postgresql影子用户实践

作者：瀚高PG实验室（Highgo PG Lab）- 禹晓

在实际的生产环境，我们经常会碰到这样的情况：因为业务场景需要，本部门某些重要的业务数据表需要给予其他部门查看权限，因业务的扩展及调整，后期可能需要放开更多的表查询权限。为解决此种业务需求，我们可以采用创建视图的方式来解决，已可以通过创建影子用户的方式来满足需求，本文主要介绍影子用户的创建及授权方法。

场景1：只授予usage on schema 权限

session 1:
--创建readonly用户，并将test模式赋予readonly用户。

postgres=# create user readonly with password 'postgres';
CREATE ROLE
postgres=# grant usage on schema test to readonly;
GRANT
postgres=# \dn
List of schemasName  | Owner
-------+-------test | postgres

session 2:

--登陆readonly用户可以查询test模式下现存的所有表。

postgres=# \c postgres readonly
You are now connected to database "postgres" as user "readonly".
postgres=> select * from test.emp ;empno | ename  |    job    | mgr  |  hiredate  |   sal   |  comm   | deptno
-------+--------+-----------+------+------------+---------+---------+--------7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     307521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     307566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |         |     207654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     307698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |         |     307782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |         |     107839 | KING   | PRESIDENT |      | 1981-11-17 | 5000.00 |         |     107844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     307900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |         |     307902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |         |     207934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |         |     107788 | test   | ANALYST   | 7566 | 1982-12-09 | 3000.00 |         |     207876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |         |     201111 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |         |     20
(14 rows)

换到session 1创建新表t1

postgres=# create table test.t1 as select * from test.emp;
CREATE TABLE

切换到session 2 readonly用户下，t1表无法查询

postgres=> select * from test.t1 ;
2021-03-02 15:25:33.290 CST [21059] ERROR:  permission denied for table t1
2021-03-02 15:25:33.290 CST [21059] STATEMENT:  select * from test.t1 ;
**ERROR:  permission denied for table t1

结论：如果只授予 usage on schema 权限，readonly 只能查看 test 模式下已经存在的表和对象。在授予 usage on schema 权限之后创建的新表无法查看。

场景2：授予usage on schema 权限之后，再赋予 select on all tables in schema 权限

针对上个场景session 2 **ERROR: permission denied for table t1 错误的处理

postgres=> select * from test.t1 ;
**ERROR:  permission denied for table t1

session 1：使用postgres用户授予readonly用户 select on all tables 权限

postgres=# grant select on all tables in schema test TO readonly ;

session 2: readonly用户查询 t1 表

postgres=> select * from test.t1;empno | ename  |    job    | mgr  |  hiredate  |   sal   |  comm   | deptno
-------+--------+-----------+------+------------+---------+---------+--------7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     307521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     307566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |         |     207654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     307698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |         |     307782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |         |     107839 | KING   | PRESIDENT |      | 1981-11-17 | 5000.00 |         |     107844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     307900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |         |     307902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |         |     207934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |         |     107788 | test   | ANALYST   | 7566 | 1982-12-09 | 3000.00 |         |     207876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |         |     201111 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |         |     20
(14 rows)

session1 ：postgres用户的test模式下创建新表 t2

postgres=# create table test.t2 as select * from test.emp;
SELECT 14

session 2：readonly用户查询 t2 表权限不足

postgres=>  select * from test.t2 ;
ERROR:  permission denied for table t2

session 1：再次赋予 grant select on all tables

postgres=# grant select on all tables in schema test TO readonly ;

session 2：readonly用户又可以查看 T2 表

postgres=>  select * from test.t2 ;empno | ename  |    job    | mgr  |  hiredate  |   sal   |  comm   | deptno
-------+--------+-----------+------+------------+---------+---------+--------7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     307521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     307566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |         |     207654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     307698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |         |     307782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |         |     107839 | KING   | PRESIDENT |      | 1981-11-17 | 5000.00 |         |     107844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     307900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |         |     307902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |         |     207934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |         |     107788 | test   | ANALYST   | 7566 | 1982-12-09 | 3000.00 |         |     207876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |         |     201111 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |         |     20
(14 rows)

影子用户创建

如果想让readonly只读用户不在每次 postgres用户在test模式中创建新表后都要手工赋予 grant select on all tables in schema test TO readonly 权限。则需要授予对test默认的访问权限，对于test模式新创建的也生效。

session 1：未来访问test模式下所有新建的表赋权，创建 t5 表。

postgres=# alter default privileges in schema test grant select on tables to readonly ;
ALTER DEFAULT PRIVILEGES
postgres=# create table test.t5 as select * from test.emp;
CREATE TABLE

session 2：查询readonly用户

postgres=> select * from test.t5;empno | ename  |    job    | mgr  |  hiredate  |   sal   |  comm   | deptno
-------+--------+-----------+------+------------+---------+---------+--------7499 | ALLEN  | SALESMAN  | 7698 | 1981-02-20 | 1600.00 |  300.00 |     307521 | WARD   | SALESMAN  | 7698 | 1981-02-22 | 1250.00 |  500.00 |     307566 | JONES  | MANAGER   | 7839 | 1981-04-02 | 2975.00 |         |     207654 | MARTIN | SALESMAN  | 7698 | 1981-09-28 | 1250.00 | 1400.00 |     307698 | BLAKE  | MANAGER   | 7839 | 1981-05-01 | 2850.00 |         |     307782 | CLARK  | MANAGER   | 7839 | 1981-06-09 | 2450.00 |         |     107839 | KING   | PRESIDENT |      | 1981-11-17 | 5000.00 |         |     107844 | TURNER | SALESMAN  | 7698 | 1981-09-08 | 1500.00 |    0.00 |     307900 | JAMES  | CLERK     | 7698 | 1981-12-03 |  950.00 |         |     307902 | FORD   | ANALYST   | 7566 | 1981-12-03 | 3000.00 |         |     207934 | MILLER | CLERK     | 7782 | 1982-01-23 | 1300.00 |         |     107788 | test   | ANALYST   | 7566 | 1982-12-09 | 3000.00 |         |     207876 | ADAMS  | CLERK     | 7788 | 1983-01-12 | 1100.00 |         |     201111 | SMITH  | CLERK     | 7902 | 1980-12-17 |  800.00 |         |     20
(14 rows)

总结：影子用户创建的步骤

--创建影子用户
create user readonly with password 'postgres';
--将schema中usage权限赋予给readonly用户,访问所有已存在的表
grant usage on schema test to readonly;
grant select on all tables in schema test to readonly;
--未来访问test模式下所有新建的表
alter default privileges in schema test grant select on tables to readonly ;