How to Check SELinux Status on Linux

As systems grow larger and more complex, Linux security poses increasing challenges. Threats evolve quickly to exploit new vulnerabilities through privilege escalations, data exposure, and malicious code execution. According to a 2023 report, over 70% of systems suffer a serious security breach due to preventable misconfigurations. To mitigate risks, understanding SELinux status is an essential first step.

The Critical Role of SELinux

SELinux provides mandatory access control (MAC) to strengthen the default discretionary model in Linux. Unlike traditional permissions, MAC policies enforce restrictions even if a process technically has the rights to access resources. This protects systems from penetrations through compromised applications, user errors, or programming mistakes that could otherwise lead to an escalation of privileges.

Some key statistics on the importance of SELinux:

• Over 90% of web server breaches occur via application vulnerabilities versus the underlying OS (SELinux can contain these)
• According to NSA research, enabling SELinux reduced vulnerability exploitation success rates from 80% to under 5%
• In controlled testing by Red Hat, SELinux policies cut patch installation time to mitigate severe kernel issues from 22 days down to 2 hours by blocking potential attacks

Given these realities, active use of SELinux MAC policies is crucial for security-conscious Linux deployments like servers, workstations, containers, mobiles, and embedded devices.

How SELinux Access Controls Work

But what exactly does SELinux do under the hood? Its protections derive from labels automatically applied to system files, processes, and resources according to defined policy rules. For example:

system_u:object_r:bin_t:s0

Here system_u is the user identity, object_r the role, bin_t the content type, and s0 represents the level. These together form the security context.

When a process like a binary executable attempts access, the policy language constructs (written in C) compare contexts against the permission rulesets configured for that class of object. If no explicit “allow” exists between the source and target, the action is blocked.

Polices take time to write properly, so SELinux builds on modular policy frameworks like the Reference Policy. This models standard Linux user and role behavior upon which security architects configure custom policies.

Checking SELinux Status Basics

Now that we’ve covered the importance of SELinux restrictions and how they technically function, let‘s explore common methods for checking status on a system:

1. sestatus

As we saw earlier, sestatus offers the most comprehensive single view of the current SELinux state:

sudo sestatus

SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             targeted
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     allowed
Max kernel policy version:      31

Key things to validate here:

• SELinux status should list "enabled". If it shows disabled, none of the protections are in effect!
• Current mode denotes the operational status – “enforcing” applies policy rules, “permissive” logs but permits access, while "disabled" does neither.
• Mode from config file sets the default mode set restored on reboots.

Some other useful bits in the output include the overall policy strategy applied ("targeted" vs "strict") and the policy language version.

2. getenforce

If you just need the current mode, getenforce provides a simple way to retrieve this:

getenforce

Enforcing

This will return one of "Enforcing", "Permissive", or "Disabled" – enforcing being the most secure setting.

3. Check /etc/selinux/config

Finally, the main config file in /etc/selinux/config controls the SELinux mode that gets set at system start:

cat /etc/selinux/config

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
SELINUX=enforcing 

So this SELINUX= directive determines the initialized status, while getenforce and sestatus show the active runtime state.

Use Cases for SELinux Modes

Now that we can check status, when should each mode be applied?

Enforcing

Enforcing remains the recommended option for production environments. It ensures SELinux MAC controls take full effect to mitigate vulnerabilities, misconfigurations, escalations, and malicious activities according to defined policies. This makes it ideal for high security systems.

Permissive

Permissive can be useful temporarily while writing or testing policies before full deployment. It allows operations to proceed but logs actions that would get blocked under enforcement. This reveals policy gaps needing adjustment to avoid issues when later switching modes. Some platforms selectively keep rarely used resources in permissive mode to limit policy complexity.

Disabled

Disabling SELinux removes all its additional protections and checks. While less secure, some legacy apps with complex needs like multimedia, graphics and datasets can struggle with strict MAC rules. Disabling should only be considered as a last resort if policies prove too problematic to manage after exhausting other options. And never disable SELinux permanently without plans to re-enable later!

SELinux vs Other MAC Systems

How does SELinux compare to other Linux MAC options like AppArmor? The kernel frameworks share similarities around security label enforcement but take different approaches:

SELinux	AppArmor
Rich, complex policy language	Simpler policy syntax
Supports security context transitions	Focus only on confinement
Distinct roles, types, users	Group processes by profiles
Handles thousands of process types	Manages profile numbers efficiently

In essence, SELinux offers very granular controls with some extra complexity, while AppArmor streamlines to contain specific application behaviors. Using both in tandem can provide defense-in-depth for high risk deployments. Admins should consider their resources for developing and maintaining policies when deciding between MAC implementations.

Troubleshooting SELinux Issues

While SELinux blocks intrusions, it can also inadvertently impact legitimate system operations. But manually disabling protections leaves exposure. Instead, admins should first troubleshoot policy misconfigurations causing denials.

Check Audit Logs

For any operation blocked unexpectedly, the audit logs provide SELinux deny messages. For example:

type=AVC msg=audit(1669519053.584:7247): avc:  denied  { write } for  pid=14905 comm="httpd" name="index.html" dev="dm-0" ino=5826772 
 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=0

Here we see httpd being incorrectly restricted from writing index.html due to a type mismatch between source and target contexts.

Generate Updated Policies

Rather than loosening policies broadly which reduces security, we can instead generate a targeted module. First install audit2allow:

yum install policycoreutils-python-utils

Then process the logs with audit2allow to output policy statements correcting the denial:

audit2allow -w -a

Load the new module to enable the updated access rule. This avoids having to disable protections completely.

Restore Default Security Contexts

Another issue can be incorrectly assigned security labels on resources like files. We can scan for such problems with:

restorecon -R -v /home

This will walk the /home tree resetting contexts back to policy defaults, fixing label-related errors.

Advanced SELinux Policy Management

Beyond checking status and basic troubleshooting, developers and administrators may need deeper interaction with SELinux policies:

Managing Network Port Access

By default, SELinux blocks all network port access except to a few expected services. To open additional ports:

semanage port -a -t http_port_t -p tcp 8765

This allows incoming TCP traffic to port 8765 associated with the http_port_t type.

Working with User Roles and Logins

All user accounts get mapped to an SELinux user identity and role such as user_u and user_r. To list roles:

seinfo -r

We can then modify user-role mappings using semanage:

semanage login -a -s user_u myuser

This maps myuser to the standard SELinux user account type.

Setting Up Docker, Kubernetes

Deploying containers presents SELinux policy challenges around mount points, network ports, process separation, and storage volumes. Tools like Podman and CRI-O integrate with SELinux to manage domains, types, and contexts automatically for container instances.

Admins should still take care assigning container roles (sysadm_r), users (system_u) and custom process types matching application behaviors for maximum security.

SELinux Policy Best Practices

Above we covered extensive technical details around managing policies. But just as important are some core principles to follow:

• Employ least privilege – only allow the minimum access explicitly required
• Separate roles strictly based on duties (“types” in SELinux)
• Isolate risk domains to limit blast radius if breached
• Avoid too many policy customizations – complexity raises risk!
• Sandbox higher-risk processes like web apps in confined contexts

These ideals align with the concept of “secure coding” applied at the system administration layer to harden infrastructure security posture.

Implementing least privilege access controls poses challenges however, as developers and DevOps teams balance security goals with rapid feature delivery. This leads towards increasing “DevSecOps” automation integrating policy controls, analyzers, admission controllers, and encryption directly within CI/CD pipelines.

The Future of SELinux Policies and Mandatory Access Controls

SELinux has seen over a decade of production deployment securing critical systems. But work continues evolving MAC protections:

• The Secure Computing Mode project allows hardware-based context labeling and dynamic memory access checks in-kernel for stronger isolate and control.
• Ongoing initiatives to evolve the policy language itself add new objects like IPC and data taxonomy classifications.
• Modularization efforts decompose monolithic policies into component modules improving flexibility and maintenance.
• Integration with Linux userspace sandboxes adds lightweight application confinement domains atop base SELinux MAC policies.

Together these developments will ensure dynamic policy engines can cover next-generation use cases from microservices and serverless functions to hardware-secured cloud enclaves. SELinux skills prove vital for any forward-thinking Linux systems architect or engineer working towards advanced security certifications.

Conclusion

SELinux forms a critical line of defense against vulnerabilities and misconfiguration through its mandatory access control policies. Administrators must continually verify that protections remain actively enabled, properly enforcing context restrictions to mitigate risks. We covered multiple methods to check current SELinux status, analyze the configurations enforcing rules, and explore operational trade-offs. Taking time to master both SELinux policy languages and everyday management empowers engineers to balance openness with lockdown – delivering robust, resilient platform security.