TypeRules

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Type Enforcement Rules

The TE rules define what access control privileges are allowed for processes. There are three types of enforcement rule: type_transition, type_change, and type_member that are explained below.

The common format of the Type Enforcement Rule is:

type_rule source_type target_type : class default_type;


Where:

type_rule The applicable type_transition, type_change, or type_member rule keyword.
source_type

target_type

One or more source / target type or attribute identifiers. Multiple entries consist of a space separated list enclosed in braces ({}).

Entries can be excluded from the list by using the negative operator (-).

class One or more object classes. Multiple entries consist of a space separated list enclosed in braces ({}).
default_type A single type identifier that will become the default process type for a domain transition or the type for object transitions.


The statements are valid in:

Monolithic Policy
Base Policy
Module Policy
Yes
Yes
Yes
Conditional Policy (if) Statement
optional Statement
require Statement
Yes
Yes
No


type_transition Statement

The type_transition statement specifies the labeling and object creation allowed between the source_type and target_type when a Domain Transition is requested.


Example - Domain Transition:

# Using the type_transition statement to show a domain transition
# (as the statement has the process object class in the 
# class). 

# The rule states that when a process of type initrc_t executes 
# a file of type acct_exec_t, the process type should be changed
# to acct_t if allowed by the policy (i.e. Transition from the
# initrc_t domain to the acc_t domain).

type_transition initrc_t acct_exec_t:process acct_t;

# Note that to be able to transition to the acc_t domain the 
# following minimum permissions need to be granted in the policy
# using allow rules (as shown in the allow Rule section).
# File needs to be executable in the initrc_t domain:

allow initrc_t acct_exec_t:file execute;

# The executable file needs an entry point into the acct_t domain:

allow acct_t acct_exec_t:file entrypoint;

# Process needs permission to transition into the acct_t domain:

allow initrc_t acct_t:process transition;


Example - Object Transition:

# Using the type_transition statement to show an object 
# transition (as it has other than process in the class).
# The rule states that when a process of type acct_t creates a 
# file in the directory of type var_log_t, by default it should 
# have the type wtmp_t if allowed by the policy.

type_transition acct_t var_log_t:file wtmp_t;

# Note that to be able to create the new file object with the
# wtmp_t type, the following minimum permissions need to be 
# granted in the policy using allow rules (as shown in the
# allow Rule section). 

# A minimum of: add_name, write and search on the var_log_t 
# directory. The actual reference policy has:
#

allow acct_t var_log_t:dir { read getattr lock search ioctl 
add_name remove_name write };

# A minimum of: create and write on the wtmp_t file. The actual
# reference policy has:
#

allow acct_t wtmp_t:file { create open getattr setattr read 
write append rename link unlink ioctl lock };


type_change Statement

The type_change statement is used to determine any re-labeling of default types for user space SELinux-aware applications that would then manage any required re-labeling via the libselinux API.

Examples:

# Using the type_change statement to show that when relabeling a 
# character file with type sysadm_devpts_t on behalf of 
# auditadm_t, the type auditadm_devpts_t should be used:

type_change auditadm_t sysadm_devpts_t:chr_file auditadm_devpts_t;
# Using the type_change statement to show that when relabeling a 
# character file with any type associated to the attribute 
# server_ptynode on behalf of staff_t, the type staff_devpts_t 
# should be used:

type_change staff_t server_ptynode:chr_file staff_devpts_t;

type_member Statement

The type_member statement determines whether an object can be polyinstantiated. It is used by SELinux-aware applications that would then manage any required polyinstantiation requirements via the libselinux API (see the Polyinstantiation section). Currently only directories are managed by SELinux-aware applications, although the actual statement is not limited to specific object classes.


Example:

# Using the type_member statement to show that if the source 
# type is sysadm_t, and the target type is user_home_dir_t, 
# then use user_home_dir_t as the type on the newly created 
# directory object.

type_member sysadm_t user_home_dir_t:dir user_home_dir_t;
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