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