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Fail2Ban on Ubuntu 10.04

Configuration files

/etc/fail2ban/jail.local

[DEFAULT]

ignoreip = 127.0.0.1
bantime  = 10 # made for test purposes
maxretry = 3

backend = polling

destemail = email@mycompany.com


banaction = iptables-multiport

mta = sendmail

protocol = tcp

action = %(action_mw)s

[ssh]

enabled = true
port    = ssh
filter  = sshd
logpath  = /var/log/auth.log
maxretry = 3

[pam-generic]

enabled = true
filter  = pam-generic
port = all
banaction = iptables-allports
port     = anyport
logpath  = /var/log/auth.log
maxretry = 6

The rest of the fail2ban configs are just the default ones.

default /etc/pam.d/common-session-noninteractive

session [default=1]                     pam_permit.so
session requisite                       pam_deny.so
session required                        pam_permit.so
session required        pam_unix.so 
session optional                        pam_winbind.so 
session required        pam_loginuid.so 

changed /etc/pam.d/common-session-noninteractive

session [default=1]                     pam_permit.so
session requisite                       pam_deny.so
session required                        pam_permit.so
session [success=1 default=ignore] pam_succeed_if.so service in cron quiet use_uid
session required        pam_unix.so 
session optional                        pam_winbind.so 
session required        pam_loginuid.so 

Please note the only difference is adding session [success=1 default=ignore] pam_succeed_if.so service in cron quiet use_uid.

Logs

extract from /var/log/auth.log with default /etc/pam.d/common-session-noninteractive

May 22 15:30:01 node1 CRON[16029]: pam_unix(cron:session): session opened for user root by (uid=0)
May 22 15:30:01 node1 CRON[16029]: pam_unix(cron:session): session closed for user root
May 22 15:35:01 node1 CRON[16514]: pam_unix(cron:session): session opened for user root by (uid=0)
May 22 15:35:01 node1 CRON[16514]: pam_unix(cron:session): session closed for user root

Summary

  1. If I execute fail2ban-client set ssh banip 1.2.3.4 in 15:26 the IP will get banned at 15:30. This is why I associate it with the above listed cron job.
  2. If I modify /etc/pam.d/common-session-noninteractive and repeat the fail2ban-client command, got no entry in /var/log/auth.log and no ban.

More info:

  1. default /etc/pam.d/common-session-noninteractive:

    fail2ban-client set ssh banip 1.2.3.4 -> the IP gets banned by an invisible cron job, which runs every 5 minutes. I checked every single file in /etc/cron* and /var/spool/cron/* and there was no such job present. Bottom line: the manual ban works with up to 5 minutes delay.

  2. added session [success=1 default=ignore] pam_succeed_if.so service in cron quiet use_uid in /etc/pam.d/common-session-noninteractive as suggested here:

    fail2ban-client set ssh banip 1.2.3.4 -> the invisible cron job does not run and no ban happens.

My question:

how does the change in /etc/pam.d/common-session-noninteractive prevents the fail2ban-client to ban an IP? And why?


Edit

  • Running in debug:
root@node1:~# fail2ban-client set loglevel 4
Current logging level is DEBUG
root@node1:~# fail2ban-client -vvv set ssh banip 1.2.3.4
DEBUG  Reading /etc/fail2ban/fail2ban
DEBUG  Reading files: ['/etc/fail2ban/fail2ban.conf', '/etc/fail2ban/fail2ban.local']
INFO   Using socket file /var/run/fail2ban/fail2ban.sock
DEBUG  OK : '1.2.3.4'
DEBUG  Beautify '1.2.3.4' with ['set', 'ssh', 'banip', '1.2.3.4']
1.2.3.4
root@zap:~# tail -f /var/log/fail2ban.log
2013-05-24 21:32:07,695 fail2ban.comm   : DEBUG  Command: ['set', 'ssh', 'banip', '1.2.3.4']
2013-05-24 21:32:07,696 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']
2013-05-24 21:32:07,696 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']
2013-05-24 21:32:07,696 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']

Result: No Ban.

  • Removing quiet from session [success=1 default=ignore] pam_succeed_if.so service in cron quiet use_uid in /etc/pam.d/common-session-noninteractive:

Result: Successful Ban.

/var/log/auth.log:

May 24 22:00:01 node1 CRON[22483]: pam_succeed_if(cron:session): requirement "service in cron" was met by user "root"
May 24 22:00:01 node1 CRON[22483]: pam_succeed_if(cron:session): requirement "service in cron" was met by user "root"

/var/log/fail2ban.log:

2013-05-24 21:56:07,955 fail2ban.comm   : DEBUG  Command: ['set', 'loglevel', '4']
2013-05-24 21:56:20,155 fail2ban.comm   : DEBUG  Command: ['set', 'ssh', 'banip', '1.2.3.4']
2013-05-24 21:56:20,156 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']
2013-05-24 21:56:20,156 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']
2013-05-24 21:56:20,156 fail2ban.filter : DEBUG  Currently have failures from 1 IPs: ['1.2.3.4']
2013-05-24 22:00:01,079 fail2ban.filter : DEBUG  /var/log/auth.log has been modified
2013-05-24 22:00:01,079 fail2ban.filter.datedetector: DEBUG  Sorting the template list
2013-05-24 22:00:01,853 fail2ban.filter : DEBUG  /var/log/auth.log has been modified
2013-05-24 22:00:01,853 fail2ban.filter.datedetector: DEBUG  Sorting the template list
2013-05-24 22:00:01,870 fail2ban.actions: WARNING [ssh] Ban 1.2.3.4
2013-05-24 22:00:01,870 fail2ban.actions.action: DEBUG  iptables -n -L INPUT | grep -q fail2ban-ssh
2013-05-24 22:00:01,876 fail2ban.actions.action: DEBUG  iptables -n -L INPUT | grep -q fail2ban-ssh returned successfully
2013-05-24 22:00:01,877 fail2ban.actions.action: DEBUG  iptables -I fail2ban-ssh 1 -s 1.2.3.4 -j DROP
2013-05-24 22:00:01,919 fail2ban.actions.action: DEBUG  iptables -I fail2ban-ssh 1 -s 1.2.3.4 -j DROP
2013-05-24 22:00:01,920 fail2ban.actions.action: DEBUG  
2013-05-24 22:00:01,923 fail2ban.actions.action: DEBUG   returned successfully
...

Fail2Ban version

fail2ban 0.8.7.1-2~ppa7~lucid from here. The stock one (version 0.8.4) kept failing with:

"global name 'time' is not defined"

which prompt me to look for newer version.

share|improve this question
1  
There is no invisible cron job. fail2ban-server is daemon that bans the IP. –  Mark Wagner May 22 '13 at 22:34
    
@MarkWagner - why fail2ban-server don't immediately ban the IP instead of waiting for up to 5 minutes? I can supply logs to prove it. –  grs May 23 '13 at 2:36
    
@grs Please post your fail2ban config and demonstrate your concern with an example. As worded this question relies on too much conjecture. –  Andrew B May 23 '13 at 15:35
    
@AndrewB - please see the updated question. Thank you! –  grs May 23 '13 at 19:18
    
Strange...I cannot repro. Can you execute fail2ban-client set loglevel 4 and fail2ban-client -vvv set ssh banip 1.2.3.4 and post output and the relevant fail2ban log file lines? –  Mark Wagner May 24 '13 at 23:00

1 Answer 1

I think (but not confirmed) what fail2ban simply waits for new lines in auth.log before applying fail2ban-client command, so ban is done not by "an invisible cron job, which runs every 5 minutes" but "by infinite loop which reads 'logpath'", auth.log in the particular case. If this is true, change you have done in /etc/pam.d/common-session-noninteractive does not prevent the fail2ban-client to ban an IP, but postpones it till any new line appear in auth.log. New log lines appear less frequently, because you disabled cron messages, and it is necessary to wait longer for IP ban.

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