abrown38andClaude Opus 5.5
d06bf8d531
Files and the journal, patterns with one <IP>, bounties within a window, bans in a Housecarl ban list with repeat offenders' bans growing; presets for sshd, jarl, housecarl, steward, bind-xfr, postfix-sasl, dovecot, nginx-auth and housecarl-drops; guard run/check/test/status/bans/ban/unban; a Debian package with a sandboxed unit; an end-to-end test with Housecarl. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
73 lines
2.5 KiB
Markdown
73 lines
2.5 KiB
Markdown
# Installing Guard
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Guard runs on any Linux machine whose logs it should watch: a web server
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behind the firewall, a mail server, the firewall itself. It needs
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Housecarl 0.2 or later (ban lists) on the firewall, reachable from the
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machine.
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## 1. A ban list and a token, in Housecarl
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On the firewall, make a ban list for this machine, and a user with a
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token that may ban into it and nothing else:
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```sh
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hc banlist add web --scope hosts --host 10.0.10.57 --host 2001:db8:10::57
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hc user add guard-web --no-password --grant bans:write:web
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sudo hc token create web --user guard-web
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```
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The scope says what a banned address is kept from:
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* `hosts`: this machine (its addresses), the usual choice for a server
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behind the firewall. Port forwards to it are covered too.
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* `firewall`: the firewall itself, for Guard running on the firewall.
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* `everything`: the firewall and everything behind it.
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A watch that reads Housecarl's own log (`housecarl-drops`) also needs
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`--grant log:read`.
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## 2. The package
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```sh
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sudo apt install ./guard_0.1.0_amd64.deb
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```
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It makes the `guard` user (in the `adm` and `systemd-journal` groups,
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to read logs), installs `guard.service` without starting it, and writes
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an example `/etc/guard/guard.yaml`.
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From source instead (Go 1.27): `make && sudo make install`, then
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`sudo systemd-sysusers guard.conf && sudo chgrp guard /etc/guard
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/etc/guard/guard.yaml && sudo systemctl daemon-reload`.
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## 3. The configuration
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Put the token in `/etc/guard/token`:
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```sh
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sudo install -m 0640 -g guard /dev/stdin /etc/guard/token <<< 'housecarl_…'
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```
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and edit `/etc/guard/guard.yaml`: Housecarl's URL, the ban list, and the
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watches ([configuration.md](configuration.md)). Then:
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```sh
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sudo -u guard guard check # the file, the patterns, Housecarl
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sudo -u guard guard test ssh # what the ssh watch finds in the journal
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sudo systemctl enable --now guard
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guard status # as root
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```
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On the firewall itself, use Housecarl's local socket instead of the URL
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(`housecarl.socket: /run/housecarl/housecarl.sock`), and give the guard
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user access to it: `SupplementaryGroups=adm systemd-journal housecarl`
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in `systemctl edit guard`. A token is still needed: Housecarl trusts
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only root and its own user on the socket without one.
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## fail2ban instead
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If you already run fail2ban, Housecarl ships an action for it that bans
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into a ban list the same way (Housecarl's docs/bans.md). Guard and
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fail2ban can also run side by side, on different machines or watching
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different logs.
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