PolicyLanguage

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Contents

SELinux Policy Language

Introduction

This section is intended as a reference to give a basic understanding of the policy language statements and rules with supporting examples taken from the Reference Policy source. The language updates to Policy DB version 24 have been captured.

Policy Statements and Rules

Policy Source Files

There are three basic types of policy source file that can contain language statements and rules. The three types of policy source file are:

Monolithic Policy - This is a single policy source file that contains all statements. By convention this file is called policy.conf and is compiled using the checkpolicy command that produces the binary policy file.
Base Policy - This is the mandatory base policy source file that supports the loadable module infrastructure. The whole system policy could be fully contained within this file, however it is more usual for the base policy to hold the mandatory components of a policy, with the optional components contained in loadable module source files. By convention this file is called base.conf and is compiled using the checkpolicy or checkmodule command.
Module (or Non-base) Policy - These are optional policy source files that when compiled, can be dynamically loaded or unloaded within the policy store. By convention these files are named after the module or application they represent, with the compiled binary having a ‘.pp’ extension. These files are compiled using the checkmodule command.

Table 1 shows the order in which the statements should appear in source files with the minimum (and therefore mandatory) statements that must be defined.


Base Entries M/O
Security Classes (class)
m
Initial SIDs
m
Access Vectors (permissions)
m
MLS sensitivity, category and level Statements
o
MLS Constraints
o
Policy Capability Statements
o
Attributes
o
Booleans
o
Type / Type Alias
m
Roles
m
Policy Rules
o
Users
m
Constraints
o
Default SID labeling
m
fs_use_xattr Statements
o
fs_use_task and fs_use_trans Statements
o
genfscon Statements
o
portcon, netifcon and nodecon Statements
o
Module Entries
module Statement
o
require Statement
o
Attributes
o
Booleans
o
Type / Type Alias
o
Roles
o
Policy Rules
o
Users
o
Table 1: Base and Module Policy Statements - A Monolithic source file would contain the same statements as the Base Module. The Mandatory policy entries are noted (the type, role and user require at least one entry each).

The language grammar defines what statements and rules can be used within the different types of source file. To highlight these rules, the following table is included in each statement and rule section to show what circumstances each one is valid within a policy source file:


Monolithic Policy
Base Policy
Module Policy
Yes/No
Yes/No
Yes/No

Where:

Monolithic Policy - Whether the statement is allowed within a monolithic policy source file or not.
Base Policy - Whether the statement is allowed within a base (for loadable module support) policy source file or not.
Module Policy - Whether the statement is allowed within the optional loadable module policy source file or not.

Table 3 shows a cross reference matrix of statements and rules allowed in each type of policy source file.

Conditional, Optional and Require Statement Rules

The language grammar specifies what statements and rules can be included within Conditional Policy, Optional Policy statements and the require statement. To highlight these rules the following table is included in each statement and rule section to show what circumstances each one is valid within a policy source file:


Conditional Policy (if) Statement
optional Statement
require Statement
Yes/No
Yes/No
Yes/No

Where:

Conditional Policy (if) Statement - Whether the statement is allowed within a conditional statement (IF / ELSE construct) as described in the if Statement section. Conditional statements can be in all types of policy source file.
optional Statement - Whether the statement is allowed within the optional { rule_list } construct as described in the optional Statement section.
require Statement - Whether the statement keyword is allowed within the require { rule_list } construct as described in the require Statement section.

Table 3 shows a cross reference matrix of statements and rules allowed in each of the above policy statements.

MLS Statements and Optional MLS Components

The MLS Statements section defines statements specifically for MLS support. However when MLS is enabled, there are other statements that require the MLS Security Context component as an argument, therefore these statements show an example taken from the Reference Policy MLS build.

General Statement Information

  • Identifiers can generally be any length but should be restricted to the following characters: a-z, A-Z, 0-9 and _ (underscore).
  • A “#” indicates the start of a comment in policy source files.
  • Statements that were defined in the older NSA documentation have been updated to capture changes such as to prohibit the use of * and ~ in type and role sets (other than in the neverallow statement). Note that some of these changes are not captured by the language grammar, but are managed within the policy_parse.y source code).
  • When multiple source and target entries are shown in a single statement or rule, the compiler (checkpolicy or checkmodule) will expand these to individual statements or rules as shown in the following example:
# This allow rule has two target entries ''console_device_t'' and ''tty_device_t'':
allow apm_t { console_device_t tty_device_t }:chr_file { getattr read write append ioctl lock };

# The compiler will expand this to become:
allow apm_t console_device_t:chr_file { getattr read write append ioctl lock };
# and:
allow apm_t tty_device_t:chr_file { getattr read write append ioctl lock };
Therefore when comparing the actual source code with a compiled binary using (for example) apol, sedispol or sedismod, the results will differ (however the resulting policy rules will be the same).
  • Some statements can be added to a policy (via the policy store) using the semanage(8) command. Examples of these are shown where applicable, however the semanage man page should be consulted for all the possible command line options.
  • Table 2 lists words reserved for the SELinux policy language.
alias allow and
attribute auditallow auditdeny
bool category cfalse
class clone common
constrain ctrue dom
domby dominance dontaudit
else eq false
fs_use_task fs_use_trans fs_use_xattr
fscon genfscon h1
h2 if incomp
inherits ipv4_addr ipv6_addr
l1 l2 level
mlsconstrain mlsvalidatetrans module
netifcon neverallow nodecon
not object_r optional
or permissive policycap
portcon r1 r2
r3 range range_transition
require role role_transition
roles sameuser self
sensitivity sid source
t1 t2 t3
target true type
type_change type_member type_transition
typealias typeattribute types
u1 u2 u3
user validatetrans version
version_identifier xor
Table 2: Policy language reserved words.
  • Table 3 shows what policy language statements and rules are allowed within each type of policy source file, and whether the statement is valid within an if / else construct, optional {rule_list}, or require {rule_list} statement.


Statement / Rule
Monolithic Policy
Base Policy
Module Policy
Conditional Statements
optional Statement
require Statement
allow
Yes
Yes
Yes
Yes
Yes
No
allow - Role
Yes
Yes
Yes
No
Yes
No
attribute
Yes
Yes
Yes
No
Yes
Yes
auditallow
Yes
Yes
Yes
Yes
Yes
No
auditdeny (Depreciated)
Yes
Yes
Yes
Yes
Yes
No
bool
Yes
Yes
Yes
No
Yes
Yes
category
Yes
Yes
No
No
No
Yes
class
Yes
Yes
No
No
No
Yes
common
Yes
Yes
No
No
No
No
constrain
Yes
Yes
No
No
No
No
dominance - MLS
Yes
Yes
No
No
No
No
dominance - Role (Depreciated)
Yes
Yes
Yes
No
Yes
No
dontaudit
Yes
Yes
Yes
Yes
Yes
No
fs_use_task
Yes
Yes
No
No
No
No
fs_use_trans
Yes
Yes
No
No
No
No
fs_use_xattr
Yes
Yes
No
No
No
No
genfscon
Yes
Yes
No
No
No
No
if
Yes
Yes
Yes
No
Yes
No
level
Yes
Yes
No
No
No
No
mlsconstrain
Yes
Yes
No
No
No
No
mlsvalidatetrans
Yes
Yes
No
No
No
No
module
No
No
Yes
No
No
No
netifcon
Yes
Yes
No
No
No
No
neverallow
Yes
Yes
Yes
No
Yes
No
nodecon
Yes
Yes
No
No
No
No
optional
No
Yes
Yes
Yes
Yes
Yes
permissive
Yes
Yes
Yes
Yes
Yes
No
policycap
Yes
Yes
No
No
No
No
portcon
Yes
Yes
No
No
No
No
range_transition
Yes
Yes
Yes
No
Yes
No
require
No
Yes *
Yes
Yes *
Yes
No
role
Yes
Yes
Yes
No
Yes
Yes
role_transition
Yes
Yes
Yes
No
Yes
No
sensitivity
Yes
Yes
No
No
No
Yes
sid
Yes
Yes
No
No
No
No
type
Yes
Yes
Yes
No
No
Yes
type_change
Yes
Yes
Yes
Yes
Yes
No
type_member
Yes
Yes
Yes
Yes
Yes
No
type_transition
Yes
Yes
Yes
Yes
Yes
No
typealias
Yes
Yes
Yes
No
Yes
No
typeattribute
Yes
Yes
Yes
No
Yes
No
user
Yes
Yes
Yes
No
Yes
Yes
validatetrans
Yes
Yes
No
No
No
No
Table 3: The policy language statements and rules that are allowed within each type of policy source file - The left hand side of the table shows what Policy Language Statements and Rules are allowed within each type of policy source file. The right hand side of the table shows whether the statement is valid within the if / else construct, optional {rule_list}, or require {rule_list} statement.

* Only if preceded by the optional statement.

Policy Language Definition Links

The policy language statement and rule sections are as follows:

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