NAME¶
SELinux - NSA Security-Enhanced Linux (SELinux)
DESCRIPTION¶
NSA Security-Enhanced Linux (SELinux) is an implementation of a flexible
mandatory access control architecture in the Linux operating system. The
SELinux architecture provides general support for the enforcement of many
kinds of mandatory access control policies, including those based on the
concepts of Type Enforcement®, Role- Based Access Control, and
Multi-Level Security. Background information and technical documentation about
SELinux can be found at
http://www.nsa.gov/research/selinux.
The
/etc/selinux/config configuration file controls whether SELinux is
enabled or disabled, and if enabled, whether SELinux operates in permissive
mode or enforcing mode. The
SELINUX variable may be set to any one of
disabled, permissive, or enforcing to select one of these options. The
disabled option completely disables the SELinux kernel and application code,
leaving the system running without any SELinux protection. The permissive
option enables the SELinux code, but causes it to operate in a mode where
accesses that would be denied by policy are permitted but audited. The
enforcing option enables the SELinux code and causes it to enforce access
denials as well as auditing them. Permissive mode may yield a different set of
denials than enforcing mode, both because enforcing mode will prevent an
operation from proceeding past the first denial and because some application
code will fall back to a less privileged mode of operation if denied access.
The
/etc/selinux/config configuration file also controls what policy is
active on the system. SELinux allows for multiple policies to be installed on
the system, but only one policy may be active at any given time. At present,
multiple kinds of SELinux policy exist: targeted, mls for example. The
targeted policy is designed as a policy where most user processes operate
without restrictions, and only specific services are placed into distinct
security domains that are confined by the policy. For example, the user would
run in a completely unconfined domain while the named daemon or apache daemon
would run in a specific domain tailored to its operation. The MLS (Multi-Level
Security) policy is designed as a policy where all processes are partitioned
into fine-grained security domains and confined by policy. MLS also supports
the Bell And LaPadula model, where processes are not only confined by the type
but also the level of the data.
You can define which policy you will run by setting the
SELINUXTYPE
environment variable within
/etc/selinux/config. You must reboot and
possibly relabel if you change the policy type to have it take effect on the
system. The corresponding policy configuration for each such policy must be
installed in the
/etc/selinux/{SELINUXTYPE}/ directories.
A given SELinux policy can be customized further based on a set of compile-time
tunable options and a set of runtime policy booleans.
system-config-selinux allows customization of these booleans and
tunables.
Many domains that are protected by SELinux also include SELinux man pages
explaining how to customize their policy.
FILE LABELING¶
All files, directories, devices ... have a security context/label associated
with them. These context are stored in the extended attributes of the file
system. Problems with SELinux often arise from the file system being
mislabeled. This can be caused by booting the machine with a non SELinux
kernel. If you see an error message containing file_t, that is usually a good
indicator that you have a serious problem with file system labeling.
The best way to relabel the file system is to create the flag file
/.autorelabel and reboot.
system-config-selinux, also has this
capability. The
restorcon/
fixfiles commands are also available
for relabeling files.
AUTHOR ¶
This manual page was written by Dan Walsh <dwalsh@redhat.com>.
FILES¶
/etc/selinux/config
SEE ALSO¶
booleans(8),
setsebool(8),
sepolicy(8),
system-config-selinux(8),
togglesebool(8),
restorecon(8),
fixfiles(8),
setfiles(8),
semanage(8),
sepolicy(8)
Every confined service on the system has a man page in the following format:
<servicename>_selinux(8)
For example, httpd has the
httpd_selinux(8) man page.
man -k selinux
Will list all SELinux man pages.