PG版本：Postgresql 9.6.5
由于版本不同代码会有所差别，本例在Postgresql 9.6.5编写而来，其他版本未经测试(Postgresql 10beta3测试不能直接用)。
1.安装插件前
sun@sun:~/PG/PG9.6.5/bin$ ./createdb testdb sun@sun:~/PG/PG9.6.5/bin$ ./createuser testuser sun@sun:~/PG/PG9.6.5/bin$ ./psql -U testuser testdb psql (9.6.5) Type "help" for help. testdb=> create table testtable(a int); CREATE TABLE testdb=> create table testtable2(a int); CREATE TABLE testdb=> \q sun@sun:~/PG/PG9.6.5/bin$ ./psql -U sun testdb psql (9.6.5) Type "help" for help. testdb=# \d List of relations Schema | Name | Type | Owner --------+------------+-------+---------- public | testtable | table | testuser public | testtable2 | table | testuser (2 rows) testdb=# drop table testtable2; DROP TABLE testdb=# \d List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testtable | table | testuser (1 row)
2.安装插件后
sun@sun:~/PG/PG9.6.5/bin$ ./psql -U sun testdb psql (9.6.5) Type "help" for help. testdb=# \d List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testtable | table | testuser (1 row) testdb=# drop table testtable; ERROR: Please drop with User: testuser STATEMENT: drop table testtable; ERROR: Please drop with User: testuser
3.插件安装方法：
在源码contrib下建立目录：limitsuperuserdrop，将C代码文件和Makefile放入其中，编译安装，如下：
sun@sun:~/Data/postgresql-9.6.5/contrib/limitsuperuserdrop$ ll 总用量 80 -rw------- 1 sun sun 76898 9月 13 21:04 limitsuperuserdrop.c -rw------- 1 sun sun 394 9月 13 19:57 Makefile sun@sun:~/Data/postgresql-9.6.5/contrib/limitsuperuserdrop$ make ; make install
安装完成后修改配置文件， 修改Data目录下的postgresql.conf中的shared_preload_libraries
shared_preload_libraries = 'limitsuperuserdrop' # (change requires restart)
重启数据库。安装完成。
4.原理：
本插件使用Postgresql的hook机制，实现对PG数据库的超级用户的删除操作的权限限制。
常用hook:
| 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 | 处理查询执行时调用的hook |
| ExecutorFinish_hook | 8.4 | 处理查询结束时调用的hook |
| ExecutorEnd_hook | 8.4 | 处理查询完成后调用的hook |
| ExecutorCheckPerms_hook | 9.1 | 处理访问权限时调用的hook |
| ProcessUtility_hook | 9.0 | 通用hook，可以处理很多的过程 |
本例使用ProcessUtility_hook
插件实现思路：
当数据库调用ProcessUtility_hook时，首先会检测是否为NULL，不为NULL的话，则调用由我们编写的函数，否则执行标准函数。 也就是说在我们不使用插件的时候，数据库总是在调用standard_ProcessUtility。因此我们的插件代码，就是在standard_ProcessUtility中执行drop操作的地方判断要删除的表是否属于进行操作的用户，不是的话就报错。因此，本插件代码绝大部分是由src/backend/tcop/utility.c文件复制而来。
if (ProcessUtility_hook) (*ProcessUtility_hook) (parsetree,queryString,context,params,dest,completionTag); else standard_ProcessUtility(parsetree,completionTag);
在此提供两套代码，完整版和精简版，精简版删除了大多数的代码。 点击下载
Makefile代码：
# contrib/limitsuperuserdrop/Makefile MODULES = limitsuperuserdrop OBJS = limitsuperuserdrop.o $(WIN32RES) PGFILEDESC = "limitsuperuserdrop" ifdef USE_PGXS PG_CONFIG = pg_config PGXS := $(shell $(PG_CONFIG) --pgxs) include $(PGXS) else subdir = contrib/limitsuperuserdrop top_builddir = ../.. include $(top_builddir)/src/Makefile.global include $(top_srcdir)/contrib/contrib-global.mk endif
/* * limitsuperuserdrop.c * 说明：限制超级用户删除表的操作。 */ #include "postgres.h" #include "miscadmin.h" #include "nodes/parsenodes.h" #include "nodes/pg_list.h" #include "catalog/pg_class.h" #include "executor/executor.h" #include "tcop/utility.h" #include "postgres.h" #include "access/htup_details.h" #include "access/reloptions.h" #include "access/twophase.h" #include "access/xact.h" #include "access/xlog.h" #include "catalog/catalog.h" #include "catalog/namespace.h" #include "catalog/toasting.h" #include "commands/alter.h" #include "commands/async.h" #include "commands/cluster.h" #include "commands/comment.h" #include "commands/collationcmds.h" #include "commands/conversioncmds.h" #include "commands/copy.h" #include "commands/createas.h" #include "commands/dbcommands.h" #include "commands/defrem.h" #include "commands/discard.h" #include "commands/event_trigger.h" #include "commands/explain.h" #include "commands/extension.h" #include "commands/matview.h" #include "commands/lockcmds.h" #include "commands/policy.h" #include "commands/portalcmds.h" #include "commands/prepare.h" #include "commands/proclang.h" #include "commands/schemacmds.h" #include "commands/seclabel.h" #include "commands/sequence.h" #include "commands/tablecmds.h" #include "commands/tablespace.h" #include "commands/trigger.h" #include "commands/typecmds.h" #include "commands/user.h" #include "commands/vacuum.h" #include "commands/view.h" #include "miscadmin.h" #include "parser/parse_utilcmd.h" #include "postmaster/bgwriter.h" #include "rewrite/rewriteDefine.h" #include "rewrite/rewriteRemove.h" #include "storage/fd.h" #include "tcop/pquery.h" #include "tcop/utility.h" #include "utils/acl.h" #include "utils/guc.h" #include "utils/syscache.h" PG_MODULE_MAGIC; void _PG_init(void); void _PG_fini(void); static ProcessUtility_hook_type My_ProcessUtility_hook_type = NULL; static void ExecDropStmt(DropStmt *stmt,bool isTopLevel); Oid MyGetOwnerId(Oid class_oid); Oid MyGetrelOid(DropStmt *drop); void My_ProcessUtility(Node *parsetree,const char *queryString,ProcessUtilityContext context,ParamListInfo params,DestReceiver *dest,char *completionTag) { bool isTopLevel = (context == PROCESS_UTILITY_TOPLEVEL); switch (nodeTag(parsetree)) { case T_DropStmt: { DropStmt *stmt = (DropStmt *) parsetree; if( MyGetOwnerId(MyGetrelOid(stmt)) != GetUserId() ) ereport(ERROR,(errcode(ERRCODE_UNDEFINED_TABLE),errmsg("Please drop with User: %s ",GetUserNameFromId(MyGetOwnerId(MyGetrelOid(stmt)),false)) ) ); else ExecDropStmt(stmt,isTopLevel); } break; } } static void ExecDropStmt(DropStmt *stmt,bool isTopLevel) { switch (stmt->removeType) { case OBJECT_INDEX: if (stmt->concurrent) PreventTransactionChain(isTopLevel,"DROP INDEX CONCURRENTLY"); /* fall through */ case OBJECT_TABLE: case OBJECT_SEQUENCE: case OBJECT_VIEW: case OBJECT_MATVIEW: case OBJECT_FOREIGN_TABLE: RemoveRelations(stmt); break; default: RemoveObjects(stmt); break; } } Oid MyGetOwnerId(Oid class_oid) { HeapTuple tuple; Oid ownerId; tuple = SearchSysCache1(RELOID,ObjectIdGetDatum(class_oid)); if (!HeapTupleIsValid(tuple)) ereport(ERROR,errmsg("relation with OID %u does not exist",class_oid))); ownerId = ((Form_pg_class) GETSTRUCT(tuple))->relowner; ReleaseSysCache(tuple); // printf("User = %d\n",ownerId); return ownerId; } Oid MyGetrelOid(DropStmt *drop) { ListCell *cell; LOCKMODE lockmode = AccessExclusiveLock; Oid relOid; foreach(cell,drop->objects) { RangeVar *rel = makeRangeVarFromNameList((List *) lfirst(cell)); relOid = RangeVarGetRelidExtended(rel,lockmode,true,false,NULL,NULL); } // printf("relOid = %d\n",relOid); return relOid; } // Install Hook void _PG_init(void) { My_ProcessUtility_hook_type = ProcessUtility_hook; ProcessUtility_hook = My_ProcessUtility; } // Uninstall Hook void _PG_fini(void) { ProcessUtility_hook = My_ProcessUtility_hook_type; }
精简后的代码运行drop操作效果一样,便于阅读学习。但是由于其他的操作(比如创建表)也会经过我们编写的代码，然而精简后的对其他操作并没有相应的实现代码，所以并不会发生真实的操作(如下，create table testtable2(a int),并没有成功创建testtable2表，因此使用精简代码进行实验的话，请在安装插件前先创建几张表备用)。
sun@sun:~/PG/PG9.6.5/bin$ ./psql -U sun testdb psql (9.6.5) Type "help" for help. testdb=# \d List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testtable | table | testuser (1 row) testdb=# create table testtable2(a int); CREATE TABLE testdb=# \d List of relations Schema | Name | Type | Owner --------+-----------+-------+---------- public | testtable | table | testuser (1 row)
