Virtual Private Databases (VPD) and Fine-Grained Access Control

Virtual Private Databases (VPD) allow multiple users to access a single schema whilst preventing them from accessing data that is not relevant to them. Although this type of access can be controlled by the application, access via other methods (SQL*Plus) would leave the data open to abuse. VPD uses Fine-Grained Access Control to limit which data is visible to specific users. Setting up a VPD involves the following steps.

Setup Test Environment
Create an Application Context
Create Login Trigger
Create Security Policies
Apply Security Policies to Tables
Test VPD
What Next

Setup Test Environment

First we must create a user to act as the schema owner for this example. Obviously, you will perform the following tasks using your current schema owner.

CONNECT sys/password@service AS SYSDBA;
CREATE USER schemaowner IDENTIFIED BY schemaowner
DEFAULT TABLESPACE users TEMPORARY TABLESPACE temp;
GRANT connect, resource TO schemaowner;
CREATE USER user1 IDENTIFIED BY user1
DEFAULT TABLESPACE users TEMPORARY TABLESPACE temp;
GRANT connect, resource TO user1;
CREATE USER user2 IDENTIFIED BY user2
DEFAULT TABLESPACE users TEMPORARY TABLESPACE temp;
GRANT connect, resource TO user2;
GRANT EXECUTE ON DBMS_RLS TO PUBLIC;
CONN schemaowner/schemaowner@service
CREATE TABLE users 
(id NUMBER(10) NOT NULL, 
 ouser VARCHAR2(30) NOT NULL,
 first_name VARCHAR2(50) NOT NULL,
 last_name VARCHAR2(50) NOT NULL);
CREATE TABLE user_data 
(column1 VARCHAR2(50) NOT NULL,
 user_id NUMBER(10) NOT NULL);
INSERT INTO users VALUES (1,'USER1','User','One');
INSERT INTO users VALUES (2,'USER2','User','Two');
COMMIT;
GRANT SELECT, INSERT ON user_data TO user1, user2;

Create an Application Context

Grant CREATE ANY CONTEXT to the schema owner then create the context and context package.

CONNECT sys/password@service AS SYSDBA;
GRANT create any context, create public synonym TO schemaowner;
CONNECT schemaowner/schemaowner@service;
CREATE CONTEXT SCHEMAOWNER USING SCHEMAOWNER.context_package;
CREATE OR REPLACE PACKAGE context_package AS
 PROCEDURE set_context;
END;
/

Next we create the context_package body which will actually set the user context.

CREATE OR REPLACE PACKAGE BODY context_package IS
 PROCEDURE set_context IS
 v_ouser VARCHAR2(30);
 v_id NUMBER;
 BEGIN
 DBMS_SESSION.set_context('SCHEMAOWNER','SETUP','TRUE');
 v_ouser := SYS_CONTEXT('USERENV','SESSION_USER');
 
 BEGIN
 SELECT id
 INTO v_id
 FROM users
 WHERE ouser = v_ouser;
 
 DBMS_SESSION.set_context('SCHEMAOWNER','USER_ID', v_id);
 EXCEPTION
 WHEN NO_DATA_FOUND THEN
 DBMS_SESSION.set_context('SCHEMAOWNER','USER_ID', 0);
 END;
 
 DBMS_SESSION.set_context('SCHEMAOWNER','SETUP','FALSE');
 END set_context;
END context_package;
/
SHOW ERRORS

Next we make sure that all users have access to the Context_Package.

GRANT EXECUTE ON SCHEMAOWNER.context_package TO PUBLIC;
CREATE PUBLIC SYNONYM context_package FOR SCHEMAOWNER.context_package;

Create Login Trigger

Next we must create a trigger to fire after the user logs onto the database.

CONNECT sys/password@service AS SYSDBA;
CREATE OR REPLACE TRIGGER SCHEMAOWNER.set_security_context
AFTER LOGON ON DATABASE
BEGIN
 SCHEMAOWNER.context_package.set_context;
END;
/
SHOW ERRORS

Create Security Policies

In order for the context package to have any effect on the users interaction with the database, we need to define a security_package for use with the security policy. This package will tell the database how to treat any interactions with the specified table.

CONNECT schemaowner/schemaowner@service;
CREATE OR REPLACE PACKAGE security_package AS
 FUNCTION user_data_insert_security(owner VARCHAR2, objname VARCHAR2)
 RETURN VARCHAR2;
 
 FUNCTION user_data_select_security(owner VARCHAR2, objname VARCHAR2)
 RETURN VARCHAR2;
END security_package;
/

Next we create the security_package body.

CREATE OR REPLACE PACKAGE BODY Security_Package IS
 FUNCTION user_data_select_security(owner VARCHAR2, objname VARCHAR2) RETURN VARCHAR2 IS
 predicate VARCHAR2(2000);
 BEGIN
 predicate := '1=2';
 IF (SYS_CONTEXT('USERENV','SESSION_USER') = 'SCHEMAOWNER') THEN
 predicate := NULL;
 ELSE 
 predicate := 'USER_ID = SYS_CONTEXT(''SCHEMAOWNER'',''USER_ID'')';
 END IF;
 RETURN predicate;
 END user_data_select_security;
 FUNCTION user_data_insert_security(owner VARCHAR2, objname VARCHAR2) RETURN VARCHAR2 IS
 predicate VARCHAR2(2000);
 BEGIN
 predicate := '1=2';
 IF (SYS_CONTEXT('USERENV','SESSION_USER') = 'SCHEMAOWNER') THEN
 predicate := NULL;
 ELSE 
 predicate := 'USER_ID = SYS_CONTEXT(''SCHEMAOWNER'',''USER_ID'')';
 END IF;
 RETURN Predicate;
 END user_data_insert_security;
END security_package;
/
SHOW ERRORS

Next we make sure that all users have access to the Security_Package.

GRANT EXECUTE ON SCHEMAOWNER.security_package TO PUBLIC;
CREATE PUBLIC SYNONYM security_package FOR SCHEMAOWNER.security_package;

Apply Security Policies to Tables

The DBMS_RlS package is used to apply the security policay, implemented by security_package, to the the relevant tables.

BEGIN
 DBMS_RLS.add_policy('SCHEMAOWNER', 'USER_DATA', 'USER_DATA_INSERT_POLICY', 
 'SCHEMAOWNER', 'SECURITY_PACKAGE.USER_DATA_INSERT_SECURITY',
 'INSERT', TRUE);
 DBMS_RLS.add_policy('SCHEMAOWNER', 'USER_DATA', 'USER_DATA_SELECT_POLICY',
 'SCHEMAOWNER', 'SECURITY_PACKAGE.USER_DATA_SELECT_SECURITY',
 'SELECT');
END;
/

Test VPD

Finally, test that the VPD is working correctly.

CONNECT user1/user1@service;
INSERT INTO schemaowner.user_data (column1, user_id) VALUES ('User 1', 1);
INSERT INTO schemaowner.user_data (column1, user_id) VALUES ('User 2', 2);
COMMIT;
CONNECT user2/user2@service
INSERT INTO schemaowner.user_data (column1, user_id) VALUES ('User 1', 1);
INSERT INTO schemaowner.user_data (column1, user_id) VALUES ('User 2', 2);
COMMIT;
CONNECT schemaowner/schemaowner@service
SELECT * FROM schemaowner.user_data;
CONNECT user1/user1@Service;
SELECT * FROM schemaowner.user_data;
CONNECT user2/user2@Service
SELECT * FROM schemaowner.user_data;

Notice that:

When connected to USER1, only the first insert will work.
When connected to USER2, only the second insert will work.
The failing inserts produce the following error.
```
ORA-28115: policy with check option violation
```
Once the inserts are finished, there will be two rows in the table, as seen when connected as SCHEMAOWNER. When connected as USER1 or USER2, only the single row they inserted will be visible.

What Next

Once you're happy with the basic mechanism you can extend the Security_Package to cover all tables where restricted access is neccessary, remembering to apply all security policies to the relevant tables.

For more information see:

Hope this helps. Regards Tim...

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