Virtual Private Database (VPD) in PPAS 9.1

Great News is Postgres Plus Advanced 9.1 is now available for users. So, I thought to write something about Virtual Private Database features, which is part of 9.1

Virtual Private Database (VPD) is a feature which enables Administrator to create security around actual data (i.e row/columns) so that multiple users can access data which is relevant to them. Steps which is require to create Virtual Private database is given below:

1. Create an Application Context
2. Create security policies functions
3. Apply security policies to tables

Lets see how user can implement it in Advanced Server.
1. Setup an environment as given below:

CREATE user merry identified by edb;
CREATE user john identified by edb;
CREATE TABLE public.john_merry(userid varchar2(200),val numeric);
grant select,update,delete,insert on john_merry to john;
grant select,update,delete,insert on john_merry to merry;

2. Now create a Policy Function as given below:

CREATE OR REPLACE FUNCTION verify_user (
    p_schema        VARCHAR2,
    p_object        VARCHAR2
)
RETURN VARCHAR2
IS
BEGIN
    RETURN 'userid = SYS_CONTEXT(''USERENV'', ''SESSION_USER'')';
END;

3. Apply Security Policy using Policy Functions as given below:
DECLARE
    v_object_schema         VARCHAR2(30) := 'public';
    v_object_name           VARCHAR2(30) := 'john_merry';
    v_policy_name           VARCHAR2(30) := 'secure_data';
    v_function_schema       VARCHAR2(30) := 'enterprisedb';
    v_policy_function       VARCHAR2(30) := 'verify_user';
    v_statement_types       VARCHAR2(30) := 'INSERT,UPDATE,DELETE,SELECT';
    v_update_check          BOOLEAN      := TRUE;
    v_enable                BOOLEAN      := TRUE;
BEGIN
    DBMS_RLS.ADD_POLICY(
        v_object_schema,
        v_object_name,
        v_policy_name,
        v_function_schema,
        v_policy_function,
        v_statement_types,
        v_update_check,
        v_enable
    );
END;

Now, lets see how it works.
First insert some records for John and Merry as given below:
1. Connect as John user and do some insert as john, as given below:

edb=> insert into john_merry values('john',1);                 
INSERT 0 1
edb=> insert into john_merry values('john',2); 
INSERT 0 1
edb=> insert into john_merry values('john',3);
INSERT 0 1

2. Now connect as merry and insert some records as merry:

edb=> insert into john_merry values('merry',1);
INSERT 0 1
edb=> insert into john_merry values('merry',2);
INSERT 0 1
edb=> insert into john_merry values('merry',3);
INSERT 0 1

Ok. Now we have some data for both users. lets see how VPD works:
1. Connect as John User and try to insert some record for merry:

edb=> insert into john_merry values('merry',4);
ERROR:  policy with check option violation
DETAIL:  Policy predicate was evaluated to FALSE with the updated values

hmm this is expected, VPD security policy won't allow me to do this activity.

2. Now try to update Merry data as John User:

edb=> update john_merry set val=4 where val=3 and userid='merry';
UPDATE 0

No rows updated. This is expected since as per security policy merry's data is not visible to john. However, john can update his record as given below:

edb=> update john_merry set val=4 where val=3 and userid='john'; 
UPDATE 1

3. Now, lets execute SELECT query on table to view data:

edb=> select current_user;
 current_user 
--------------
 john
(1 row)

edb=> select * from john_merry ;
 userid | val 
--------+-----
 john   |   1
 john   |   2
 john   |   4
(3 rows)

As you can see, john can see his records not merry's. Similary user can try for Merry. Below is a snapshot of SELECT query executed by merry:
using dumb terminal settings.

edb=> select current_user;      
 current_user 
--------------
 merry
(1 row)

edb=> select * from john_merry ;
 userid | val 
--------+-----
 merry  |   1
 merry  |   2
 merry  |   3
(3 rows)

Interesting!!