SELinux (Enforcing Mode) Configuration
SELinux (Security-Enhanced Linux) is a mandatory access control system for Linux that provides a granular level of security by defining access controls for applications, processes, and files. It uses security policies, which are a set of rules that tell SELinux what can or can’t be accessed, to enforce the access allowed by a policy.
SELinux has two modes, enforcing and permissive. When running in enforcing mode, it strictly enforces the SELinux policy and denies access based on policy rules. This can sometimes cause conflicts with applications that aren’t explicitly allowed to perform certain actions.
Cribl Edge and SELinux
To effectively integrate Cribl Edge with SELinux, consider the different policy requirements for in-stream processing and network ports.
- Cribl Edge’s in-stream processing often involves predefined processes and files, allowing for a relatively restrictive SELinux policy.
- Network ports might require a more permissive policy because users configure them within the UI.
Key Steps for SELinux Configuration
To ensure optimal integration of Cribl Edge with SELinux, begin by verifying the current SELinux status and the context of the Cribl Edge binary.
Check SELinux Status
Use the getenforce
command to determine the current status of SELinux on your system.
The output will be one of the following:
Enforcing
Permissive
Disabled
If the output is Enforcing
, SELinux is enabled and enforcing policies.
Verify Cribl Edge’s SELinux Context
Use the command ls -Z /opt/cribl/bin/cribl
to list the contents of the directory /opt/cribl/bin
while displaying their SELinux security contexts.
The output should show the SELinux context for the Cribl Edge binary.
Example output:
-rwxr-xr-x. cribl cribl cribl unconfined /opt/cribl/bin/cribl
Deploy Cribl Edge directly to
/opt
to avoid context issues. Do not deploy Cribl Edge to a user’s home directory, or to root (/
), and then move it to/opt
.
Revert Labels on Files and Directories
If needed, you can also use restorecon
,
an SELinux policy utility from the policycoreutils-python-utils
package,
to revert labels on files and directories to their default SELinux security context:
restorecon -R -v /opt/cribl
Check for SELinux Denials
Use auditd
to log SELinux denials. Look for messages related to Cribl Edge in the /var/log/audit/audit.log
file.
Modify SELinux Policy
If you encounter SELinux denials, you might need to modify the SELinux policy. There are three options ranging from least secure to most secure.
Use semanage
(Less Secure)
Using semanage
is the simplest but least secure method. It grants permissive access to the cribl_t type
, allowing all operations.
semanage permissive -a cribl_t
Use audit2allow
(Slightly More Secure)
Using audit2allow
creates SELinux policy rules to permit actions that were previously denied.
To identify and address SELinux denials related to Cribl Edge, follow these steps:
Find denied operations:
sudo grep cribl /var/log/audit/audit.log | audit2allow -M cribl
Install the generated policy:
sudo semodule -i cribl.pp
Create a Custom Policy (Most Secure)
Use tools like secil
or policycoreutils
to create a custom policy tailored to Cribl Edge’s needs. This provides the highest level of security but requires more technical expertise.
Reload SELinux Policy
Once you’ve altered the SELinux policy using tools like semanage
, audit2allow
, or through custom policy creation, use this command to ensure that the new rules take effect immediately.
sudo semanage reload -a
Specific Cribl Edge Considerations
In addition to the general SELinux guidelines, pay close attention to these Cribl Edge–specific factors:
- Cribl Edge configuration: Review Cribl Edge configuration files for any settings that might conflict with SELinux restrictions.
- Integration with other applications: Ensure that Cribl Edge’s interactions with other applications are compatible with their SELinux contexts and permissions.
Additional Considerations
In addition to the basic configuration, these factors are also important for optimal performance:
- SELinux booleans: Check the SELinux documentation for relevant booleans that might affect Cribl Edge’s behavior.
- SELinux context labeling: Ensure files and directories used by Cribl Edge have the correct SELinux context. Use tools like
restorecon
to relabel files. - SELinux troubleshooting tools: Use tools like
audiscan
andaudit2why
to analyze SELinux audit logs.
SELinux Troubleshooting
SELinux problems usually surface when you try to start the Cribl Edge service. Users immediately receive an error like the following:
Job for cribl.service failed because the control process exited with error code.
See "systemctl status cribl.service" and "journalctl -xe" for details.
One indication that the problem is in SELinux configuration, not in the Cribl Edge service itself, is when (1) nothing has been logged in $CRIBL_HOME/log/cribl.log
, and (2), when you run journalctl -xe
you see errors like the following:
cribl.service: Failed to execute command: Permission denied
cribl.service: Failed at step EXEC spawning /opt/cribl/bin/cribl: Permission denied
cribl.service: Control process exited, code=exited status=203
cribl.service: Failed to execute command: No such file or directory
cribl.service: Failed at step EXEC spawning /bin/rm -f /opt/cribl/pid/cribl.pid: Permission denied
You can confirm that SELinux configuration is the issue by verifying that the Cribl Edge service is able to start up on its own. To do this, run the cribl start
command.
Here are three commands that you can think of as a basic SELinux troubleshooting toolkit:
getenforce
verifies that SELinux is enabled and enforcing policy.sestatus -v
shows details of the SELinux policy that’s in effect.ls
with the-Z
or--context
option shows the SELinux tags on files and/or folders. In the output, the fifth column reports the SELinux context in the formuser:role:type:level
.
Example Problem
Suppose you run ls -lZ /opt/cribl
to see the SElinux context for /opt/cribl
.
If the output looks like the following, there is a problem: the presence of “home” among the type
part of the Linux context. In this case, user_home_t
is the offending type. When the type is user_home_t
or admin_home_t
, SELinux will not permit the service to read, write, or execute files.
$ ls -laZ /opt/cribl
total 0
drwxr-xr-x. 6 cribl cribl unconfined_u:object_r:user_home_t:s0 62 Feb 16 08:31 .
drwxr-xr-x. 3 root root system_u:object_r:usr_t:s0 19 Feb 16 19:54 ..
drwxr-xr-x. 2 cribl cribl unconfined_u:object_r:user_home_t:s0 202 Feb 16 08:31 bin
drwxr-xr-x. 5 cribl cribl unconfined_u:object_r:user_home_t:s0 49 Feb 16 08:20 data
drwxr-xr-x. 6 cribl cribl unconfined_u:object_r:user_home_t:s0 59 Feb 16 08:31 default
drwxr-xr-x. 3 cribl cribl unconfined_u:object_r:user_home_t:s0 22 Feb 16 08:31 thirdparty
Example Solution
To fix the labeling, download Cribl Edge again directly to /opt
. Do not download Cribl Edge to a user’s home directory, or to root (/
), and then move it to /opt
- that was what caused our example problem.
curl -Lso - $(curl -s https://cdn.cribl.io/dl/latest) | sudo tar zxvf - -C /opt
A simpler option is to revert the labels using restorecon
:
restorecon -R -v /opt/cribl
systemctl restart cribl
Once you correct the problem, the output will look like the following. Instead of *home_t
listings in the type
field, this SELinux context has usr_t
, a type that will satisfy SELinux’s criteria for allowing the service to read, write, and execute files.
# ls -laZ /opt/cribl
total 0
drwxr-xr-x. 6 cribl cribl unconfined_u:object_r:usr_t:s0 62 Feb 16 08:31 .
drwxr-xr-x. 3 root root system_u:object_r:usr_t:s0 19 Feb 16 20:05 ..
drwxr-xr-x. 2 cribl cribl unconfined_u:object_r:usr_t:s0 202 Feb 16 08:31 bin
drwxr-xr-x. 5 cribl cribl unconfined_u:object_r:usr_t:s0 49 Feb 16 08:20 data
drwxr-xr-x. 6 cribl cribl unconfined_u:object_r:usr_t:s0 59 Feb 16 08:31 default
drwxr-xr-x. 3 cribl cribl unconfined_u:object_r:usr_t:s0 22 Feb 16 08:31 thirdparty