Oracle7 Server Concepts

Privileges

A privilege is a right to execute a particular type of SQL statement or to access another user's object. Some examples of privileges include

the right to connect to the database (create a session)

the right to create a table

the right to select rows from another user's table

the right to execute another user's stored procedure

Complete listings of all system and object privileges, as well as instructions for privilege management, are included in the Oracle7 Server Administrator's Guide.

You grant privileges to users so these users can accomplish tasks required for their job. You should grant a privilege only to a user who absolutely requires the privilege to accomplish necessary work. Excessive granting of unnecessary privileges can lead to compromised security. A user can receive a privilege in two different ways:

You can grant privileges to users explicitly. For example, you can explicitly grant the privilege to insert records into the EMP table to the user SCOTT.

You can also grant privileges to a role (a named group of privileges), and then grant the role to one or more users. For example, you can grant the privileges to select, insert, update, and delete records from the EMP table to the role named CLERK, which in turn you can grant to the users SCOTT and BRIAN.

Because roles allow for easier and better management of privileges, you should normally grant privileges to roles and not to specific users.

There are two distinct categories of privileges:

system privileges

object privileges

System Privileges

A system privilege is the right to perform a particular action, or to perform a particular action on a particular type of object. For example, the privileges to create tablespaces and to delete the rows of any table in a database are system privileges. There are over 60 distinct system privileges.

Granting and Revoking System Privileges

You can grant or revoke system privileges to users and roles. If system privileges are granted to roles, the advantages of roles can be used to manage system privileges (for example, roles permit privileges to be made selectively available).

System privileges are granted to or revoked from users and roles using either of the following:

the Users or the Roles folders of Server Manager

the SQL commands GRANT and REVOKE

Note: Usually, you should grant system privileges only to administrative personnel and application developers because end users normally do not require the associated capabilities.

Who Can Grant or Revoke System Privileges?

Only users granted a specific system privilege with the ADMIN OPTION or users with the GRANT ANY PRIVILEGE system privilege (typically database or security administrators) can grant or revoke system privileges to other users.

Object Privileges

An object privilege is a privilege or right to perform a particular action on a specific table, view, sequence, procedure, function, or package. For example, the privilege to delete rows from the table DEPT is an object privilege. Depending on the type of object, there are different types of object privileges.

Some schema objects (such as clusters, indexes, triggers, and database links) do not have associated object privileges; their use is controlled with system privileges. For example, to alter a cluster, a user must own the cluster or have the ALTER ANY CLUSTER system privilege.

Object privileges granted for a table, view, sequence, procedure, function, or package apply whether referencing the base object by name or using a synonym. For example, assume there is a table JWARD.EMP with a synonym named JWARD.EMPLOYEE. JWARD issues the following statement:

GRANT SELECT ON emp TO swilliams;

The user SWILLIAMS can query JWARD.EMP by referencing the table by name or using the synonym JWARD.EMPLOYEE:

SELECT * FROM jward.emp;

SELECT * FROM jward.employee;

If you grant object privileges on a table, view, sequence, procedure, function, or package to a synonym for the object, the effect is the same as if no synonym were used For example, if JWARD wanted to grant the SELECT privilege for the EMP table to SWILLIAMS, JWARD could issue either of the following statements:

GRANT SELECT ON emp TO swilliams;

GRANT SELECT ON employee TO swilliams;

If a synonym is dropped, all grants for the underlying object remain in effect, even if the privileges were granted by specifying the dropped synonym.

Granting and Revoking Object Privileges

Object privileges can be granted to and revoked from users and roles. If you grant object privileges to roles, you can make the privileges selectively available. Object privileges can be granted to, or revoked from, users and roles using the SQL commands GRANT and REVOKE, respectively.

Who Can Grant Object Privileges?

A user automatically has all object privileges for the objects contained in the schema that corresponds to the user's name -- in other words, the schema the user owns. A user can grant any object privilege on any object he or she owns to any other user or role. If the grant includes the GRANT OPTION (of the GRANT command), the grantee can further grant the object privilege to other users; otherwise, the grantee can only use the privilege but not grant it to other users.

Table Security Topics

The object privileges for tables allow table security at two levels:

Data Manipulation Language Operations The DELETE, INSERT, SELECT, and UPDATE privileges allow the DELETE, INSERT, SELECT, and UPDATE DML operations, respectively, on a table or view (DML operations are those to view or change a table's contents). You should grant these privileges only to users and roles that need to view or manipulate a table's data. For more information on these operations, see the Oracle7 Server SQL Reference.

You can restrict the INSERT and UPDATE privileges for a table to specific columns of the table. With selective INSERT, a privileged user can insert a row, but only with values for the selected columns; all other columns receive NULL or the column's default value. With selective UPDATE, a user can update only specific column values of a row. Selective INSERT and UPDATE privileges are used to restrict a user's access to sensitive data.

For example, if you do not want data entry users to alter the SAL column of the employee table, selective INSERT and/or UPDATE privileges can be granted that exclude the SAL column. Alternatively, a view could satisfy this need for additional security.

Data Definition Language Operations The ALTER, INDEX, and REFERENCES privileges allow DDL operations to be performed on a table. Because these privileges allow other users to alter or create dependencies on a table, you should grant the privileges conservatively. In addition to these privileges, a user attempting to perform a DDL operation on a table may need other system and/or object privileges (for example, to create a trigger on a table, the user requires both the ALTER TABLE object privilege for the table and the CREATE TRIGGER system privilege).

As with the INSERT and UPDATE privileges, the REFERENCES privilege can be granted on specific columns of a table. The REFERENCES privilege enables the grantee to use the table on which the grant is made as a parent key to any foreign keys that the grantee wishes to create in his/her own tables. This action is controlled with a special privilege because the presence of foreign keys restricts the data manipulation and table alterations that can be done to the parent key. A column-specific REFERENCES privilege restricts the grantee to using the named columns, which, of course, must include at least one primary or unique key of the parent table. See Chapter 7, "Data Integrity," for more information about primary keys, unique keys, and integrity constraints.

View Security Topics

The object privileges for views allow various DML operations. Of course, a DML statement performed on a view actually affects the base tables from which the view is derived. DML object privileges for tables can be applied similarly to views.

Privileges Required To Create Views To create a view, you must meet the following requirements:

You must have been granted the CREATE VIEW (to create a view in your schema) or CREATE ANY VIEW (to create a view in another user's schema) system privilege, either explicitly or via a role.

You must have been explicitly granted the SELECT, INSERT, UPDATE, and/or DELETE object privileges on all base objects underlying the view or the SELECT ANY TABLE, INSERT ANY TABLE, UPDATE ANY TABLE, and/or DELETE ANY TABLE system privileges. You may not have obtained these privileges through roles.

Additionally, if you intend to grant access to your view to other users, you must have received the object privilege(s) to the base objects with the GRANT OPTION or to the system privileges with the ADMIN OPTION. If you have not, and grant access to your view, grantees cannot access your view.

Increasing Table Security Using Views To use a view, you only require the appropriate privilege for the view itself. You do not require any privileges on the base object(s) underlying the view.

Views are useful for adding two more levels of security for tables:

A view can provide access to selected columns of the base table(s) that define the view. For example, you can define a view on the EMP table to show only the EMPNO, ENAME, and MGR columns:

		CREATE VIEW emp_mgr AS

		   SELECT ename, empno, mgr FROM emp;

A view can provide value-based security for the information in a table. A WHERE clause in the definition of a view displays only selected rows of the associated base tables. Consider the following two examples:

		CREATE VIEW lowsal AS

		   SELECT * FROM emp

		   WHERE sal < 10000;

The LOWSAL view allows access to all rows of the base table EMP that have a salary value less than 10000. Value-based security is defined on the salary value in a row. Notice that all columns of the EMP table are accessible by the definition of the LOWSAL view.

		CREATE VIEW own_salary AS

		   SELECT ename, sal

		   FROM emp

		   WHERE ename = USER;

The OWN_SALARY view uses the USER pseudocolumn. The values in the USER pseudocolumn are always the current user. In the OWN_SALARY view, only the rows with an ENAME that matches the user using the view are accessible. Value-based security is defined on the user accessing the view. This view combines both column-level security and value-based security.

Procedure Security Topics

The one object privilege for procedures (including standalone procedures and functions, and packages) is EXECUTE. You should grant this privilege only to users who need to execute a procedure.

You can use procedures to add a level of database security. A user requires only the privilege to execute a procedure and no privileges on the underlying objects that a procedure's code accesses. By writing a procedure and granting only the EXECUTE privilege to a user (and not the privileges on the objects referenced by the procedure), the user can be forced to access the referenced objects only through the procedure (that is, the user cannot submit ad hoc SQL statements to the database).

Privileges Needed to Create or Alter a Procedure To create a procedure, a user must have the CREATE PROCEDURE or CREATE ANY PROCEDURE system privilege. To alter a procedure, that is, to manually recompile a procedure, a user must own the procedure or have the ALTER ANY PROCEDURE system privilege.

Additionally, the user who owns the procedure must have the required privileges for the objects referenced in the body of a procedure. To create a procedure, you must have been explicitly granted the necessary privileges (system and/or object) on all objects referenced by the stored procedure; you cannot have obtained the required privileges through roles. This includes the EXECUTE privilege for any procedures that are called inside the stored procedure being created. Triggers also require that privileges to referenced objects be granted explicitly to the trigger owner. Anonymous PL/SQL blocks can use any privilege, whether the privilege is granted explicitly or via a role.

Procedure Execution and Security Domains A user with the EXECUTE privilege for a specific procedure can execute the procedure. A user with the EXECUTE ANY PROCEDURE system privilege can execute any procedure in the database. A user can be granted the privileges to execute procedures via roles.

When you execute a procedure, it operates under the security domain of the user who owns the procedure, regardless of who is executing it. Therefore, a user does not need privileges on the referenced objects to execute a procedure. Because the owner of a procedure must have the necessary object privileges for referenced objects, fewer privileges have to be granted to users of the procedure and tighter control of database access can be obtained.

The current privileges of the owner of a stored procedure are always checked before the procedure is executed. If a necessary privilege on a referenced object is revoked from the owner of a procedure, the procedure cannot be executed by the owner or any other user.

Note: Trigger execution follows these same patterns. The user executes a SQL statement, which he/she is privileged to execute. As a result of the SQL statement, a trigger is fired. The statements within the triggered action temporarily execute under the security domain of the user that owns the trigger.

Packages and Package Objects A user with the EXECUTE privilege for a package can execute any (public) procedure or function in the package, and access or modify the value of any (public) package variable. Specific EXECUTE privileges cannot be granted for a package's constructs. Because of this, you may find it useful to consider two alternatives for establishing security when developing procedures, functions, and packages for a database application. These alternatives are described in the following examples.

Example 1

This example shows four procedures created in the bodies of two packages.

CREATE PACKAGE BODY hire_fire AS

	PROCEDURE hire(...) IS

		BEGIN

			INSERT INTO emp . . .

		END hire;

	PROCEDURE fire(...) IS

		BEGIN

			DELETE FROM emp . . .

		END fire;

END hire_fire;

CREATE PACKAGE BODY raise_bonus AS

	PROCEDURE give_raise(...) IS

		BEGIN

			UPDATE EMP SET sal = . . .

		END give_raise;

	PROCEDURE give_bonus(...) IS

		BEGIN

			UPDATE EMP SET bonus = . . .

		END give_bonus;

END raise_bonus;

Access to execute the procedures is given by granting the EXECUTE privilege for the encompassing package, as in the following statements:

GRANT EXECUTE ON hire_fire TO big_bosses;

GRANT EXECUTE ON raise_bonus TO little_bosses;

This method of security for package objects is not discriminatory for any specific object in a package. The EXECUTE privilege granted for the package provides access to all package objects.

Example 2

This example shows four procedure definitions within the body of a single package. Two additional standalone procedures and a package are created specifically to provide access to the procedures defined in the main package.

CREATE PACKAGE BODY employee_changes AS

	PROCEDURE change_salary(...) IS BEGIN ... END;

	PROCEDURE change_bonus(...) IS BEGIN ... END;

	PROCEDURE insert_employee(...) IS BEGIN ... END;

	PROCEDURE delete_employee(...) IS BEGIN ... END;

END employee_change;

CREATE PROCEDURE hire

	BEGIN

		insert_employee(...)

	END hire;

CREATE PROCEDURE fire

	BEGIN

		delete_employee(...)

	END fire;

PACKAGE raise_bonus IS

	PROCEDURE give_raise(...) AS

		BEGIN

			change_salary(...)

		END give_raise;

	PROCEDURE give_bonus(...)

		BEGIN

			change_bonus(...)

		END give_bonus;

Using this method, the procedures that actually do the work (the procedures in the EMPLOYEE_CHANGES package) are defined in a single package and can share declared global variables, cursors, on so on. By declaring the top-level procedures HIRE and FIRE, and the additional package RAISE_BONUS, you can indirectly grant selective EXECUTE privileges on the procedures in the main package.

GRANT EXECUTE ON hire, fire TO big_bosses;

GRANT EXECUTE ON raise_bonus TO little_bosses;