Simplicity is a form of art...

Overriding the default SELinux policies

Extending SELinux policies with additional rules is easy. As SELinux uses a deny by default approach, all you need to do is to create a policy module that contains the additional (allow) rules, load that and you're all set. But what if you want to remove some rules?

Well, sadly …

Highlevel assessment of Cdorked and Gentoo Hardened/SELinux

With all the reports surrounding Cdorked, I took a look at if SELinux and/or other Gentoo Hardened technologies could reduce the likelihood that this infection occurs on your system.

First of all, we don't know yet how the malware gets installed on the server. We do know that the …

SECMARK and SELinux

When using SECMARK, the administrator configures the iptables or netfilter rules to add a label to the packet data structure (on the host itself) that can be governed through SELinux policies. Unlike peer labeling, here the labels assigned to the network traffic is completely locally defined. Consider the following command …

Peer labeling in SELinux policy

Allow me to start with an important warning: I don't have much hands-on experience with the remainder of this post. Its based on the few resources I found on the Internet and a few tests done locally which I've investigated in my attempt to understand SELinux policy writing for networking …

SELinux policy and network controls

Let's talk about how SELinux governs network streams (and how it reflects this into the policy).

When you don't do fancy stuff like SECMARK or netlabeling, then the classes that you should keep an eye on are tcp_socket and udp_socket (depending on the protocol). There used to be node and …

Overview of Linux capabilities, part 2

As I've (in a very high level) described capabilities and talked a bit on how to work with them, I started with a small overview of file-related capabilities. So next up are process-related capabilities (note, this isn't a conform terminology, more some categorization that I do myself).

CAP_IPC_LOCK

Allow the …

Capabilities, a short intro

Capabilities. You probably have heard of them already, but when you start developing SELinux policies, you'll notice that you come in closer contact with them than before. This is because SELinux, when applications want to do something "root-like", checks the capability of that application. Without SELinux, this either requires the …

SELinux mount options

When you read through the Gentoo Hardened SELinux handbook, you'll notice that we sometimes update /etc/fstab with some SELinux-specific settings. So, what are these settings about and are there more of them?

First of all, let's look at a particular example from the installation instructions so you see what …

Securely handling libffi

I've recently came across libffi again. No, not because it was mentioned during the Gentoo Hardened online meeting, but because my /var/tmp wasn't mounted correctly, and emerge (actually python) uses libffi. Most users won't notice this, because libffi works behind the scenes. But when it fails, it fails bad …

How logins get their SELinux user context

Sometimes, especially when users are converting their systems to be SELinux-enabled, their user context is wrong. An example would be when, after logon (in permissive mode), the user is in the system_u:system_r:local_login_t domain instead of a user domain like staff_u:staff_r:staff_t.
So, how does a login get …