Feedback on a new simple firewall service

Feedback on a new simple firewall service

[Solene Rapenne]

Hello,

I'm looking for advices and feedback. I wrote a simple service (reusing
the iptables service as a start) that I called "firewall", the purpose
is to block all incoming ports and list the ports you want to allow.
The point is to allow users to easily manage their firewall without
knowing about to use iptables. Most of the time opening a few ports and
blocking everything is enough.

However, while this works in its current state, I'm not satisfied of my
code and the way it works.

- it's not compatible with iptables and not extendable, should I merge
  this into the iptables service?

- I'm defining the configuration file in a long string with map calls
  and conditions, it looks very ugly. I didn't write much Scheme in my
  life and I struggled a bit to get the pieces to form the string, this
  is noticeable in the result

- what should happend when you stop the service? I'm currently using a
  default rules set that keep incoming traffic blocked on every ports but
  this may not be desirable.


Exemple of configuration:

(service firewall-service-type
  (firewall-configuration
    (udp '(53))
    (tcp '(22 70 1965))))

The according iptables -L output:
---------
Chain INPUT (policy DROP)
target     prot opt source               destination
ACCEPT     all  --  anywhere             anywhere             ctstate RELATED,ESTABLISHED
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:ssh
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:gopher
ACCEPT     tcp  --  anywhere             anywhere             tcp dpt:1965
ACCEPT     udp  --  anywhere             anywhere             udp dpt:domain

Chain FORWARD (policy DROP)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination
--------

Here is my code in its current state

;;;
;;; Firewall
;;;

(define %firewall-accept-all-rules
  (plain-file "firewall-block-all.rules"
              "*filter
:INPUT DROP
:FORWARD DROP
:OUTPUT ACCEPT
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
COMMIT
"))

(define-record-type* <firewall-configuration>
  firewall-configuration make-firewall-configuration
  firewall-configuration?
  (tcp firewall-configuration-tcp
       (default #f))
  (udp firewall-configuration-udp
       (default #f)))

(define firewall-shepherd-service
  (match-lambda
   (($ <firewall-configuration> tcp udp)
    (let* ((iptables-restore (file-append iptables "/sbin/iptables-restore"))
          (ip6tables-restore (file-append iptables "/sbin/ip6tables-restore"))
          (custom-rules
           (plain-file
            "iptables-defined.rules"
            (format #f
                    "*filter~%:INPUT DROP~%:FORWARD DROP~%:OUTPUT ACCEPT~%~a~%~a~%~a~%COMMIT~%"
                    "-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT"
                    (if tcp
                        (string-join
                         (map (lambda (tcp) (format #f "-A INPUT -p tcp --dport ~a -j ACCEPT" tcp)) tcp)
                         "\n")
                        "")
                    
                    (if udp
                        (string-join
                         (map (lambda (udp) (format #f "-A INPUT -p udp --dport ~a -j ACCEPT" udp)) udp)
                         "\n")
                        ""))))
          (ruleset (if (or udp tcp) ;; if no ports defined, use the default ruleset
                       custom-rules
                       %firewall-accept-all-rules)))
      (shepherd-service
       (documentation "Easy firewall management")
       (provision '(firewall))
       (start #~(lambda _
                  (invoke #$iptables-restore  #$ruleset)
                  (invoke #$ip6tables-restore #$ruleset)))
       (stop #~(lambda _
                 (invoke #$iptables-restore #$%firewall-accept-all-rules)
                 (invoke #$ip6tables-restore #$%firewall-accept-all-rules))))))))

(define firewall-service-type
  (service-type
   (name 'firewall)
   (description
    "Run @command{iptables-restore}, setting up the specified rules.")
   (extensions
    (list (service-extension shepherd-root-service-type
                             (compose list firewall-shepherd-service))))))

Re: Feedback on a new simple firewall service OFF TOPIC PRAISE

[Joshua Branson]

Solene Rapenne <solene@perso.pw> writes:

> Hello,
>
> I'm looking for advices and feedback. I wrote a simple service (reusing
> the iptables service as a start) that I called "firewall", the purpose

maybe eventually it could use nftables, which is the better newer version.

> is to block all incoming ports and list the ports you want to allow.
> The point is to allow users to easily manage their firewall without
> knowing about to use iptables. Most of the time opening a few ports and
> blocking everything is enough.

YES!  SWEET, ICY COLD, HOLY ALASKAN ASPARAGUS TIPS! THIS IS AWESOME!
How cool is it to abstract away the details for a firewall!?  Man I've
tried learning iptables, and it is just very weird syntax and hard to
understand!  Thanks for working on this!

I invite you to forward your original email to guix-patches@gnu.org.
That way you open a specific issue and your code is assigned a bug
number!

--
Joshua Branson (joshuaBPMan in #guix)
Sent from Emacs and Gnus
  https://gnucode.me
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  https://propernaming.org
  "You can have whatever you want, as long as you help
enough other people get what they want." - Zig Ziglar