MySQL Bugs: #102186: mysql_real_connect hangs when network is faulty.

Bug #102186	mysql_real_connect hangs when network is faulty.
Submitted:	7 Jan 2021 18:42	Modified:	7 Jan 2021 21:47
Reporter:	Bruno Junqueira Adami	Email Updates:
Status:	Can't repeat	Impact on me:	None
Category:	MySQL Server: C API (client library)	Severity:	S2 (Serious)
Version:	21	OS:	Ubuntu
Assigned to:		CPU Architecture:	Any

Description:
Hi,

I have the following problem using the C client library: even using MYSQL_OPT_CONNECT_TIMEOUT (set to 4), whenever there is a server network instability event, the connect function hangs indefinitely. Here is a core dump of the process that called the mysql library, which was stuck for more than 20 minutes:

```
#0  __libc_read (nbytes=5, buf=0x7fd88c0107d3, fd=43) at ../sysdeps/unix/sysv/linux/read.c:26
#1  __libc_read (fd=43, buf=0x7fd88c0107d3, nbytes=5) at ../sysdeps/unix/sysv/linux/read.c:24
#2  0x00007fd8c4fbe389 in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.1.1
#3  0x00007fd8c4fb962e in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.1.1
#4  0x00007fd8c4fb8484 in ?? () from /lib/x86_64-linux-gnu/libcrypto.so.1.1
#5  0x00007fd8c4fb8a57 in BIO_read () from /lib/x86_64-linux-gnu/libcrypto.so.1.1
#6  0x00007fd8c3e64b91 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.1
#7  0x00007fd8c3e68e1e in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.1
#8  0x00007fd8c3e666d0 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.1
#9  0x00007fd8c3e99901 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.1
#10 0x00007fd8c3e8f525 in ?? () from /lib/x86_64-linux-gnu/libssl.so.1.1
#11 0x00007fd8c3e7ad58 in SSL_do_handshake () from /lib/x86_64-linux-gnu/libssl.so.1.1
#12 0x00007fd8c4064a60 in ?? () from /lib/x86_64-linux-gnu/libmysqlclient.so.21
#13 0x00007fd8c4014195 in ?? () from /lib/x86_64-linux-gnu/libmysqlclient.so.21
#14 0x00007fd8c401448e in ?? () from /lib/x86_64-linux-gnu/libmysqlclient.so.21
#15 0x00007fd8c4017b99 in mysql_real_connect () from /lib/x86_64-linux-gnu/libmysqlclient.so.21
```

I am not sure how the timeouts I set in the mysql library affects the SSL library timeouts, maybe it is related?

Thanks in advance.

How to repeat:
I could not reproduce yet, since reproducing the same network conditions is hard. This has happened 3 times in the last 2 days.

Not enough information was provided for us to be able to handle this bug. Please re-read the instructions at http://bugs.mysql.com/how-to-report.php 

If you can provide more information a repeatable test case, feel free to add it to this bug.

Thank you for your interest in MySQL.

I was able to reproduce now, but I will create a new bug, because the connection did timeout, it just took 30+ minutes.