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* the policy store is moved out of /etc
 
* the policy store is moved out of /etc
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** can be configured in ''semanage.conf''
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<pre>
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store-root = <path>
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* performance improvements
 
* performance improvements
 
** reduce of memory peak usage  
 
** reduce of memory peak usage  

Revision as of 14:27, 14 June 2015


SELinux policy store migration

Summary

The newest SELinux userspace project release 2015-02-02 includes a change of the location of the SELinux policy store, which defaults to /var/lib/selinux/.

Owner

Current status

  • Targeted release: Fedora 23
  • Last updated: 2015-06-10
  • Tracker bug: <will be assigned by the Wrangler>

Detailed Description

SELinux security policy is located in /etc/selinux directory together with configuration files. In Fedora, we use a modular policy. It means the policy is not one large source policy but it can be built from modules. These modules together with a base policy (contains the mandatory information) are compiled, linked and located in a policy store where can be built into a binary format and then loaded into the security server. This binary policy is located in /etc/selinux/<SELINUXTYPE>/policy/policy.29 for example.

The above mentioned policy store is located at

  • /etc/selinux/<SELINUXTYPE>/modules - default for systems that support versions < 2.4 of libsemanage, libsepol, and policycoreutils.
  • /var/lib/selinux/<SELINUXTYPE>/modules - default for systems that support versions >= 2.4 of libsemanage, libsepol, and policycoreutils.

This change builds CIL into libsepol, libsemanage, semodule, semanage to understand CIL and add ability to manage /var/lib/selinux as a new store location. It means this new location only matters if a policy is rebuilt or manipulated.

The new policy store

  • has a new complex structure
  • supports priority of modules
  • the CIL language is used for cached modules
  • original modules are converted using an HLL compiler in /usr/libexec/selinux/hll/. The pp compiler converts pp format to CIL language.

The following options are added by libsepol(v2.4) with CIL support to semanage.conf

store-root = <path>
compiler-directory = <path>
ignore-module-cache = true|false
target-platform = selinux | xen

"store-root" option can be changed from the default /var/lib/selinux to a custom location according to distribution requirements.


Benefit to Fedora

The new store implementation and the CIL language bring improvements to system:

  • the policy store is moved out of /etc
    • can be configured in semanage.conf
store-root = <path>
  • performance improvements
    • reduce of memory peak usage
    • speed-up of SELinux tools like semodule, semanage, setsebool
      • semodule -B on rawhide virtual machine
CIL: real 0m6.171s
REGULAR: real 0m22.414s
  • cached SELinux policy module can be overwritten by a module with same name and with higher priority
    • readable CIL format vs. compiled policy modules
    • ability to override distribution provided policy!
semodule --priority 100 --install fedora_distro/openstack.pp
semodule --priority 400 --install custom/openstack.pp

Both openstack modules are installed in the policy store, but only the custom openstack module is included in the final kernel binary.

See http://blog-bachradsusi.rhcloud.com/2015/06/05/selinux-modules-priority/


Scope

  • Proposal owners:
    • prepare SELinux userspace packages with the release 2015-02-02
    • prepare SELinux policy packages with the new store location
    • prepare a migration script for users modifications and modules
    • check if all packages containing SELinux modules use the right location
    • check if all SELinux modules used in Fedora packages are compatible with the new SELinux userspace and are convertible to CIL language
  • Other developers:


  • Release engineering: N/A
  • Policies and guidelines:
    • there's no need to update policies
    • there might be guidelines which mention the old store location which should be updated
  • Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

There should be no impact on upgrade. Existing modules will be migrated during the update of userspace packages and SELinux policy package will use the new location by default.


How To Test

TBD

  • Update system with libselinux-2.4 release and reboot.
  • Display list of installed modules
# semodule -l
  • Create a policy module and install it.
# cat mytestmodule.te
policy_module(mytestmodule, 1.0)
require{
 type glusterd_t;
 type smbd_t;
}
allow glusterd_t smbd_t:process signal;

# dnf install selinux-policy-devel
# make -f /usr/share/selinux/devel/Makefile mytestmodule.pp
# semodule -i mytestmodule.pp
# semodule --list-modules=full |grep mytestmodule
400 mytestmodule      pp
  • Try to disable/enable/remove the existing module (see semodule -h).
# semodule -d mytestmodule
# semodule -e mytestmodule
# semodule -r mytestmodule
  • Try to convert compiled policy module to CIL.
# cat mytestmodule.pp | /usr/libexec/selinux/hll/pp > mytestmodule.cil
# cat mytestmodule.cil
(roleattributeset cil_gen_require system_r)
(typeattributeset cil_gen_require glusterd_t)
(typeattributeset cil_gen_require smbd_t)
(allow glusterd_t smbd_t (process (signal)))

# semodule -i mytestmodule.cil
# semodule --list-modules=full |grep mytestmodule
400 mytestmodule      cil

User Experience

Regular users should not experience any change. The migration should be transparent. There'll be change only for the modules store and operations on SELinux modules should be faster.

Dependencies

N/A (not a System Wide Change)

Contingency Plan

  • use the previous SELinux userspace project release
  • use the selinux-policy packages with the policy store located in /etc/selinux
  • Contingency mechanism:
    • selinux-policy maintainers will revert selinux-policy spec file changes to use the original store in /etc/selinux
    • SELinux userspace maintainers will drop SELinux userspace tools version 2.4 and use tools version 2.3
  • Contingency deadline: beta freeze
  • Blocks release? Yes
  • Blocks product? N/A

Documentation

Release Notes