Dovecot 2.2.27 proxy - enforcing per client IP connection limits

[Sami Ketola]

Hi,

mail_max_userip_connections is only enforced at the backend level. The setting has no effect on proxy. If you want to force the limit then you can only do it in the backend.

Sami

> On 9 Mar 2017, at 12.05, Adi Pircalabu <adi at ddns.com.au> wrote:
> 
> Quick follow-up: updated the proxies to 2.2.28, but I still couldn't find a way to limit the inbound IMAP connections per IP & username. I know "mail_max_userip_connections" limit works for the mail stores, but it doesn't seem to have any effect on the proxies. I'm using a mix of Dovecot & Courier-IMAP servers as backends.
> Basically I need to find a way to enforce the maximum limit for the username<>remoteip so that, if I have:
> ESTCONNS=`doveadm -f flow proxy list | grep "username=usern at domain.com.proto=imap" | wc -l`
> $ESTCONNS is lower or equal than the configured limit.
> The proxies are configured as per https://wiki2.dovecot.org/PasswordDatabase/ExtraFields/Proxy to forward the password to the remote server using MySQL. In dovecot-sql.conf.ext I have:
> password_query = SELECT NULL AS password, 'Y' as nopassword, host, email as email, 'any-cert' as 'starttls', 'Y' AS proxy FROM mailbox WHERE email = '%u' AND disabled_smtpauth=0
> 
> At the moment the only way I can limit the number of established connections per source IP address on the Dovecot proxies is using iptables, which isn't what I want.
> Where else can I look?
> 
> Adi Pircalabu, System Administrator
> DDNS, a Total Internet Company
> 159 Barkly Avenue, Burnley, Vic 3121, T +61 3 9815 6868
> 
> On 08/03/17 12:32, Adi Pircalabu wrote:
>> Hi,
>> Trying to keep abusive/buggy IMAP clients at bay on a number of Dovecot proxy servers, I've reconfigured them to use "mail_max_userip_connections = 50" in the "protocol imap" section, followed by restarting Dovecot. Yet, I'm still seeing 160+ established connections from a single IP address for the same email account. Am I missing anything?
>> # 2.2.27 (c0f36b0): /etc/dovecot/dovecot.conf
>> # Pigeonhole version 0.4.16 (fed8554)
>> # OS: Linux 2.6.32-642.4.2.el6.x86_64 x86_64 CentOS release 6.8 (Final)
>> auth_cache_negative_ttl = 5 mins
>> auth_cache_size = 16 M
>> auth_cache_ttl = 18 hours
>> default_client_limit = 6120
>> default_process_limit = 500
>> managesieve_notify_capability = mailto
>> managesieve_sieve_capability = fileinto reject envelope encoded-character vacation subaddress comparator-i;ascii-numeric relational regex imap4flags copy include variables body enotify environment mailbox date index ihave duplicate mime foreverypart extracttext imapflags notify
>> mbox_write_locks = fcntl
>> namespace inbox {
>>   inbox = yes
>>   location =
>>   mailbox Drafts {
>>     special_use = \Drafts
>>   }
>>   mailbox Junk {
>>     special_use = \Junk
>>   }
>>   mailbox Sent {
>>     special_use = \Sent
>>   }
>>   mailbox "Sent Messages" {
>>     special_use = \Sent
>>   }
>>   mailbox Trash {
>>     special_use = \Trash
>>   }
>>   prefix =
>> }
>> passdb {
>>   args = /etc/dovecot/dovecot-sql.conf.ext
>>   driver = sql
>> }
>> plugin {
>>   sieve = file:~/sieve;active=~/.dovecot.sieve
>>   sieve_extensions = +notify +imapflags
>> }
>> protocols = imap pop3 lmtp sieve
>> service auth {
>>   client_limit = 6120
>> }
>> service imap-login {
>>   process_limit = 2048
>>   process_min_avail = 20
>>   service_count = 0
>>   vsz_limit = 256 M
>> }
>> service imap {
>>   process_limit = 2048
>> }
>> service managesieve-login {
>>   inet_listener sieve {
>>     port = 4190
>>   }
>>   service_count = 0
>>   vsz_limit = 128 M
>> }
>> service managesieve {
>>   process_limit = 1024
>> }
>> service pop3 {
>>   process_limit = 1024
>> }
>> [...]
>> protocol imap {
>>   imap_capability = IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE
>>   mail_max_userip_connections = 50
>> }