Linux Security Modules

This repository contains a small collection of linux security modules, which were written as a part of a learning/experimentation process.

The code present has been compiled and tested against the most recent long-term kernel, at the time of writing that is 5.10.17.

If you want to port this code to a newer kernel, in the future, then the following bug-report is a good overview of how I approach things:

• https://github.com/skx/linux-security-modules/issues/13

Included Modules

There are three modules contained within this repository, two of which are simple tests and one of which is more "real".

The only real/useful module is:

• can-exec
  • The user-space helper /sbin/can-exec is invoked to determine whether a user can execute a specific command.
  • Because user-space controls execution policies can be written/updated dynamically.

The following two modules were written as I started the learning-process, and demonstrate creating simple standalone modules, albeit ones which do not actually provide any significant security benefit:

• whitelist
  • Only allow execution of binaries which have a specific xattr present.
• hashcheck
  • Only allow execution of commands with xattr containing valid SHA1sum of binaries.
  • This builds upon the previous module.

Compilation

Copy the contents of security/ into your local Kernel-tree, and run make menuconfig to enable the appropriate options.

Further notes are available within the appropriate module subdirectories.

For a Debian GNU/Linux host, these are the kernel build-dependencies you'll need to install, if they're not already present:

  # apt-get install flex bison bc libelf-dev libssl-dev \
                    build-essential make libncurses5-dev \
                    git-core

Tracking Kernel Changes

As new kernels are released it is possible the two files security/Kconfig & security/Makefile might need resyncing with the base versions installed with the Linux source-tree.

You should be able to update them just by running diff and copying any lines referring to the modules CAN_EXEC, HASH_CHECK, & WHITELIST into place.