MySQL Bugs: #93394: memory leak when csv engine has no permission to meta file

Bug #93394	memory leak when csv engine has no permission to meta file
Submitted:	29 Nov 2018 5:46	Modified:	29 Nov 2018 6:26
Reporter:	Yan Huang (OCA)	Email Updates:
Status:	Verified	Impact on me:	None
Category:	MySQL Server: CSV	Severity:	S3 (Non-critical)
Version:	5.7.21	OS:	Any
Assigned to:		CPU Architecture:	Any
Tags:	Contribution

Description:
memory leak when csv engine has no permission to meta file

How to repeat:
Take table `general_log` as an example:

1. make mysql no write permission to meta file: `chown root: data/general_log.*` and `chmod 744 data/general_log.*`
2. query "select * from mysql.general_log" after restarting mysql
3. the query hang, and mysqld keep consuming memory

Suggested fix:
I think the causes of the memory leak are:

1. `ha_tina::open` open meta file (.CSM file) with `O_RDWR|O_CREAT`, which will fail with permission denied in this case
2. `ha_tina::repair` check only data file (.CSV file)
3. When `ha_tina::open` failed, mysqld will repair engine. And `ha_tina::repair` succeed, then mysqld reopen table with `ha_tina::open`, which will loop forever.
4. In the loop, memory is allocated from `THD::mem_root`, which will be free when sql finish.

A patch is attached to fix the loop.

patch

Attachment: 93394.diff (application/octet-stream, text), 3.67 KiB.

patch (*) I confirm the code being submitted is offered under the terms of the OCA, and that I am authorized to contribute it.

Contribution: 93394.diff (application/octet-stream, text), 3.67 KiB.

Hello Yan Huang,

Thank you for the report and contribution!

Thanks,
Umesh