042 - dbms_rls.add_policy

245.
You want to enforce a company's business policy on several objects by using a single policy function. Which two types of policies can be assigned to the policy_type argument in the dbms_rls.add_policy procedure to achieve the above objective? (Choose two.)
A. DBMS_RLS.STATIC
B. DBMS_RLS.DYNAMIC
C. DBMS_RLS.SHARED_STATIC
D. DBMS_RLS.CONTEXT_SENSITIVE

E. DBMS_RLS.SHARED_CONTEXT_SENSITIVE

Answer: C E 

ADD_POLICY Procedure

This procedure adds a fine-grained access control policy to a table, view, or synonym.

The procedure causes the current transaction, if any, to commit before the operation is carried out. However, this does not cause a commit first if it is inside a DDL event trigger.

See Also:

Operational Notes

A COMMIT is also performed at the end of the operation.

Syntax

DBMS_RLS.ADD_POLICY (   object_schema            IN VARCHAR2 NULL,   object_name              IN VARCHAR2,   policy_name              IN VARCHAR2,   function_schema          IN VARCHAR2 NULL,   policy_function          IN VARCHAR2,   statement_types          IN VARCHAR2 NULL,   update_check             IN BOOLEAN  FALSE,   enable                   IN BOOLEAN  TRUE,   static_policy            IN BOOLEAN  FALSE,   policy_type              IN BINARY_INTEGER NULL,   long_predicate           IN BOOLEAN  FALSE,   sec_relevant_cols        IN VARCHAR2,   sec_relevant_cols_opt    IN BINARY_INTEGER NULL);

Parameters

Table 89-3 ADD_POLICY Procedure Parameters

ParameterDescription

object_schema

Schema containing the table, view, or synonym. If no object_schema is specified, the current log-on user schema is assumed.

object_name

Name of table, view, or synonym to which the policy is added.

policy_name

Name of policy to be added. It must be unique for the same table or view.

function_schema

Schema of the policy function (current default schema, if NULL).

policy_function

Name of a function which generates a predicate for the policy. If the function is defined within a package, then the name of the package must be present.

statement_types

Statement types to which the policy applies. It can be any combination of INDEX, SELECT, INSERT, UPDATE, or DELETE. The default is to apply to all of these types except INDEX.

update_check

Optional argument for INSERT or UPDATE statement types. The default is FALSE. Setting update_check to TRUE causes the server to also check the policy against the value after insert or update.

enable

Indicates if the policy is enabled when it is added. The default is TRUE.

static_policy

The default is FALSE. If it is set to TRUE, the server assumes that the policy function for the static policy produces the same predicate string for anyone accessing the object, except for SYS or the privilege user who has the EXEMPT ACCESS POLICY privilege.

policy_type

Default is NULL, which means policy_type is decided by the value of static_policy. The available policy types are listed in Table 89-4. Specifying any of these policy types overrides the value of static_policy.

long_predicate

Default is FALSE, which means the policy function can return a predicate with a length of up to 4000 bytes. TRUE means the predicate text string length can be up to 32K bytes.Policies existing prior to the availability of this parameter retain a 32K limit.

sec_relevant_cols

Enables column-level Virtual Private Database (VPD), which enforces security policies when a column containing sensitive information is referenced in a query. Applies to tables and views, but not to synonyms. Specify a list of comma- or space-separated valid column names of the policy-protected object. The policy is enforced only if a specified column is referenced (or, for an abstract datatype column, its attributes are referenced) in the user SQL statement or its underlying view definition. Default is all the user-defined columns for the object.

sec_relevant_cols_opt

Use with sec_relevant_cols to display all rows for column-level VPD filtered queries (SELECT only), but where sensitive columns appear as NULL. Default is set to NULL, which allows the filtering defined with sec_relevant_cols to take effect. Set to dbms_rls.ALL_ROWS to display all rows, but with sensitive column values, which are filtered by sec_relevant_cols, displayed as NULL. See "Usage Notes" for restrictions and additional information about this option.

Table 89-4 DBMS_RLS.ADD_POLICY Policy Types

Policy TypeDescription

STATIC

Predicate is assumed to be the same regardless of the runtime environment. Static policy functions are executed once and then cached in SGA. Statements accessing the same object do not reexecute the policy function. However, each execution of the same cursor could produce a different row set even for the same predicate because the predicate may filter the data differently based on attributes such as SYS_CONTEXT or SYSDATE. Applies to only one object.

SHARED_STATIC

Same as STATIC except that the server first looks for a cached predicate generated by the same policy function of the same policy type. Shared across multiple objects.

CONTEXT_SENSITIVE

Server re-evaluates the policy function at statement execution time if it detects context changes since the last use of the cursor. For session pooling where multiple clients share a database session, the middle tier must reset context during client switches. Note that the server does not cache the value returned by the function for this policy type; it always executes the policy function on statement parsing. Applies to only one object.

SHARED_CONTEXT_SENSITIVE

Same as CONTEXT_SENSITIVE except that the server first looks for a cached predicate generated by the same policy function of the same policy type within the same database session. If the predicate is found in the session memory, the policy function is not reexecuted and the cached value is valid until session private application context changes occur. Shared across multiple objects.

DYNAMIC

The default policy type. Server assumes the predicate may be affected by any system or session environment at any time, and so always reexecutes the policy function on each statement parsing or execution. Applies to only one object.

策略类型

正确的使用策略类型能提高VPD的效率，通过缓存策略函数的输出，使得随后的查询语句，不再执行策略函数，

DBMS_RLS.ADD_POLICY存储过程的策略类型参数可以设置5种策略类型中的一种。

Ø  静态类型：缓存策略函数的返回值，可以被个别对象重复利用，所以策略函数的返回值必须静态。

Ø  共享静态类型，同静态类型一样，但是生成的谓语能够被应用与多个对象。

Ø  敏感上下文类型：当策略基于本地应用上下文的时候使用，策略函数的结果被缓存和重复使用，只有当应用

上下文改变的时候策略函数才会再一次执行。

Ø  共享敏感上下文：同敏感上下文类型一样，但是生成的谓语能够应用与多个对象。

动态类型：策略函数在每此执行SQL语句的时候都被执行。

Usage Notes

• SYS is free of any security policy.

• If no object_schema is specified, the current log-on user schema is assumed.

• The policy functions which generate dynamic predicates are called by the server. Following is the interface for the function:

FUNCTION policy_function (object_schema IN VARCHAR2, object_name VARCHAR2)         RETURN VARCHAR2     --- object_schema is the schema owning the table of view.    --- object_name is the name of table, view, or synonym to which the policy applies. 

• The policy functions must have the purity level of WNDS (write no database state).

  See Also:

  The Oracle Database Application Developer's Guide - Fundamentals has more details about the RESTRICT_REFERENCESpragma.

• Dynamic predicates generated out of different policies for the same object have the combined effect of a conjunction (ANDed) of all the predicates.

• The security check and object lookup are performed against the owner of the policy function for objects in the subqueries of the dynamic predicates.

• If the function returns a zero length predicate, then it is interpreted as no restriction being applied to the current user for the policy.

• When a table alias is required (for example, parent object is a type table) in the predicate, the name of the table or view itself must be used as the name of the alias. The server constructs the transient view as something like

  "select c1, c2, ... from tab tab where <predicate>" 

• Validity of the function is checked at runtime for ease of installation and other dependency issues during import and export.

• Column-level VPD column masking behavior (specified with sec_relevant_cols_opt => dbms_rls.ALL_ROWS) is fundamentally different from all other VPD policies, which return only a subset of rows. Instead the column masking behavior returns all rows specified by the user's query, but the sensitive column values display as NULL. The restrictions for this option are as follows:

  • Only applies to SELECT statements

  • Unlike regular VPD predicates, the masking condition that is generated by the policy function must be a simple boolean expression.

  • If your application performs calculations, or does not expect NULL values, then you should use the default behavior of column-level VPD, which is specified with the sec_relevant_cols parameter.

  • If you use UPDATE AS SELECT with this option, then only the values in the columns you are allowed to see will be updated.

  • This option may prevent some rows from displaying. For example:

    select * from employeeswhere salary = 10

    This query may not return rows if the salary column returns a NULL value because the column masking option has been set.

Examples

As the first of two examples, the following creates a policy that applies to the hr.employee table. This is a column-level VPD policy that will be enforced only if aSELECT or an INDEX statement refers to the salary, birthdate, or SSN columns of the table explicitly, or implicitly through a view. It is also a CONTEXT_SENSITIVEpolicy, so the server will invoke the policy function hr.hrfun at parse time. During execution, it will only invoke the function if there has been any session private context change since the last use of the statement cursor. The predicate generated by the policy function must not exceed 4000 bytes, the default length limit, since the long_predicate parameter is omitted from the call.

BEGINdbms_rls.add_policy(object_schema => 'hr',

object_name => 'employee',policy_name => 'hr_policy',function_schema =>'hr',policy_function => 'hrfun',statement_types =>'select,index',policy_type => dbms_rls.CONTEXT_SENSITIVE,sec_relevant_cols=>'salary,birthdate,ssn');

END;/

As the second example, the following command creates another policy that applies to the same object for hosting, so users can access only data based on their subscriber ID. Since it is defined as a SHARED_STATIC policy type, the server will first try to find the predicate in the SGA cache. The server will only invoke the policy function, subfun, if that search fails.

BEGINdbms_rls.add_policy(object_schema => 'hr',

object_name => 'employee',policy_name => 'hosting_policy',function_schema =>'hr',policy_function => 'subfun',policy_type => dbms_rls.SHARED_STATIC);

END;/