PostgreSQL下如何修改用户权限的介绍以及hook机制对超级用户的权限修改

要想修改PG的用户权限，那么首先要对PG权限控制做一下了解：

PG的权限控制是针对到各个对象的。大家可以看一下，所有系统表（pg_catalog下）几乎都会有aclitem[]数组类型的**acl的字段，这就是对权限的标识。

这里的标识情况如下：

rolename=xxxx -- privileges granted to a role
        =xxxx -- privileges granted to PUBLIC
 
            r -- SELECT ("read")
            w -- UPDATE ("write")
            a -- INSERT ("append")
            d -- DELETE
            D -- TRUNCATE
            x -- REFERENCES
            t -- TRIGGER
            X -- EXECUTE
            U -- USAGE
            C -- CREATE
            c -- CONNECT
            T -- TEMPORARY
      arwdDxt -- ALL PRIVILEGES (for tables,varies for other objects)
            * -- grant option for preceding privilege
 
        /yyyy -- role that granted this privilege

这里有一个非常重要的结构体：

typedef struct AclItem
{
	Oid			ai_grantee;		/* ID that this item grants privs to */
	Oid			ai_grantor;		/* grantor of privs */
	AclMode		ai_privs;		/* privilege bits */
} AclItem;

typedef uint32 AclMode;

然后注释对AclMode的解释是这样的：

/*
 * The upper 16 bits of the ai_privs field of an AclItem are the grant option
 * bits,and the lower 16 bits are the actual privileges.  We use "rights"
 * to mean the combined grant option and privilege bits fields.
 */

高16位存储的是grant option，而低16位存储的是各个权限位的授予情况，有没有对应的权限。

对低16位的解释：

低16位很简单的可以明白就是在这16bit上表示权限。通过下面的宏定义可以了解一下：

#define ACL_INSERT		(1<<0)	/* for relations */
#define ACL_SELECT		(1<<1)
#define ACL_UPDATE		(1<<2)
#define ACL_DELETE		(1<<3)
#define ACL_TRUNCATE	(1<<4)
#define ACL_REFERENCES	(1<<5)
#define ACL_TRIGGER		(1<<6)
#define ACL_EXECUTE		(1<<7)	/* for functions */
#define ACL_USAGE		(1<<8)	/* for languages,namespaces,FDWs,and
								 * servers */
#define ACL_CREATE		(1<<9)	/* for namespaces and databases */
#define ACL_CREATE_TEMP (1<<10) /* for databases */
#define ACL_CONNECT		(1<<11) /* for databases */
#define N_ACL_RIGHTS	12		/* 1 plus the last 1<<x */
#define ACL_NO_RIGHTS	0
/* Currently,SELECT ... FOR [KEY] UPDATE/SHARE requires UPDATE privileges */
#define ACL_SELECT_FOR_UPDATE	ACL_UPDATE

低16位上便是上面对应的权限有无了。对应权限，大家看一下名字就能明白了。

高16位存储的是各权限对应的授出或者被转授选项。其实就是上一次的受权情况，对高16位的操作我只在grant和revoke发现，还有就是对权限进行读入，对*还有处理。这两处的用法就是将上一次的受权低16位存储到高16位。

#define ACL_INSERT_CHR			'a'		/* formerly known as "append" */
#define ACL_SELECT_CHR			'r'		/* formerly known as "read" */
#define ACL_UPDATE_CHR			'w'		/* formerly known as "write" */
#define ACL_DELETE_CHR			'd'
#define ACL_TRUNCATE_CHR		'D'		/* super-delete,as it were */
#define ACL_REFERENCES_CHR		'x'
#define ACL_TRIGGER_CHR			't'
#define ACL_EXECUTE_CHR			'X'
#define ACL_USAGE_CHR			'U'
#define ACL_CREATE_CHR			'C'
#define ACL_CREATE_TEMP_CHR		'T'
#define ACL_CONNECT_CHR			'c'

而以宏定义定义的是相应权限所对应的字符。这就是我们经常能看到的**acl字段所存储的信息了。

现在通过一个给数据库赋权的例子来解释一下**acl字段存储的信息：

create user ff createdb;
\c test ff
create database tain;
select * from pg_database where datname = 'tain';
  datname  | datdba | encoding | datcollate  |  datctype   | datistemplate | datallowconn | datconnlimit | datlastsysoid | da
tfrozenxid | datminmxid | dattablespace |                         datacl                         
-----------+--------+----------+-------------+-------------+---------------+--------------+--------------+---------------+---
-----------+------------+---------------+--------------------------------------------------------
 tain      |  16438 |        6 | en_US.UTF-8 | en_US.UTF-8 | f             | t            |           -1 |         12917 |   
      1674 |          1 |          1663 | 
(5 rows)

grant all on database tain to ss; select * from pg_database where datname = 'tain';  datname  | datdba | encoding | datcollate  |  datctype   | datistemplate | datallowconn | datconnlimit | datlastsysoid | da
tfrozenxid | datminmxid | dattablespace |                         datacl                         
-----------+--------+----------+-------------+-------------+---------------+--------------+--------------+---------------+---
-----------+------------+---------------+--------------------------------------------------------
 tain      |  16438 |        6 | en_US.UTF-8 | en_US.UTF-8 | f             | t            |           -1 |         12917 |   
      1674 |          1 |          1663 | {=Tc/ff,ff=CTc/ff,ss=CTc/ff}
(5 rows)

\c postgres postgres
alter database tain owner to postgres;
select * from pg_database where datname = 'tain';
  datname  | datdba | encoding | datcollate  |  datctype   | datistemplate | datallowconn | datconnlimit | datlastsysoid | da
tfrozenxid | datminmxid | dattablespace |                         datacl                         
-----------+--------+----------+-------------+-------------+---------------+--------------+--------------+---------------+---
-----------+------------+---------------+--------------------------------------------------------
 tain      |     10 |        6 | en_US.UTF-8 | en_US.UTF-8 | f             | t            |           -1 |         12917 |   
      1674 |          1 |          1663 | {=Tc/postgres,postgres=CTc/postgres,ss=CTc/postgres}
(5 rows)

上面有这么三种情况:

1、创建数据库后，默认为空。
2、为用户赋权后，将默认和赋权的情况都写在了datacl字段内。
=前的为受权的用户，/后的为数据库所属的用户，/前的为受权用户对其拥有的权限。
3、改变数据库属主后的权限情况。

说完权限情况，下面介绍一下用户情况，

PG的用户可以分为两类：1超级用户，2普通用户。

为什么这会分出这两类呢？
1、普通用户的权限控制可以直接用命令直接进行修改权限：

postgres=# \help grant
Command:     GRANT
Description: define access privileges
Syntax:
GRANT { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | TRIGGER }
    [,...] | ALL [ PRIVILEGES ] }
    ON { [ TABLE ] table_name [,...]
         | ALL TABLES IN SCHEMA schema_name [,...] }
    TO { [ GROUP ] role_name | PUBLIC } [,...] [ WITH GRANT OPTION ]

GRANT { { SELECT | INSERT | UPDATE | REFERENCES } ( column_name [,...] )
    [,...] | ALL [ PRIVILEGES ] ( column_name [,...] ) }
    ON [ TABLE ] table_name [,...]
    TO { [ GROUP ] role_name | PUBLIC } [,...] [ WITH GRANT OPTION ]

GRANT { { USAGE | SELECT | UPDATE }
    [,...] | ALL [ PRIVILEGES ] }
    ON { SEQUENCE sequence_name [,...]
         | ALL SEQUENCES IN SCHEMA schema_name [,...] [ WITH GRANT OPTION ]

GRANT { { CREATE | CONNECT | TEMPORARY | TEMP } [,...] | ALL [ PRIVILEGES ] }
    ON DATABASE database_name [,...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON DOMAIN domain_name [,...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON FOREIGN DATA WRAPPER fdw_name [,...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON FOREIGN SERVER server_name [,...] [ WITH GRANT OPTION ]

GRANT { EXECUTE | ALL [ PRIVILEGES ] }
    ON { FUNCTION function_name ( [ [ argmode ] [ arg_name ] arg_type [,...] ] ) [,...]
         | ALL FUNCTIONS IN SCHEMA schema_name [,...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON LANGUAGE lang_name [,...] [ WITH GRANT OPTION ]

GRANT { { SELECT | UPDATE } [,...] | ALL [ PRIVILEGES ] }
    ON LARGE OBJECT loid [,...] [ WITH GRANT OPTION ]

GRANT { { CREATE | USAGE } [,...] | ALL [ PRIVILEGES ] }
    ON SCHEMA schema_name [,...] [ WITH GRANT OPTION ]

GRANT { CREATE | ALL [ PRIVILEGES ] }
    ON TABLESPACE tablespace_name [,...] [ WITH GRANT OPTION ]

GRANT { USAGE | ALL [ PRIVILEGES ] }
    ON TYPE type_name [,...] [ WITH GRANT OPTION ]

GRANT role_name [,...] TO role_name [,...] [ WITH ADMIN OPTION ]

\help revoke
Command:     REVOKE
Description: remove access privileges
Syntax:
REVOKE [ GRANT OPTION FOR ]
    { { SELECT | INSERT | UPDATE | DELETE | TRUNCATE | REFERENCES | TRIGGER }
    [,...] }
    FROM { [ GROUP ] role_name | PUBLIC } [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { { SELECT | INSERT | UPDATE | REFERENCES } ( column_name [,...]
    FROM { [ GROUP ] role_name | PUBLIC } [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { { USAGE | SELECT | UPDATE }
    [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { { CREATE | CONNECT | TEMPORARY | TEMP } [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { USAGE | ALL [ PRIVILEGES ] }
    ON DOMAIN domain_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { USAGE | ALL [ PRIVILEGES ] }
    ON FOREIGN DATA WRAPPER fdw_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { USAGE | ALL [ PRIVILEGES ] }
    ON FOREIGN SERVER server_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { EXECUTE | ALL [ PRIVILEGES ] }
    ON { FUNCTION function_name ( [ [ argmode ] [ arg_name ] arg_type [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { USAGE | ALL [ PRIVILEGES ] }
    ON LANGUAGE lang_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { { SELECT | UPDATE } [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { { CREATE | USAGE } [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { CREATE | ALL [ PRIVILEGES ] }
    ON TABLESPACE tablespace_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ GRANT OPTION FOR ]
    { USAGE | ALL [ PRIVILEGES ] }
    ON TYPE type_name [,...]
    [ CASCADE | RESTRICT ]

REVOKE [ ADMIN OPTION FOR ]
    role_name [,...] FROM role_name [,...]
    [ CASCADE | RESTRICT ]

这是对普通用户权限的修改。

2、对于超级用户，权限修改在这里有没有用了。

对于超级用户来说，所有的操作只有如下的判断就可以操作了：

bool
superuser(void)
{
	return superuser_arg(GetUserId());
}

Oid
GetUserId(void)
{
	AssertState(OidIsValid(CurrentUserId));
	return CurrentUserId;
}

只要判断是超级用户即可进行操作。超级用户的权限很大，在这里提醒各位超级用户慎用。而且在PG里默认用户postgres是就是超级用户，而且不能删除。

所以你可能就需要修改超级用户的权限了，那么如何修改呢？必须通过编写代码进行对超级用户进行限制。这就用到了Postgresql的hook机制。

hook可以修改和中断用户的操作。

下面是常用hook列表，大家可以根据列表进行对数据库相关过程进行修改，不需要直接在PG源码下修改，仅需要加一个扩展组件即可。

Hook	初始版本	说明
check_password_hook	9.0	处理用户密码时调用的hook，可以对用户的密码进行限制，增加密码的规范。
ClientAuthentication_hook	9.1	处理连接时调用的hook，可以对连接进行管理。
ExecutorStart_hook	8.4	处理查询执行开始时调用的hook
ExecutorRun_hook	8.4	处理查询执行调用的hook
ExecutorFinish_hook	8.4	处理查询结束调用的hook
ExecutorEnd_hook	8.4	处理查询完成后调用的hook
ExecutorCheckPerms_hook	9.1	处理访问权限调用的hook
ProcessUtility_hook	9.0	通用hook，可以处理很多的过程。

下面也是一些hook，不过使用的较少：

Hook	使用	初始版本	说明
explain_get_index_name_hook		8.3	在寻找索引name时调用的hook
ExplainOneQuery_hook	IndexAdvisor	8.3
fmgr_hook	sepgsql	9.1	函数调用潜的hook
get_attavgwidth_hook		8.4
get_index_stats_hook		8.4
get_relation_info_hook	plantuner	8.3	得到数据库对象信息的时候调用的hook
get_relation_stats_hook		8.4
join_search_hook	saio	8.3
needs_fmgr_hook	sepgsql	9.1
object_access_hook	sepgsql	9.1
planner_hook	planinstr	8.3	在计划开始执行前调用的hook，可以修改一些查询计划的行为
shmem_startup_hook	pg_stat_statements	8.4	在初始化共享内存是调用的hook

hook工作原理：每一个hook是由一个全局性的函数指针构成的。服务端进行运行初始化其为NULL，当数据库必须调用的时候，首先会检测是否为NULL，不是则优先调用函数，否则执行标准函数。

设置函数指针：当数据库载入共享库时，首先会将其载入到内存中，然后执行一个函数调用_PG_init。这个函数存在大多数共享库中是有效的。所以我们可以通过这个函数来加载我们自己的hook。

取消函数指针设置：当数据库需要卸载其共享库时，会调用函数_PG_fini() 。我们可以再此进行设置函数指针为NULL，这样就取消设置了。

下面来一个实战型的：

目的：超级用户sure不能对任何表进行访问。

1、在contrib下建立目录：acl_super。

[root@localhost contrib]# mkdir acl_super;
[root@localhost contrib]#

2、建立C文件：

/*
 * acl_super.c
 * the super user sure can not have not permission to operate the 
 * ordinary table.
 */
#include "postgres.h"
#include "miscadmin.h"
#include "nodes/parsenodes.h"
#include "nodes/pg_list.h"
#include "catalog/pg_class.h"
#include "executor/executor.h"

PG_MODULE_MAGIC;

void _PG_init(void);
void _PG_fini(void);

static ExecutorCheckPerms_hook_type prev_ExecutorCheckPerms_hook = NULL;

static void myExecCheckRTPerms(List *rangeTable,bool ereport_on_violation);

/*
 * Stop the super user sure from operating the ordinary table  */

static
void myExecCheckRTPerms(List *rangeTable,bool ereport_on_violation)
{
        ListCell   *l;
        Oid        cuser = InvalidOid;
        char*      cusername = NULL;

        cuser = GetSessionUserId();
        cusername = GetUserNameFromId(cuser);

        if(strcmp("sure",cusername) == 0)
        {
                foreach(l,rangeTable)
                {
                        RangeTblEntry *rte = (RangeTblEntry *) lfirst(l);
                        if(rte->relkind == RELKIND_RELATION)      //  ereport(ERROR,(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),errmsg("permission denied to table")));
                }
        }

return true;
}

/*
 * _PG_init
 * Install the hook.
 */
void
_PG_init(void)
{
        prev_ExecutorCheckPerms_hook = ExecutorCheckPerms_hook;
        ExecutorCheckPerms_hook = myExecCheckRTPerms;
}

/*
 * _PG_fini
 * Uninstall the hook.
 */
void
_PG_fini(void)
{
        ExecutorCheckPerms_hook = prev_ExecutorCheckPerms_hook;
}

3、建立Makefile：

# contrib/dbrestrict/Makefile

MODULES = acl_super
OBJS = acl_super.so

ifdef USE_PGXS
PG_CONFIG = pg_config
PGXS := $(shell $(PG_CONFIG) --pgxs)
include $(PGXS)
else
subdir = contrib/acl_super
top_builddir = ../..
include $(top_builddir)/src/Makefile.global
include $(top_srcdir)/contrib/contrib-global.mk
endif

现在目录下的文件为：

[root@localhost acl_super]# ls
acl_super.c  Makefile
[root@localhost acl_super]#

4、编译与安装

[root@localhost acl_super]# make
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -I. -I. -I../../src/include -D_GNU_SOURCE   -c -o acl_super.o acl_super.c
gcc -O2 -Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement -Wendif-labels -Wmissing-format-attribute -Wformat-security -fno-strict-aliasing -fwrapv -fpic -L../../src/port -L../../src/common  -Wl,-rpath,'/opt/pgdbdevel/lib',--enable-new-dtags  -shared -o acl_super.so acl_super.o
[root@localhost acl_super]# make install
/bin/mkdir -p '/opt/pgdbdevel/lib/postgresql'
/usr/bin/install -c -m 755  acl_super.so '/opt/pgdbdevel/lib/postgresql/'
[root@localhost acl_super]#

5、配置文件：

将data目录下的postgresql.conf中的shared_preload_libraries进行修改：

原：

#shared_preload_libraries = ''		# (change requires restart)

修改为：

shared_preload_libraries = 'acl_super'	# (change requires restart)

6、重启数据库服务

[postgres@localhost bin]$  ./pg_ctl -D ../data restart
waiting for server to shut down....LOG:  received smart shutdown request
LOG:  autovacuum launcher shutting down
LOG:  shutting down
LOG:  database system is shut down
 done
server stopped
server starting
[postgres@localhost bin]$ LOG:  database system was shut down at 2014-09-12 00:21:22 PDT
LOG:  autovacuum launcher started
LOG:  database system is ready to accept connections

[postgres@localhost bin]$ ./psql 
psql (9.5devel)
Type "help" for help.

postgres=#

7、实验结果：

postgres=# create table sure_test(s1 int);
insert into sure_test values (1),(2),(3);
select * from sure_test;
 s1 
----
  1
  2
  3
(3 rows)

\c postgres sure
You are now connected to database "postgres" as user "sure".
postgres=# select * from sure_test;
ERROR:  permission denied to table
STATEMENT:  select * from sure_test;
ERROR:  permission denied to table
postgres=#

以上就是对超级用户进行权限限制，当然这里的处理是简单暴力的，而更深层次的权限修改，那就需要花费比较大的时间进行改动，甚至会修改源代码，这里就暂不涉及。

参考：

http://www.cnblogs.com/gaojian/p/3259147.html
http://michael.otacoo.com/postgresql-2/hooks-in-postgres-super-superuser-restrictions/
http://wiki.postgresql.org/images/e/e3/Hooks_in_postgresql.pdf

以后会继续对hook进行详细介绍的，欢迎大家来使用与讨论hook机制。

PostgreSQL下如何修改用户权限的介绍以及hook机制对超级用户的权限修改

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