Entendiendo SELinux (Parte III)

Retomando esta casi olvidada serie sobre SELinux, hoy veremos los booleanos. Son variables que nos permiten encender o apagar funcionalidades para servicios específicos. Lo interesante de estos es que no hay que hacer un curso ni buscar un howto para introducirse a ellos, debido a que cuando necesitemos que SELinux haga algo respecto a un servicio, simplemente buscaremos los booleanos relacionados con dicho servicio o daemon.

Los comandos que nos ayudarán a trabajar con los mismos son getsebool y setsebool. Usando el comando getsebool -a obtendremos una lista completa de todos los booleanos disponible en nuestro sistema.

[fraterneo@rainbow ~]$ getsebool -a
abrt_anon_write --> off
abrt_handle_event --> off
abrt_upload_watch_anon_write --> on
antivirus_can_scan_system --> off
antivirus_use_jit --> off
auditadm_exec_content --> on
authlogin_nsswitch_use_ldap --> off
authlogin_radius --> off
authlogin_yubikey --> off
awstats_purge_apache_log_files --> off
boinc_execmem --> on
cdrecord_read_content --> off
cluster_can_network_connect --> off
cluster_manage_all_files --> off
cluster_use_execmem --> off
cobbler_anon_write --> off
cobbler_can_network_connect --> off
cobbler_use_cifs --> off
cobbler_use_nfs --> off
collectd_tcp_network_connect --> off
condor_tcp_network_connect --> off
cron_can_relabel --> off
cups_execmem --> off
cvs_read_shadow --> off
daemons_dump_core --> off
daemons_enable_cluster_mode --> off
daemons_use_tcp_wrapper --> off
daemons_use_tty --> off
dbadm_exec_content --> on
dbadm_manage_user_files --> off
dbadm_read_user_files --> off
deny_execmem --> off
deny_ptrace --> off
dhcpc_exec_iptables --> off
dhcpd_use_ldap --> off
docker_connect_any --> off
docker_transition_unconfined --> off
domain_fd_use --> on
domain_kernel_load_modules --> off
entropyd_use_audio --> on
exim_can_connect_db --> off
exim_manage_user_files --> off
exim_read_user_files --> off
fcron_crond --> off
fenced_can_network_connect --> off
fenced_can_ssh --> off
fips_mode --> on
ftp_home_dir --> off
ftpd_anon_write --> off
ftpd_connect_all_unreserved --> off
ftpd_connect_db --> off
ftpd_full_access --> on
ftpd_use_cifs --> off
ftpd_use_fusefs --> off
ftpd_use_nfs --> off
ftpd_use_passive_mode --> off
git_cgi_enable_homedirs --> off
git_cgi_use_cifs --> off
git_cgi_use_nfs --> off
git_session_bind_all_unreserved_ports --> off
git_session_users --> off
git_system_enable_homedirs --> off
git_system_use_cifs --> off
git_system_use_nfs --> off
gitosis_can_sendmail --> off
glance_use_fusefs --> off
global_ssp --> off
gluster_anon_write --> off
gluster_export_all_ro --> off
gluster_export_all_rw --> on
gpg_agent_env_file --> off
gpg_web_anon_write --> off
gssd_read_tmp --> on
guest_exec_content --> on
haproxy_connect_any --> off
httpd_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_connect_ftp --> off
httpd_can_connect_ldap --> off
httpd_can_connect_mythtv --> off
httpd_can_connect_zabbix --> off
httpd_can_network_connect --> off
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> off
httpd_dbus_avahi --> off
httpd_dbus_sssd --> off
httpd_dontaudit_search_dirs --> off
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> on
httpd_execmem --> off
httpd_graceful_shutdown --> on
httpd_manage_ipa --> off
httpd_mod_auth_ntlm_winbind --> off
httpd_mod_auth_pam --> off
httpd_read_user_content --> on
httpd_run_stickshift --> off
httpd_serve_cobbler_files --> off
httpd_setrlimit --> off
httpd_ssi_exec --> off
httpd_sys_script_anon_write --> off
httpd_tmp_exec --> off
httpd_tty_comm --> off
httpd_unified --> off
httpd_use_cifs --> off
httpd_use_fusefs --> off
httpd_use_gpg --> off
httpd_use_nfs --> off
httpd_use_openstack --> off
httpd_use_sasl --> off
httpd_verify_dns --> off
icecast_use_any_tcp_ports --> off
irc_use_any_tcp_ports --> off
irssi_use_full_network --> off
kdumpgui_run_bootloader --> off
kerberos_enabled --> on
ksmtuned_use_cifs --> off
ksmtuned_use_nfs --> off
logadm_exec_content --> on
logging_syslogd_can_sendmail --> off
logging_syslogd_use_tty --> on
login_console_enabled --> on
logrotate_use_nfs --> off
logwatch_can_sendmail --> off
lsmd_plugin_connect_any --> off
mailman_use_fusefs --> off
mcelog_client --> off
mcelog_exec_scripts --> on
mcelog_foreground --> off
mcelog_server --> off
mmap_low_allowed --> off
mock_enable_homedirs --> off
mount_anyfile --> on
mozilla_plugin_bind_unreserved_ports --> off
mozilla_plugin_can_network_connect --> off
mozilla_plugin_use_bluejeans --> off
mozilla_plugin_use_gps --> off
mozilla_plugin_use_spice --> off
mozilla_read_content --> off
mpd_enable_homedirs --> on
mpd_execmem --> off
mpd_use_cifs --> off
mpd_use_nfs --> off
mplayer_execstack --> off
mysql_connect_any --> off
named_tcp_bind_http_port --> off
named_write_master_zones --> off
neutron_can_network --> off
nfs_export_all_ro --> on
nfs_export_all_rw --> on
nfsd_anon_write --> off
nis_enabled --> off
nscd_use_shm --> on
openshift_use_nfs --> off
openvpn_can_network_connect --> on
openvpn_enable_homedirs --> on
openvpn_run_unconfined --> off
pcp_bind_all_unreserved_ports --> off
piranha_lvs_can_network_connect --> off
polipo_connect_all_unreserved --> off
polipo_session_bind_all_unreserved_ports --> off
polipo_session_users --> off
polipo_use_cifs --> off
polipo_use_nfs --> off
polyinstantiation_enabled --> off
postfix_local_write_mail_spool --> on
postgresql_can_rsync --> off
postgresql_selinux_transmit_client_label --> off
postgresql_selinux_unconfined_dbadm --> on
postgresql_selinux_users_ddl --> on
pppd_can_insmod --> off
pppd_for_user --> off
privoxy_connect_any --> on
prosody_bind_http_port --> off
puppetagent_manage_all_files --> off
puppetmaster_use_db --> off
racoon_read_shadow --> off
rsync_anon_write --> off
rsync_client --> off
rsync_export_all_ro --> off
rsync_full_access --> off
samba_create_home_dirs --> off
samba_domain_controller --> off
samba_enable_home_dirs --> off
samba_export_all_ro --> off
samba_export_all_rw --> off
samba_portmapper --> off
samba_run_unconfined --> off
samba_share_fusefs --> off
samba_share_nfs --> off
sanlock_use_fusefs --> off
sanlock_use_nfs --> off
sanlock_use_samba --> off
saslauthd_read_shadow --> off
secadm_exec_content --> on
secure_mode --> off
secure_mode_insmod --> off
secure_mode_policyload --> off
selinuxuser_direct_dri_enabled --> on
selinuxuser_execheap --> off
selinuxuser_execmod --> on
selinuxuser_execstack --> on
selinuxuser_mysql_connect_enabled --> off
selinuxuser_ping --> on
selinuxuser_postgresql_connect_enabled --> off
selinuxuser_rw_noexattrfile --> on
selinuxuser_share_music --> off
selinuxuser_tcp_server --> off
selinuxuser_use_ssh_chroot --> off
sftpd_anon_write --> off
sftpd_enable_homedirs --> on
sftpd_full_access --> off
sftpd_write_ssh_home --> on
sge_domain_can_network_connect --> off
sge_use_nfs --> off
smartmon_3ware --> off
smbd_anon_write --> off
spamassassin_can_network --> off
spamd_enable_home_dirs --> on
squid_connect_any --> on
squid_use_tproxy --> off
ssh_chroot_rw_homedirs --> off
ssh_keysign --> off
ssh_sysadm_login --> off
staff_exec_content --> on
staff_use_svirt --> off
swift_can_network --> off
sysadm_exec_content --> on
telepathy_connect_all_ports --> off
telepathy_tcp_connect_generic_network_ports --> on
tftp_anon_write --> on
tftp_home_dir --> on
tor_bind_all_unreserved_ports --> off
tor_can_network_relay --> off
unconfined_chrome_sandbox_transition --> on
unconfined_login --> on
unconfined_mozilla_plugin_transition --> on
unprivuser_use_svirt --> off
use_ecryptfs_home_dirs --> off
use_fusefs_home_dirs --> off
use_lpd_server --> off
use_nfs_home_dirs --> on
use_samba_home_dirs --> off
user_exec_content --> on
varnishd_connect_any --> off
vbetool_mmap_zero_ignore --> off
virt_sandbox_use_all_caps --> off
virt_sandbox_use_audit --> on
virt_sandbox_use_mknod --> off
virt_sandbox_use_netlink --> off
virt_sandbox_use_nfs --> off
virt_sandbox_use_samba --> off
virt_sandbox_use_sys_admin --> off
virt_transition_userdomain --> off
virt_use_comm --> off
virt_use_execmem --> off
virt_use_fusefs --> off
virt_use_nfs --> off
virt_use_rawip --> off
virt_use_samba --> off
virt_use_sanlock --> off
virt_use_usb --> on
virt_use_xserver --> off
webadm_manage_user_files --> off
webadm_read_user_files --> off
wine_mmap_zero_ignore --> off
xdm_exec_bootloader --> off
xdm_sysadm_login --> off
xdm_write_home --> off
xen_use_nfs --> off
xend_run_blktap --> on
xend_run_qemu --> on
xguest_connect_network --> on
xguest_exec_content --> on
xguest_mount_media --> on
xguest_use_bluetooth --> on
xserver_clients_write_xshm --> off
xserver_execmem --> off
xserver_object_manager --> off
zabbix_can_network --> off
zarafa_setrlimit --> off
zebra_write_config --> off
zoneminder_anon_write --> off
zoneminder_run_sudo --> off

Pero como la lista podría ser muy larga, lo recomendable sería filtrarla en búsqueda de lo que necesitamos, por ejemplo booleanos relacionados con el servicio NFS.

[fraterneo@rainbow ~]$ getsebool -a | grep nfs
cobbler_use_nfs --> off
ftpd_use_nfs --> off
git_cgi_use_nfs --> off
git_system_use_nfs --> off
httpd_use_nfs --> off
ksmtuned_use_nfs --> off
logrotate_use_nfs --> off
mpd_use_nfs --> off
nfs_export_all_ro --> on
nfs_export_all_rw --> on
nfsd_anon_write --> off
openshift_use_nfs --> off
polipo_use_nfs --> off
samba_share_nfs --> off
sanlock_use_nfs --> off
sge_use_nfs --> off
use_nfs_home_dirs --> on
virt_sandbox_use_nfs --> off
virt_use_nfs --> off
xen_use_nfs --> off

O con el servicio Samba.

[fraterneo@rainbow ~]$ getsebool -a | grep samba
samba_create_home_dirs --> off
samba_domain_controller --> off
samba_enable_home_dirs --> off
samba_export_all_ro --> off
samba_export_all_rw --> off
samba_portmapper --> off
samba_run_unconfined --> off
samba_share_fusefs --> off
samba_share_nfs --> off
sanlock_use_samba --> off
use_samba_home_dirs --> off
virt_sandbox_use_samba --> off
virt_use_samba --> off

Ahora puedes usar el comando setsebool para encender o apagar un booleano en particular. La sintaxis sería: setsebool [booleano] [0|1]. Por ejemplo, decirle a SELinux que permita a Samba compartir los directorios de los usuarios.

[fraterneo@rainbow ~]$ setsebool -P use_samba_home_dirs 1
[fraterneo@rainbow ~]$ getsebool use_samba_home_dirs --> on

Además en sistemas como Fedora podemos consultar unas páginas man de todo lo relacionado a un servicio en particular con SELinux. Por ejemplo con el comando man nfsd_selinux nos dará toda la información relacionada al manejo de SELinux en el servicio nfs.