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DBMS_RLS

The DBMS_RLS package contains the fine-grained access control administrative interface.

Note: DBMS_RLS is only available with the Enterprise Edition.

Dynamic Predicates

The functionality to support fine-grained access control is based on dynamic predicates, where security rules are not embedded in views, but are acquired at the statement parse time, when the base table or view is referenced in a DML statement.

A dynamic predicate for a table or view is generated by a PL/SQL function, which is associated with a security policy through a PL/SQL interface. For example:

DBMS_RLS.ADD_POLICY (
   'scott', 'emp', 'emp_policy', 'secusr', 'emp_sec', 'select');

Whenever EMP table, under SCOTT schema, is referenced in a query or subquery (SELECT), the server calls the EMP_SEC function (under SECUSR schema). This returns a predicate specific to the current user for the EMP_POLICY policy. The policy function may generate the predicates based on whatever session environment variables are available during the function call. These variables usually appear in the form of application contexts.

The server then produces a transient view with the text:

SELECT * FROM scott.emp WHERE P1

Here, P1 (e.g., SAL > 10000, or even a subquery) is the predicate returned from the EMP_SEC function. The server treats the EMP table as a view and does the view expansion just like the ordinary view, except that the view text is taken from the transient view instead of the data dictionary.

If the predicate contains subqueries, then the owner (definer) of the policy function is used to resolve objects within the subqueries and checks security for those objects. In other words, users who have access privilege to the policy protected objects do not need to know anything about the policy. They do not need to be granted object privileges for any underlying security policy. Furthermore, the users also do not require EXECUTE privilege on the policy function, because the server makes the call with the function definer's right.

Note: The transient view can preserve the updatability of the parent object because it is derived from a single table or view with predicate only; i.e., no JOIN, ORDER BY, GROUP BY, etc.

The DBMS_RLS package also provides the interface to drop and enable/disable security policies. For example, you can drop or disable the EMP_POLICY with the following PL/SQL statements:

DBMS_RLS.DROP_POLICY('scott', 'emp', 'emp_policy'); 
DBMS_RLS.ENABLE_POLICY('scott', 'emp', 'emp_policy', FALSE)

Security

A security check is performed when the transient view is created with subquery. 
The schema owning the policy function, which generates the dynamic predicate, is 
the transient view's definer for the purpose of security check and object look-up.

Usage Notes

The DBMS_RLS procedures cause current DML transactions, if any, to commit before the operation. However, the procedures do not cause a commit first if they are inside a DDL event trigger. With DDL transactions, the DBMS_RLS procedures are part of the DDL transaction.

For example, you may create a trigger for CREATE TABLE. Inside the trigger, you may add a column through ALTER TABLE, and you can add a policy through DBMS_RLS. All these operations are in the same transaction as CREATE TABLE, even though each one is a DDL statement. The CREATE TABLE succeeds only if the trigger is completed successfully.