Welcome!

Open Source Cloud Authors: Pat Romanski, Elizabeth White, Zakia Bouachraoui, Liz McMillan, Yeshim Deniz

Related Topics: Open Source Cloud

Open Source Cloud: Article

EOS Cover Story — Linux Authentication Using PAM and LDAP

An improvement over distributing flat files or relying on RPC services

In an environment with more than a few Linux servers, managing users, groups, and other information securely across those systems is critical. Pluggable Authentication Modules (PAM) and the Lightweight Directory Access Protocol (LDAP) give administrators a way to accomplish this without having to distribute flat files or rely on RPC services, such as the insecure Network Information Service (NIS).

LDAP is a very mature protocol supported by everyone from Microsoft to IBM and Oracle. And reference implementations, such as OpenLDAP, have been available since the mid-'90s. PAM bridges the gap between traditional Unix and Linux login functionality and LDAP-enabled directory servers without requiring that applications or services be recompiled or reconfigured.

Aside from the obvious benefit of centralized storage and secure access, using LDAP has other key benefits depending on the server technology being used. These benefits generally include more granular password policy support, distributed or delegated administration of different groups of users in the same directory, and generally better performance and scalability than the alternatives.

Getting the Pieces
Most Linux distributions today support PAM out-of-the-box. However, the PAM_LDAP module, which is responsible for connecting the PAM framework to the LDAP-enabled directory service, usually needs to be downloaded and compiled separately. The source can be downloaded at www.padl.com.

PAM_LDAP itself has several dependencies, including SSL, LDAP, and SASL libraries, and it can be finicky about the specific versions used. While it's possible to install without some dependencies, such as SSL, not including them can render the system less secure. The most common issues with deployment are often related to getting a secure version of this module operational.

The directory that will be used to store and access account data is the other major component that will have to be installed. There are many options here and the choice of product is usually made on factors such as price, scalability, performance, and other key characteristics. Besides the base service, most commercial offerings include or have compatible tools to do everything from synchronize with other data sources to graphical user management and user self-service (e.g., password resets). Replicating data between servers and data centers is another key functionality that exists in most products, but in different ways.

LDAP-enabled directories have extensible schema that defines the type of data that can be stored. A standard set of schema, defined in IETF RFC 2307, may have to be imported or created in the directory to support the storage of Linux account information. In addition to accounts, this standard also defines schema for the storage of hosts, netgroups, services, and other types of data that has traditionally been stored in flat files, NIS, and related technology.

Making It Work
Once the modules are installed and the required directory servers are properly configured, the key steps remaining will be to migrate existing account information into the directory server and enable the PAM service.

Fortunately the first step is straightforward, given the ability of free migration tools from the same source as the PAM_LDAP module itself. These migration tools are capable of migrating all major information that would commonly be found in NIS or the equivalent flat files. The output of these files is a format called LDIF that can be used by standard LDAP tools for importing and modifying data in the directory.

With the data in place, the PAM module can be turned on and configured to point to the appropriate directory server. At this stage it's probably a good idea to keep a backup shell to help ensure that a mistake doesn't lock all the users out of the system.

Once authenticated, many applications will still need access to other data normally stored in passwd, group, and other files. This can be solved by configuring the system's name service switch configuration file (nsswitch.conf) to use LDAP. This defines the source and order that data ranging from account information to groups and even host name information will be checked in sources such as NIS, LDAP, and flat files.

Increasing Performance with Caching
Since many servers may be using the same directory, using a local server cache to reduce search and authentication requests may increase both performance and the number of servers that can be used with a single directory. This is especially true when using SSL and other overhead that can put an additional load on the directory servers.

In smaller environments this is less of a concern given that a typical directory server supports thousands of requests per second on modest hardware, but medium and large environments should look at using the Name Service Cache Daemon (NSCD). This service is included in most Linux distributions and requires no serious configuration. That said, it's important to realize that making a change to the directory, such as disabling an account, won't take immediate effect with the cache enabled.

Stronger Password Hashes & Security over the Wire
Many servers still support the CRYPT password hashing algorithm. This algorithm is easy to crack and a stronger algorithm, such as SMD5 or SSHA, should be selected instead. Access controls on the directory should still be configured to limit access to the hashed password.

Enabling either TLS/SSL or using SASL authentication mechanisms is an absolute requirement, since the alternative is to have the PAM module communicate with the LDAP directory server in a way that sends passwords in clear text over the network. Making this work is easier on some Linux distributions than others, but is an absolute must and can be accomplished on any system with the right combination of libraries as indicated in the PAM_LDAP and dependency documentation.

Conclusion
Together, LDAP and PAM provide a secure and scalable way to authenticate Linux users across multiple servers. Sites still using insecure and less scalable technology, such as NIS, can make the move to LDAP easily using existing modules and migration tools. Care needs to be taken to ensure that performance is maintained and that the security benefits of using the directory aren't sacrificed to bad practices such as weak hashing choices and transmitting passwords in the clear.

Useful Links

  • PAM LDAP Configuration
    Unix Manual Page for PAM LDAP Configuration
    www.scit.wlv.ac.uk/cgi-bin/mansec?5+pam_ldap
  • LDAP entry
    Directory Entries Administration
    http://ftp.unex.es/oradoc/application_server_10g/manage.904/b12118/entries.htm
  • NIS Schema
    http://docs.sun.com/source/816-6682-10/oc_hpuxt.htm
  • www.oracle.com/pls/wocprod/docs/page/ocom/technology/products/oid/unix_pam_oid_wp.pdf
  • More Stories By Clayton Donley

    Currently responsible for Oracle’s directory services product-lines, Clayton Donley’s technical background in this area includes experience in IT, consulting, and development in addition to authoring the book “LDAP Programming”. Prior to Oracle, Clayton founded Octet String, Inc., a developer of virtual directory technology that was acquired by Oracle in 2005. Previous positions have included a wide range of roles at Motorola and IBM. Clayton received a BA from DePaul University in Chicago.

    More Stories By Quan Dinh

    As a principal member of the technical staff at Oracle, Quan Dinh specializes in network and Internet security. Dinh is currently responsible for overall security of the Oracle Internet Directory and Virtual Directory products and has acted as a security advisor to Oracle’s Data Center. Previously, he was responsible for helping to secure Oracle Application Server, Oracle Database, and Oracle SQL Net with PKI, SSL/TLS, and related security technologies. Dinh’s other areas of expertise include Kerberos, SASL, and Single Sign-on technology. He graduated from the University of California at Berkeley with a degree in computer science and mathematics.

    Comments (0)

    Share your thoughts on this story.

    Add your comment
    You must be signed in to add a comment. Sign-in | Register

    In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


    IoT & Smart Cities Stories
    While the focus and objectives of IoT initiatives are many and diverse, they all share a few common attributes, and one of those is the network. Commonly, that network includes the Internet, over which there isn't any real control for performance and availability. Or is there? The current state of the art for Big Data analytics, as applied to network telemetry, offers new opportunities for improving and assuring operational integrity. In his session at @ThingsExpo, Jim Frey, Vice President of S...
    @CloudEXPO and @ExpoDX, two of the most influential technology events in the world, have hosted hundreds of sponsors and exhibitors since our launch 10 years ago. @CloudEXPO and @ExpoDX New York and Silicon Valley provide a full year of face-to-face marketing opportunities for your company. Each sponsorship and exhibit package comes with pre and post-show marketing programs. By sponsoring and exhibiting in New York and Silicon Valley, you reach a full complement of decision makers and buyers in ...
    The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound e...
    Two weeks ago (November 3-5), I attended the Cloud Expo Silicon Valley as a speaker, where I presented on the security and privacy due diligence requirements for cloud solutions. Cloud security is a topical issue for every CIO, CISO, and technology buyer. Decision-makers are always looking for insights on how to mitigate the security risks of implementing and using cloud solutions. Based on the presentation topics covered at the conference, as well as the general discussions heard between sessio...
    The Jevons Paradox suggests that when technological advances increase efficiency of a resource, it results in an overall increase in consumption. Writing on the increased use of coal as a result of technological improvements, 19th-century economist William Stanley Jevons found that these improvements led to the development of new ways to utilize coal. In his session at 19th Cloud Expo, Mark Thiele, Chief Strategy Officer for Apcera, compared the Jevons Paradox to modern-day enterprise IT, examin...
    Rodrigo Coutinho is part of OutSystems' founders' team and currently the Head of Product Design. He provides a cross-functional role where he supports Product Management in defining the positioning and direction of the Agile Platform, while at the same time promoting model-based development and new techniques to deliver applications in the cloud.
    In his keynote at 18th Cloud Expo, Andrew Keys, Co-Founder of ConsenSys Enterprise, provided an overview of the evolution of the Internet and the Database and the future of their combination – the Blockchain. Andrew Keys is Co-Founder of ConsenSys Enterprise. He comes to ConsenSys Enterprise with capital markets, technology and entrepreneurial experience. Previously, he worked for UBS investment bank in equities analysis. Later, he was responsible for the creation and distribution of life settl...
    There are many examples of disruption in consumer space – Uber disrupting the cab industry, Airbnb disrupting the hospitality industry and so on; but have you wondered who is disrupting support and operations? AISERA helps make businesses and customers successful by offering consumer-like user experience for support and operations. We have built the world’s first AI-driven IT / HR / Cloud / Customer Support and Operations solution.
    LogRocket helps product teams develop better experiences for users by recording videos of user sessions with logs and network data. It identifies UX problems and reveals the root cause of every bug. LogRocket presents impactful errors on a website, and how to reproduce it. With LogRocket, users can replay problems.
    Rafay enables developers to automate the distribution, operations, cross-region scaling and lifecycle management of containerized microservices across public and private clouds, and service provider networks. Rafay's platform is built around foundational elements that together deliver an optimal abstraction layer across disparate infrastructure, making it easy for developers to scale and operate applications across any number of locations or regions. Consumed as a service, Rafay's platform elimi...