NB SQL 9.3

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SE-PostgreSQL

This section gives an overview of PostgreSQL version 9.3 with the sepgsql extension to support SELinux labeling. It assumes some basic knowledge of PostgreSQL that can be found at: http://wiki.postgresql.org/wiki/Main_Page

It is important to note that PostgreSQL from version 9.3 has the necessary infrastructure to support labeling of database objects via external 'providers'. An sepgsql extension has been added that provides SELinux labeling. This is not installed by default but as an option as outlined in the sections that follow. Because of these changes the original version 9.0 patches are no longer supported (i.e. the SE-PostgreSQL database engine is replaced by PostgreSQL database engine 9.3 plus the sepgsql extension). A consequence of this change is that row level labeling is no longer supported.

The features of sepgsql 9.3 and its setup are covered in the following document:

http://www.postgresql.org/docs/9.3/static/sepgsql.html

sepgsql Overview

The sepgsql extension adds SELinux mandatory access controls (MAC) to database objects such as tables, columns, views, functions, schemas and sequences. Figure 1 shows a simple database with one table, two columns and three rows, each with their object class and associated security context (the Internal Tables section shows these entries from the testdb database in the Notebook tarball example). The database object classes and permissions are described in the Object Classes and Permissions section.

Figure 1: Database Security Context Information - Showing the security contexts that can be associated to a schema, table and columns.
database
context = 'unconfined_u:object_r:postgresql_db_t:s0'
This context is inherited from the database directory label - ls -Z /var/lib/pgsql/data
schema (db_schema)
security_label = 'unconfined_u:object_r:sepgsql_schema_t:s10'
table (db_table)
security_label = 'unconfined_u:object_r:sepgsql_table_t:s0:c20'
column 1 (db_column)
security_label = 'unconfined_u:object_r:sepgsql_table_t:s0:c30'
column 2 (db_column)
security_label = 'unconfined_u:object_r:sepgsql_table_t:s0:c40'


To use SE-PostgreSQL each GNU / Linux user must have a valid PostgreSQL database role (not to be confused with an SELinux role). The default installation automatically adds a user called pgsql with a suitable database role.

If a client is connecting remotely and labeled networking is required, then it is possible to use IPSec or NetLabel as discussed in the SELinux Networking Support section (the "Security-Enhanced PostgreSQL Security Wiki" also covers these methods of connectivity with examples).

Using the SE-PostgreSQL Services diagram, the database client application (that could be provided by an API for Perl/PHP or some other programming language) connects to a database and executes SQL commands. As the SQL commands are processed by PostgreSQL, each operation performed on an object is checked by the object manager (OM) to see if the opration is allowed by the security policy or not.

SE-PostgreSQL supports SELinux services via the libselinux library with AVC audits being logged into the standard PostgreSQL file as described in the outline Logging Security Events section.

Installing SE-PostgreSQL

The http://www.postgresql.org/docs/devel/static/sepgsql.html page contains all the information required to install PostgreSQL and the sepgsql extension, however the Notebook tarball sepgsql-9.3/README file also explains this and adds a simple test database.

SECURITY LABEL SQL Command

The 'SECURITY LABEL' SQL command has been added to PostgreSQL to allow security providers to label or change a label on database objects. The command format is:

SECURITY LABEL [ FOR provider ] ON
{
    TABLE object_name |
    COLUMN table_name.column_name |
    AGGREGATE agg_name (agg_type [, ...] ) |
    DATABASE object_name |
    DOMAIN object_name |
    EVENT TRIGGER object_name |
    FOREIGN TABLE object_name
    FUNCTION function_name ( [ [ argmode ] [ argname ] argtype [, ...] ] ) |
    LARGE OBJECT large_object_oid |
    [ PROCEDURAL ] LANGUAGE object_name |
    ROLE object_name |
    SCHEMA object_name |
    SEQUENCE object_name |
    TABLESPACE object_name |
    TYPE object_name |
    VIEW object_name
} IS 'label'

The full syntax is defined at http://www.postgresql.org/docs/9.3/static/sql-security-label.html and also in the security_label(7) man page. Some examples taken from the Notebook tarball are:

--- These set the security label on objects (default provider is SELinux):
SECURITY LABEL ON SCHEMA test_ns IS 'unconfined_u:object_r:sepgsql_schema_t:s0:c10';
SECURITY LABEL ON TABLE test_ns.info IS 'unconfined_u:object_r:sepgsql_table_t:s0:c20';
SECURITY LABEL ON COLUMN test_ns.info.user_name IS 'unconfined_u:object_r:sepgsql_table_t:s0:c30';
SECURITY LABEL ON COLUMN test_ns.info.email_addr IS 'unconfined_u:object_r:sepgsql_table_t:s0:c40';

Additional SQL Functions

The following functions have been added:

sepgsql_getcon() Returns the client security context.
sepgsql_mcstrans_in(text con) Translates the readable range of the context into raw format provided the mcstransd daemon is running.
sepgsql_mcstrans_out(text con) Translates the raw range of the context into readable format provided the mcstransd daemon is running.
sepgsql_restorecon(text specfile) Sets security contexts on all database objects (must be superuser) according to the specfile. This is normally used for initialisation of the database by the sepgsql.sql script. If the parameter is NULL, then the default sepgsql_contexts file is used. See selabel_db(5) details.


Additional postgresql.conf Entries

The postgresql.conf file supports the following additional entries to enable and manage SE-PostgreSQL:

  • This entry is mandatory to enable the sepgsql extention to be loaded:
shared_preload_libraries = 'sepgsql'
  • These entries are optional and default to 'off'. The 'custom_variable_classes' entry must contain 'sepgsql' to enable these to be configured.
# This entry allows sepgsql customised entries:
custom_variable_classes = 'sepgsql'

# These are the possible entries:
# This enables sepgsql to always run in permissive mode:
sepgsql.permissive = on

# This enables printing of audit messages regardless of the policy setting:
sepgsql.debug_audit = on
To view these settings the SHOW SQL statement can be used (psql output shown):
SHOW sepgsql.permissive;
sepgsql.permissive
---------------
on
(1 row)
SHOW sepgsql.debug_audit;
sepgsql.debug_audit
---------------
on
(1 row)

Logging Security Events

SE-PostgreSQL manages its own AVC audit entries in the standard PostgreSQL log normally located within the /var/lib/pgsql/data/pg_log directory and by default only errors are logged (Note that there are no SE-PostgreSQL AVC entries added to the standard audit.log). The 'sepgsql.debug_audit = on' can be set to log all audit events.

Internal Tables

To support the overall database operation PostgreSQL has internal tables in the system catalog that hold information relating to databases, tables etc. This section will only highlight the pg_seclabel table that holds the security label and other references. The pg_seclabel is described in Table 1 that has been taken from http://www.postgresql.org/docs/9.3/static/catalog-pg-seclabel.html.

Table 1: pg_seclabel Table Columns
Name
Type
References
Comment
objoid
oid
any OID column The OID of the object this security label pertains to.
classoid
oid
pg_class.oid The OID of the system catalog this object appears in.
objsubid
int4
For a security label on a table column, this is the column number (the objoid and classoid refer to the table itself). For all other objects this column is zero.
provider
text
The label provider associated with this label. Currently only SELinux is supported.
label
text
The security label applied to this object.


These are entries taken from a 'SELECT * FROM pg_seclabel;' command that refer to the example testdb database built using the Notebook tarball samples:

objoid | classoid | objsubid | provider | label 
-------+----------+----------+----------+----------------------------------------------
16390  | 2615     | 0        | selinux  | unconfined_u:object_r:sepgsql_schema_t:s0:c10
16391  | 1259     | 0        | selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c20
16391  | 1259     | 1        | selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c30
16391  | 1259     | 2        | selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c40

The first entry is the schema, the second entry is the table itself, and the third and fourth entries are columns 1 and 2.

There is also a built-in 'view' to show additional detail regarding security labels called 'pg_seclabels'. Using 'SELECT * FROM pg_seclabels;' command, the entries shown above become:

objoid | classoid | objsubid | objtype | objnamespace | objname                | provider | label 
-------+----------+----------+-----------+------------+------------------------+----------+----------------------------------------------
16390  | 2615     | 0        | schema  | 16390        | test_ns                | selinux  | unconfined_u:object_r:sepgsql_schema_t:s0:c10
16391  | 1259     | 0        | table   | 16390        | test_ns.info           | selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c20
16391  | 1259     | 1        | column  | 16390        | test_ns.info.user_name | selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c30
16391  | 1259     | 2        | column  | 16390        | test_ns.info.email_addr| selinux  | unconfined_u:object_r:sepgsql_table_t:s0:c40


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