Red Hat Training

A Red Hat training course is available for RHEL 8

Chapter 4. Configuring SELinux for applications and services with non-standard configurations

When SELinux is in enforcing mode, the default policy is the targeted policy. The following sections provide information about setting up and configuring the SELinux policy for various services after you change configuration defaults, such as ports, database locations, or file-system permissions for processes.

You learn to change SELinux types for non-standard ports, to identify and fix incorrect labels for changes of default directories, and to adjust the policy using SELinux booleans.

4.1. Customizing the SELinux policy for the Apache HTTP server in a non-standard configuration

You can configure the Apache HTTP server to listen on a different port and to provide content in a non-default directory. To prevent consequent SELinux denials, follow the steps in this procedure to adjust your system’s SELinux policy.

Prerequisites

  • The httpd package is installed and the Apache HTTP server is configured to listen on TCP port 3131 and to use the /var/test_www/ directory instead of the default /var/www/ directory.
  • The policycoreutils-python-utils and setroubleshoot-server packages are installed on your system.

Procedure

  1. Start the httpd service and check the status: 

    # systemctl start httpd
# systemctl status httpd
...
httpd[14523]: (13)Permission denied: AH00072: make_sock: could not bind to address [::]:3131
...
systemd[1]: Failed to start The Apache HTTP Server.
...

  2. The SELinux policy assumes that httpd runs on port 80: 

    # semanage port -l | grep http
http_cache_port_t              tcp      8080, 8118, 8123, 10001-10010
http_cache_port_t              udp      3130
http_port_t                    tcp      80, 81, 443, 488, 8008, 8009, 8443, 9000
pegasus_http_port_t            tcp      5988
pegasus_https_port_t           tcp      5989

  3. Change the SELinux type of port 3131 to match port 80: 

    # semanage port -a -t http_port_t -p tcp 3131

  4. Start httpd again: 

    # systemctl start httpd

  5. However, the content remains inaccessible: 

    # wget localhost:3131/index.html
...
HTTP request sent, awaiting response... 403 Forbidden
...

    Find the reason with the sealert tool: 

    # sealert -l "*"
...
SELinux is preventing httpd from getattr access on the file /var/test_www/html/index.html.
...

  6. Compare SELinux types for the standard and the new path using the matchpathcon tool: 

    # matchpathcon /var/www/html /var/test_www/html
/var/www/html       system_u:object_r:httpd_sys_content_t:s0
/var/test_www/html  system_u:object_r:var_t:s0

  7. Change the SELinux type of the new /var/test_www/html/ content directory to the type of the default /var/www/html directory: 

    # semanage fcontext -a -e /var/www /var/test_www

  8. Relabel the /var directory recursively: 

    # restorecon -Rv /var/
...
Relabeled /var/test_www/html from unconfined_u:object_r:var_t:s0 to unconfined_u:object_r:httpd_sys_content_t:s0
Relabeled /var/test_www/html/index.html from unconfined_u:object_r:var_t:s0 to unconfined_u:object_r:httpd_sys_content_t:s0

Verification

  1. Check that the httpd service is running: 

    # systemctl status httpd
...
Active: active (running)
...
systemd[1]: Started The Apache HTTP Server.
httpd[14888]: Server configured, listening on: port 3131
...

  2. Verify that the content provided by the Apache HTTP server is accessible: 

    # wget localhost:3131/index.html
...
HTTP request sent, awaiting response... 200 OK
Length: 0 [text/html]
Saving to: ‘index.html’
...

Additional resources

  • The semanage(8), matchpathcon(8), and sealert(8) man pages.

4.2. Adjusting the policy for sharing NFS and CIFS volumes by using SELinux booleans

You can change parts of SELinux policy at runtime using booleans, even without any knowledge of SELinux policy writing. This enables changes, such as allowing services access to NFS volumes, without reloading or recompiling SELinux policy. The following procedure demonstrates listing SELinux booleans and configuring them to achieve the required changes in the policy.

NFS mounts on the client side are labeled with a default context defined by a policy for NFS volumes. In RHEL, this default context uses the nfs_t type. Also, Samba shares mounted on the client side are labeled with a default context defined by the policy. This default context uses the cifs_t type. You can enable or disable booleans to control which services are allowed to access the nfs_t and cifs_t types.

To allow the Apache HTTP server service (httpd) to access and share NFS and CIFS volumes, perform the following steps:

Prerequisites

  • Optionally, install the selinux-policy-devel package to obtain clearer and more detailed descriptions of SELinux booleans in the output of the semanage boolean -l command.

Procedure

  1. Identify SELinux booleans relevant for NFS, CIFS, and Apache: 

    # semanage boolean -l | grep 'nfs\|cifs' | grep httpd
httpd_use_cifs                 (off  ,  off)  Allow httpd to access cifs file systems
httpd_use_nfs                  (off  ,  off)  Allow httpd to access nfs file systems

  2. List the current state of the booleans: 

    $ getsebool -a | grep 'nfs\|cifs' | grep httpd
httpd_use_cifs --> off
httpd_use_nfs --> off

  3. Enable the identified booleans: 

    # setsebool httpd_use_nfs on
# setsebool httpd_use_cifs on
    Note

    Use setsebool with the -P option to make the changes persistent across restarts. A setsebool -P command requires a rebuild of the entire policy, and it might take some time depending on your configuration.

Verification

  1. Check that the booleans are on: 

    $ getsebool -a | grep 'nfs\|cifs' | grep httpd
httpd_use_cifs --> on
httpd_use_nfs --> on

Additional resources

  • semanage-boolean(8), sepolicy-booleans(8), getsebool(8), setsebool(8), booleans(5), and booleans(8) man pages

4.3. Additional resources