SELinux Infrastructure SOP
SELinux is a fundamental part of our Operating System but still has a large learning curve and remains quite intimidating to both developers and system administrators. Fedora’s Infrastructure has been growing at an unfathomable rate, and is full of custom software that needs to be locked down. The goal of this SOP is to make it simple to track down and fix SELinux policy related issues within Fedora’s Infrastructure.
Fedora Infrastructure Team
#fedora-admin, sysadmin-main, sysadmin-web groups
To ensure that we are able to fully wield the power of SELinux within our infrastructure.
Step One: Realizing you have a problem
If you are trying to find a specific problem on a host go look in the audit.log per-host on our cental log server. See the syslog SOP for more information.
Step Two: Tracking down the violation
Generate SELinux policy allow rules from logs of denied operations. This is useful for getting a quick overview of what has been getting denied on the local machine:
You can obtain more detailed audit messages by using ausearch to get the most recent violations:
ausearch -m avc -ts recent
Again -see the syslog SOP for more information here.
Step Three: Fixing the violation
Below are examples of using our current ansible configuration to make SELinux deployment changes. These constructs are currently home-brewed, and do not exist in upstream Ansible. For these functions to work, you must ensure that the host or servergroup is configured with 'include selinux', which will enable SELinux in permissive mode. Once a host is properly configured, this can be changed to 'include selinux-enforcing' to enable SELinux Enforcing mode.
Most services have $service_selinux manpages that are automatically generated from policy.
Toggling an SELinux boolean
SELinux booleans, which can be viewed by running
semanage boolean -l,
can easily be configured using the following syntax within
your ansible configuration.:
seboolean: name=httpd_can_network_connect_db state=yes persistent=yes
Setting custom context
Our infrastructure contains many custom applications, which may utilize non-standard file locations. These issues can lead to trouble with SELinux, but they can easily be resolved by setting custom file context.:
"file: path=/var/tmp/l10n-data recurse=yes setype=httpd_sys_content_t"
Fixing odd errors from the logs
If you see messages like this in the log reports:
restorecon:/etc/selinux/targeted/contexts/files/file_contexts: Multiple same / specifications for /home/fedora. matchpathcon: / /etc/selinux/targeted/contexts/files/file_contexts: Multiple same / / specifications for /home/fedora.
Then it is likely you have an overlapping filecontext in your local selinux context configuration - in this case likely one added by ansible accidentally.
To find it run this:
semanage fcontext -l | grep /path/being/complained/about
sometimes it is just an ordering problem and reversing them solves it other times it is just an overlap, period.
look at the context and delete the one you do not want or reorder.
To delete run:
semanage fcontext -d '/entry/you/wish/to/delete'
This just removes that filecontext - no need to worry about files being deleted.
Then rerun the triggering command and see if the problem is solved.
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