MySQL权限系统(三).权限表 Grant Tables

These mysql database tables contain grant information: mysql数据库表包含的授权信息:

• user: User accounts, global privileges, and other non-privilege columns users账户，全局权限,和其他非特权列账户

• db: Database-level privileges  数据库级别权限

• tables_priv: Table-level privileges 表级别权限

• columns_priv: Column-level privileges 列级别权限

• procs_priv: Stored procedure and function privileges 存储存储过程和函数权限

• proxies_priv: Proxy-user privileges 用户代理权限

Each grant table contains scope columns and privilege columns:每个授权表包含范围列和特权列：

• Scope columns determine the scope of each row in the tables; that is, the context in which the row applies. For example, a user table row with Host and User values of ‘thomas.loc.gov‘ and ‘bob‘ applies to authenticating connections made to the server from the host thomas.loc.gov by a client that specifies a user name of bob. Similarly, a db table row with Host, User, and Db column values of ‘thomas.loc.gov‘, ‘bob‘ and ‘reports‘ applies when bob connects from the host thomas.loc.gov to access the reports database. The tables_priv and columns_priv tables contain scope columns indicating tables or table/column combinations to which each row applies. The procs_priv scope columns indicate the stored routine to which each row applies.

• Privilege columns indicate which privileges a table row grants; that is, which operations it permits to be performed. The server combines the information in the various grant tables to form a complete description of a user‘s privileges. Section 7.2.5, “Access Control, Stage 2: Request Verification”, describes the rules for this.

The server uses the grant tables in the following manner:

• The user table scope columns determine whether to reject or permit incoming connections. For permitted connections, any privileges granted in the user table indicate the user‘s global privileges. Any privileges granted in this table apply to all databases on the server.

  Caution

  Because any global privilege is considered a privilege for all databases, any global privilege enables a user to see all database names with SHOW DATABASES or by examining the SCHEMATA table of INFORMATION_SCHEMA.

• The db table scope columns determine which users can access which databases from which hosts. The privilege columns determine the permitted operations. A privilege granted at the database level applies to the database and to all objects in the database, such as tables and stored programs.

• The tables_priv and columns_priv tables are similar to the db table, but are more fine-grained: They apply at the table and column levels rather than at the database level. A privilege granted at the table level applies to the table and to all its columns. A privilege granted at the column level applies only to a specific column.

• The procs_priv table applies to stored routines (procedures and functions). A privilege granted at the routine level applies only to a single procedure or function.

• The proxies_priv table indicates which users can act as proxies for other users and whether a user can grant the PROXY privilege to other users.

The server uses the user and db tables in the mysql database at both the first and second stages of access control (see Section 7.2, “The MySQL Access Privilege System”). The columns in the user and db tables are shown here.

Table 7.3 user and db Table Columns

The user table plugin, Password, and authentication_string columns store authentication plugin and credential information. In MySQL 5.7.6, the Password column was removed and all credentials are stored in the authentication_string column.

If an account row names a plugin in the plugin column, the server uses it to authenticate connection attempts for the account. It is up to the plugin whether it uses the Password and authentication_string column values.

As of MySQL 5.7.2, the plugin column must be nonempty.

Before MySQL 5.7.2, the plugin column for an account row is permitted to be empty. In this case, the server authenticates the account using the mysql_native_password or mysql_old_password plugin implicitly, depending on the format of the password hash in the Password column. If the Password value is empty or a 4.1 password hash (41 characters), the server uses mysql_native_password. If the password value is a pre-4.1 password hash (16 characters), the server uses mysql_old_password. (For additional information about these hash formats, see Section 7.1.2.4, “Password Hashing in MySQL”.) Clients must match the password in the Password column of the account row.

At startup, and at runtime when FLUSH PRIVILEGES is executed, the server checks user table rows. As of MySQL 5.7.2, for any row with an empty plugin column, the server writes a warning to the error log of this form:

[Warning] User entry ‘user_name‘@‘host_name‘ has an empty plugin
value. The user will be ignored and no one can login with this user
anymore.

To address this problem, see Section 7.5.1.3, “Migrating Away from Pre-4.1 Password Hashing and the mysql_old_password Plugin”.

The password_expired column permits DBAs to expire account passwords and require users to reset their password. The default password_expired value is ‘N‘, but can be set to ‘Y‘ with the ALTER USER statement. After an account‘s password has been expired, all operations performed by the account in subsequent connections to the server result in an error until the user issues an ALTER USER statement (for MySQL 5.7.6 and up) or SET PASSWORD statement (before MySQL 5.7.6) to establish a new account password.

It is possible after password expiration to “reset” a password by setting it to its current value. As a matter of good policy, it is preferable to choose a different password.

password_last_changed (added in MySQL 5.7.4) is a TIMESTAMP column indicating when the password was last changed. The value is non-NULL only for accounts that use MySQL built-in authentication methods (accounts that use an authentication plugin of mysql_native_password, mysql_old_password, or sha256_password). The value is NULL for other accounts, such as those authenticated using an external authentication system.

password_last_changed is updated by the CREATE USER, ALTER USER, and SET PASSWORD statements, and by GRANT statements that create an account or change an account password.

password_lifetime (added in MySQL 5.7.4) indicates the account password lifetime, in days. If the password is past its lifetime (assessed using the password_last_changed column), the server considers the password expired when clients connect using the account. A value of N greater than zero means that the password must be changed every N days. A value of 0 disables automatic password expiration. If the value is NULL (the default), the global expiration policy applies, as defined by the default_password_lifetime system variable.

account_locked (added in MySQL 5.7.6) indicates whether the account is locked (see Section 7.3.10, “User Account Locking”).

During the second stage of access control, the server performs request verification to ensure that each client has sufficient privileges for each request that it issues. In addition to the user and db grant tables, the server may also consult the tables_priv and columns_priv tables for requests that involve tables. The latter tables provide finer privilege control at the table and column levels. They have the columns shown in the following table.

Table 7.4 tables_priv and columns_priv Table Columns

The Timestamp and Grantor columns are set to the current timestamp and the CURRENT_USER value, respectively, but are otherwise unused.

For verification of requests that involve stored routines, the server may consult the procs_priv table, which has the columns shown in the following table.

Table 7.5 procs_priv Table Columns

The Routine_type column is an ENUM column with values of ‘FUNCTION‘ or ‘PROCEDURE‘ to indicate the type of routine the row refers to. This column enables privileges to be granted separately for a function and a procedure with the same name.

The Timestamp and Grantor columns are unused.

The proxies_priv table records information about proxy accounts. It has these columns:

• Host, User: The proxy account; that is, the account that has the PROXY privilege for the proxied account.

• Proxied_host, Proxied_user: The proxied account.

• Grantor, Timestamp: Unused.

• With_grant: Whether the proxy account can grant the PROXY privilege to other accounts.

For an account to be able to grant the PROXY privilege to other accounts, it must have a row in the proxies_priv table with With_grant set to 1 and Proxied_host and Proxied_user set to indicate the account or accounts for which the privilege can be granted. For example, the ‘root‘@‘localhost‘ account created during MySQL installation has a row in the proxies_priv table that enables granting the PROXY privilege for ‘‘@‘‘, that is, for all users and all hosts. This enables root to set up proxy users, as well as to delegate to other accounts the authority to set up proxy users. See Section 7.3.9, “Proxy Users”.

Scope columns in the grant tables contain strings. The default value for each is the empty string. The following table shows the number of characters permitted in each column.

Table 7.6 Grant Table Scope Column Lengths

For access-checking purposes, comparisons of User, Proxied_user, Password, authentication_string, Db, and Table_name values are case sensitive. Comparisons of Host, Proxied_host, Column_name, and Routine_name values are not case sensitive.

The user and db tables list each privilege in a separate column that is declared as ENUM(‘N‘,‘Y‘) DEFAULT ‘N‘. In other words, each privilege can be disabled or enabled, with the default being disabled.

The tables_priv, columns_priv, and procs_priv tables declare the privilege columns as SET columns. Values in these columns can contain any combination of the privileges controlled by the table. Only those privileges listed in the column value are enabled.

Table 7.7 Set-Type Privilege Column Values

Only the user table specifies administrative privileges, such as RELOAD and SHUTDOWN. Administrative operations are operations on the server itself and are not database-specific, so there is no reason to list these privileges in the other grant tables. Consequently, the server need consult only the user table to determine whether a user can perform an administrative operation.

The FILE privilege also is specified only in the user table. It is not an administrative privilege as such, but a user‘s ability to read or write files on the server host is independent of the database being accessed.

The server reads the contents of the grant tables into memory when it starts. You can tell it to reload the tables by issuing a FLUSH PRIVILEGES statement or executing a mysqladmin flush-privileges or mysqladmin reload command. Changes to the grant tables take effect as indicated in Section 7.2.6, “When Privilege Changes Take Effect”.

When you modify an account, it is a good idea to verify that your changes have the intended effect. To check the privileges for a given account, use the SHOW GRANTS statement. For example, to determine the privileges that are granted to an account with user name and host name values of bob and pc84.example.com, use this statement:

SHOW GRANTS FOR ‘bob‘@‘pc84.example.com‘;

To display nonprivilege properties of an account, use SHOW CREATE USER:

SHOW CREATE USER ‘bob‘@‘pc84.example.com‘;

MySQL权限系统(三).权限表 Grant Tables

标签：cal   oba   string   .com   exp   space   ref   direct   lin