Random Ramblings

While trying to set up fail2ban to watch the gNewSense MoinMoin instance (It powers the main website and the wiki) I hit an error which didn't seem to make any sense

My filter called 'moinmoin-page-with-spaces' was inexplicably causing fail2ban to return error 200. Annoyingly, my moinmoin-captcha filter appeared to loading perfectly, and both were syntactically identical.

2012-01-19 05:21:09,093 fail2ban.jail   : INFO   Jail 'moinmoin-page-with-spaces' started
2012-01-19 05:21:09,141 fail2ban.jail   : INFO   Jail 'moinmoin-captcha' started
2012-01-19 05:21:09,215 fail2ban.jail   : INFO   Jail 'ssh' started
2012-01-19 05:21:09,213 fail2ban.actions.action: ERROR  iptables -N fail2ban-moinmoin-page-with-spaces
iptables -A fail2ban-moinmoin-page-with-spaces -j RETURN
iptables -I INPUT -p tcp -m multiport --dports www -j fail2ban-moinmoin-page-with-spaces returned 200
2012-01-19 05:28:20,779 fail2ban.jail   : INFO   Jail 'moinmoin-captcha' stopped
2012-01-19 05:28:21,077 fail2ban.jail   : INFO   Jail 'ssh' stopped
2012-01-19 05:28:21,364 fail2ban.actions.action: ERROR  iptables -D INPUT -p tcp -m multiport --dports www -j fail2ban-moinmoin-page-with-spaces
iptables -F fail2ban-moinmoin-page-with-spaces
iptables -X fail2ban-moinmoin-page-with-spaces returned 200
2012-01-19 05:28:21,904 fail2ban.jail   : INFO   Jail 'moinmoin-page-with-spaces' stopped
2012-01-19 05:28:21,910 fail2ban.server : INFO   Exiting Fail2ban

Upon running the iptables commands individually it turned out that it was iptables returning 200 (not fail2ban).

Seems that iptables has a maximum string size of 30 chars for its labels. Because fail2ban adds 'fail2ban-' and your filter name together it was pushing the total string length ('fail2ban-moinmoin-page-with-spaces') to 35 chars long. Resolving the issue meant renaming the filter down until it was under 20 chars, so fail2ban could add its 9 chars onto the front and still be ok.