DSI: A New Architecture for Secure Carrier-Class Linux Clusters

An approach for distributed security architecture that supports advanced security mechanisms for current and future security needs, targeted at telecom applications running on carrier-class Linux clusters.

Editor's note: This is the full version of the article "DSI: Secure Carrier-Class Linux" found in the July 2002 print edition of Linux Journal.

The telecommunication industry's interest in clustering originates from the fact that clusters address carrier-class characteristics such as guaranteed service availability, reliability and scaled performance, using cost-effective hardware and software. These carrier-class characteristics have evolved with time to include requirements for advanced levels of security. However, few efforts exist to build a coherent distributed framework to provide advanced security levels in clustered systems.

At Ericsson Research, our work targets soft real-time distributed applications running on large-scale carrier-class Linux clusters. These clusters must operate non-stop, regardless of hardware or software errors, and must allow operators to upgrade hardware and software during operation, without disturbing the application that run on them. In such clusters, software and hardware configurations are under the tight control of administrators. Communications between the nodes inside the cluster to computers external to the cluster are restricted.

In this article, we present the rationale behind developing a new architecture named the Distributed Security Infrastructure (DSI). We describe the main elements of this architecture and discuss our preliminary results.

DSI supports different security mechanisms to address the needs of telecom application servers running on Linux clusters. DSI provides applications running on clustered systems with distributed mechanisms for access control services, authentication services, integrity of communications and auditing services.

The Need for a New Approach

Many security solutions exist for clustered servers ranging from external solutions, such as firewalls, to internal solutions, such as integrity checking software. However, there is no solution dedicated for clusters. The most commonly used security approach is to package several existing solutions. Nevertheless, the integration and management of these different packages is complex, and often results in the absence of interoperability between different security mechanisms. Additional difficulties also arise when integrating these many packages, including the decreased ease of system maintenance and upgrades and the difficulty of keeping up with numerous security patches and upgrades.

Carrier-class clusters have tight restrictions on performance and response time. Therefore, much pressure is put on the system designer while designing security solutions. In fact, many security solutions cannot be used due to their high resource consumption. The currently implemented security mechanisms are based on user privileges and do not support authentication checks for interactions between two processes belonging to the same user (even if the processes are created on remote processors). However, for carrier-class applications, there are only a few users running the same application for a long period without any interruption.

Applying the above concept will grant the same security privileges to all processes created on different nodes. This would lead to no security checks for many actions through the distributed system. The granularity of the basic entity for the above security control is the user. For carrier-class applications, this granularity is not sufficient. Therefore, DSI is based on a more fine-grained basic entity: the individual process.

DSI Characteristics

As part of a carrier-class cluster, DSI must comply with carrier-class requirements, such as reliability, scalability and high availability. Furthermore, DSI supports the following requirements:

  • Coherent framework: Security must be coherent through different layers of heterogeneous hardware, applications, middleware, operating systems and networking technologies. All mechanisms must fit together to prevent any exploitable security gap in the system. Therefore, DSI aims at integrating together different security solutions and adapting them to soft real-time applications.

  • Process level approach: DSI is based on a fine-grained basic entity, the individual process.

  • Maximum performance: The introduction of security features must not impose high performance penalties. Performance can be expected to degrade slightly during the first establishment of a security context; however, the impact on subsequent accesses must be negligible.

  • Pre-emptive security: Any changes in the security context will be reflected immediately on the running security services. Whenever the security context of a subject changes, the system will re-evaluate its current use of resources against this new security context.

  • Dynamic security policy: It must be possible to support runtime changes in the distributed security policy. Carrier-class server nodes must provide continuous and long-term availability, and it is thus impossible to interrupt the service to enforce a new security policy.

  • Transparent key management: Cryptographic keys are generated in order to secure connections. This results in numerous keys that must be securely stored and managed.