is a loadable module that supports label-based
mandatory access control (MAC) based on
The current implementation has significant limitations, and does not enforce mandatory access control for all actions. See Section F.35.7 .
This module integrates with SELinux to provide an additional layer of security checking above and beyond what is normally provided by PostgreSQL . From the perspective of SELinux , this module allows PostgreSQL to function as a user-space object manager. Each table or function access initiated by a DML query will be checked against the system security policy. This check is in addition to the usual SQL permissions checking performed by PostgreSQL .
access control decisions are made using
security labels, which are represented by strings such as
. Each access control
decision involves two labels: the label of the subject attempting to
perform the action, and the label of the object on which the operation is
to be performed. Since these labels can be applied to any sort of object,
access control decisions for objects stored within the database can be
(and, with this module, are) subjected to the same general criteria used
for objects of any other type, such as files. This design is intended to
allow a centralized security policy to protect information assets
independent of the particulars of how those assets are stored.
The SECURITY LABEL statement allows assignment of a security label to a database object.
can only be used on
2.6.28 or higher with
It is not available on any other platform. You will also need
2.1.10 or higher and
3.9.13 or higher (although some
distributions may backport the necessary rules into older policy
command allows you to check the status of
. A typical display is:
$ sestatus SELinux status: enabled SELinuxfs mount: /selinux Current mode: enforcing Mode from config file: enforcing Policy version: 24 Policy from config file: targeted
If SELinux is disabled or not installed, you must set that product up first before installing this module.
To build this module, include the option
command. Be sure that the
RPM is installed at build time.
To use this module, you must include
. The module will not function correctly
if loaded in any other manner. Once the module is loaded, you
in each database.
This will install functions needed for security label management, and
assign initial security labels.
Here is an example showing how to initialize a fresh database cluster
functions and security labels installed.
Adjust the paths shown as appropriate for your installation:
$ export PGDATA=/path/to/data/directory $ initdb $ vi $PGDATA/postgresql.conf change #shared_preload_libraries = '' # (change requires restart) to shared_preload_libraries = 'sepgsql' # (change requires restart) $ for DBNAME in template0 template1 postgres; do postgres --single -F -c exit_on_error=true $DBNAME \ /dev/null done
Please note that you may see some or all of the following notifications depending on the particular versions you have of libselinux and selinux-policy :
/etc/selinux/targeted/contexts/sepgsql_contexts: line 33 has invalid object type db_blobs /etc/selinux/targeted/contexts/sepgsql_contexts: line 36 has invalid object type db_language /etc/selinux/targeted/contexts/sepgsql_contexts: line 37 has invalid object type db_language /etc/selinux/targeted/contexts/sepgsql_contexts: line 38 has invalid object type db_language /etc/selinux/targeted/contexts/sepgsql_contexts: line 39 has invalid object type db_language /etc/selinux/targeted/contexts/sepgsql_contexts: line 40 has invalid object type db_language
These messages are harmless and should be ignored.
If the installation process completes without error, you can now start the server normally.
F.35.3. Regression Tests
Due to the nature of
, running the
regression tests for
requires several extra
configuration steps, some of which must be done as root.
The regression tests will not be run by an ordinary
command; you must
set up the configuration and then invoke the test script manually.
The tests must be run in the
of a configured PostgreSQL build tree. Although they require a build tree,
the tests are designed to be executed against an installed server,
that is they are comparable to
First, set up
in a working database
according to the instructions in
Note that the current operating system user must be able to connect to the
database as superuser without password authentication.
Second, build and install the policy package for the regression test.
policy is a special purpose policy package
which provides a set of rules to be allowed during the regression tests.
It should be built from the policy source file
, which is done using
with a Makefile supplied by SELinux.
You will need to locate the appropriate
Makefile on your system; the path shown below is only an example.
(This Makefile is usually supplied by the
Once built, install this policy package using the
command, which loads supplied policy packages
into the kernel. If the package is correctly installed,
available policy package:
$ cd .../contrib/sepgsql $ make -f /usr/share/selinux/devel/Makefile $ sudo semodule -u sepgsql-regtest.pp $ sudo semodule -l | grep sepgsql sepgsql-regtest 1.07
Third, turn on
For security reasons, the rules in
are not enabled by default;
the rules needed to launch the regression tests.
It can be turned on using the
$ sudo setsebool sepgsql_regression_test_mode on $ getsebool sepgsql_regression_test_mode sepgsql_regression_test_mode --> on
Fourth, verify your shell is operating in the
$ id -Z unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
See Section F.35.8 for details on adjusting your working domain, if necessary.
Finally, run the regression test script:
This script will attempt to verify that you have done all the configuration
steps correctly, and then it will run the regression tests for the
After completing the tests, it's recommended you disable
$ sudo setsebool sepgsql_regression_test_mode off
You might prefer to remove the
$ sudo semodule -r sepgsql-regtest
F.35.4. GUC Parameters
This parameter enables
sepgsqlto function in permissive mode, regardless of the system setting. The default is off. This parameter can only be set in the
postgresql.conffile or on the server command line.
When this parameter is on,
sepgsqlfunctions in permissive mode, even if SELinux in general is working in enforcing mode. This parameter is primarily useful for testing purposes.
This parameter enables the printing of audit messages regardless of the system policy settings. The default is off, which means that messages will be printed according to the system settings.
The security policy of SELinux also has rules to control whether or not particular accesses are logged. By default, access violations are logged, but allowed accesses are not.
This parameter forces all possible logging to be turned on, regardless of the system policy.
F.35.5.1. Controlled Object Classes
The security model of
describes all the access
control rules as relationships between a subject entity (typically,
a client of the database) and an object entity (such as a database
object), each of which is
identified by a security label. If access to an unlabeled object is
attempted, the object is treated as if it were assigned the label
allows security labels to be
assigned to schemas, tables, columns, sequences, views, and functions.
is in use, security labels are
automatically assigned to supported database objects at creation time.
This label is called a default security label, and is decided according
to the system security policy, which takes as input the creator's label,
the label assigned to the new object's parent object and optionally name
of the constructed object.
A new database object basically inherits the security label of the parent object, except when the security policy has special rules known as type-transition rules, in which case a different label may be applied. For schemas, the parent object is the current database; for tables, sequences, views, and functions, it is the containing schema; for columns, it is the containing table.
F.35.5.2. DML Permissions
checked for all the referenced target tables depending on the kind of
statement; in addition,
is also checked for
all the tables that contain columns referenced in the
clause, as a data source
, and so on.
Column-level permissions will also be checked for each referenced column.
is checked on not only the columns being
, but those being referenced in other DML
will also be checked for columns being modified by
For example, consider:
UPDATE t1 SET x = 2, y = func1(y) WHERE z = 100;
will be checked for
, since it is being updated,
will be checked for
, since it is both updated and referenced, and
will be checked for
it is only referenced.
will also be checked
at the table level.
is checked when we
reference a sequence object using
; however, note that we
do not currently check permissions on execution of corresponding functions
will be checked, then any other
required permissions will be checked on the objects being
expanded from the view, individually.
will be checked when
user tries to execute a function as a part of query, or using fast-path
invocation. If this function is a trusted procedure, it also checks
permission to check whether it
can perform as entry point of trusted procedure.
In order to access any schema object,
permission is required on the containing schema. When an object is
referenced without schema qualification, schemas on which this
permission is not present will not be searched (just as if the user did
privilege on the schema). If an explicit schema
qualification is present, an error will occur if the user does not have
the requisite permission on the named schema.
The client must be allowed to access all referenced tables and columns, even if they originated from views which were then expanded, so that we apply consistent access control rules independent of the manner in which the table contents are referenced.
The default database privilege system allows database superusers to
modify system catalogs using DML commands, and reference or modify
toast tables. These operations are prohibited when
F.35.5.3. DDL Permissions
SELinux defines several permissions to control common operations for each object type; such as creation, alter, drop and relabel of security label. In addition, several object types have special permissions to control their characteristic operations; such as addition or deletion of name entries within a particular schema.
Creating a new database object requires
will grant or deny this permission based on the
client's security label and the proposed security label for the new
object. In some cases, additional privileges are required:
CREATE DATABASE additionally requires
getattrpermission for the source or template database.
Creating a schema object additionally requires
add_namepermission on the parent schema.
Creating a table additionally requires permission to create each individual table column, just as if each table column were a separate top-level object.
Creating a function marked as
installpermission. (This permission is also checked when
LEAKPROOFis set for an existing function.)
command is executed,
checked on the object being removed. Permissions will be also checked for
objects dropped indirectly via
. Deletion of objects
contained within a particular schema (tables, views, sequences and
procedures) additionally requires
on the schema.
command is executed,
checked on the object being modified for each object types, except for
subsidiary objects such as the indexes or triggers of a table, where
permissions are instead checked on the parent object. In some cases,
additional permissions are required:
Moving an object to a new schema additionally requires
remove_namepermission on the old schema and
add_namepermission on the new one.
LEAKPROOFattribute on a function requires
Using SECURITY LABEL on an object additionally requires
relabelfrompermission for the object in conjunction with its old security label and
relabeltopermission for the object in conjunction with its new security label. (In cases where multiple label providers are installed and the user tries to set a security label, but it is not managed by SELinux , only
setattrshould be checked here. This is currently not done due to implementation restrictions.)
F.35.5.4. Trusted Procedures
Trusted procedures are similar to security definer functions or setuid commands. SELinux provides a feature to allow trusted code to run using a security label different from that of the client, generally for the purpose of providing highly controlled access to sensitive data (e.g., rows might be omitted, or the precision of stored values might be reduced). Whether or not a function acts as a trusted procedure is controlled by its security label and the operating system security policy. For example:
postgres=# CREATE TABLE customer ( cid int primary key, cname text, credit text ); CREATE TABLE postgres=# SECURITY LABEL ON COLUMN customer.credit IS 'system_u:object_r:sepgsql_secret_table_t:s0'; SECURITY LABEL postgres=# CREATE FUNCTION show_credit(int) RETURNS text AS 'SELECT regexp_replace(credit, ''-[0-9]+$'', ''-xxxx'', ''g'') FROM customer WHERE cid = $1' LANGUAGE sql; CREATE FUNCTION postgres=# SECURITY LABEL ON FUNCTION show_credit(int) IS 'system_u:object_r:sepgsql_trusted_proc_exec_t:s0'; SECURITY LABEL
The above operations should be performed by an administrative user.
postgres=# SELECT * FROM customer; ERROR: SELinux: security policy violation postgres=# SELECT cid, cname, show_credit(cid) FROM customer; cid | cname | show_credit -----+--------+--------------------- 1 | taro | 1111-2222-3333-xxxx 2 | hanako | 5555-6666-7777-xxxx (2 rows)
In this case, a regular user cannot reference
directly, but a trusted procedure
allows the user
to print the credit card numbers of customers with some of the digits
F.35.5.5. Dynamic Domain Transitions
It is possible to use SELinux's dynamic domain transition feature
to switch the security label of the client process, the client domain,
to a new context, if that is allowed by the security policy.
The client domain needs the
permission and also
from the old to the new domain.
Dynamic domain transitions should be considered carefully, because they
allow users to switch their label, and therefore their privileges,
at their option, rather than (as in the case of a trusted procedure)
as mandated by the system.
permission is only considered
safe when used to switch to a domain with a smaller set of privileges than
the original one. For example:
regression=# select sepgsql_getcon(); sepgsql_getcon ------------------------------------------------------- unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 (1 row) regression=# SELECT sepgsql_setcon('unconfined_u:unconfined_r:unconfined_t:s0-s0:c1.c4'); sepgsql_setcon ---------------- t (1 row) regression=# SELECT sepgsql_setcon('unconfined_u:unconfined_r:unconfined_t:s0-s0:c1.c1023'); ERROR: SELinux: security policy violation
In this example above we were allowed to switch from the larger MCS
to the smaller range
switching back was denied.
A combination of dynamic domain transition and trusted procedure
enables an interesting use case that fits the typical process life-cycle
of connection pooling software.
Even if your connection pooling software is not allowed to run most
of SQL commands, you can allow it to switch the security label
of the client using the
from within a trusted procedure; that should take some
credential to authorize the request to switch the client label.
After that, this session will have the privileges of the target user,
rather than the connection pooler.
The connection pooler can later revert the security label change by
argument, again invoked from within a trusted
procedure with appropriate permissions checks.
The point here is that only the trusted procedure actually has permission
to change the effective security label, and only does so when given proper
credentials. Of course, for secure operation, the credential store
(table, procedure definition, or whatever) must be protected from
We reject the LOAD command across the board, because any module loaded could easily circumvent security policy enforcement.
F.35.6. Sepgsql Functions
Table F.29 shows the available functions.
Table F.29. Sepgsql Functions
Returns the client domain, the current security label of the client.
Switches the client domain of the current session to the new domain,
if allowed by the security policy.
It also accepts
Translates the given qualified MLS/MCS range into raw format if the mcstrans daemon is running.
Translates the given raw MLS/MCS range into qualified format if the mcstrans daemon is running.
Sets up initial security labels for all objects within the
current database. The argument may be
- Data Definition Language (DDL) Permissions
Due to implementation restrictions, some DDL operations do not check permissions.
- Data Control Language (DCL) Permissions
Due to implementation restrictions, DCL operations do not check permissions.
- Row-level access control
PostgreSQL supports row-level access, but
- Covert channels
sepgsqldoes not try to hide the existence of a certain object, even if the user is not allowed to reference it. For example, we can infer the existence of an invisible object as a result of primary key conflicts, foreign key violations, and so on, even if we cannot obtain the contents of the object. The existence of a top secret table cannot be hidden; we only hope to conceal its contents.
F.35.8. External Resources
- SE-PostgreSQL Introduction
This wiki page provides a brief overview, security design, architecture, administration and upcoming features.
- SELinux User's and Administrator's Guide
This document provides a wide spectrum of knowledge to administer SELinux on your systems. It focuses primarily on Red Hat operating systems, but is not limited to them.
- Fedora SELinux FAQ
This document answers frequently asked questions about SELinux . It focuses primarily on Fedora, but is not limited to Fedora.