Gotcha

Sometimes event logs are not enough, and you need to supply your security systems with something more. For instance, you might want to improve the detection of anomalies or facilitate the hunt for an intruder on your network. Many commercial solutions are available for file integrity monitoring in Linux. However, some budgets don't allow for a large investment. The good news is that Linux systems have a great selection of open source tools for securing systems, and these tools provide a means for maintaining file integrity at low cost. The Integrity Measurement Architecture comes in handy.

Integrity Measurement Architecture (IMA) [1] is a component of the Linux kernel's integrity subsystem (see the "Components of the Integrity Subsystem" box.) IMA is responsible for calculating hashes of files before loading them, and it supports reporting on the hashes. The integrity subsystem also consists of an Extended Verification Module (EVM) that detects tampering with offline security attribute extensions (e.g., SELinux), which are the basis for clearance decisions of the Linux Security Modules (LSM) framework.

What Is IMA?

The main purpose of IMA is to detect if files have been accidentally or intentionally changed, evaluate the measurement of a file against a value stored as an extension attribute, and enforce the integrity of local files. These objectives are complemented by Mandatory Access Control (MAC) protections provided by LSM modules such as SELinux and Smack.

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