise environments and policies. This document defines
the model and the protocol extensions (controls and extended
operations).
This draft does not (and cannot) fully specify the behavior
of the Access Control Model in a distributed environment
(e.g. propagating access control information across servers
and ACI administration) because there is no LDAP standard
defining how to distribute directory data between LDAP
servers. The behavior of the Access Control Model in
distributed environments is beyond the scope of this draft.
2. The LDAPv3 Access Control Model
Access Control mechanisms evaluate requests for access to
protected resources and make decisions about whether those
requests should be granted or denied. In order to make a
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grant/deny decision about a request for access to a
protected resource, an access control mechanism needs to
evaluate policy data. This policy data describes security-
relevant characteristics of the requesting subject and the
rules which govern the use of the target object.
No mechanism is defined in this document for storage of
access control information at the server beyond indicating
that the attribute holding access control information is an
operational attribute.
The access control mechanisms specified in this document are
neutral with respect to policy inheritance mechanisms,
explicit vs. implicit denial, and group nesting.
The access control model defines
- What flows on the wire for interoperability
The existing LDAP protocol flows for ldap operations
are used to manipulate access control information. A
set of permissions and their semantics with respect to
ldap operations is defined. The permissions parallel
the types of ldap operations defined. What is
transmitted is exactly what is read back. Encoding of
access control information on the wire is per the
LDAPv3 specifications.
There is an additional LDAP control and extended
protocol operation defined, getEffectiveRights. LDAP
clients use the control and extended operation to
manage and administer access control policy enforced by
LDAP servers.
Servers may store access control information in any way
they choose. In particular, servers may use the access
control mechanisms of their datastores to store and
enforce LDAP access control, or they may implement
access control managers external to their datastores.
Datastores and external access control managers MAY
implement any access control rule syntax and semantics
they choose, but the semantics MUST be compatible with
those defined in the section titled "Operational
Semantics of Access Control Operations".
- Attributes and classes for application portability of
access control information
An access control information attribute (ldapACI) for
application portability: This attribute is used as
input to the LDAP APIs so access control information
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can be addressed uniformly independent of how that
information is addressed and stored at the server.
This same attribute appears in LDIF output for
interchange of access control information.
An access control information subentry class
(ldapACISubEntry) and a set of attributes
(supportedAccessControlSchemes which is used in the
rootDSE and accessControlSchemes which is used in the
subentry ldapACISubEntry) to identity the access
control mechanisms supported by a server and in a given
part of the namespace, respectively.
- An attribute in the rootDSE, discloseOnError, to
control whether it is permissible for the server to
return the name of an entry or attribute in an error
(or empty set) operation result. This closes a hole on
the ability to discover information you are not
authorized to discover.
- A mechanism to control access to access control
information: The access control information attribute,
ldapACI, is used to control access to access control
information (controls access to itself). How to get an
initial ldapACI in the directory is server specific and
beyond the scope of this model.
Servers can support multiple access control mechanisms, but
MUST be capable of supporting the LDAP Mechanism in the DIT
scoped by the rootDSE (entire server's DIT) for that server
and SHOULD be capable of supporting the LDAP mechanism in an
arbitrary part (subtree) of the DIT.
The accessControlSchemes attribute in the ldapACISubEntry
indicates which access control mechanism is in effect for
the scope of that ldapACISubEntry. The
supportedAccessControlSchemes attribute in the rootDSE
indicates which acess control mechanisms are supported by
the server; those mechanisms are in effect in that server's
DIT unless overridden by a mechanism defined in a
ldapACISubEntry elsewhere in that DIT.
Changing the value(s) of either the
supportedAccessControlSchemes or accessControlSchemes
attributes changes the mechanism(s) in effect for the scope
of those attributes (where scope is either that of the
rootDSE or ldapACISubEntry).
Through the use of the mechanism rootDSE attribute and
ldapACI subentry, it is possible to run multiple mechanisms
in either the same subtree or separate subtrees. If two
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mechanisms are run in the same subtree, it is desirable that
the result be the same independent of mechanism, but
definition and discussion of this is beyond the scope of
this model.
3. Access Control Mechanism Attributes
Two attributes are defined to identify which access control
mechanisms are supported by a given server and by a given
subtree: supportedAccessControlSchemes and
accessControlSchemes. (We chose these names based on the
X.500 attribute, AccessControlScheme which is single-valued
and defined in X.501).
3.1 Root DSE Attribute for Access Control Mechanism
The server advertises which access control mechanisms it
supports by inclusion of the 'supportedAccessControlSchemes'
attribute in the root DSE. This attribute is a list of
OIDs, each of which identify an access control mechanism
supported by the server. By default, these are also the
mechanisms in effect in subtrees beneath the root in that
server unless overridden by a ldapACISubEntry (see section
"Subentry Class Access Control Mechanism").
(<OID to be assigned>
NAME 'supportedAccessControlSchemes'
DESC list of access control mechanisms supported
by this directory server
SYNTAX LDAPOID
USAGE dSAOperation
)
The access control mechanism defined is:
LDAPv3 <OID to be assigned>
Other vendor access control mechanisms MAY be defined (by
OID) and are the responsibility of those vendors to provide
the definition and OID.
3.2 Root DSE Attribute for Control of Disclosing Errors
The server specifies whether it is permissible for the name
of an entry or attribute to be disclosed in an error (or
empty) operation result. This rootDSE attribute is
discloseOnError. The default for discloseOnError is false
(0) or not to disclose on error. The lack of this attribute
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in the rootDSE is interpreted as the default.
(<OID to be assigned>
NAME 'discloseOnError'
DESC specify whether to return the name of an
entry or attribute in an error (or
empty) operation result; 0=do not
disclose (default); 1=disclose
SYNTAX LDAPString
USAGE dSAOperation
3.3 Subentry Class Access Control Mechanism
A given naming context MUST provide information about which
access control mechanisms are in effect for that portion of
the namespace. This information is contained in a subentry
(ldapACISubEntry class), derived from [SUBENTRY].
ldapACISubEntry MAY be used to define the scope of an access
control mechanism. The value(s) held in the rootDSE
attribute, supportedAccessControlSchemes, are the mechanisms
in effect in subtrees beneath the root in that server unless
overridden in a ldapACISubEntry further down the tree held
by that server. The scope of that ldapACISubEntry is to the
end of the subtree held by that server or until another
ldapACISubEntry is encountered in that subtree held by that
server. The ldapACISubEntry class is defined as:
( <OID to be assigned>
NAME 'ldapACISubEntry'
DESC 'LDAP ACI Subentry class'
SUP ldapSubEntry STRUCTURAL
MUST ( accessControlSchemes )
)
The accessControlSchemes attribute MUST be in each ldap
access control subentry entry associated with a naming
context whose access control mechanism is different from
adjacent naming contexts supported by that directory server.
accessControlSchemes lists the values (list of OIDs) that
define the access control mechanisms in effect for the scope
of that ldap access control subentry. Although, in general,
this attribute will define only a single mechanism (single
value), more than one mechanism MAY be in effect for the
scope of that subentry.
(<OID to be assigned>
NAME 'accessControlSchemes'
DESC list of access control mechanisms supported
in this subtree
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SYNTAX LDAPOID
USAGE dSAOperation
)
4. The Access Control Information Attribute (ldapACI)
The access control information attribute, ldapACI, is
defined as:
(<OID to be assigned>
NAME 'ldapACI'
DESC 'ldap access control information'
EQUALITY caseIgnoreMatch
SYNTAX directoryString
USAGE directoryOperation
)
The intent of the attribute definition is to design a common
interchange format. Any given LDAP server should be able to
translate the below defined attribute into meaningful
operation requests. Each server should be able to understand
the attribute; there should not be any ambiguity into what
any part of the syntax means.
While the end goal is to have a common behavior model
between different LDAP server implementations, the attribute
definition alone will not ensure identical ACL processing
behavior between servers. The semantics of how a server
interprets the ACI syntax are defined in the "Operational
Semantics of Access Control" section of this document.
Additionally, while the server must recognize and act on the
attribute when received over the wire, there are no
requirements for the server to physically store this
attribute.
The attribute definition maintains an assumption that the
receiving server supports inheritance within the security
model. If the server does not support inheritance, the
receiving server must expand any inherited information based
on the scope flag. If the server does not support partial
inheritance and both the entry and subtree scope are used,
then entry is the prevailing scope. (It is possible for two
values in the ldapACI attribute to have different scopes
given the syntax of ldapACI; one might contain 'entry' and
another might contain 'subtree'. This implies that some
ldapACI values inherit down the DIT and othersdo not - hence
partial inheritance of the ldapACI attribute.)
The attribute is defined so access control information (ACI)
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can be addressed in a server independent of server
implementation. This attribute is used in typical LDAP APIs
and in LDIF output of ACI. This attribute may be queried or
set on all directory objects. The BNF and definitions are
given below.
4.1 The BNF
4.1.1 ACI String Representation
Values of this syntax are encoded according to the
following BNF which follows the BNF encoding
conventions described in [ABNF]:
ldapACI = scope "#" rights "#" attr "#" subject
scope = "entry" / "subtree"
rights = (("grant:" / "deny:") permissions) /
("grant:" permissions ";deny:" permissions)
permissions = [permission *("," permission)]
permission = "a" / ; add
"d" / ; delete
"e" / ; export
"i" / ; import
"n" / ; renameDN
"b" / ; browseDN
"t" / ; returnDN
"r" / ; read
"s" / ; search
"w" / ; write (mod-add)
"o" / ; obliterate (mod-del)
"c" / ; compare
"m" / ; make
attr = "[all]" / "[entry]" / (attribute *("," attribute))
attribute = ; OID syntax (1.3.6.1.4.1.1466.115.121.1.38)
; from [ATTR]
subject = ["authnLevel:" authnLevel ":"]
(("authzID-" authzID) /
("role:" dn) /
("group:" dn) /
("subtree:" dn) /
("ipAddress:" ipAddress) /
"public:" /
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"this:")
authnLevel = "any" /
"simple" /
sasl
sasl = "sasl:"
("any" /
mechanism)
mechanism = ; sasl mechanism from 4.2 of [LDAPv3]
authzID = ; authzID from [AuthMeth] repeated below
; for convenience
authzId = dnAuthzId / uAuthzId
; distinguished-name-based authz id.
dnAuthzId = "dn:" dn
dn = utf8string ; with syntax defined in [UTF]
; unspecified userid, UTF-8 encoded.
uAuthzId = "u:" userid
userid = utf8string ; syntax unspecified
ipAddress = printableString
; dotted decimal form (e.g. 10.0.0.6)
; or use wildcards such as 12.3.45.* to
; specify a specific subnetwork
; or 123.45.6.*+255.255.255.115 to
; specify a subnetmask
; or use a wildcard domain name such as
; *.airius.com to specify a specific
; DNS domain
printableString ; printableString syntax from [ATTR]
Note that the colon following the "public" and "this"
subject options exist only to simplify string parsing.
Note also that per [AuthMeth], authzID may be expanded in
the future.
See section titled 'ACI Examples' for examples of the string
representation.
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4.1.2 ACI Binary Representation
The following ASN.1 data type is used to represent this
syntax when transferred in binary form:
ldapACI ::= SEQUENCE {
scope ENUMERATED {
entry (0),
subtree (1) },
rights SEQUENCE OF CHOICE {
grant [0] Permissions,
deny [1] Permissions },
attr CHOICE {
all [0] NULL,
entry [1] NULL,
attributes [2] SEQUENCE OF Attribute },
subject SEQUENCE {
authnLevel CHOICE {
any [0] NULL,
simple [1] NULL,
sasl [2] CHOICE {
any [0] NULL,
mechanism [1] LDAPString -- from [LDAPv3]
}
},
subject CHOICE {
dn [0] DN,
user [1] utf8String
role [1] DN,
group [2] DN,
subtree [3] DN,
ipAddress [4] IPAddress,
public [6] NULL,
this [7] NULL }, } -- may be expanded
per [AuthMeth]
Permissions ::= SEQUENCE OF ENUMERATED {
add (0),
delete (1),
export (2),
import (3),
renameDN (4),
browseDN (5),
returnDN (6),
read (7),
search (8),
write (9),
obliterate (10),
compare (11),
make (12) }
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Attribute ::= AttributeType -- from [LDAPv3]
IPAddress ::= PrintableString -- (e.g. 10.0.0.6)
4.2 The Components of ldapACI Attribute
This section defines components that comprise the access
control information attribute, ldapACI.
4.2.1 Scope
Two scopes for access control information are defined:
- entry - the access control information in the ldapACI
attribute applies only to the entry in which it is
contained
- subtree - the access control information in the ldapACI
attribute applies to each entry down the subtree unless
it is overridden by an entry-specific ldapACI whose
values are more specific.
Use of prescriptive ACIs and scoping via use of a
ldapACISubEntry is outside the scope of this document.
4.2.2 Access Rights and Permissions
Access rights can apply to an entire object or to attributes
of the object. Access can be granted or denied. Either or
both of the actions "grant" | "deny" may be used when
creating or updating ldapACI.
Each of the LDAP access permissions are discrete. One
permission does not imply another permission. The
permissions which apply to attributes and the entry parallel
the type of ldap operations that can be performed.
Permissions which apply to attributes:
r Read Read attribute values
w Write Modify-add values
o Obliterate Modify-delete values
s Search Search entries with specified attributes
c Compare Compare attributes
m Make Make attributes on a new entry below
this entry
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1. r Read
If granted, permits attributes and values to be
returned in a read or search operation.
2. w Write
If granted, permits attributes and values to be added
in a modify operation.
3. o Obliterate
If granted, permits attributes and values to be
deleted in a modify operation.
4. s Search
If granted, permits attributes and values to be
included in a search operation.
5. c Compare
If granted, permites attributes and value to be used
in a compare operation.
6. m Make
The attribute permission "m" is required for all
attributes that are placed on an object when it is
created. Just as the "w" and "o" permissions are used
in the Modify operation, the "m" permission is used in
the Add operation. Additionally, note that "w" and "o"
have no bearing on the Add operation and "m" has no
bearing on the Modify operation. Since a new object
does not yet exist, the "a" and "m" permissions needed
to create it must be granted on the new object's
parent. This differs from "w" and "o" which must be
granted on the object being modified. The "m"
permission is distinct and separate from the "w" and
"o" permissions so that there is no conflict between
the permissions needed to add new children to an entry
and the permissions needed to modify existing children
of the same entry.
Note: Modify-replace values of an attribute requires "w"
and "o" permission.
Permissions that apply to an entire entry:
a Add Add an entry below this entry
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d Delete Delete this entry
e Export Export entry & subordinates to new
location
i Import Import entry & subordinates from some
location
n RenameDN Rename an entry's DN
b BrowseDN Browse an entry's DN
t ReturnDN Allows DN of entry to be disclosed in
an operation result
1. a Add
If granted, permits creation of an entry in the DIT
subject to control on all attributes and values to be
placed in the new entry at time of creation. In order
to add an entry, permission must also be granted to
add at least the mandatory attributes.
2. d Delete
If granted, permits the entry to be removed from the
DIT regardless of controls on attributes within the
entry.
3. e Export
If granted, permits an entry and its subordinates (if
any) to be exported; that is, removed from the current
location and placed in a new location subject to the
granting of suitable permission at the destination.
If the last RDN is changed, Rename is also required at
the current location. In order to export an entry or
its subordinates, there are no prerequisite
permissions to contained attributed, including the RDN
attributes; this is true even when the operation
causes new attribute values to be added or removed as
the result of the changes of RDN.
4. i Import
If granted, permits an entry and its suordinates (if
any) to be imported; that is, removed from some other
location and placed a t the location to which the
permission applies subject to the granting of suitable
permissions at the source location. In order to
import an entry or its subordinates, there are no
prerequisite permissions to contained attributed,
including the RDN attributes; this is true even when
the operation causes new attribute values to be added
or removed as the result of the changes of RDN.
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5. n RenameDN
Granting Rename is necessary for an entry to be
renamed with a new RDN, taking into account
consequential changes to the distinguished names of
subordinate entries, if any; if the name of the
superior is unchanged, the grant is sufficient. In
order to rename an entry, there are no prerequisite
permissions to contained attributed, including the RDN
attributes; this is true even when the operation
causes new attribute values to be added or removed as
the result of the changes of RDN.
6. b BrowseDN
If granted, permits entries to be accessed using
directory operations which do not explicitly provide
the name of the entry.
7. t ReturnDN
If granted, allows the distinguished name of the entry
to be disclosed in the operation result.
All permissions (for grant and deny) for an attribute/entry
and a given subject MUST be contained within one ldapACI
value, i.e. (in abbreviated form)
ldapACI: ...grant OID.attr1 subjectA
ldapACI: ...deny OID.attr1 subjectA
must be ldapACI: ...grant ... deny... OID.attr1 subjectA
Using the defined BNF it is possible for the permission
string to be empty. The ACI
ldapACI: subtree#grant#OID.attr1#group:cn=Dept XYZ,c=US
ldapACI: subtree#grant:r,s#[all]#group:cn=Dept XYZ,c=US
means that this group (Dept XYZ) is granted permission to
read and search all attributes except OID.attr1 because
OID.attr1 is more specific than "[all]".
4.2.3 Attributes
Attribute describes an attribute name in the form of a
dotted decimal OID for that <attr>. If the string (OID)
refers to an attribute not defined in the given server's
schema, the server SHOULD report an error. "[entry]" means
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the permissions apply to the entire object. This could mean
actions such as delete the object, or add a child object.
"[all]" means the permission set apply to all attributes of
the entry.
If the keyword "[all]" and another attribute are both
specified within an ACI, the more specific permission set
for the attribute overrides the less specific permission set
for "[all]".
4.2.4 Subjects and Associated Authentication
The following subjects are defined and MUST be supported:
- authzID, defined per [authmeth]
- group, defined as the distinguished name of a
groupOfNames or groupOfUniqueNames entry
- role
- subtree, defined as the distinguished name of a non-
leaf node in the DIT
- ipAddress,
- public, defined as public access
- this, defined as the user whose name matches that of
the entry being accessed
Other parties MAY define other subjects. It is the
responsibility of those parties to provide the definition.
A subject may be qualified by the type of authentication
required for access to a given attribute(s) or entry. If no
authnLevel is present, then no specific type of
authentication is additionally required for access. If
authnLevel is specified, then that type of authentication is
additionally required for access. The authnLevels parallel
the authentication mechanisms specified for LDAPv3: simple,
SASL (any type of SASL mechanism), and a SASL-specific
mechanism. The authnLevel of is not an acceptable mechanism
for this case) as part of obtaining access.
4.3 Grant/Deny Evaluation Rules
The decision whether to grant or deny a client access to a
particular piece of information is based on several pieces
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of information found within the ldapaci value. Throughout
the decision making process, there are guiding principals.
- Specificity: More specific policies MUST override less
specific ones (e.g. individual user entry in ACI takes
precedence over group entry).
- Deny takes precedence over Grant.
- When there are conflicting ACI values, deny takes
precedence over grant.
- Deny is the default when there is no access control
information.
Precendence of Scope Types (highest to lowest)
- entry
- subtree
Precedence of Subjects within a Scope (highest to lowest):
- ipAddress
- authzID, this
- group, role, this, public
- subtree, public
Although other types MAY be defined given the BNF, use of
the well-known types aids in interoperability and
operational consistency.
Access Decision algorithm:
1. Determine all the ldapACI values which could apply to
the target DN which is being accessed. This is the DN
of the entry which is being queried in a search,
modified, deleted, etc. When determining all the
ldapACI values, the scope field should be used. All
ldapACI values with a scope of 'entry' take precedence
over ldapACI values with a scope of 'subtree'.
2. Determine which ldapACI (of the set determined in step
1) apply to the bound DN. This is determined by
looking at the subject (combination of subject type
and subject value) and bind type. If no bind is in
effect (this is possible in ldapv3), then treat this
lack of bind as if bound as anonymous. Start with the
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most specific subject type. If at any time, at least
one ldapACI value exists for a specificity level, then
processing stops; the exception here is 'this' because
this may also be combined with group to use power of
'this'. Evaluation should take place on set of
ldapACI values which are all of the same specificity
level. Subjects of the same precedence are combined
using union semantics.
3. Evaluate the remaining ldapACI values and determine a
grant/deny decision. If conflicting ldapACI value
exists for the same attribute, or attributes (i.e. one
ldapACI grants permission and another denies
permission), then deny takes precedence over grant.
For example, if one is granted permission to
"objectclass" in one ldapACI value by being a member
of group cn=Admin, and denied permission by being a
member of cn = NontrustedAdmins, then the bound user
would not receive permission to objectclass.
The rule of specificity also applies to the
attributes. If one is denied permission to "[ all ]"
attributes, but granted permission to "objectclass"
then the more specific value of "objectclass" takes
precedence over the less specific value of "[ all ] ".
In this case the user would be granted permission to
"objectclass" but denied permission to all other
attributes.
5. Required Permissions for each LDAP Operation
This section defines the required permissions for each LDAP
operation but even if these requirements are satisfied the
server MAY refuse to carry out the operation due to other
implementation specific security considerations. For
example, a server may refuse to modify an entry because the
database where that entry resides is in read only mode.
Another example might be that although the access control is
available to the userPassword attribute a server may refuse
modifications due to some server specific policy governing
access to passwords.
Here, we specify the rights required by a user when
performing an LDAP operation in terms of the LDAP
permissions specified in section 6.1. Recall that "a, d,
e, i, n, b,t" are permissions that apply to entries as a
whole while permissions "r, s, w, o, c, m" apply to
attributes within entries.
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Required permissions for LDAP extended operations and LDAP
controls are beyond the scope of this draft.
There is a requirement that a user should not be able to
infer the existence of data in the Directory, if the user
does not have the required access rights to that data. An
example of this requirement would be in a hosting
environment where you would not want any users from the coke
subtree to be able to even discover that the pepsi tree was
hosted on the same server. This "discloseOnError" feature
will be set once for server in the rootDSE advertised by the
attribute discloseOnError. The default for discloseOnError
is false (0). The lack of this attribute in the rootDSE is
interpreted as the default. The details of its effects are
addressed below, operation by operation.
For the following, assume that the authorization identity of
the user doing the operation is authzID.
5.1 Bind Operation
This draft does not require any permissions to allow a bind
operation to proceed.
5.2 Search Operation
Recall that the parameters of the Search operation per RFC
2251 [LDAPv3] Section 4.5 are:
SearchRequest ::= [APPLICATION 3] SEQUENCE {
baseObject LDAPDN,
scope ENUMERATED {
baseObject (0),
singleLevel (1),
wholeSubtree (2) },
derefAliases ENUMERATED {
neverDerefAliases (0),
derefInSearching (1),
derefFindingBaseObj (2),
derefAlways (3) },
sizeLimit INTEGER (0 .. maxInt),
timeLimit INTEGER (0 .. maxInt),
typesOnly BOOLEAN,
filter Filter,
attributes AttributeDescriptionList }
Suppose a server is processing a search request from user
authzID with parameters as above and is processing the entry
with dn candidateDN to decide if it may be returned or not.
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Then the permissions required by authzID that need to be
evaluated are as follows:
1. permission "b" to the entry candidateDN
If this permission is not granted then the dn
candidateDN MUST not be returned nor any attribute
type nor attribute value from this entry.
If this permission is granted then the dn candidateDN
MAY be returned.
Note: The idea of the "b" permission is to say "a user
has discovery rights" at a certain entry in the
directory. Assuming that the further required
permissions below are satisfied then having "b" right
is enough to allow the server to return candidateDN.
Of course candidateDN contains in it's components,
attributes and attribute values for all the ancestors
of candidateDN. This can lead to the slightly odd
situation that we can discover the naming attribute of
an entry and that attribute's value by virtue of
having the required searching permissions to it's
child but not by searching the entry directly.
2. permission "s" to each attribute appearing in a
presence test during the evaluation of the search
filter. permission "r" to each attribute appearing in
non-presence tests (see rfc1960, section 3:
equalityMatch, substrings, greaterOrEquial,
lessOrEqual, present, approxMatch, extensibleMatch)
during the evaluation of the search filter.
The above statement covers the case where the
attributes are being evaluated as part of an
extensibleMatch (RFC 2251 section 4.5.1) which appears
in the filter. In the case where the dnAttributes
field of the extensibleMatch is true then we do not
require any access checks to the attributes of the dn
candidateDN as access to these is taken to be granted
by the "b" permission, which has already been required
above.
If there is an attribute in a filter element to which
the required permission is not granted then that
filter element evaluates to "Undefined" of the three-
valued-logic of X.511(93).
Note A: Although both "r" and "s" permissions will
typically be granted to attributes we keep both
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permissions as there are cases where the distinction
is useful. For example, the ability to grant the
right to discover that a user entry contains a
userPassword attribute, but not to read it's value
("s" but not "r"). The converse, granting "r" but not
"s" permission is less easy to motivate.
Note B: There is an unusual behaviour with respect to
naming attributes illustrated in the following
example:
Suppose I have "b" rights to cn=fred,o=sun.com and "r"
rights to attribute objectclass but not "r" rights to
cn then with search filter (objectclass=*) I get back
the dn and objectclass (and so can see the value of
cn), but with a search filter of (cn=fred) I do not
get anything.
3. permission "r" to each attribute in the attribute list
AttributeDescriptionList (or all attributes in the
entry candidateDN if AttributeDescriptionList is *)
whose type and/or value will be returned.
Note: The presence of an attribute in an entry is only
ever volunteered by the server if "r" permission is
granted to it, though a user may infer the presence of
an attribute with "s" permission by using a presence
test on that attribute in the search filter.
4. permission "t" to the entry candidateDN
If this permission is not granted then the dn
candidateDN MUST NOT be returned. If the server knows
of an alias for the entry, this alias may be returned
instead. If no alias name is available then the entry
candidateDN MUST be omitted from the search results.
5. Disclose on error for the Search operation
If every entry in the scope of the search fails to
satisfy item 1 (browse right on the candidate entry)
or item 2 (right to use the filter on that entry) and
if discloseOnError is not granted to the baseObject
entry then the operation MUST fail with a "no such
object error" and the matchedDN of the LDAPResult MUST
be set to "". If every entry in the scope of the
search fails to satisfy items 1 or 2 above and
discloseOnError is granted to the baseObject then the
empty set of results is returned.
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5.3 Modify Operation
Recall that the parameters of the Modify operation per
RFC2251 [LDAPv3] Section 4.6 are:
ModifyRequest ::= [APPLICATION 6] SEQUENCE {
object LDAPDN,
modification SEQUENCE OF SEQUENCE {
operation ENUMERATED {
add (0),
delete (1),
replace (2) },
modification AttributeTypeAndValues } }
AttributeTypeAndValues ::= SEQUENCE {
type AttributeDescription,
vals SET OF AttributeValue }
Then the permissions required by authzID that need to be
evaluated are as follows:
1. permission "w" to each attribute being added to object
If this permission is not granted to such an
attribute, then the operation MUST fail. In this
case, if discloseOnError is not granted to the entry
then "no such object" error is returned; if
discloseOnError is granted to the entry and a
duplicate attribute value is being added then
"attribute value already exists" error is returned; if
discloseOnError is granted to the entry and no
duplicate value is being added then an "insufficient
access" error is returned.
2. permission "o" to each attribute for which a value is
being deleted from object
If this permission is not granted to such an attribute
then the operation MUST fail. In this case, if
discloseOnError is not granted to the entry then "no
such object" error is returned; if discloseOnError is
granted to the entry and the attribute or one of the
values to be deleted does not exist then a "no such
attribute or value" error is returned; if
discloseOnError is granted to the entry and the
attribute and all values specified to be deleted exist
then an "insufficient access" error is returned.
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3. permissions "o" and "w" to each attribute being
replaced in object
If one of these these permissions is not granted to
such an attribute then the operation MUST fail. In
this case, if discloseOnError is not granted to the
entry then a "no such object" error is returned; if
discloseOnError is granted to the entry then
"insufficient access" error is returned.
5.4 Add Operation
Recall that the parameters of the Add operation per RFC2251
[LDAPv3] Section 4.7 are:
AddRequest ::= [APPLICATION 8] SEQUENCE {
entry LDAPDN,
attributes AttributeList }
AttributeList ::= SEQUENCE OF SEQUENCE {
type AttributeDescription,
vals SET OF AttributeValue }
Then the permissions required by authzID that need to be
evaluated are as follows:
permission "a" to the parent of entry
The access rights required for the creation of a root
entry in the Directory are beyond the scope of this
document. They will be vendor specific.
1. permission "m" to the parent of entry for each
attribute being added to entry
If any of these permissions are not granted then the
operation MUST fail. In this case if discloseOnError is on
and the entry to be added does not already exist then
"insufficient access" is returned. If it does exist then
"Entry already exists" is returned. If discloseOnError is
off then "No such object" is returned (meaning the parent
object).
If they are all granted then the operation MAY proceed.
Note: We require "m" permission to each attribute to prevent
an entry from aquiring "unintended" rights (via group or
role membership), to stop a "rogue" ACI being added that
would prevent even admins deleting the entry and general
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consistency with the MODIFY operation.
Note: The access rights required for the creation of the
first entry in the directory are beyond the scope of this
document.
5.5 Delete Operation
Recall that the parameters of the Delete operation per
RFC2251 [LDAPv3] Section 4.10 are:
DelRequest ::= [APPLICATION 10] LDAPDN
Then the permissions required by authzID that need to be
evaluated are as follows:
1. permission "d" to the entry in the Delete request
If this permission is not granted, then the operation MUST
fail. In this case if discloseOnError is on and the entry
to be deleted exists then "insufficient access" is returned.
If it does not exist then "No such Object" is returned. If
discloseOnError is off then "No such object" is returned
(meaning the parent object).
If this permission is granted, then the operation MAY
proceed.
Note: One could also require the "o" permission to be
granted to allow the operation to proceed, but customer
experience has shown that the requirement of the additional
permission is not useful nor expected, and X.500 requires
only the "d" permission.
5.6 Modify DN Operation
Recall that the parameters of the Modify DN operation per
RFC2251 [LDAPv3] Section 4.6 are:
ModifyDNRequest ::= [APPLICATION 12] SEQUENCE {
entry LDAPDN,
newrdn RelativeLDAPDN,
deleteoldrdn BOOLEAN,
newSuperior [0] LDAPDN OPTIONAL }
Then the permissions required by authzID that need to be
evaluated are as follows:
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1. If newSuperior is not present (ie. only the RDN is
being renamed) then permission "n" to entry is
required.
2. If newSuperior is present then permission "e" to entry
and permission "i" to newSuperior are required.
If any of these permissions are not granted then the
operation MUST fail. In this case, if discloseOnError is on
then an "insufficient access error" is returned. Otherwise,
"No such object" is returned.
If they are all granted then the operation MAY proceed.
Note A: We do not require any additional permissions in the
case where deleteoldrdn is TRUE.
Note B: These permissions allow the naming attribute of an
entry (or entries) to be changed even though "o" and "w"
permissions are not available on the entry. Distinguishing
the permissions like this allows us to grant permissions for
the ModifyDN operation, but not the Modify operation and
vice versa.
5.7 Compare Operation
Recall that the parameters of the Compare operation per
RFC2251 [LDAPv3] Section 4.10 are:
CompareRequest ::= [APPLICATION 14] SEQUENCE {
entry LDAPDN,
ava AttributeValueAssertion }
Then the permissions required by authzID that need to be
evaluated are as follows:
1. permission "c" to the attribute in entry on which the
comparison is being made.
If any of these permissions are not granted then the
operation MUST fail. In this case, if discloseOnError is on
then an "insufficient access error" is returned. Otherwise,
"No such object" is returned.
If they are all granted then the operation MAY proceed.
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5.8 Abandon Operation
Recall that the parameters of the Abandon operation per
RFC2251 [LDAPv3] Section 4.6 are:
AbandonRequest ::= [APPLICATION 16] MessageID
authzID always has the right to send an Abandon Operation
for an operation he previously initiated.
5.9 Extended Operation
Recall that the parameters of the Extended operation per
RFC2251 [LDA{v3] Section 4.12 are:
ExtendedRequest ::= [APPLICATION 23] SEQUENCE {
requestName [0] LDAPOID,
requestValue [1] OCTET STRING OPTIONAL }
The access required for an Extended Operation is beyond the
scope of this document. The required access will normally
be defined by the implementor of the extended request.
6. Required Permissions for Handling Aliases and References
Use of aliases and referrals are part of LDAPv3. However,
neither is particularly well-defined. Alias
objects/attributes are defined in RFC 2256 as derived from
X.500, but LDAPv3 does not explicitly define its semantics
or behavior. X.500 does define alias semantics and behavior
with respect to access control; we define its behavior in
LDAPv3 based on the X.511, section 7.11.1. Referrals and
knowledge information are still under design in LDAPv3; they
are defined in X.500, however, X.500 punts on their
semantics and behavior with respect to access control. We
define their semantics and behavior in LDAPv3 in terms that
should be independent of the future LDAPv3 definition of
referrals and knowledge information.
6.1 ACI Distribution
Currently there is no LDAP standard defining how to
distribute directory data between LDAP servers. Consequently
this draft cannot fully specify the behavior of the Access
Control Model in a distributed environment. The case of
distribution via referrals is treated in the "Referrals"
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section below. In the case of chaining (where one LDAP
server forwards a request to another on behalf of a client)
then it is server specific how the access control model
behaves in this environment. Similarly it is server specific
how the server determines whether the chaining of an
operation is permitted in the first place. For example, the
implementation may choose to regard the local naming context
and the remote subordinate naming context as seperate Access
Control Specific Areas, or it may regard the DIT as one
Access Control Specific Area and implement mechanisms to
propagate access control information between the two
servers. The behavior of the Access Control Model in
distributed environments such as these is beyond the scope
of this draft.
6.2 Aliases
There are two things to protect with respect to aliases:
the real name of the aliased object and the location of the
server holding it.
If alias de-referencing is required in the process of
locating a target entry, no specifc permissions are
necessary for alias de-referencing to take place. Access
control is enforced at the object pointed to by the alias.
If alias de-referencing would result in a
continuationReference (e.g. from a search operation), then
browse permission is required to the alias entry and read
permission is required to the 'aliasedObjectName' attribute.
Requiring these permission closes the hole of discovery.
6.3 Referrals
If a referral is to be followed, no specifc permissions are
necessary for the ldap client to follow the referral. Access
control is enforced at the referenced object. If a referral
is returned, then browse is required on the entry and read
permission is required to the attribute containing the
referral (we cannot name this attribute exactly today
because there are no RFCs on this - only drafts). If the
server implements a default referral, then no special
permissions are required to read and return that referral.
Requiring these permissions closes the hole of discovery.
In the default case, it is assumed that a default referral
is public.
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7. Controlling Access to Access Control Information
The ldapACI attribute is used to specify control for who has
permission to set/change access control information
(ldapACI). The ldapACI attribute/OID is just another
attribute described with a scope, set of rights and
permissions, and subject as a value of the ldapACI
attribute. (See the example in the "ACI Examples" section).
If the policy for controlling the ldapACI attribute is not
specified for any object in the tree, behavior is
implementation defined. For instance, if no object anywhere
in the tree defines the access for ldapACI within the
ldapACI attribute, then the server could simply assert that
the 'root DN' is considered the policy owner (controller for
controlling access control) for all objects.
8. ACI Examples
Note that in the examples, the form "OID.<attrname>" refers
to the OID in dotted decimal form for the attribute
<attrname>. This shorthand notation is used only for the
examples. In implementation, the dotted decimal form of the
OID is used.
8.1 Attribute Definition
The following examples show the access required to control
access to the ldapACI attribute. The first example shows
controlling the access control on an individual entry and
its attributes. The second example shows controlling the
access control on a subtree.
ldapACI: entry#grant:r,w#
OID.ldapACI#authnLevel:any:role:cn=aciAdmin
ldapACI: subtree#grant:r,w#
OID.ldapACI#authnLevel:any:role:cn=aciAdmin
The next example shows a ldapACI attribute where a group
"cn=Dept XYZ, c=US" is being given permissions to read,
search, and compare attribute attr1. The permission applies
to the entire subtree below the node containing this ACI.
Authentication of a specified type is not required.
ldapACI:subtree#grant;r,s,c#
OID.attr1#group:cn=Dept XYZ,c=US
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The next example shows an ACI attribute where a role
"cn=SysAdmins,o=Company" is being given permissions to add
objects below this node and read, search, and compare
attributes attr2 and attr3. The permission applies to the
entire subtree below the node containing this ACI.
ldapACI: subtree#grant:a#
[entry]#role:cn=SysAdmins,o=Company
ldapACI: subtree#grant:r,s,c#
OID.attr2#role:cn=SysAdmins,o=Company
ldapACI: subtree#grant:r,s,c#
OID.attr3#role:cn=SysAdmins,o=Company
8.2 Modifying the ldapACI Values
Modify-Replace works as defined in the ldap operation
modify. If the attribute value does not exist, create the
value. If the attribute does exist, replace the value. If
the ldapACI value is replaced, all ldapACI values are
replaced.
A given ldapACI for an entry:
ldapACI: subtree#deny:r,w#[all]#group:cn=Dept ABC
ldapACI: subtree#grant:r#OID.attr1#group:cn=Dept XYZ
perform the following change:
dn: cn=someEntry
changetype: modify
replace: ldapACI
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept LMN
The resulting ACI is:
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept LMN
( ldapACI values for Dept XYZ and ABC are lost through the
replace )
During an ldapmodify-add, if the ACI does not exist, the
create the ACI with the specific ldapACI value(s). If the
ACI does exist, then add the specified values to the given
ldapACI. For example a given ACI:
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept XYZ
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with a modification:
dn: cn=someEntry
changetype: modify
add: ldapACI
ldapACI: subtree#grant:r#OID.attr1#group:cn=Dept XYZ
would yield an multi-valued ACI of:
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept XYZ
ldapACI: subtree#grant:r#OID.attr1#group:cn=Dept XYZ
To delete a particular ACI value, use the regular ldapmodify
- delete syntax
Given an ACI of:
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept XYZ
ldapACI: subtree#grant:r#OID.attr1#group:cn=Dept XYZ
dn: cn = some Entry
changetype: modify
delete: ldapACI
ldapACI: subtree#grant:r#OID.attr1#group:cn=Dept XYZ
would yield a remaining ACI on the server of
ldapACI: subtree#grant:r,w#[all]#group:cn=Dept XYZ
The attributes which are defined for access control
interchange may be used in all LDAP operations.
Within the ldapmodify-delete operation, the entire acl may
be deleted by specifying
dn: cn = some Entry
changetype: modify
delete: ldapACI
In this case, the entry would then inherit its ACI from some
other node in the tree depending on the server inheritance
model.
Similarly, if all values of ldapACI are deleted, then the
access control information for that entry is defined by that
implementation's inheritance model.
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8.3 Evaluation
These examples assume that the ldapACI entries listed in
each example are the only ACI which applies to the entry in
question; if backing-store ACI also exists, the effective
policy may be different from that listed in each example.
See section 10 for a discussion of the semantics of ldapACI
entries when backing-store ACI administration is also used.
Assume cn=jsmith is a member of group cn=G1. Assume
cn=jsmith is a member of group cn=G2.
Example #1
dn: o=XYZ, c=US
ldapACI: subtree#grant:r#attr1
#authzID-dn:cn=jsmith,ou=ABC,o=XYZ,c=US
ldapACI: subtree#grant:w#attr1
#group:cn=G1,ou=ABC,o=XYZ,c=US
What rights does cn=jsmith have to attr1 of o=XYZ,c=US?
Read (r) access; authzID is higher precedence than
group.
Example #2
dn: o=XYZ, c=US
ldapACI: subtree#grant:r#attr2
#group:cn=G1,ou=ABC,o=XYZ,c=US
ldapACI: subtree#grant:w#attr2
#group:cn=G2,ou=ABC,o=XYZ,c=US
What rights does cn=jsmith have to attr2 of o=XYZ,c=US?
Read-write (r,w) access; ACI is combined because both
subjects (group) have same precedence.
Example #3
dn: o=XYZ, c=US
ldapACI: subtree#grant:r,w#attr3
#group:cn=G1,ou=ABC,o=XYZ,c=US
ldapACI: subtree#deny:w#attr3#group:cn=G2,ou=ABC,o=XYZ,c=US
What rights does cn=jsmith have to attr3 of o=XYZ, c=US?
Read access; write is denied (deny has precedence over
grant).
Example #4
dn: o=XYZ, c=US
ldapACI: subtree#grant:w#attr4
#authzID-dn:cn=jsmith,ou=ABC,o=XYZ,c=US
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ldapACI: subtree#grant:r#attr4#subtree:ou=ABC,ou=XYZ,c=US
What rights does cn=jsmith have to attr4 of o=XYZ, c=US?
Write (w); rights given to an authzID take precedence
over those given to a subtree.
Example #5
dn: o=XYZ, c=US
ldapACI: subtree#grant:m#OID.attr5
#authzID-dn:cn=jsmith,o=ABC,c=US
ldapACI: subtree#grant:m#OID.cn
#authzID-dn:cn=jsmith,o=ABC,c=US
ldapACI: subtree#grant:m#OID.sn
#authzID-dn:cn=jsmith,o=ABC,c=US
ldapACI: subtree#grant:a#[entry]
#authzID-dn:#cn=jsmith,o=ABC,c=US
What rights does cn=jsmith have to o=XYZ, c=US?
Make(m) on attributes attr5, cn, and sn and Add(a)
on the entry. These are the minimal yet sufficient
permissions to create a new object,
cn=New, o=XYZ, c=US with values for the attr5, cn,
and sn attributes. This example illustrates how the
"m" permission can be used to limit the attributes
that can be created on a new entry.
Example #6
dn: c=US
ldapACI: subtree#grant:m#[all]#subtree:c=US
dn: o=XYZ, c=US
ldapACI: subtree#grant:a#[entry]#
authzID-dn:cn=jsmith,o=ABC,c=US
What rights does cn=jsmith have to o=XYZ, c=US?
Make(m) on attributes all attributes and Add(a) on the
entry. These are sufficient permissions to create a new
object, cn=New, o=XYZ, c=US with values any desired
attributes. For administrators who do not wish to limit
the attributes that can be created on new entries, this
example shows how a single ldapACI at the top of the
domain solves the problem.
9. Operational Semantics of Access Control Operations
The semantics of access control operations described in this
document are defined operationally in terms of "histories".
A history is a sequence of actions (x1, x2, ..., xN).
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9.1 Types of actions
We consider five types of actions:
- LDAP Access Control Policy Update actions: invocations
of ldap modify when used to add, delete, or replace the
aci attribute; invocations of ldap add when used to add
an entry with an aci attribute. A LDAP Access Control
Policy Update action may replace the policy (by
completely replacing the aci attribute with new policy
information) or it may grant or deny specific rights
while leaving others unaffected.
- LDAP Access Control Policy Query operations:
invocations of ldap search when used to retrieve the
aci attribute; invocations of ldap search with the
getEffectiveRightsRequest control; invocations of the
ldapGetEffectiveRightsRequest extended operation.
- Datastore Access Control Policy Update Actions: any
operation implemented by the server which LDAP is using
as its datastore which changes the access policy
enforced with respect to attempts to access LDAP
directory entries and their attributes.
- LDAP Access Request operations: invocations of LDAP
entry or attribute access operations (Read, Update,
Search, Compare, etc...).
- Other operations: anything else, including Datastore
operations which do not change the access policy
enforced by the server.
9.2 Semantics of Histories
The semantics of histories are defined as follows:
- LDAP Update (Replace), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted by
the Update operation, depending on the policy in force
before the Update operation.
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- LDAP Update (Deny), LDAP Query
The Query will show that the subject does not have any
right denied by the Update operation. The Query may
show that the subject has rights not denied by the
Update operation, depending on the policy in force
before the Update operation.
- LDAP Update (Replace), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail if it requires any
right not granted by the Update operation.
- LDAP Update (Grant), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation, depending
on the policy in force before the Update operation.
- LDAP Update (Deny), LDAP Access Request
The Request will fail if it requires any right denied
to the requesting subject by the Update operation. If
the Request requires only rights which were not denied
by the Update operation, it may succeed, depending on
the policy in force before the Update operation.
- LDAP Update (Replace), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted by
the Update operation, depending on the policy in force
before the Update operation.
- LDAP Update (Deny), Other, LDAP Query
The Query will show that the subject does not have any
right denied by the Update operation. The Query may
show that the subject has rights not denied by the
Update operation, depending on the policy in force
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before the Update operation.
- LDAP Update (Replace), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail if it requires any
right not granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation, depending
on the policy in force before the Update operation.
- LDAP Update (Deny), Other, LDAP Access Request
The Request will fail if it requires any right denied
to the requesting subject by the Update operation. If
the Request requires only rights which were not denied
by the Update operation, it may succeed, depending on
the policy in force before the Update operation.
- LDAP Update (Replace), Datastore Policy Update, LDAP
Query
The result of the Query is not defined.
- LDAP Update (Grant), Datastore Policy Update, LDAP
Query
The result of the Query is not defined.
- LDAP Update (Deny), Datastore Policy Update, LDAP Query
The result of the Query is not defined.
- LDAP Update (Replace), Datastore Policy Update, LDAP
Access Request
The result of the Access Request is not defined.
- LDAP Update (Grant), Datastore Policy Update, LDAP
Access Request
The result of the Access Request is not defined.
- LDAP Update (Deny), Datastore Policy Update, LDAP
Access Request
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The result of the Access Request is not defined.
10. Access Control Parameters for LDAP Controls & Extended
Operations
This section defines the parameters used in the access
control LDAP controls and extended operations in this
document.
targetDN specifies the initial directory entry in DN syntax
on which the control or extended operation is performed.
whichObject specifies whether the access control information
(in the get effective rights control) which is retrieved is
for the target directory entry (ENTRY) or the target
directory entry and its subtree (SUBTREE).
rights in the get effective rights control or extended
operation response is of the form specified in the BNF for
<rights>.
subject is a LDAP string that defines the subject. Access
control is get/set on a subject. The syntax of the subject
is the same as the subject field in the BNF.
11. Access Control Information (ACI) Controls
The access control information controls provide a way to
manipulate access control information in conjunction with a
LDAP operation. One LDAP control is defined. This control
allows access control information to be retrieved while
manipulating other directory information for that entry.
The control is:
- getEffectiveRights to obtain the effective rights for a
given directory entry(s) for a given subject during a
ldap_search operation
11.1 getEffectiveRights Control
11.1.1 Request Control
This control may only be included in the ldap_search
message as part of the controls field of the
LDAPMessage, as defined in Section 4.1.12 of [LDAPv3].
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The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
getEffectiveRightsRequest ::= SEQUENCE {
effectiveRightsRequest SEQUENCE OF SEQUENCE {
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subject <see <subject > in BNF> | "*"
}
}
The effectiveRightsRequest is a set of sequences that state
the whichObject (entry or entry plus subtree) and specifics
of the control request to be performed. A "*" in the subject
field specifies that all DN types are to be used in
returning the effective rights. This control is applied to
the filter and scope set by the ldap_search operation, i.e.
base, one-level, subtree. So the attributes/values returned
are defined by the ldap_search operation.
11.1.2 Response Control
This control is included in the ldap_search_response message
as part of the controls field of the LDAPMessage, as defined
in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. There is no
need to set the criticality on the response. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
getEffectiveRightsResponse ::= {
result ENUMERATED {
success (0),
operationsError (1),
unavailableCriticalExtension (12),
noSuchAttribute (16),
undefinedAttributeType (17),
invalidAttributeSyntax (21),
insufficientRights (50),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
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The effective rights returned are returned with each entry
returned by the search result. The control response for
ldap_search is:
PartialEffectiveRightsList ::= SEQUENCE OF SEQUENCE {
rights <see <rights> in BNF>,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subject < see <subject> in BNF >
}
Although this extends the search operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control, hence the above structure cannot be returned to a
LDAPv2 client. A LDAPv3 client cannot send this request to
a LDAPv2 server. A LDAPv3 server not supporting this
control cannot return the additional data.
11.1.3 Client-Server Interaction
The getEffectiveRightsRequest control requests the rights
that MUST be in effect for requested directory
entry/attribute based on the subject DN. The server that
consumes the search operation looks up the rights for the
returned directory information based on the subject DN and
returns that rights information.
There are six possible scenarios that may occur as a result
of the getEffectiveRights control being included on the
search request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
unavailableCriticalExtension as a return code in the
searchResponse message and not send back any other
results. This behavior is specified in section 4.1.12
of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's criticality
field, then the server MUST ignore the control and
process the request as if it were not present. This
behavior is specified in section 4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified family and the
client specified TRUE for the control's criticality
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field, then the server SHOULD do the following: return
unavailableCriticalExtension as a return code in the
searchResult message.
4. If the server supports this control but for some
reason such as cannot process specified family and the
client specified FALSE for the control's criticality
field, then the server should process as 'no rights
returned for that family' and include the result
Unavailable in the getEffectiveRightsResponse control
in the searchResult message.
5. If the server supports this control and can return the
rights per the family information, then it should
include the getEffectiveRightsResponse control in the
searchResult message with a result of success.
6. If the search request failed for any other reason,
then the server SHOULD omit the
getEffectiveRightsResponse control from the
searchResult message.
The client application is assured that the correct rights
are returned for scope of the search operation if and only
if the getEffectiveRightsResponse control returns the
rights. If the server omits the getEffectiveRightsResponse
control from the searchResult message, the client SHOULD
assume that the control was ignored by the server.
The getEffectiveRightsResponse control, if included by the
server in the searchResponse message, should have the
getEffectiveRightsResult set to either success if the rights
are returned or set to the appropriate error code as to why
the rights could not be returned.
The server may not be able to return a right because it may
not exist in that directory object's attribute; in this
case, the rights request is ignored with success.
12. Access Control Extended Operation
An extended operation, get effective rights, is defined to
obtain the effective rights for a given directory entry for
a given subject. This operation may help with the
management of access control information independent of
manipulating other directory information.
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12.1 LDAP Get Effective Rights Operation
ldapGetEffectiveRightsRequest ::= [APPLICATION 23] SEQUENCE
{
requestName [0] <OID to be assigned>,
requestValue [1] OCTET STRING OPTIONAL }
where
requestValue ::= SEQUENCE {
targetDN LDAPDN,
updates SEQUENCE OF SEQUENCE {
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
attr SEQUENCE {
attr <see <attr> in BNF >
},
subject < see <subject> in BNF > | "*"
}
}
The requestName is a dotted-decimal representation of the
OBJECT IDENTIFIER corresponding to the request. The
requestValue is information in a form defined by that
request, encapsulated inside an OCTET STRING.
The server will respond to this with an LDAPMessage
containing the ExtendedResponse which is a rights list.
ldapGetEffectiveRightsResponse ::= [APPLICATION 24] SEQUENCE
{
COMPONENTS OF LDAPResult,
responseName [10] <OID to be assigned> OPTIONAL,
effectiveRights [11] OCTET STRING OPTIONAL }
where
effectiveRights ::= SEQUENCE OF SEQUENCE {
rights <see <rights> in BNF>,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subject < see <subject> in BNF >
}
If the server does not recognize the request name, it MUST
return only the response fields from LDAPResult, containing
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the protocolError result code.
13. Security Considerations
This document proposes protocol elements for transmission of
security policy information. Security considerations are
discussed throughout this draft. Because subject security
attribute information is used to evaluate decision requests,
it is security-sensitive information and must be protected
against unauthorized modification whenever it is stored or
transmitted.
Interaction of access control with other directory functions
(other than the ones defined in this document) are not
defined in this document, but instead in the documents where
those directory functions are defined. For example, the
directory replication documents should address the
interaction of access control with the replication function.
14. References
[LDAPv3] M. Wahl, T. Howes, S. Kille, "Lightweight Directory
Access Protocol (v3)", RFC 2251, December 1997.
[ECMA] ECMA, "Security in Open Systems: A Security
Framework" ECMA TR/46, July 1988.
[REQTS] Stokes, Byrne, Blakley, "Access Control Requirements
for LDAP", RFC 2820, May 2000.
[ATTR] M.Wahl, A, Coulbeck, T. Howes, S. Kille, "Lightweight
Directory Access Protocol (v3)": Attribute Syntax
Definitions, RFC 2252, December 1997.
[UTF] M. Wahl, S. Kille, "Lightweight Directory Access
Protocol (v3)": A UTF-8 String Representation of
Distinguished Names", RFC 2253, December 1997.
[Bradner97] Bradner, Scott, "Key Words for use in RFCs to
Indicate Requirement Levels", RFC 2119.
[AuthMeth] Wahl, M., Alvestrand, H., Hodges, J. and R.
Morgan, "Authentication Methods for LDAP", RFC 2829, May
2000.
[ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
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ACKNOWLEDGEMENT
This is to acknowledge the numerous companies and individuals who have
contributed their valuable help and insights to the development of this
specification.
AUTHOR(S) ADDRESS
Ellen Stokes Bob Blakley
Tivoli Systems Tivoli Systems
6300 Bridgepoint Parkway 6300 Bridgepoint Parkway
Austin, TX 78731 Austin, TX 78731
USA USA
mail-to: estokes@tivoli.com mail-to: blakley@tivoli.com
phone: +1 512 436 9098 phone: +1 512 436 1564
fax: +1 512 436 1199 fax: +1 512 436 1199
Debbie Rinkevich Robert Byrne
IBM Sun Microsystems
11400 Burnet Rd 29 Chemin du Vieux Chene
Austin, TX 78758 Meylan ZIRST 38240
USA France
mail-to: djbrink@us.ibm.com mail-to: rbyrne@france.sun.com
phone: +1 512 838 1960 phone: +33 (0)4 76 41 42 05
fax: +1 512 838 8597
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CONTENTS
1. Introduction....................................... 2
2. The LDAPv3 Access Control Model.................... 2
3. Access Control Mechanism Attributes................ 5
3.1 Root DSE Attribute for Access Control
Mechanism.................................... 5
3.2 Root DSE Attribute for Control of Disclosing
Errors....................................... 5
3.3 Subentry Class Access Control Mechanism...... 6
4. The Access Control Information Attribute
(ldapACI).......................................... 7
4.1 The BNF...................................... 8
4.1.1 ACI String Representation 8
4.1.2 ACI Binary Representation 10
4.2 The Components of ldapACI Attribute.......... 11
4.2.1 Scope 11
4.2.2 Access Rights and Permissions 11
4.2.3 Attributes 14
4.2.4 Subjects and Associated
Authentication 15
4.3 Grant/Deny Evaluation Rules.................. 15
5. Required Permissions for each LDAP Operation....... 17
5.1 Bind Operation............................... 18
5.2 Search Operation............................. 18
5.3 Modify Operation............................. 21
5.4 Add Operation................................ 22
5.5 Delete Operation............................. 23
5.6 Modify DN Operation.......................... 23
5.7 Compare Operation............................ 24
5.8 Abandon Operation............................ 25
5.9 Extended Operation........................... 25
6. Required Permissions for Handling Aliases and
References......................................... 25
6.1 ACI Distribution............................. 25
6.2 Aliases...................................... 26
6.3 Referrals.................................... 26
7. Controlling Access to Access Control
Information........................................ 27
8. ACI Examples....................................... 27
8.1 Attribute Definition......................... 27
8.2 Modifying the ldapACI Values................. 28
8.3 Evaluation................................... 30
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9. Operational Semantics of Access Control
Operations......................................... 31
9.1 Types of actions............................. 32
9.2 Semantics of Histories....................... 32
10. Access Control Parameters for LDAP Controls &
Extended Operations................................ 35
11. Access Control Information (ACI) Controls.......... 35
11.1 getEffectiveRights Control................... 35
11.1.1 Request Control 35
11.1.2 Response Control 36
11.1.3 Client-Server Interaction 37
12. Access Control Extended Operation.................. 38
12.1 LDAP Get Effective Rights Operation.......... 39
13. Security Considerations............................ 40
14. References......................................... 40
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