We never used this simple firewall utility and in at least one case
a user on the server tried to use it and messed up the rules I had
set via firewalld.
For some reason the nftables set support in firewalld doesn't seem
to be working. I see that sets (aka ipsets in nftables lingo) are
created, but they are empty. For now I will just leave these tasks
as they are to revert the behavior on current hosts (should do no
change on new installed, as the regexp won't match).
This is active banning of IPs that are brute forcing login attempts
to SSH, versus the passive banning of 10,000 abusive IPs from the
abuseipdb.com blacklist. For now I am banning IPs that fail to log
in successfully more than twelve times in a one-hour period, but
these settings might change, and I can override them at the group
and host level if needed.
Currently this works for CentOS 7, Ubuntu 16.04, and Ubuntu 18.04,
with minor differences in the systemd configuration due to older
versions on some distributions.
You can see the status of the jail like this:
# fail2ban-client status sshd
Status for the jail: sshd
|- Filter
| |- Currently failed: 0
| |- Total failed: 0
| `- Journal matches: _SYSTEMD_UNIT=sshd.service + _COMM=sshd
`- Actions
|- Currently banned: 1
|- Total banned: 1
`- Banned IP list: 106.13.112.20
You can unban IPs like this:
# fail2ban-client set sshd unbanip 106.13.112.20
Seems to work around an issue when firewalld is using the nftables
backend with iptables 1.8.2 on Debian 10. Alternatively I could go
back to using the iptables backend... hmm.
See: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914694
This causes problems every time I re-run the Ansible tag because the
nightly apt security uses a different sources.list and the indexes
are then missing buster-backports. I could add a cache update to the
task, but actually I think the original bug I was trying to solve is
finally fixed, and I'm going to switch to nftables anyways.
This uses the ipsets feature of the Linux kernel to create lists of
IPs (though could be MACs, IP:port, etc) that we can block via the
existing firewalld zone we are already using. In my testing it works
on CentOS 7, Ubuntu 16.04, and Ubuntu 18.04.
The list of abusive IPs currently comes from HPC's systemd journal,
where I filtered for hosts that had attempted and failed to log in
over 100 times. The list is formatted with tidy, for example:
$ tidy -xml -iq -m -w 0 roles/common/files/abusers-ipv4.xml
See: https://firewalld.org/2015/12/ipset-support
There is a bug in iptables 1.8.2 in Debian 10 "Buster" that causes
firewalld to fail when restoring rules. The bug has been fixed in
iptables 1.8.3, which is currently in buster-backports.
See: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=914694
For some reason the key ID I had here was wrong. According to the
Tarsnap website the key ID is 0x6D97F5A4CA38CF33.
ee: https://www.tarsnap.com/pkg-deb.html
Debian 10 comes with Python 2 and Python 3 (at least from the ISO),
so we should prefer the Python 3 version of pycurl. We'll see whet-
her cloud providers like Linode and Digital Ocean ship with Python
3 or not in their default image.
We can register changes when adding repositories and keys and then
update the apt package index conditionally. This should make it be
more consistent between initial host setup and subsequent re-runs.
Ansible errors on adding the tarsnap signing key because it is not
valid (expired a month ago). I contacted Colin Percival about this
on Twitter but he did not seem worried for some reason.
I had previously been removing some packages for security reasons,
then removing others because they were annoying, and yet *others*
because they were annoying on newer Ubuntus only. It is easier to
just unify these tasks and remove them all in one go.
On older Ubuntus where some packages don't exist the task will just
succeed because the package is absent anyways.
The default systemd journal configuration on CentOS 7 and Ubuntu
16.04 does not keep journal logs for multiple boots. This limits
the usefulness of the journal entirely (for example, try to see
sshd logs from even two or three months ago!).
Changing the storage to "persistent" makes systemd keep the logs
on disk in /var/log/journal for up to 2% of the partition size.
After reörganizing for dynamic includes these tags will never be reached
because the children of dynamic includes do not inherit tags from their
parents as they did with static imports.
Use dynamic includes instead of static imports when you are running
tasks conditionally or using variable interpolation. The down side
is that you need to then tag the parent task as well as all child
tasks, as tags only apply to children of statically imported tasks.
Basically, when using conditionals or variables in your tasks you should
use include_tasks instead of import_tasks. The down side is that you now
need to tag all included tasks individually or with a block, unlike when
using static imports (tags are applied to all imported child tasks).
I would actually like to reduce this task to a single one that uses the
host's ansible_distribution variable, but Ansible 2.5.1 currently gives
the following error: ansible_distribution is undefined.
We stopped being able to do dynamic includes from the playbooks around
Ansible 2.4.0.0 if I recall correctly. Instead we can create a task to
include the variables and make it always run by using the special tag.
For now the Debian and Ubuntu vars files are the same, but I will keep
them separate so that it is more flexible in the future.
