privilege: fix auth_socket bug, should only allow os user name to login (#54032)

[ti-chi-bot]

This is an automated cherry-pick of #54032

What problem does this PR solve?

Issue Number: close #54031

Problem Summary:

What changed and how does it work?

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

1. my os user is wangchao

$ whoami
wangchao

2. create users:

> CREATE USER 'u1'@'localhost' IDENTIFIED WITH auth_socket;
Query OK, 0 rows affected
Time: 0.017s
> CREATE USER 'u2'@'localhost' IDENTIFIED WITH auth_socket AS "wangchao";
Query OK, 0 rows affected
Time: 0.012s
> CREATE USER 'wangchao'@'localhost' IDENTIFIED WITH auth_socket;
Query OK, 0 rows affected
Time: 0.025s
TiDB root@127.0.0.1:test> select host,user,authentication_string,plugin from mysql.user;
+-----------+----------+-----------------------+-----------------------+
| host      | user     | authentication_string | plugin                |
+-----------+----------+-----------------------+-----------------------+
| %         | root     |                       | mysql_native_password |
| localhost | u1       |                       | auth_socket           |
| localhost | u2       | wangchao              | auth_socket           |
| localhost | wangchao |                       | auth_socket           |
+-----------+----------+-----------------------+-----------------------+
4 rows in set
Time: 0.011s

3. Try log in:

u1 is rejected because it is not same with os user:

$ mysql --comments -uu1 -S/tmp/tidb-4001.sock
ERROR 1045 (28000): Access denied for user 'u1'@'localhost' (using password: YES)

u2 is allowed because its authenticate string is same with os user:

$ mysql --comments -uu2 -S/tmp/tidb-4001.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2097182
Server version: 8.0.11-TiDB-None TiDB Server (Apache License 2.0) Community Edition, MySQL 8.0 compatible
...

wangchao is allowed because its the os user name:

> mysql --comments -uwangchao -S/tmp/tidb-4001.sock
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2097184
Server version: 8.0.11-TiDB-None TiDB Server (Apache License 2.0) Community Edition, MySQL 8.0 compatible
...

• No need to test

  • I checked and no code files have been changed.

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

fix `auth_socket` bug, should only allow os user name to login

[codecov]

Codecov Report

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Additional details and impacted files

@@               Coverage Diff                @@
##             release-7.5     #54052   +/-   ##
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  Coverage               ?   72.0204%           
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  Files                  ?       1411           
  Lines                  ?     410750           
  Branches               ?          0           
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  Hits                   ?     295824           
  Misses                 ?      95025           
  Partials               ?      19901           

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Components	Coverage Δ
dumpling	53.9913% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	53.4573% <0.0000%> (?)

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CbcWestwolf, lcwangchao

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-06-18 06:56:54.059392662 +0000 UTC m=+97940.544881486: ☑️ agreed by lcwangchao.
• 2024-06-18 07:11:58.862417982 +0000 UTC m=+98845.347906816: ☑️ agreed by CbcWestwolf.