MUNGE(7) MUNGE Uid 'N' Gid Emporium MUNGE(7)NAMEmunge - MUNGE overview
INTRODUCTION
MUNGE (MUNGE Uid 'N' Gid Emporium) is an authentication service for
creating and validating credentials. It is designed to be highly scal‐
able for use in an HPC cluster environment. It allows a process to
authenticate the UID and GID of another local or remote process within
a group of hosts having common users and groups. These hosts form a
security realm that is defined by a shared cryptographic key. Clients
within this security realm can create and validate credentials without
the use of root privileges, reserved ports, or platform-specific meth‐
ods.
RATIONALE
The need for MUNGE arose out of the HPC cluster environment. Consider
the scenario in which a local daemon running on a login node receives a
client request and forwards it on to remote daemons running on compute
nodes within the cluster. Since the user has already logged on to the
login node, the local daemon just needs a reliable means of ascertain‐
ing the UID and GID of the client process. Furthermore, the remote
daemons need a mechanism to ensure the forwarded authentication data
has not been subsequently altered.
A common solution to this problem is to use Unix domain sockets to
determine the identity of the local client, and then forward this
information on to remote hosts via trusted rsh connections. But this
presents several new problems. First, there is no portable API for
determining the identity of a client over a Unix domain socket. Sec‐
ond, rsh connections must originate from a reserved port; the limited
number of reserved ports available on a given host directly limits
scalability. Third, root privileges are required in order to bind to a
reserved port. Finally, the remote daemons have no means of determin‐
ing whether the client identity is authentic.
USAGE
A process creates a credential by requesting one from the local MUNGE
service, either via the munge_encode() C library call or the munge exe‐
cutable. The encoded credential contains the UID and GID of the origi‐
nating process. This process sends the credential to another process
within the security realm as a means of proving its identity. The
receiving process validates the credential with the use of its local
MUNGE service, either via the munge_decode() C library call or the
unmunge executable. The decoded credential provides the receiving
process with a reliable means of ascertaining the UID and GID of the
originating process. This information can be used for accounting or
access control decisions.
DETAILS
The contents of the credential (including any optional payload data)
are encrypted with a key shared by all munged daemons within the secu‐
rity realm. The integrity of the credential is ensured by a message
authentication code (MAC). The credential is valid for a limited time
defined by its time-to-live (TTL); this presumes clocks within a secu‐
rity realm are in sync. Unexpired credentials are tracked by the local
munged daemon in order to prevent replay attacks on a given host.
Decoding of a credential can be restricted to a particular user and/or
group ID. The payload data can be used for purposes such as embedding
the destination's address to ensure the credential is only valid on a
specific host. The internal format of the credential is encoded in a
platform-independent manner. And the credential itself is base64
encoded to allow it to be transmitted over virtually any transport.
AUTHOR
Chris Dunlap <cdunlap@llnl.gov>
COPYRIGHT
Copyright (C) 2007-2011 Lawrence Livermore National Security, LLC.
Copyright (C) 2002-2007 The Regents of the University of California.
MUNGE is free software: you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation, either version 3 of the License, or (at your
option) any later version.
Additionally for the MUNGE library (libmunge), you can redistribute it
and/or modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation, either version 3
of the License, or (at your option) any later version.
SEE ALSOmunge(1), remunge(1), unmunge(1), munge(3), munge_ctx(3),
munge_enum(3), munged(8).
http://munge.googlecode.com/
munge-0.5.10 2011-02-25 MUNGE(7)
