slapo-rwm(5)
SLAPO-RWM(5) FILE FORMATS SLAPO-RWM(5)
NAME
slapo-rwm - rewrite/remap overlay
SYNOPSIS
/etc/openldap/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.
name> | *}
rwm-
map {attribute | objectclass} [<local name> | *] {<foreign
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's schema, some attribute names might be
different but serve the same purpose, etc. If local or
foreign name is `*', 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
`*', and removed if local name is omitted and foreign
name is `*'.
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 attri-
buteTypes 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 attribu-
teType is mapped; while mapping from remote to local, first
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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 nameAndOp-
tionalUID, whose values are currently not rewritten.
SUFFIX MASSAGING
A basic feature of the rwm overlay is the capability to per-
form suffix massaging between a virtual and a real naming
context by means of the rwm-suffixmassage directive.
text>
rwm-
suffixmassage [<virtual naming context>] <real naming con-
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, newSu-
periorDN, deleteDN, exopPasswdDN, and from the real to
the virtual naming context in the searchEntryDN, sear-
chAttrDN 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'. The rules are based on POSIX
(''extended'') 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
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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 to refer
to substrings matched in the incoming string. The actions,
if any, are finally performed. Each rule is executed recur-
sively, 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 Syn-
tax" section. The substitution pattern allows map resolu-
tion 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' honors case in matching (default is case insensitive)
`R' use POSIX ''basic'' regular expressions (default is
''extended'')
`M{n}'
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
`:' apply the rule once only (default is recursive)
`@' stop applying rules in case of match; the current rule
is still applied recursively; combine with `:' to apply
the current rule only once and then stop.
`#' stop current operation if the rule matches, and issue
an `unwilling to perform' error.
`G{n}'
jump n rules back and forth (watch for loops!). Note
that `G{1}' is implicit in every rule.
`I' 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' is not overridden.
`U{n}'
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 com-
bination with `:', e.g. `:U{32}' returns the value
`32' (indicating noSuchObject) after exactly one
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execution of the rule, if the pattern matches. As a
consequence, its behavior is equivalent to `@', with
the return code set to n; or, in other words, `@' is
equivalent to `U{0}'. 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}' means ignore errors and jump two lines ahead both in
case of match and in case of error, while `G{2}I' 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 `$' requires substitution;
the only obvious exception is `$$', which is turned into a
single `$';
the basic substitution is `$<d>', where `<d>' is a digit; 0
means the whole string, while 1-9 is a submatch, as dis-
cussed in regex(7) and/or re_format(7).
a `$' followed by a `{' invokes an advanced substitution.
The pattern is:
`$' `{' [ <operator> ] <name> `(' <substitution> `)'
`}'
where <name> must be a legal name for the map, i.e.
<name> ::= [a-z][a-z0-9]* (case insensitive)
<operator> ::= `>' `|' `&' `&&' `*' `**' `$'
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
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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 exist-
ing parameter; the idea is to make some run-time param-
eters 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 direc-
tive.
Substitution escaping has been delegated to the `$' symbol,
which is used instead of `\' in string substitution patterns
because `\' is already escaped by slapd's low level parsing
routines; as a consequence, regex escaping requires two `\'
symbols, e.g. `.*\.foo\.bar' must be written as
`.*\\.foo\\.bar'.
Rewrite Context
A rewrite context is a set of rules which are applied in
sequence. The basic idea is to have an application initial-
ize a rewrite engine (think of Apache'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 con-
text; 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
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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)
modrDN modrdn
newSuperiorDN modrdn
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', the requested rewriting is performed; if
`off', 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 access-
ing the aliased one.
]
rwm-
rewriteRule <regex match pattern> <substitution pattern> [
Determines how a string can be rewritten if a pattern
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is matched. Examples are reported below.
Additional Configuration Syntax
rwm-rewriteMap <map type> <map name> [ <map attrs> ]
Allows 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 derefer-
enced by the command `${$paramName}'.
rwm-rewriteMaxPasses <number of passes> [<number of
Sets the maximum number of total rewriting passes that
can be performed in a single rewrite operation (to
avoid loops). A safe default is set to 100; note that
reaching this limit is still treated as a success;
recursive invocation of rules is simply interrupted.
The count applies to the rewriting operation as a
whole, not to any single rule; an optional per-rule
limit can be set. This limit is overridden by setting
specific per-rule limits with the `M{n}' flag.
REWRITE CONFIGURATION EXAMPLES
# set to `off' to disable rewriting
rwm-rewriteEngine on
# the rules the "suffixmassage" directive implies
rwm-rewriteEngine on
# all dataflow from client to server referring to DNs
rwm-rewriteContext default
rwm-rewriteRule "(.+,)?<virtualnamingcontext>$" "$1<realnamingcontext>" ":"
# empty filter rule
rwm-rewriteContext searchFilter
# all dataflow from server to client
rwm-rewriteContext searchEntryDN
rwm-rewriteRule "(.+,)?<realnamingcontext>$" "$1<virtualnamingcontext>" ":"
rwm-rewriteContext searchAttrDN alias searchEntryDN
rwm-rewriteContext matchedDN alias searchEntryDN
# misc empty rules
rwm-rewriteContext referralAttrDN
rwm-rewriteContext referralDN
# Everything defined here goes into the `default' context.
# This rule changes the naming context of anything sent
# to `dc=home,dc=net' to `dc=OpenLDAP, dc=org'
rwm-rewriteRule "(.+,)?dc=home,[ ]?dc=net$"
"$1dc=OpenLDAP, dc=org" ":"
# since a pretty/normalized DN does not include spaces
# after rdn separators, e.g. `,', this rule suffices:
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rwm-rewriteRule "(.+,)?dc=home,dc=net$"
"$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,$2"
# Here control goes back to the default rewrite
# context; rules are appended to the existing ones.
# anything that gets here is piped into rule `addBlanks'
rwm-rewriteContext default
rwm-rewriteRule ".*" "${>addBlanks($0)}" ":"
# Rewrite the search base according to `default' rules.
rwm-rewriteContext searchDN alias default
# Search results with OpenLDAP DN are rewritten back with
# `dc=home,dc=net' naming context, with spaces eaten.
rwm-rewriteContext searchEntryDN
rwm-rewriteRule "(.*[^ ],)?[ ]?dc=OpenLDAP,[ ]?dc=org$"
"${>eatBlanks($1)}dc=home,dc=net" ":"
# Bind with email instead of full DN: we first need
# an ldap map that turns attributes into a DN (the
# argument used when invoking the map is appended to
# the URI and acts as the filter portion)
rwm-rewriteMap ldap attr2dn "ldap://host/dc=my,dc=org?dn?sub"
# Then we need to detect DN made up of a single email,
# e.g. `mail=someone@example.com'; note that the rule
# in case of match stops rewriting; in case of error,
# it is ignored. In case we are mapping virtual
# to real naming contexts, we also need to rewrite
# regular DNs, because the definition of a bindDN
# rewrite context overrides the default definition.
rwm-rewriteContext bindDN
rwm-rewriteRule "^mail=[^,]+@[^,]+$" "${attr2dn($0)}" ":@I"
# This is a rather sophisticated example. It massages a
# search filter in case who performs the search has
# administrative privileges. First we need to keep
# track of the bind DN of the incoming request, which is
# stored in a variable called `binddn' with session scope,
# and left in place to allow regular binding:
rwm-rewriteContext bindDN
rwm-rewriteRule ".+" "${&&binddn($0)}$0" ":"
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# A search filter containing `uid=' is rewritten only
# if an appropriate DN is bound.
# To do this, in the first rule the bound DN is
# dereferenced, while the filter is decomposed in a
# prefix, in the value of the `uid=<arg>' AVA, and
# in a suffix. A tag `<>' is appended to the DN.
# If the DN refers to an entry in the `ou=admin' subtree,
# the filter is rewritten OR-ing the `uid=<arg>' with
# `cn=<arg>'; otherwise it is left as is. This could be
# useful, for instance, to allow apache's auth_ldap-1.4
# module to authenticate users with both `uid' and
# `cn', but only if the request comes from a possible
# `cn=Web auth,ou=admin,dc=home,dc=net' user.
rwm-rewriteContext searchFilter
rwm-rewriteRule "(.*\\()uid=([a-z0-9_]+)(\\).*)"
"${**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'
to the object class `groupOfUniqueNames' and the attribute
type `member' to the attribute type `uniqueMember':
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 them-
selves, 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
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you get the point.
FILES
/etc/openldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd-ldap(5), slapd-meta(5), slapd-relay(5),
slapd(8), regex(7), re_format(7).
AUTHOR
Pierangelo Masarati; based on back-ldap rewrite/remap
features by Howard Chu, Pierangelo Masarati.
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