MySQL client reports `Malformed packet` when it connects to TiDB without a password

[djshow832]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Create a user with a password:
create user u1 identified with 'caching_sha2_password' by '123456';

Then connect to TiDB with mysql client without a password:
mysql -h127.1 -uu1 -P4000

2. What did you expect to see? (Required)

mysql -h127.1 -uu1 -P3306
ERROR 1045 (28000): Access denied for user 'u1'@'localhost' (using password: NO)

3. What did you see instead (Required)

mysql -h127.1 -uu1 -P4000
ERROR 2027 (HY000): Malformed packet

4. What is your TiDB version? (Required)

master

mysql --version
mysql  Ver 8.0.29 for macos12.2 on x86_64 (Homebrew)

[dveeden]

I can reproduce this with:

$ ./bin/tidb-server -V
Release Version: v6.6.0-alpha-306-g28d0325ae
Edition: Community
Git Commit Hash: 28d0325ae12f080b978a147bba9f8467557019cd
Git Branch: master
UTC Build Time: 2023-01-30 06:26:21
GoVersion: go1.19.5
Race Enabled: false
TiKV Min Version: 6.2.0-alpha
Check Table Before Drop: false
Store: unistore

$ mysql --version
mysql  Ver 8.0.32 for Linux on x86_64 (MySQL Community Server - GPL)

[dveeden]

This is what happens with TiDB:

$ tshark -r /tmp/tidb.pcap -Y mysql -O mysql
...
MySQL Protocol
    Packet Length: 107
    Packet Number: 0
    Server Greeting
        Protocol: 10
        Version: 5.7.25-TiDB-v6.6.0-alpha-306-g28d0325ae
...
        Authentication Plugin: mysql_native_password

...
MySQL Protocol
    Packet Length: 179
    Packet Number: 1
    Login Request
...
        Username: u1
        Client Auth Plugin: mysql_native_password
...

...
MySQL Protocol - authentication switch request
    Packet Length: 44
    Packet Number: 2
    Response Code: EOF Packet (0xfe)
    EOF marker: 254
    Auth Method Name: caching_sha2_password
    Auth Method Data: 141c294141672a4d315a5150362c713a7a4b601000

...
MySQL Protocol
    Packet Length: 1
    Packet Number: 3
    Auth Method Data: 00

...
MySQL Protocol
    Packet Length: 2
    Packet Number: 4
    Payload: 0104
...

...
MySQL Protocol - response ERROR
    Packet Length: 12
    Packet Number: 5
    Response Code: ERR Packet (0xff)
    Error Code: 1105
    SQL state: HY000
    Error message: EOF

This is what happens with MySQL, with default_authentication_plugin=mysql_native_password set to make it behave similar to TiDB:

$ tshark -r /tmp/mysql2.pcap -Y mysql -O mysql
...
MySQL Protocol
    Packet Length: 74
    Packet Number: 0
    Server Greeting
        Protocol: 10
        Version: 8.0.32
...
        Authentication Plugin: mysql_native_password

...
MySQL Protocol
    Packet Length: 179
    Packet Number: 1
    Login Request
...
        Username: u1
        Client Auth Plugin: mysql_native_password
...

...
MySQL Protocol - authentication switch request
    Packet Length: 44
    Packet Number: 2
    Response Code: EOF Packet (0xfe)
    EOF marker: 254
    Auth Method Name: caching_sha2_password
    Auth Method Data: 2f7e06191a4c03613239043d663d120d2b5c355400

...
MySQL Protocol
    Packet Length: 1
    Packet Number: 3
    Auth Method Data: 00

...
MySQL Protocol - response ERROR
    Packet Length: 69
    Packet Number: 4
    Response Code: ERR Packet (0xff)
    Error Code: 1045
    SQL state: 28000
    Error message: Access denied for user 'u1'@'localhost' (using password: NO)