MUNGE Uid 'N' Gid Emporium is an authentication service for creating and validating credentials. It is designed to be highly scalable 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 methods.
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 ascertaining 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. Second, 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 determining whether the client identity is authentic.
Overview
A process creates a credential by requesting one from the local MUNGE service. The encoded credential contains the UID and GID of the originating 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. 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.
The contents of the credential (including any optional payload data) are encrypted with a key shared by all munged daemons within the security 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). The daemon ensures unexpired credentials are not replayed on a particular 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.
What's New in This Release:
· Performance improvements were made to the caching of supplementary group information.
· The --group-check-mtime and --group-update-time command line options were added to munged.
· A SIGHUP handler for updating the supplementary group information was added to munged.
· Errors encountered at munged exit were made nonfatal in order to work around a libc6 bug reported on Debian.
