and foreign key references, will bypass row security to ensure that
data integrity is maintained. Care must be taken when developing
schemas and row level policies to avoid a "covert channel" leak of
- information through these referntial integrity checks.
+ information through these referential integrity checks.
normal privileges system.
+ Below is a larger example of how this feature can be used in
+ production environments, based on a unix password file.
+
+
+-- Simple passwd-file based example
+CREATE TABLE passwd (
+ username text UNIQUE NOT NULL,
+ pwhash text,
+ uid int PRIMARY KEY,
+ gid int NOT NULL,
+ real_name text NOT NULL,
+ home_phone text,
+ extra_info text,
+ home_dir text NOT NULL,
+ shell text NOT NULL
+);
+
+CREATE ROLE admin; -- Administrator
+CREATE ROLE bob; -- Normal user
+CREATE ROLE alice; -- Normal user
+
+-- Populate the table
+INSERT INTO passwd VALUES
+ ('admin','xxx',0,0,'Admin','111-222-3333',null,'/root','/bin/dash');
+INSERT INTO passwd VALUES
+ ('bob','xxx',1,1,'Bob','123-456-7890',null,'/home/bob','/bin/zsh');
+INSERT INTO passwd VALUES
+ ('alice','xxx',2,1,'Alice','098-765-4321',null,'/home/alice','/bin/zsh');
+
+-- Be sure to enable row level security on the table
+ALTER TABLE passwd ENABLE ROW LEVEL SECURITY;
+
+-- Create policies
+-- Administrator can see all rows and add any rows
+CREATE POLICY admin_all ON passwd TO admin USING (true) WITH CHECK (true);
+-- Normal users can view all rows
+CREATE POLICY all_view ON passwd FOR SELECT USING (true);
+-- Normal users can update their own records, but
+-- limit which shells a normal user is allowed to set
+CREATE POLICY user_mod ON passwd FOR UPDATE
+ USING (current_user = username)
+ WITH CHECK (
+ current_user = username AND
+ shell IN ('/bin/bash','/bin/sh','/bin/dash','/bin/zsh','/bin/tcsh')
+ );
+
+-- Allow admin all normal rights
+GRANT SELECT, INSERT, UPDATE, DELETE ON passwd TO admin;
+-- Users only get select access on public columns
+GRANT SELECT
+ (username, uid, gid, real_name, home_phone, extra_info, home_dir, shell)
+ ON passwd TO public;
+-- Allow users to update certain columns
+GRANT UPDATE
+ (pwhash, real_name, home_phone, extra_info, shell)
+ ON passwd TO public;
+
+
+ As with any security settings, it's important to test and ensure that
+ the system is behaving as expected. Using the example above, this
+ demonstrates that the permission system is working properly.
+
+
+-- admin can view all rows and fields
+postgres=> set role admin;
+SET
+postgres=> table passwd;
+ username | pwhash | uid | gid | real_name | home_phone | extra_info | home_dir | shell
+----------+--------+-----+-----+-----------+--------------+------------+-------------+-----------
+ admin | xxx | 0 | 0 | Admin | 111-222-3333 | | /root | /bin/dash
+ bob | xxx | 1 | 1 | Bob | 123-456-7890 | | /home/bob | /bin/zsh
+ alice | xxx | 2 | 1 | Alice | 098-765-4321 | | /home/alice | /bin/zsh
+(3 rows)
+
+-- Test what Alice is able to do
+postgres=> set role alice;
+SET
+postgres=> table passwd;
+ERROR: permission denied for relation passwd
+postgres=> select username,real_name,home_phone,extra_info,home_dir,shell from passwd;
+ username | real_name | home_phone | extra_info | home_dir | shell
+----------+-----------+--------------+------------+-------------+-----------
+ admin | Admin | 111-222-3333 | | /root | /bin/dash
+ bob | Bob | 123-456-7890 | | /home/bob | /bin/zsh
+ alice | Alice | 098-765-4321 | | /home/alice | /bin/zsh
+(3 rows)
+
+postgres=> update passwd set username = 'joe';
+ERROR: permission denied for relation passwd
+-- Allowed to change her own real_name, but no others
+postgres=> update passwd set real_name = 'Alice Doe';
+UPDATE 1
+postgres=> update passwd set real_name = 'John Doe' where username = 'admin';
+UPDATE 0
+postgres=> update passwd set shell = '/bin/xx';
+ERROR: new row violates WITH CHECK OPTION for "passwd"
+postgres=> delete from passwd;
+ERROR: permission denied for relation passwd
+postgres=> insert into passwd (username) values ('xxx');
+ERROR: permission denied for relation passwd
+-- Alice can change her own password
+postgres=> update passwd set pwhash = 'abc';
+UPDATE 1
+
+
referenced table. These issues can be addressed by carefully crafting
policies which prevent users from being able to insert, delete, or update
records at all which might possibly indicate a value they are not otherwise
- able to see, or by using generated values (eg: surrogate keys) instead.
+ able to see, or by using generated values (e.g.: surrogate keys) instead.
records from the relation which pass the SELECT
policy will be returned, even if other records exist in the relation.
The SELECT policy only accepts the USING expression
- as it only ever applies in cases where records are being retrived from
+ as it only ever applies in cases where records are being retrieved from
the relation.
for the DELETE, and rows which are not visible
through the SELECT policy may be deleted if they
pass the DELETE USING policy. The
- DELETE policy only accept the USING expression as
+ DELETE policy only accepts the USING expression as
it only ever applies in cases where records are being extracted from
the relation for deletion.
( 7, 33, 2, 'rls_regress_user2', 'great technology book'),
( 8, 44, 1, 'rls_regress_user2', 'great manga');
ALTER TABLE document ENABLE ROW LEVEL SECURITY;
--- user's security level must be higher that or equal to document's
+-- user's security level must be higher than or equal to document's
CREATE POLICY p1 ON document
USING (dlevel <= (SELECT seclv FROM uaccount WHERE pguser = current_user));
-- viewpoint from rls_regress_user1
DELETE FROM category WHERE cid = 33; -- fails with FK violation
ERROR: update or delete on table "category" violates foreign key constraint "document_cid_fkey" on table "document"
DETAIL: Key (cid)=(33) is still referenced from table "document".
--- cannot insert FK referencing invisible PK
+-- can insert FK referencing invisible PK
SET SESSION AUTHORIZATION rls_regress_user2;
SELECT * FROM document d FULL OUTER JOIN category c on d.cid = c.cid;
did | cid | dlevel | dauthor | dtitle | cid | cname
-----+-----+--------+---------+--------
(0 rows)
--- database superuser cannot bypass RLS policy when enabled
+-- database superuser does bypass RLS policy when enabled
RESET SESSION AUTHORIZATION;
SET row_security TO ON;
SELECT * FROM document;
44 | manga
(4 rows)
--- database superuser cannot bypass RLS policy when FORCE enabled.
+-- database superuser does not bypass RLS policy when FORCE enabled.
RESET SESSION AUTHORIZATION;
SET row_security TO FORCE;
SELECT * FROM document;
-----+-------
(0 rows)
--- database superuser can bypass RLS policy when disabled
+-- database superuser does bypass RLS policy when disabled
RESET SESSION AUTHORIZATION;
SET row_security TO OFF;
SELECT * FROM document;
ALTER TABLE document ENABLE ROW LEVEL SECURITY;
--- user's security level must be higher that or equal to document's
+-- user's security level must be higher than or equal to document's
CREATE POLICY p1 ON document
USING (dlevel <= (SELECT seclv FROM uaccount WHERE pguser = current_user));
SELECT * FROM document d FULL OUTER JOIN category c on d.cid = c.cid;
DELETE FROM category WHERE cid = 33; -- fails with FK violation
--- cannot insert FK referencing invisible PK
+-- can insert FK referencing invisible PK
SET SESSION AUTHORIZATION rls_regress_user2;
SELECT * FROM document d FULL OUTER JOIN category c on d.cid = c.cid;
INSERT INTO document VALUES (10, 33, 1, current_user, 'hoge');
INSERT INTO document VALUES (8, 44, 1, 'rls_regress_user1', 'my third manga'); -- Must fail with unique violation, revealing presence of did we can't see
SELECT * FROM document WHERE did = 8; -- and confirm we can't see it
--- database superuser cannot bypass RLS policy when enabled
+-- database superuser does bypass RLS policy when enabled
RESET SESSION AUTHORIZATION;
SET row_security TO ON;
SELECT * FROM document;
SELECT * FROM category;
--- database superuser cannot bypass RLS policy when FORCE enabled.
+-- database superuser does not bypass RLS policy when FORCE enabled.
RESET SESSION AUTHORIZATION;
SET row_security TO FORCE;
SELECT * FROM document;
SELECT * FROM category;
--- database superuser can bypass RLS policy when disabled
+-- database superuser does bypass RLS policy when disabled
RESET SESSION AUTHORIZATION;
SET row_security TO OFF;
SELECT * FROM document;
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