xref: /external/libselinux

This directory contains a small port of libselinux for Android.
It was originally forked in mid-2011, circa libselinux 2.1.0.
Some changes have been cherry-picked from the upstream libselinux.
Upstream git repository is https://github.com/SELinuxProject/selinux
(libselinux subdirectory) and official releases are available from
https://github.com/SELinuxProject/selinux/wiki/Releases.

This fork differs from upstream libselinux in at least the following ways:

* Dependencies on glibc-specific features have been removed/replaced
in order to work with bionic,

* Legacy code and compatibility interfaces have been removed,

* Many interfaces, functions, and files are omitted since they are
unused in Android,

* The python bindings are omitted since they are unused in Android,

* The setrans (context translation) support has been removed since
there is no need for MLS label translation in Android and the support
imposes extra overhead on calls passing security contexts,

* The SELinux policy files are all located in / rather than under
/etc/selinux since /etc is not available in Android until /system
is mounted and use fixed paths, not dependent on /etc/selinux/config,

* The kernel policy file (sepolicy in Android, policy.N in Linux) does
not include a version suffix since Android does not need to support
booting multiple kernels,

* The policy loading logic does not support automatic downgrading of
the kernel policy file to a version known to the kernel, since this
requires libsepol on the device and is only needed to support mixing
and matching kernels and userspace easily,

* The selabel interface and label_file backend have been extended to
support label-by-symlink and partial matching support for use by ueventd
in labeling device nodes based on stable symlink names and by init for
optimizing its restorecon_recursive of /sys,

* Since the fork, upstream libselinux has switched the label_file
backend to use a binary version of the file_contexts file
(file_contexts.bin) that contains precompiled versions of the pcre
regexes.  This reduces the time to load the file_contexts
configuration, which in Linux can be significant due to the large
number of entries (> 5000).  As Android has far fewer entries (~400),
this has not yet seemed necessary.

* restorecon functionality, including recursive restorecon, has been
fully implemented within new libselinux functions, along with optimizations
to prune the tree walk if no change has occurred in file_contexts since
the last restorecon,

* Support for new Android-specific SELinux configuration files, such
as seapp_contexts, property_contexts, and service_contexts, has been
added.

New files added for Android:
* libselinux/include/selinux/android.h
* libselinux/src/android.c
* libselinux/src/label_android_property.c (later added upstream)