11.2.3. Booleans

⁠11.2.3. Booleans

SELinux is based on the least level of access required for a service to run. Services can be run in a variety of ways; therefore, you must tell SELinux how you are running services. This can be achieved via Booleans that allow parts of SELinux policy to be changed at runtime, without any knowledge of SELinux policy writing. This allows changes, such as allowing services access to NFS file systems, without reloading or recompiling SELinux policy.

To modify the state of a Boolean, use the setsebool command. For example, to turn the allow_httpd_anon_write Boolean on, run the following command as the root user:

# setsebool -P allow_httpd_anon_write on

To turn a Boolean off, using the same example, simply change on to off in the command, as shown below:

# setsebool -P allow_httpd_anon_write off

Note

Do not use the -P option if you do not want setsebool changes to persist across reboots.

Below is a description of common Booleans available that cater for the way httpd is running:

allow_httpd_anon_write: When disabled, this Boolean allows httpd only read access to files labeled with the public_content_rw_t type. Enabling this Boolean will allow httpd to write to files labeled with the public_content_rw_t type, such as a public directory containing files for a public file transfer service.
allow_httpd_mod_auth_ntlm_winbind: Enabling this Boolean allows access to NTLM and Winbind authentication mechanisms via the mod_auth_ntlm_winbind module in httpd.
allow_httpd_mod_auth_pam: Enabling this Boolean allows access to PAM authentication mechanisms via the mod_auth_pam module in httpd.
allow_httpd_sys_script_anon_write: This Boolean defines whether or not HTTP scripts are allowed write access to files labeled with the public_content_rw_t type, as used in a public file transfer service.
httpd_builtin_scripting: This Boolean defines access to httpd scripting. Having this Boolean enabled is often required for PHP content.
httpd_can_network_connect: When disabled, this Boolean prevents HTTP scripts and modules from initiating a connection to a network or remote port. Turn this Boolean on to allow this access.
httpd_can_network_connect_db: When disabled, this Boolean prevents HTTP scripts and modules from initiating a connection to database servers. Turn this Boolean on to allow this access.
httpd_can_network_relay: Turn this Boolean on when httpd is being used as a forward or reverse proxy.
httpd_can_sendmail: When disabled, this Boolean prevents HTTP modules from sending mail. This can prevent spam attacks should a vulnerability be found in httpd. Turn this Boolean on to allow HTTP modules to send mail.
httpd_dbus_avahi: When off, this Boolean denies httpd access to the avahi service via D-Bus. Turn this Boolean on to allow this access.
httpd_enable_cgi: When disabled, this Boolean prevents httpd from executing CGI scripts. Turn this Boolean on to allow httpd to execute CGI scripts (CGI scripts must be labeled with the httpd_sys_script_exec_t type).
httpd_enable_ftp_server: Turning this Boolean on will allow httpd to listen on the FTP port and act as an FTP server.
httpd_enable_homedirs: When disabled, this Boolean prevents httpd from accessing user home directories. Turn this Boolean on to allow httpd access to user home directories; for example, content in /home/*/.
httpd_execmem: When enabled, this Boolean allows httpd to execute programs that require memory addresses that are both executable and writeable. Enabling this Boolean is not recommended from a security standpoint as it reduces protection against buffer overflows, however certain modules and applications (such as Java and Mono applications) require this privilege.
httpd_ssi_exec: This Boolean defines whether or not server side include (SSI) elements in a web page can be executed.
httpd_tmp_exec: Enabling this Boolean allows httpd to execute files in temporary directories.
httpd_tty_comm: This Boolean defines whether or not httpd is allowed access to the controlling terminal. Usually this access is not required, however in cases such as configuring an SSL certificate file, terminal access is required to display and process a password prompt.
httpd_unified: When enabled, this Boolean allows httpd_t complete access to all of the httpd types (i.e. to execute, read, or write sys_content_t). When disabled, there is separation in place between web content that is read-only, writeable or executable. Disabling this Boolean ensures an extra level of security but adds the administrative overhead of having to individually label scripts and other web content based on the file access that each should have.
httpd_use_cifs: Turn this Boolean on to allow httpd access to files on CIFS file systems that are labeled with the cifs_t type, such as file systems mounted via Samba.
httpd_use_gpg: Enabling this Boolean allows httpd to make use of GPG encryption.
httpd_use_nfs: Turn this Boolean on to allow httpd access to files on NFS file systems that are labeled with the nfs_t type, such as file systems mounted via NFS.