How to use the command 'secon' (with examples)

The secon command is part of the Security-Enhanced Linux (SELinux) toolkit. It provides a way to retrieve and display the SELinux security context associated with various system resources on a Linux-based machine. Security contexts in SELinux are essential for maintaining strict access controls and ensuring that processes and files have appropriate permissions. Understanding and working with these contexts helps administrators maintain a secure environment.

Use case 1: Get the security context of the current execution context

Code:

secon

Motivation:

Understanding the security context of the current execution environment is crucial for troubleshooting and verifying the permissions and access controls in place. When you execute a command in a terminal, it runs under a specific security context, which determines what operations the command is allowed to perform. By examining this context, administrators can verify that a shell session is running with the correct permissions as per their security policies.

Explanation:

• secon: This command, when run without any arguments, displays the security context of the current shell or executing process. It includes details like user identity, role, type, and security level, which are integral components of SELinux’s security model.

Example output:

unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

In this example, the current execution environment is operating with the unconfined user, role, and type, which means it is not restricted by additional SELinux constraints, often typical for administrative sessions.

Use case 2: Get the current security context of a process

Code:

secon --pid 1

Motivation:

Processes on a system each have their own security context. When troubleshooting or verifying the security constraints applied to a specific process, it’s useful to retrieve this information. By obtaining the context of a process such as the init process (pid 1), you can verify its operational capabilities and whether it aligns with your security policies.

Explanation:

• --pid 1: This argument tells secon to fetch and display the SELinux security context of the process with the process ID 1, which is usually the init process (or systemd, depending on the Linux distribution). This process is crucial as it is the first process started by the kernel and is responsible for initializing the system.

Example output:

system_u:system_r:init_t:s0

Here, the init process is running as the system_u user, with the system_r role, and the init_t type, indicating it’s operating with elevated privileges typical for system management.

Use case 3: Get the current security context of a file, resolving all intermediate symlinks

Code:

secon --file path/to/file_or_directory

Motivation:

Understanding the security context of files and directories is essential for enforcing file access controls on a system. By resolving all intermediate symlinks, secon ensures that you are retrieving the security context of the actual file, rather than the symlink itself. This is critical for verifying the permissions of the target file and ensuring compliance with your security directives.

Explanation:

• --file path/to/file_or_directory: This argument specifies that secon should retrieve the security context of the file or directory specified by the given path. The command resolves all symlinks to ensure the security context is retrieved for the actual file.

Example output:

system_u:object_r:etc_t:s0

In this output, the file resides under the system_u user domain, with the object_r role and the etc_t type, likely indicating a configuration file within the /etc directory.

Use case 4: Get the current security context of a symlink itself (i.e. do not resolve)

Code:

secon --link path/to/symlink

Motivation:

When dealing with symlinks, sometimes it is essential to know the security context of the symlink itself, not just the target file it points to. This can be important for ensuring that symlinks are not manipulated by unauthorized users, potentially redirecting to malicious or unintended files.

Explanation:

• --link path/to/symlink: This argument indicates that secon should evaluate and return the security context of the symlink, not what it points to. This distinction is crucial when analyzing security paths within the filesystem that involve symbolic links.

Example output:

system_u:object_r:symlink_t:s0

Here, the symlink is labeled with an object_r role and a symlink_t type, designating it specifically as a symbolic link object under SELinux labeling.

Use case 5: Parse and explain a context specification

Code:

secon system_u:system_r:container_t:s0:c899,c900

Motivation:

Parsing a specified security context gives insight into how a theoretical or intended SELinux policy would be interpreted by the system. It allows administrators to simulate and understand complex access control situations or verify policies before applying them system-wide.

Explanation:

• system_u:system_r:container_t:s0:c899,c900: This argument is an explicit SELinux context provided to secon for parsing. The format includes user:role:type:sensitivity:category. Understanding these elements helps in configuring appropriate domains and enhancing security postures.

Example output:

user: system_u
role: system_r
type: container_t
sensitivity: s0
categories: c899,c900

The parsed output breaks down each component of the context, showing that this context is intended for processes operating as system_u with a system_r, within a container_t environment, and additional sensitivity and category specifications.

Conclusion:

The secon command is an invaluable tool for administrators and security professionals working with SELinux. By providing insights into the security contexts of processes, files, and symlinks, it aids in enforcing and verifying system permissions and security policies. Understanding these security contexts is vital for maintaining a secure and controlled Linux environment.