Linux man pages

Section (5) slapo-rwm

Linux manual pages	Section 5

Name

slapo−rwm — rewrite/remap overlay to slapd

Synopsis

ETCDIR/slapd.conf

DESCRIPTION

The rwm overlay to slapd(8) performs basic DN/data rewrite and objectClass/attributeType mapping. Its usage is mostly intended to provide virtual views of existing data either remotely, in conjunction with the proxy backend described in slapd-ldap(5), or locally, in conjunction with the relay backend described in slapd-relay(5).

This overlay is experimental.

MAPPING

An important feature of the rwm overlay is the capability to map objectClasses and attributeTypes from the local set (or a subset of it) to a foreign set, and vice versa. This is accomplished by means of the rwm−map directive.

rwm−map {attribute | objectclass} [<local name> | *] {<foreign name> | *}: Map attributeTypes and objectClasses from the foreign server to different values on the local slapd. The reason is that some attributes might not be part of the local slapd_zsingle_quotesz_s schema, some attribute names might be different but serve the same purpose, etc. If local or foreign name is `*_zsingle_quotesz_, the name is preserved. If local name is omitted, the foreign name is removed. Unmapped names are preserved if both local and foreign name are `*_zsingle_quotesz_, and removed if local name is omitted and foreign name is `*_zsingle_quotesz_.

The local objectClasses and attributeTypes must be defined in the local schema; the foreign ones do not have to, but users are encouraged to explicitly define the remote attributeTypes and the objectClasses they intend to map. All in all, when remapping a remote server via back-ldap ( slapd-ldap(5)) or back-meta ( slapd-meta(5)) their definition can be easily obtained by querying the subschemaSubentry of the remote server; the problem should not exist when remapping a local database. Note, however, that the decision whether to rewrite or not attributeTypes with distinguishedName syntax, requires the knowledge of the attributeType syntax. See the REWRITING section for details.

Note that when mapping DN-valued attributes from local to remote, first the DN is rewritten, and then the attributeType is mapped; while mapping from remote to local, first the attributeType is mapped, and then the DN is rewritten. As such, it is important that the local attributeType is appropriately defined as using the distinguishedName syntax. Also, note that there are DN-related syntaxes (i.e. compound types with a portion that is DN-valued), like nameAndOptionalUID, whose values are currently not rewritten.

If the foreign type of an attribute mapping is not defined on the local server, it might be desirable to have the attribute values normalized after the mapping process. Not normalizing the values can lead to wrong results, when the rwm overlay is used together with e.g. the pcache overlay. This normalization can be enabled by means of the rwm−normalize−mapped−attrs directive.

rwm−normalize−mapped−attrs {yes|no}: Set this to yes, if the rwm overlay should try to normalize the values of attributes that are mapped from an attribute type that is unknown to the local server. The default value of this setting is no.
rwm-drop-unrequested-attrs {yes|no}: Set this to yes, if the rwm overlay should drop attributes that are not explicitly requested by a search operation. When this is set to no, the rwm overlay will leave all attributes in place, so that subsequent modules can further manipulate them. In any case, unrequested attributes will be omitted from search results by the frontend, when the search entry response package is encoded. The default value of this setting is yes.

SUFFIX MASSAGING

A basic feature of the rwm overlay is the capability to perform suffix massaging between a virtual and a real naming context by means of the rwm−suffixmassage directive. This, in conjunction with proxy backends, slapd-ldap(5) and slapd-meta(5), or with the relay backend, slapd-relay(5), allows one to create virtual views of databases. A distinguishing feature of this overlay is that, when instantiated before any database, it can modify the DN of requests before database selection. For this reason, rules that rewrite the empty DN () or the subschemaSubentry DN (usually cn=subschema), would prevent clients from reading the root DSE or the DSA_zsingle_quotesz_s schema.

rwm−suffixmassage [<virtual naming context>] <real naming context>: Shortcut to implement naming context rewriting; the trailing part of the DN is rewritten from the virtual to the real naming context in the bindDN, searchDN, searchFilterAttrDN, compareDN, compareAttrDN, addDN, addAttrDN, modifyDN, modifyAttrDN, modrDN, newSuperiorDN, deleteDN, exopPasswdDN, and from the real to the virtual naming context in the searchEntryDN, searchAttrDN and matchedDN rewrite contexts. By default no rewriting occurs for the searchFilter and for the referralAttrDN and referralDN rewrite contexts. If no <virtual naming context> is given, the first suffix of the database is used; this requires the rwm−suffixmassage directive be defined after the database suffix directive. The rwm−suffixmassage directive automatically sets the rwm−rewriteEngine to ON.

See the REWRITING section for details.

REWRITING

A string is rewritten according to a set of rules, called a `rewrite context_zsingle_quotesz_. The rules are based on POSIX (_zsingle_quotesz__zsingle_quotesz_extended_zsingle_quotesz__zsingle_quotesz_) regular expressions with substring matching; basic variable substitution and map resolution of substrings is allowed by specific mechanisms detailed in the following. The behavior of pattern matching/substitution can be altered by a set of flags.

<rewrite context> ::= <rewrite rule> [...]
<rewrite rule> ::= <pattern> <action> [<flags>]

The underlying concept is to build a lightweight rewrite module for the slapd server (initially dedicated to the LDAP backend):

Passes

An incoming string is matched against a set of rewriteRules. Rules are made of a regex match pattern, a substitution pattern and a set of actions, described by a set of optional flags. In case of match, string rewriting is performed according to the substitution pattern that allows one to refer to substrings matched in the incoming string. The actions, if any, are finally performed. Each rule is executed recursively, unless altered by specific action flags; see Action Flags for details. A default limit on the recursion level is set, and can be altered by the rwm−rewriteMaxPasses directive, as detailed in the Additional Configuration Syntax section. The substitution pattern allows map resolution of substrings. A map is a generic object that maps a substitution pattern to a value. The flags are divided in Pattern Matching Flags and Action Flags; the former alter the regex match pattern behavior, while the latter alter the actions that are taken after substitution.

Pattern Matching Flags

`C_zsingle_quotesz_: honors case in matching (default is case insensitive)
`R_zsingle_quotesz_: use POSIX _zsingle_quotesz__zsingle_quotesz_basic_zsingle_quotesz__zsingle_quotesz_ regular expressions (default is _zsingle_quotesz__zsingle_quotesz_extended_zsingle_quotesz__zsingle_quotesz_)
`M{n}_zsingle_quotesz_: allow no more than n recursive passes for a specific rule; does not alter the max total count of passes, so it can only enforce a stricter limit for a specific rule.

Action Flags

`:_zsingle_quotesz_: apply the rule once only (default is recursive)
`@_zsingle_quotesz_: stop applying rules in case of match; the current rule is still applied recursively; combine with `:_zsingle_quotesz_ to apply the current rule only once and then stop.
`#_zsingle_quotesz_: stop current operation if the rule matches, and issue an `unwilling to perform_zsingle_quotesz_ error.
`G{n}_zsingle_quotesz_: jump n rules back and forth (watch for loops!). Note that `G{1}_zsingle_quotesz_ is implicit in every rule.
`I_zsingle_quotesz_: ignores errors in rule; this means, in case of error, e.g. issued by a map, the error is treated as a missed match. The `unwilling to perform_zsingle_quotesz_ is not overridden.
`U{n}_zsingle_quotesz_: uses n as return code if the rule matches; the flag does not alter the recursive behavior of the rule, so, to have it performed only once, it must be used in combination with `:_zsingle_quotesz_, e.g. `:U{32}_zsingle_quotesz_ returns the value `32_zsingle_quotesz_ (indicating noSuchObject) after exactly one execution of the rule, if the pattern matches. As a consequence, its behavior is equivalent to `@_zsingle_quotesz_, with the return code set to n; or, in other words, `@_zsingle_quotesz_ is equivalent to `U{0}_zsingle_quotesz_. Positive errors are allowed, indicating the related LDAP error codes as specified in draft-ietf-ldapbis-protocol.

The ordering of the flags can be significant. For instance: `IG{2}_zsingle_quotesz_ means ignore errors and jump two lines ahead both in case of match and in case of error, while `G{2}I_zsingle_quotesz_ means ignore errors, but jump two lines ahead only in case of match.

More flags (mainly Action Flags) will be added as needed.

Pattern Matching

See regex(7) and/or re_format(7).

Substitution Pattern Syntax

Everything starting with `$_zsingle_quotesz_ requires substitution;

the only obvious exception is `$$_zsingle_quotesz_, which is turned into a single `$_zsingle_quotesz_;

the basic substitution is `$<d>_zsingle_quotesz_, where `<d>_zsingle_quotesz_ is a digit; 0 means the whole string, while 1-9 is a submatch, as discussed in regex(7) and/or re_format(7).

a `$_zsingle_quotesz_ followed by a `{_zsingle_quotesz_ invokes an advanced substitution. The pattern is:

`$_zsingle_quotesz_ `{_zsingle_quotesz_ [ <operator> ] <name> `(_zsingle_quotesz_ <substitution> `)_zsingle_quotesz_ `}_zsingle_quotesz_

where <name> must be a legal name for the map, i.e.

<name> ::= [a-z][a-z0-9]* (case insensitive)
<operator> ::= `>_zsingle_quotesz_ `|_zsingle_quotesz_ `&_zsingle_quotesz_ `&&_zsingle_quotesz_ `*_zsingle_quotesz_ `**_zsingle_quotesz_ `$_zsingle_quotesz_

and <substitution> must be a legal substitution pattern, with no limits on the nesting level.

The operators are:

>

sub-context invocation; <name> must be a legal, already defined rewrite context name

|

external command invocation; <name> must refer to a legal, already defined command name (NOT IMPLEMENTED YET)

&

variable assignment; <name> defines a variable in the running operation structure which can be dereferenced later; operator & assigns a variable in the rewrite context scope; operator && assigns a variable that scopes the entire session, e.g. its value can be dereferenced later by other rewrite contexts

variable dereferencing; <name> must refer to a variable that is defined and assigned for the running operation; operator * dereferences a variable scoping the rewrite context; operator ** dereferences a variable scoping the whole session, e.g. the value is passed across rewrite contexts

$

parameter dereferencing; <name> must refer to an existing parameter; the idea is to make some run-time parameters set by the system available to the rewrite engine, as the client host name, the bind DN if any, constant parameters initialized at config time, and so on; no parameter is currently set by either back−ldap or back−meta, but constant parameters can be defined in the configuration file by using the rewriteParam directive.

Substitution escaping has been delegated to the `$_zsingle_quotesz_ symbol, which is used instead of `\_zsingle_quotesz_ in string substitution patterns because `\_zsingle_quotesz_ is already escaped by slapd_zsingle_quotesz_s low level parsing routines; as a consequence, regex escaping requires two `\_zsingle_quotesz_ symbols, e.g. `.*.foo.bar_zsingle_quotesz_ must be written as `.*\.foo\.bar_zsingle_quotesz_.

Rewrite Context

A rewrite context is a set of rules which are applied in sequence. The basic idea is to have an application initialize a rewrite engine (think of Apache_zsingle_quotesz_s mod_rewrite ...) with a set of rewrite contexts; when string rewriting is required, one invokes the appropriate rewrite context with the input string and obtains the newly rewritten one if no errors occur.

Each basic server operation is associated to a rewrite context; they are divided in two main groups: client −> server and server −> client rewriting.

client −> server:

(default)            if defined and no specific context 
                     is available
bindDN               bind
searchDN             search
searchFilter         search
searchFilterAttrDN   search
compareDN            compare
compareAttrDN        compare AVA
addDN                add
addAttrDN            add AVA (DN portion of ref excluded)
modifyDN             modify
modifyAttrDN         modify AVA (DN portion of ref excluded)
referralAttrDN       add/modify DN portion of referrals
                     (default to none)
renameDN             modrdn (the old DN)
newSuperiorDN        modrdn (the new parent DN, if any)
newRDN               modrdn (the new relative DN)
deleteDN             delete
exopPasswdDN         password modify extended operation DN

server −> client:

searchEntryDN        search (only if defined; no default;
                     acts on DN of search entries)
searchAttrDN         search AVA (only if defined; defaults
                     to searchEntryDN; acts on DN-syntax
                     attributes of search results)
matchedDN            all ops (only if applicable; defaults
                     to searchEntryDN)
referralDN           all ops (only if applicable; defaults
                     to none)

Basic Configuration Syntax

All rewrite/remap directives start with the prefix rwm−; for backwards compatibility with the historical slapd-ldap(5) and slapd-meta(5) builtin rewrite/remap capabilities, the prefix may be omitted, but this practice is strongly discouraged.

rwm−rewriteEngine { on | off }: If `on_zsingle_quotesz_, the requested rewriting is performed; if `off_zsingle_quotesz_, no rewriting takes place (an easy way to stop rewriting without altering too much the configuration file).
rwm−rewriteContext <context name> [ alias <aliased context name> ]: <Context name> is the name that identifies the context, i.e. the name used by the application to refer to the set of rules it contains. It is used also to reference sub contexts in string rewriting. A context may alias another one. In this case the alias context contains no rule, and any reference to it will result in accessing the aliased one.
rwm−rewriteRule <regex match pattern> <substitution pattern> [ <flags> ]: Determines how a string can be rewritten if a pattern is matched. Examples are reported below.

Additional Configuration Syntax

rwm−rewriteMap <map type> <map name> [ <map attrs> ]: Allows one to define a map that transforms substring rewriting into something else. The map is referenced inside the substitution pattern of a rule.
rwm−rewriteParam <param name> <param value>: Sets a value with global scope, that can be dereferenced by the command `${$paramName}_zsingle_quotesz_.
rwm−rewriteMaxPasses <number of passes> [<number of passes per rule>]: Sets the maximum number of total rewriting passes that can be performed in a single rewrite operation (to avoid loops). A safe default is set to 100; note that reaching this limit is still treated as a success; recursive invocation of rules is simply interrupted. The count applies to the rewriting operation as a whole, not to any single rule; an optional per-rule limit can be set. This limit is overridden by setting specific per-rule limits with the `M{n}_zsingle_quotesz_ flag.

MAPS

Currently, few maps are builtin but additional map types may be registered at runtime.

Supported maps are:

LDAP <URI> [bindwhen=<when>] [version=<version>] [binddn=<DN>] [credentials=<cred>]

The LDAP map expands a value by performing a simple LDAP search. Its configuration is based on a mandatory URI, whose attrs portion must contain exactly one attribute (use entryDN to fetch the DN of an entry). If a multi-valued attribute is used, only the first value is considered.

The parameter bindwhen determines when the connection is established. It can take the values now, later, and everytime, respectively indicating that the connection should be created at startup, when required, or any time it is used. In the former two cases, the connection is cached, while in the latter a fresh new one is used all times. This is the default.

The parameters binddn and credentials represent the DN and the password that is used to perform an authenticated simple bind before performing the search operation; if not given, an anonymous connection is used.

The parameter version can be 2 or 3 to indicate the protocol version that must be used. The default is 3.

slapd <URI>

The slapd map expands a value by performing an internal LDAP search. Its configuration is based on a mandatory URI, which must begin with ldap:/// (i.e., it must be an LDAP URI and it must not specify a host). As with the LDAP map, the attrs portion must contain exactly one attribute, and if a multi-valued attribute is used, only the first value is considered.

REWRITE CONFIGURATION EXAMPLES

# set to `off_zsingle_quotesz_ to disable rewriting
rwm−rewriteEngine on

# the rules the suffixmassage directive implies
rwm−rewriteEngine on
# all dataflow from client to server referring to DNs
rwm−rewriteContext default
rwm−rewriteRule (.+,)?<virtualnamingcontext>$ $1<realnamingcontext> :
# empty filter rule
rwm−rewriteContext searchFilter
# all dataflow from server to client
rwm−rewriteContext searchEntryDN
rwm−rewriteRule (.+,)?<realnamingcontext>$ $1<virtualnamingcontext> :
rwm−rewriteContext searchAttrDN alias searchEntryDN
rwm−rewriteContext matchedDN alias searchEntryDN
# misc empty rules
rwm−rewriteContext referralAttrDN
rwm−rewriteContext referralDN

# Everything defined here goes into the `default_zsingle_quotesz_ context.
# This rule changes the naming context of anything sent
# to `dc=home,dc=net_zsingle_quotesz_ to `dc=OpenLDAP, dc=org_zsingle_quotesz_

rwm−rewriteRule (.+,)?dc=home,[ ]?dc=net$
            $1dc=OpenLDAP, dc=org  :

# since a pretty/normalized DN does not include spaces
# after rdn separators, e.g. `,_zsingle_quotesz_, this rule suffices:

rwm−rewriteRule (.+,)?dc=home,dc=net$
            $1dc=OpenLDAP,dc=org  :

# Start a new context (ends input of the previous one).
# This rule adds blanks between DN parts if not present.
rwm−rewriteContext  addBlanks
rwm−rewriteRule     (.*),([^ ].*) $1, $2

# This one eats blanks
rwm−rewriteContext  eatBlanks
rwm−rewriteRule     (.*), (.*) $1,$2

# Here control goes back to the default rewrite
# context; rules are appended to the existing ones.
# anything that gets here is piped into rule `addBlanks_zsingle_quotesz_
rwm−rewriteContext  default
rwm−rewriteRule     .* ${>addBlanks($0)} :

# Rewrite the search base according to `default_zsingle_quotesz_ rules.
rwm−rewriteContext  searchDN alias default

# Search results with OpenLDAP DN are rewritten back with
# `dc=home,dc=net_zsingle_quotesz_ naming context, with spaces eaten.
rwm−rewriteContext  searchEntryDN
rwm−rewriteRule     (.*[^ ],)?[ ]?dc=OpenLDAP,[ ]?dc=org$
                ${>eatBlanks($1)}dc=home,dc=net    :

# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to 
# the URI and acts as the filter portion)
rwm−rewriteMap ldap attr2dn ldap://host/dc=my,dc=org?dn?sub

# Then we need to detect DN made up of a single email,
# e.g. `[email protected]_zsingle_quotesz_; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored.  In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDN
# rewrite context overrides the default definition.
rwm−rewriteContext bindDN
rwm−rewriteRule ^mail=[^,][email protected][^,]+$ ${attr2dn($0)} :@I

# This is a rather sophisticated example. It massages a
# search filter in case who performs the search has
# administrative privileges.  First we need to keep
# track of the bind DN of the incoming request, which is
# stored in a variable called `binddn_zsingle_quotesz_ with session scope,
# and left in place to allow regular binding:
rwm−rewriteContext  bindDN
rwm−rewriteRule     .+ ${&&binddn($0)}$0 :

# A search filter containing `uid=_zsingle_quotesz_ is rewritten only
# if an appropriate DN is bound.
# To do this, in the first rule the bound DN is
# dereferenced, while the filter is decomposed in a
# prefix, in the value of the `uid=<arg>_zsingle_quotesz_ AVA, and 
# in a suffix. A tag `<>_zsingle_quotesz_ is appended to the DN. 
# If the DN refers to an entry in the `ou=admin_zsingle_quotesz_ subtree, 
# the filter is rewritten OR-ing the `uid=<arg>_zsingle_quotesz_ with
# `cn=<arg>_zsingle_quotesz_; otherwise it is left as is. This could be
# useful, for instance, to allow apache_zsingle_quotesz_s auth_ldap-1.4
# module to authenticate users with both `uid_zsingle_quotesz_ and
# `cn_zsingle_quotesz_, but only if the request comes from a possible
# `cn=Web auth,ou=admin,dc=home,dc=net_zsingle_quotesz_ user.
rwm−rewriteContext searchFilter
rwm−rewriteRule (.*\()uid=([a−z0−9_]+)(\).*)
  ${**binddn}<>${&prefix($1)}${&arg($2)}${&suffix($3)}
  :I
rwm−rewriteRule ^[^,]+,ou=admin,dc=home,dc=net$
  ${*prefix}|(uid=${*arg})(cn=${*arg})${*suffix} :@I
rwm−rewriteRule .*<>$ ${*prefix}uid=${*arg}${*suffix} :

# This example shows how to strip unwanted DN-valued
# attribute values from a search result; the first rule
# matches DN values below ou=People,dc=example,dc=com;
# in case of match the rewriting exits successfully.
# The second rule matches everything else and causes
# the value to be rejected.
rwm−rewriteContext searchEntryDN
rwm−rewriteRule .+,ou=People,dc=example,dc=com$ $0 :@
rwm−rewriteRule .*  #

MAPPING EXAMPLES

The following directives map the object class `groupOfNames_zsingle_quotesz_ to the object class `groupOfUniqueNames_zsingle_quotesz_ and the attribute type `member_zsingle_quotesz_ to the attribute type `uniqueMember_zsingle_quotesz_:

map objectclass groupOfNames groupOfUniqueNames
map attribute uniqueMember member

This presents a limited attribute set from the foreign server:

map attribute cn *
map attribute sn *
map attribute manager *
map attribute description *
map attribute *

These lines map cn, sn, manager, and description to themselves, and any other attribute gets removed from the object before it is sent to the client (or sent up to the LDAP server). This is obviously a simplistic example, but you get the point.

FILES

ETCDIR/slapd.conf: default slapd configuration file

AUTHOR

Pierangelo Masarati; based on back-ldap rewrite/remap features by Howard Chu, Pierangelo Masarati.