淺談Mysql連接數據庫時host和user的匹配規則

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–連接數據庫時，host和user的匹配規則

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

–host和user的匹配規則如下：

–是host為明確的最先匹配，host帶%模糊的時候最後匹配，但host為”(空)位於%之後才匹配

–相同的host時候，比較user為明確的最先匹配，user為”(空)最後匹配

–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.

–查看當前的host及用戶信息匹配順序，先host順序匹配、後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)

–查看當前的host及用戶信息匹配順序，先host順序匹配、後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 優先匹配到瞭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$ ，就可以正常登陸瞭

[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.

–查看當前用戶連接方式 和 當前用戶認證方式

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匹配到瞭% ，user匹配到瞭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>

–查看當前用戶連接方式 和 當前用戶認證方式

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

–任意用戶、任意host，隻要密碼和建立的第二個空用戶空host的密碼”doubleKong123$”匹配瞭， 就可以進入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>

–查看當前用戶連接方式 和 當前用戶認證方式

mysql> select user(),CURRENT_USER();
+---------------------+----------------+
| user()    | CURRENT_USER() |
+---------------------+----------------+
| [email protected] | @    |
+---------------------+----------------+
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時的匹配規則

mysql數據庫中user表的host字段，是用來控制用戶訪問數據庫“權限”的。

可以使用“%”，表示所有的網段；

也可以使用具體的ip地址，表示隻有該ip的客戶端才可以登錄到mysql服務器；

也可以使用“_”進行模糊匹配，表示某個網段的客戶端可以登錄到mysql服務器。

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

mysql采用的策略是：當服務器讀取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，那麼隻有localhost的root客戶端可以登錄到mysql服務器。

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

以上為個人經驗，希望能給大傢一個參考，也希望大傢多多支持WalkonNet。如有錯誤或未考慮完全的地方，望不吝賜教。

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