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淺談Mysql連接數(shù)據(jù)庫時host和user的匹配規(guī)則

--連接數(shù)據(jù)庫時，host和user的匹配規(guī)則

官方文檔：https://dev.mysql.com/doc/refman/5.7/en/connection-access.html

--host和user的匹配規(guī)則如下：

--是host為明確的最先匹配，host帶%模糊的時候最后匹配，但host為''(空)位于%之后才匹配

--相同的host時候，比較user為明確的最先匹配，user為''(空)最后匹配

--相同的host和user時，排序是不確定的

When multiple matches are possible, the server must determine which of them to use. It resolves this issue as follows: 
Whenever the server reads the user table into memory, it sorts the rows. 
When a client attempts to connect, the server looks through the rows in sorted order. 
The server uses the first row that matches the client host name and user name. 
The server uses sorting rules that order rows with the most-specific Host values first. Literal host names and IP addresses are the most specific. (The specificity of a literal IP address is not affected by whether it has a netmask, so 198.51.100.13 and 198.51.100.0/255.255.255.0 are considered equally specific.) The pattern '%' means “any host” and is least specific. The empty string '' also means “any host” but sorts after '%'. Rows with the same Host value are ordered with the most-specific User values first (a blank User value means “any user” and is least specific). For rows with equally-specific Host and User values, the order is nondeterministic.

--查看當(dāng)前的host及用戶信息匹配順序，先host順序匹配、后user順序匹配

mysql> SELECT authentication_string, host, user,account_locked FROM mysql.USER ORDER BY host desc ,user desc;
+-------------------------------------------+--------------+---------------+----------------+
| authentication_string      | host   | user   | account_locked |
+-------------------------------------------+--------------+---------------+----------------+
| *511C0A408C5065XXEC90D60YYA1AB9437281AF28 | localhost | root   | N    |
| *THISISNOTAVALIXXASSWORDYYATCANBEUSEDHERE | localhost | mysql.sys  | Y    |
| *THISISNOTAVALIXXASSWORDYYATCANBEUSEDHERE | localhost | mysql.session | Y    |
| *485CE31BA547A4XXC047659YY10DF200F361CD4E | localhost | bkpuser  | N    |
| *7B502777D8FF69XX4B56BC2YY2867F4B47321BA8 | 192.168.56.% | repl   | N    |
| *AECCE73463829AXX3968838YYF6F85E43C3F169C | %   | flyremote  | N    |
| *566AC8467DAAAEXXE247AE7YY0A770E9B97D9FB0 |    | flylocal  | N    |
+-------------------------------------------+--------------+---------------+----------------+
8 rows in set (0.00 sec)

--舉個特殊例子

--建立兩個特殊用戶如下，一個用戶名為''(空)、一個用戶名和host都為''(空)

mysql> create user ''@'localhost' identified by "Kong123$";
Query OK, 0 rows affected (0.00 sec) 
mysql> create user ''@'' identified by "doubleKong123$";   
Query OK, 0 rows affected (0.00 sec)

--查看當(dāng)前的host及用戶信息匹配順序，先host順序匹配、后user順序匹配

mysql> SELECT authentication_string, host, user,account_locked FROM mysql.USER ORDER BY host desc ,user desc;
+-------------------------------------------+--------------+---------------+----------------+
| authentication_string      | host   | user   | account_locked |
+-------------------------------------------+--------------+---------------+----------------+
| *511C0VVV8C5065CBEC90D6TTTT1AB9437281AF28 | localhost | root   | N    |
| *THISIVVVTAVALIDPASSWORTTTTTCANBEUSEDHERE | localhost | mysql.sys  | Y    |
| *THISIVVVTAVALIDPASSWORTTTTTCANBEUSEDHERE | localhost | mysql.session | Y    |
| *485CEVVVA547A48CC04765TTTT0DF200F361CD4E | localhost | bkpuser  | N    |
| *256D7VVV91F7363EBDADEFTTTTB74B2B318746FC | localhost |    | N    |
| *7B502VVVD8FF69164B56BCTTTT867F4B47321BA8 | 192.168.56.% | repl   | N    |
| *AECCEVVV63829A5F396883TTTT6F85E43C3F169C | %   | flyremote  | N    |
| *566ACVVV7DAAAE79E247AETTTTA770E9B97D9FB0 |    | flylocal  | N    |
| *AE162VVV68403D1D98A4C9TTTT50A508B8C56F3F |    |    | N    |
+-------------------------------------------+--------------+---------------+----------------+
9 rows in set (0.00 sec)

--這樣本地登錄flyremote用戶時會報錯，因為按以上的順序優(yōu)先匹配到了host為localhost、user為''(空)的用戶，而不是flyremote用戶 (因為user為''(空)的用戶可以匹配任意用戶名)

[root@hostmysql-m mysql]# mysql -uflyremote -pFlyremote123$
mysql: [Warning] Using a password on the command line interface can be insecure.
ERROR 1045 (28000): Access denied for user 'flyremote'@'localhost' (using password: YES)

--那就是說本地登錄flyremote用戶時，用匹配到的host為localhost、user為''(空)的密碼 Kong123$ ，就可以正常登陸了

[root@hostmysql-m mysql]# mysql -uflyremote -pKong123$
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 15
Server version: 5.7.23-log MySQL Community Server (GPL) 
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. 
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners. 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

--查看當(dāng)前用戶連接方式和當(dāng)前用戶認(rèn)證方式

mysql> select user(),CURRENT_USER();
+---------------------+----------------+
| user()    | CURRENT_USER() |
+---------------------+----------------+
| flyremote@localhost | @localhost  |
+---------------------+----------------+
1 row in set (0.06 sec)

--用帶入ip的方式登錄flyremote用戶時無問題， ip匹配到了% ，user匹配到了flyremote

[root@hostmysql-m mysql]# mysql -uflyremote -pFlyremote123$ -h127.11.22.33 
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 12
Server version: 5.7.23-log MySQL Community Server (GPL) 
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. 
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners. 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 
mysql>

--查看當(dāng)前用戶連接方式和當(dāng)前用戶認(rèn)證方式

mysql> select user(),CURRENT_USER();
+------------------------+----------------+
| user()     | CURRENT_USER() |
+------------------------+----------------+
| flyremote@127.11.22.33 | flyremote@% |
+------------------------+----------------+
1 row in set (0.00 sec)

--任意用戶、任意host，只要密碼和建立的第二個空用戶空host的密碼"doubleKong123$"匹配了，就可以進(jìn)入mysql

--測試一個不存在的用戶hahaha

[root@hostmysql-m ~]# mysql -uhahaha -pdoubleKong123$ -h127.11.22.33
mysql: [Warning] Using a password on the command line interface can be insecure.
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 6
Server version: 5.7.23-log MySQL Community Server (GPL) 
Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. 
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners. 
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. 
mysql>

--查看當(dāng)前用戶連接方式和當(dāng)前用戶認(rèn)證方式

mysql> select user(),CURRENT_USER();
+---------------------+----------------+
| user()    | CURRENT_USER() |
+---------------------+----------------+
| hahaha@127.11.22.33 | @    |
+---------------------+----------------+
1 row in set (0.01 sec)

--解決方案：

1、手工刪除空用戶和空host用戶確保安全

或者

2、使用 mysql_secure_installation 來進(jìn)行安全配置

--安全配置如下，其中有刪除匿名用戶的操作

This program enables you to improve the security of your MySQL installation in the following ways:
 You can set a password for root accounts.
 You can remove root accounts that are accessible from outside the local host.
 You can remove anonymous-user accounts.
 You can remove the test database (which by default can be accessed by all users, even anonymous users), and privileges that permit anyone to access databases with names that start with test_.

--刪除匿名用戶的源碼 mysql_secure_installation.cc 如下：

 //Remove anonymous users
 remove_anonymous_users(); 
/**
 Removes all the anonymous users for better security.
*/
void remove_anonymous_users()
{
 int reply;
 reply= get_response((const char *) "By default, a MySQL installation has an "
      "anonymous user,\nallowing anyone to log "
      "into MySQL without having to have\na user "
      "account created for them. This is intended "
      "only for\ntesting, and to make the "
      "installation go a bit smoother.\nYou should "
      "remove them before moving into a production\n"
      "environment.\n\nRemove anonymous users? "
      "(Press y|Y for Yes, any other key for No) : ", 'y');
 
 if (reply == (int) 'y' || reply == (int) 'Y')
 {
 const char *query;
 query= "SELECT USER, HOST FROM mysql.user WHERE USER=''";
 if (!execute_query(query, strlen(query)))
  DBUG_PRINT("info", ("query success!"));
 MYSQL_RES *result= mysql_store_result(mysql);
 if (result)
  drop_users(result);
 mysql_free_result(result);
 fprintf(stdout, "Success.\n\n");
 }
 else
 fprintf(stdout, "\n ... skipping.\n\n");
}

補充：mysql 用戶表中多個host時的匹配規(guī)則

mysql數(shù)據(jù)庫中user表的host字段，是用來控制用戶訪問數(shù)據(jù)庫“權(quán)限”的。

可以使用“%”，表示所有的網(wǎng)段；

也可以使用具體的ip地址，表示只有該ip的客戶端才可以登錄到mysql服務(wù)器；

也可以使用“_”進(jìn)行模糊匹配，表示某個網(wǎng)段的客戶端可以登錄到mysql服務(wù)器。

如果在user表中存在一個用戶兩條不同host值的記錄，那么mysql服務(wù)器該如何匹配該用戶的權(quán)限呢？

mysql采用的策略是：當(dāng)服務(wù)器讀取user表時，它首先以最具體的Host值排序（主機名和IP號是最具體的）。有相同Host值的條目首先以最具體的User匹配。

舉例：

如下，有兩條root用戶，那么只有l(wèi)ocalhost的root客戶端可以登錄到mysql服務(wù)器。

| root | localhost | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |
| root | %   | *81F5E21E35407D884A6CD4A731AEBFB6AF209E1B |

以上為個人經(jīng)驗，希望能給大家一個參考，也希望大家多多支持腳本之家。如有錯誤或未考慮完全的地方，望不吝賜教。

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