proxy-protocol doesn't take in consideration connect_timeout, possible DOS

[Frederic Descamps]

When proxy_protocol_network =* is used, it's impossible to connect directly to MySQL (bypassing the proxy sending proxy-protocol header).
The problem is that if mysql client tries to connect anyway , there is no timeout (connect_timeout) used. This can lead to max connection easily reached:

pxc1 mysql> show full processlist;
+-----+----------------------+-----------------+------+---------+------+--------------------+-----------------------+-----------+---------------+
| Id | User | Host | db | Command | Time | State | Info | Rows_sent | Rows_examined |
+-----+----------------------+-----------------+------+---------+------+--------------------+-----------------------+-----------+---------------+
| 1 | system user | | NULL | Sleep | 1969 | NULL | NULL | 0 | 0 |
| 2 | system user | | NULL | Sleep | 1969 | wsrep aborter idle | NULL | 0 | 0 |
| 9 | root | localhost | NULL | Query | 0 | init | show full processlist | 0 | 0 |
| 990 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
| 992 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
| 993 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
| 994 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
| 996 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
| 997 | unauthenticated user | connecting host | NULL | Connect | NULL | login | NULL | 0 | 0 |
+-----+----------------------+-----------------+------+---------+------+--------------------+-----------------------+-----------+---------------+

[Shahriyar Rzayev (rzayev-sehriyar)]

Percona now uses JIRA for bug reports so this bug report is migrated to: https://jira.percona.com/browse/PS-3314