the issue with tidb socket

[wangtianyi2004]

Bug Report

Please answer these questions before submitting your issue. Thanks!
after I drop the root@'%', I can still logon tidb by root@'XXX'.

### 1. Minimal reproduce step (Required)

[root@r40 topology]# cat tidb-c1.yaml | grep -C 10 sock

# readpool.storage.use-unified-pool

# You can overwrite this configuration via the instance-level config field.

server_configs:
tidb:
log.slow-threshold: 300
binlog.enable: false
binlog.ignore-error: false
tikv-client.copr-cache.enable: true
socket: "/tmp/mysql.sock"
tikv:
server.grpc-concurrency: 4
raftstore.apply-pool-size: 2
raftstore.store-pool-size: 2
rocksdb.max-sub-compactions: 1
storage.block-cache.capacity: "16GB"
readpool.unified.max-thread-count: 12
readpool.storage.use-unified-pool: false
readpool.coprocessor.use-unified-pool: true
raftdb.rate-bytes-per-sec: 0

check the logon user

[root@r40 topology]# mysql -uroot -P14000 -hr41 -e 'select user()'
+----------------+
| user() |
+----------------+
| root@localhost |
+----------------+

create a new user root@'localhost'
mysql> create user 'root'@'%' identified by 'mysql';
ERROR 1396 (HY000): Operation CREATE USER failed for 'root'@'%'
mysql> create user root@'localhost' identified by 'mysql'
-> ;
Query OK, 0 rows affected (0.14 sec)

mysql> grant all privileges on . to root@'localhost';
mysql> flush privileges;

mysql> drop user root@'%';
mysql> flush privileges;

[root@r40 topology]# mysql -uroot -P14000 -hr41 -p
mysql> select host, user from mysql.user;
+-----------+------+
| host | user |
+-----------+------+
| localhost | root |
+-----------+------+
1 row in set (0.01 sec)

### 2. What did you expect to see? (Required)
I logon with the user root@'r41'.
when I check the query select user(), It should show me root@localhost
And after I drop the user root@'%', I shouldn't logon the database from non-tidb server.

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

v4.0.9

[morgo]

Verified as described. I will take a look.

[ti-srebot]

Please edit this comment or add a new comment to complete the following information

Bug

TiDB incorrectly handled the user-host portion of privileges when listening on both unix socket and tcp socket.

1. Root Cause Analysis (RCA) (optional)

2. Symptom (optional)

3. All Trigger Conditions (optional)

4. Workaround (optional)

5. Affected versions

[v4.0.1:v4.0.12], [v5.0.0:v5.0.1]

6. Fixed versions

master