trAvis - MANAGER

Edit File: run-rootless.txt

Fail2ban normally requires root privileges to insert iptables rules through calls to /sbin/iptables and also to read the logfiles. Fail2ban can run as an unprivileged user provided that those two capabilities are preserved. The idea is to run fail2ban as a normal user (e.g. fail2ban) who belongs to a group which is allowed to read logfiles. The user should also be allowed to write to /proc/net/xt_recent/fail2ban-<name> (name is specified in the iptables rule). /proc/net/xt_recent/* is created by the xt_recent kernel module when an iptables rule with '-m limit' is inserted. This file contains a dynamic list of IP addresses which can than be used in iptables rules. Addresses can be matched against this list, with an optional timeout. One way to use xt_recent is to insert IPs into this list from an iptables rule, e.g. after connecting to the SSH port three times in a minute. This is the standard usage described in iptables(3). Another way to use xt_recent is by inserting the rules by writing to /proc/net/xt_recent/fail2ban-<name>. This can be performed by a fail2ban action. Files in /proc/net/xt_recent/ are protected by normal filesystem rules, so can be chown'ed and chmod'ed to be writable by a certain user. After the necessary iptables rules are inserted (which requires root privileges), blacklisting can be performed by an unprivileged user. Using fail2ban with xt_recent allows smarter filtering than normal iptables rules with the xt_recent module can provide. The disadvantage is that fail2ban cannot perform the setup by itself, which would require the privilege to call /sbin/iptables, and it must be done through other means. The primary advantage is obvious: it's generally better to run services not as root. This setup is more robust, because xt_recent has it's own memory management and should behave smartly in case a very large amount of IPs is blocked. Also in case the fail2ban process dies the rules expire automatically. In case of a large amount of blocked IPs, traversing rules linearly for each SYN packet as fail2ban normally inserts them will be slow, but xt_recent with the same number of IPs would be much faster. (Didn't test this, so this is pure handwaving, but it should really be this way ;)) From the administrators point of view, a setup with xt_recent might also be easier, because it's very simple to modify the permissions on /proc/net/xt_recent/fail2ban-<name> to be readable or writable by some user and thus allow delisting IPs by helper administrators without the ability to mess up other iptables rules. The xt_recent-echo jail can be used under the root user without further configuration. To run not as root, further setup is necessary: - Create user: - set FAIL2BAN_USER in /etc/default/fail2ban. This probably should be fail2ban. - add user fail2ban who can read /var/log/auth.log and other necessary log files. Log files are owned by group 'adm', so it is enough if this user belongs to this group. The user can be created e.g. with useradd --system --no-create-home --home-dir / --groups adm fail2ban - Statically initialize chains firewall: - put a rule to check the xt_recent list in the static firewall initialization script, with names like fail2ban-ssh (action uses separate chains per each jail, so define here the ones you need 1-per-jail) Sample invocation might be iptables -I INPUT -m recent --update --seconds 3600 --name fail2ban-<name> -j DROP with <name> suitably replaced. - Permissions: make sure that configuration files under /etc/fail2ban are readable by fail2ban user. Make sure that logfiles of fail2ban itself are writable by the fail2ban user. /etc/init.d/fail2ban will change the ownership at startup, but it is also necessary to modify /etc/logrotate.d/fail2ban. The simplest way is to replace '# create ...' with the following # create 640 fail2ban adm