Sandboxing with Landlock

Unprivileged self-sandboxing on Linux

Linux 5.13 is going to include the unprivileged sandboxing feature Landlock, which has been in the making for many years now.

Unprivileged means that you don’t need special system-level privileges like root or CAP_MAC_ADMIN to use it, as some other Linux sandboxing mechanisms do. Philosophically speaking, you should not need additional special privileges just to drop the privileges that you already have.

How it works

With Landlock, processes can restrict themselves to only use a specified set of file paths, and it lets them control which operations are available on these paths and their subdirectories (for example opening for reading, writing, and directory operations1).

A similar sandboxing feature has been around in OpenBSD for a while now with unveil(): This slide deck and talk by Bob Beck talks about the lessons learned and has examples on how to sandbox software with it, which should translate well to Landlock.

Download

To make it easier to play with, I forked the Landlock example tool from the kernel sources and made it compile standalone: You can get it at https://github.com/gnoack/landlockjail, or you can just download a precompiled statically linked version.


  1. At the moment, there are still some gaps, like stat(), which can still be done even in landlocked processes. But it’s moving in the right direction, and at least accesses to the files' contents can already be restricted. ↩︎

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