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Network Working Group H. Chu
Internet-Draft Symas Corp.
Intended status: Informational February 28, 2007
Expires: September 1, 2007
Using LDAP Over IPC Mechanisms
draft-chu-ldap-ldapi-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
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
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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
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This Internet-Draft will expire on September 1, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Chu Expires September 1, 2007 [Page 1]
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Abstract
When both the LDAP client and server reside on the same machine,
communication efficiency can be greatly improved using host- specific
IPC mechanisms instead of a TCP session. Such mechanisms can also
implicitly provide the client's identity to the server for extremely
lightweight authentication. This document describes the
implementation of LDAP over Unix IPC that has been in use in OpenLDAP
since January 2000, including the URL format used to specify an IPC
session.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . 5
4. User-Visible Specification . . . . . . . . . . . . . . 6
4.1. URL Scheme . . . . . . . . . . . . . . . . . . . . . . 6
5. Implementation Details . . . . . . . . . . . . . . . . 7
5.1. Client Authentication . . . . . . . . . . . . . . . . 7
5.2. Other Platforms . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . 10
7.1. Normative References . . . . . . . . . . . . . . . . . 10
7.2. Informative References . . . . . . . . . . . . . . . . 10
Appendix A. IANA Considerations . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . 13
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1. Introduction
While LDAP is a distributed access protocol, it is common for clients
to be deployed on the same machine that hosts the server. Many
applications are built on a tight integration of the client code and
a co-resident server. In these tightly integrated deployments, where
no actual network traffic is involved in the communication, the use
of TCP/IP is overkill. Systems like Unix offer native IPC mechanisms
that still provide the stream-oriented semantics of a TCP session,
but with much greater efficiency.
Since January 2000, OpenLDAP releases have provided the option to
establish LDAP sessions over Unix Domain sockets as well as over
TCP/IP. Such sessions are inherently as secure as TCP loopback
sessions, but they consume fewer system resources, are much faster to
establish and tear down, and they also provide secure identification
of the client without requiring any additional passwords or other
credentials.
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2. Conventions
Imperative keywords defined in [RFC2119] are used in this document,
and carry the meanings described there.
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3. Motivation
Many LDAP sessions consist of just one or two requests. Connection
setup and teardown can become a significant portion of the time
needed to process these sessions. Also under heavy load, the
constraints of the 2MSL limit in TCP become a bottleneck. For
example, a modest single processor dual-core AMD64 server running
OpenLDAP can handle over 32,000 authentication requests per second on
100Mbps ethernet, with one connection per request. Connected over a
host's loopback interface, the rate is much higher, but connections
get completely throttled in under one second, because all of the
host's port numbers have been used up and are in TIME_WAIT state. So
even when the TCP processing overhead is insignificant, the
constraints imposed in [RFC0793] create an artificial limit on the
server's performance. No such constraints exist when using IPC
mechanisms instead of TCP.
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4. User-Visible Specification
The only change clients need to implement to use this feature is to
use a special URL scheme instead of an ldap:// URL when specifying
the target server. Likewise, the server needs to include this URL in
the list of addresses on which it will listen.
4.1. URL Scheme
The "ldapi:" URL scheme is used to denote an LDAP over IPC session.
The address portion of the URL is the name of a Unix Domain socket,
which is usually a fully qualified Unix filesystem pathname. Slashes
in the pathname must be percent-encoded as described in section 2.1
of [RFC3986] since they do not represent URL path delimiters in this
usage. E.g., for a socket named "/var/run/ldapi" the server URL
would be "ldapi://%26var%26run%26ldapi/". In all other respects, an
ldapi URL conforms to [RFC4516].
If no specific address is supplied, a default address MAY be used
implicitly. In OpenLDAP the default address is a compile-time
constant and its value is chosen by whoever built the software.
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5. Implementation Details
The basic transport uses a stream-oriented Unix Domain socket. The
semantics of communication over such a socket are essentially
identical to using a TCP session. Aside from the actual connection
establishment, no special considerations are needed in the client,
libraries, or server.
5.1. Client Authentication
Since their introduction in 4.2 BSD Unix, Unix Domain sockets have
also allowed passing credentials from one process to another. Modern
systems may provide a server with easier means of obtaining the
client's identity. The OpenLDAP implementation exploits multiple
methods to acquire the client's identity. The discussion that
follows is necessarily platform-specific.
The OpenLDAP library provides a getpeereid() function to encapsulate
all of the mechanisms used to acquire the identity.
On FreeBSD and MacOSX the native getpeereid() is used.
On modern Solaris systems the getpeerucred() system call is used.
On systems like Linux that support the SO_PEERCRED option to
getsockopt(), that option is used.
On Unix systems lacking these explicit methods, descriptor passing is
used. In this case, the client must send a message containing the
descriptor as its very first action immediately after the socket is
connected. The descriptor is attached to an LDAP Abandon Request
[RFC4511] with message ID zero, whose parameter is also message ID
zero. This request is a pure no-op, and will be harmlessly ignored
by any server that doesn't implement the protocol.
For security reasons, the passed descriptor must be tightly
controlled. The client creates a pipe and sends the pipe descriptor
in the message. The server receives the descriptor and does an
fstat() on it to determine the client's identity. The received
descriptor MUST be a pipe, and its permission bits MUST only allow
access to its owner. The owner uid and gid are then used as the
client's identity.
Note that these mechanisms are merely used to make the client's
identity available to the server. The server will not actually use
the identity information unless the client performs a SASL Bind
[RFC4513] using the EXTERNAL mechanism. I.e., as with any normal
LDAP session, the session remains in the anonymous state until the
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client issues a Bind request.
5.2. Other Platforms
It is possible to implement the corresponding functionality on
Microsoft Windows-based systems using Named Pipes, but thus far there
has been no demand for it, so the implementation has not been
written. These are brief notes on the steps required for an
implementation.
The Pipe should be created in byte-read mode, and the client must
specify SECURITY_IMPERSONATION access when it opens the pipe. The
server can then retrieve the client's identity using the
GetNamedPipeHandleState() function.
Since Windows socket handles are not interchangeable with IPC
handles, an alternate event handler would have to be provided instead
of using Winsock's select() function.
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6. Security Considerations
This document describes a mechanism for accessing an LDAP server that
is co-resident with the client machine. As such, it is inherently
immune to security issues associated with using LDAP across a
network. The mechanism also provides a means for a client to
authenticate itself to the server without exposing any sensitive
passwords. The security of this authentication is equal to the
security of the host machine.
Chu Expires September 1, 2007 [Page 9]
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2717] Petke, R. and I. King, "Registration Procedures for URL
Scheme Names", BCP 35, RFC 2717, November 1999.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4511] Sermersheim, J., "Lightweight Directory Access Protocol
(LDAP): The Protocol", RFC 4511, June 2006.
[RFC4513] Harrison, R., "Lightweight Directory Access Protocol
(LDAP): Authentication Methods and Security Mechanisms",
RFC 4513, June 2006.
[RFC4516] Smith, M. and T. Howes, "Lightweight Directory Access
Protocol (LDAP): Uniform Resource Locator", RFC 4516,
June 2006.
7.2. Informative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
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Appendix A. IANA Considerations
This document satisfies the requirements of [RFC2717] for
registration of a new URL scheme.
Chu Expires September 1, 2007 [Page 11]
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Author's Address
Howard Chu
Symas Corp.
18740 Oxnard Street, Suite 313A
Tarzana, California 91356
USA
Phone: +1 818 757-7087
Email: hyc@symas.com
Chu Expires September 1, 2007 [Page 12]
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Chu Expires September 1, 2007 [Page 13]
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