This repository contains tool designed to help increase the quality of SELinux policy by identifying possibly dangerous permission pathways, simplifying regression testing and evaluating CVE (Common Vulnerabilities and Exposures).

Due to practical reasons SELinux policy (type enforcement) does not adhere to any formal model that would ensure complete security of target system. This means that security issues can be present and their existence goes unseen unless someone manages to exploit them. Such issues can be caused by:

• Overly relaxed policy modules
• Unintended side effects of attribute/macro use
• Unforeseen module interactions

Encapsulation and interdependence of policy statements together with policy size make manual analysis difficult and extremely time consuming. This project aims at automation of policy analysis leading to simplification of proactive security approach.

Permission pathways (given combinations of permissions between multiple SELinux types) corresponding to potentially harmful actions in the system are found and reported to the user. Even very specific queries (focusing on given type) can be entered which can serve as (potentially more complex) "neverallow" rules.

Build graph file derived from SELinux policy (active policy is used by default):
$ sebuild_graph -fb -c file,process policy_snapshot
Search for potential security issues (query function names and descriptions can be found in graph_query_functions.py):
$ segraph_query policy_snapshot transition_write

The tool makes it easy to compare query results between different policy versions. This feature ensures that recent changes (bug fixing, new policy modules, etc.) aren't decreasing security of the policy. Compared to "sediff", only relevant results are shown (potential security issues) and the process is more resource effective (especially memory usage).

Build second graph file based on different policy version:
$ sebuild_graph -fb -c file,process policy_snapshot2 -p policy_data/policy.30
Search for newly introduced issues (first snapshot is used as a baseline):
$ segraph_query policy_snapshot2 -d policy_snapshot transition_write

The tool could be used to evaluate feasibility of exploiting common vulnerabilities and exposures (CVE) on systems protected by SELinux. This could help pinpoint cases where SELinux can be used to prevent the attack and therefore expedite removal of the threat (temporary policy module can be shipped and applied significantly faster than new package version).

Understanding policy statements can be difficult because of the use of macros and attributes. Now it's possible to visualise policy section (given module) in a way that requires only basic understanding of mandatory access control (type enforcement). This feature is aimed at new policy writers and package maintainers who know what access permissions are necessary, but don't have deep understanding of SELinux. Visualisation of more complex policy modules can aid more skilled policy writers with bug fixing and module integration. Generate "graphml" file containing policy concerning selected module:

$seexport_graph <policy_module> -fb

e.g.

$seexport_graph keyboardd -fb

Open in Gephi. (tested on Gephi 0.9.1) In "Layout" tab select "Force Atlas" from the drop down menu, set "Repulsion strength" to 2000 and run it. Use "Show node labels" button (black letter T on the bottom of the screen) and adjust their sizes using adjacent slider. Edge labels can be shown using adjacent button (white letter T). Edge labels contain permissions (or permission sets) concerning adjacent nodes. More thorough tutorial will be added soon.

[comment]: <>https://docs.google.com/a/redhat.com/presentation/d/14DcfzxbX9P0jqMtEeEe7fcj_iKlbn464YjVO5zYP1Ac/editusp=sharing)