postgresql影子用戶實踐場景分析

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在實際的生產環境 ，我們經常會碰到這樣的情況：因為業務場景需要，本部門某些重要的業務數據表需要給予其他部門查看權限，因業務的擴展及調整，後期可能需要放開更多的表查詢權限。為解決此種業務需求，我們可以采用創建視圖的方式來解決，已可以通過創建影子用戶的方式來滿足需求，本文主要介紹影子用戶的創建及授權方法。

場景1：隻授予usage on schema 權限

session 1:
–創建readonly用戶，並將test模式賦予readonly用戶。

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

session 2:

–登陸readonly用戶可以查詢test模式下現存的所有表。

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 |   30
 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 |   30
 7566 | JONES | MANAGER  | 7839 | 1981-04-02 | 2975.00 |     |   20
 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 |   30
 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 | 2850.00 |     |   30
 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 | 2450.00 |     |   10
 7839 | KING  | PRESIDENT |   | 1981-11-17 | 5000.00 |     |   10
 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 |  0.00 |   30
 7900 | JAMES | CLERK   | 7698 | 1981-12-03 | 950.00 |     |   30
 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 | 3000.00 |     |   20
 7934 | MILLER | CLERK   | 7782 | 1982-01-23 | 1300.00 |     |   10
 7788 | test  | ANALYST  | 7566 | 1982-12-09 | 3000.00 |     |   20
 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 | 1100.00 |     |   20
 1111 | SMITH | CLERK   | 7902 | 1980-12-17 | 800.00 |     |   20
(14 rows)

換到session 1創建新表t1

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

切換到session 2 readonly用戶下，t1表無法查詢

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

結論：如果隻授予 usage on schema 權限，readonly 隻能查看 test 模式下已經存在的表和對象。在授予 usage on schema 權限之後創建的新表無法查看。

場景2：授予usage on schema 權限之後，再賦予 select on all tables in schema 權限

針對上個場景session 2 **ERROR: permission denied for table t1 錯誤的處理

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

session 1： 使用postgres用戶授予readonly用戶 select on all tables 權限

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

session 2: readonly用戶查詢 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 |   30
 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 |   30
 7566 | JONES | MANAGER  | 7839 | 1981-04-02 | 2975.00 |     |   20
 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 |   30
 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 | 2850.00 |     |   30
 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 | 2450.00 |     |   10
 7839 | KING  | PRESIDENT |   | 1981-11-17 | 5000.00 |     |   10
 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 |  0.00 |   30
 7900 | JAMES | CLERK   | 7698 | 1981-12-03 | 950.00 |     |   30
 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 | 3000.00 |     |   20
 7934 | MILLER | CLERK   | 7782 | 1982-01-23 | 1300.00 |     |   10
 7788 | test  | ANALYST  | 7566 | 1982-12-09 | 3000.00 |     |   20
 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 | 1100.00 |     |   20
 1111 | SMITH | CLERK   | 7902 | 1980-12-17 | 800.00 |     |   20
(14 rows)

session1 ：postgres用戶的test模式下創建新表 t2

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

session 2：readonly用戶查詢 t2 表權限不足

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

session 1：再次賦予 grant select on all tables

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

session 2：readonly用戶又可以查看 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 |   30
 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 |   30
 7566 | JONES | MANAGER  | 7839 | 1981-04-02 | 2975.00 |     |   20
 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 |   30
 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 | 2850.00 |     |   30
 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 | 2450.00 |     |   10
 7839 | KING  | PRESIDENT |   | 1981-11-17 | 5000.00 |     |   10
 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 |  0.00 |   30
 7900 | JAMES | CLERK   | 7698 | 1981-12-03 | 950.00 |     |   30
 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 | 3000.00 |     |   20
 7934 | MILLER | CLERK   | 7782 | 1982-01-23 | 1300.00 |     |   10
 7788 | test  | ANALYST  | 7566 | 1982-12-09 | 3000.00 |     |   20
 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 | 1100.00 |     |   20
 1111 | SMITH | CLERK   | 7902 | 1980-12-17 | 800.00 |     |   20
(14 rows)

影子用戶創建

如果想讓readonly隻讀用戶不在每次 postgres用戶在test模式中創建新表後都要手工賦予 grant select on all tables in schema test TO readonly 權限。則需要授予對test默認的訪問權限，對於test模式新創建的也生效。

session 1：未來訪問test模式下所有新建的表賦權，創建 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：查詢readonly用戶

postgres=> select * from test.t5;
 empno | ename |  job  | mgr | hiredate |  sal  | comm  | deptno 
-------+--------+-----------+------+------------+---------+---------+--------
 7499 | ALLEN | SALESMAN | 7698 | 1981-02-20 | 1600.00 | 300.00 |   30
 7521 | WARD  | SALESMAN | 7698 | 1981-02-22 | 1250.00 | 500.00 |   30
 7566 | JONES | MANAGER  | 7839 | 1981-04-02 | 2975.00 |     |   20
 7654 | MARTIN | SALESMAN | 7698 | 1981-09-28 | 1250.00 | 1400.00 |   30
 7698 | BLAKE | MANAGER  | 7839 | 1981-05-01 | 2850.00 |     |   30
 7782 | CLARK | MANAGER  | 7839 | 1981-06-09 | 2450.00 |     |   10
 7839 | KING  | PRESIDENT |   | 1981-11-17 | 5000.00 |     |   10
 7844 | TURNER | SALESMAN | 7698 | 1981-09-08 | 1500.00 |  0.00 |   30
 7900 | JAMES | CLERK   | 7698 | 1981-12-03 | 950.00 |     |   30
 7902 | FORD  | ANALYST  | 7566 | 1981-12-03 | 3000.00 |     |   20
 7934 | MILLER | CLERK   | 7782 | 1982-01-23 | 1300.00 |     |   10
 7788 | test  | ANALYST  | 7566 | 1982-12-09 | 3000.00 |     |   20
 7876 | ADAMS | CLERK   | 7788 | 1983-01-12 | 1100.00 |     |   20
 1111 | SMITH | CLERK   | 7902 | 1980-12-17 | 800.00 |     |   20
(14 rows)

總結：影子用戶創建的步驟

--創建影子用戶
create user readonly with password 'postgres';
--將schema中usage權限賦予給readonly用戶,訪問所有已存在的表
grant usage on schema test to readonly;
grant select on all tables in schema test to readonly;
--未來訪問test模式下所有新建的表
alter default privileges in schema test grant select on tables to readonly ;

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