Qubes-os port forwarding to allow external connections

qvm-portfwd-iptables

#!/bin/sh
# Inspired by https://gist.github.com/daktak/f887352d564b54f9e529404cc0eb60d5
# Inspired by https://gist.github.com/jpouellet/d8cd0eb8589a5b9bf0c53a28fc530369

ip() { qvm-prefs -g -- "$1" ip; }
netvm() { qvm-prefs -g -- "$1" netvm; }

forward() {
	local from_domain=$1
	local to_domain=$2
	local port=$3
	local type=$4

	local from_ip=$(ip "$from_domain")
	local to_ip=$(ip "$to_domain")
	local iface=$(qvm-run -p -u root "$from_domain" "ifconfig \
		| grep cast -B 1 --no-group-separator | grep -vE '^(vif|lo)' | grep -oE '^[^: ]+' | head -1")

	local from_ip=$(qvm-run -p -u root "$from_domain" "hostname -I | cut -d ' ' -f 1")
	if [ X"$from_ip" = XNone ] ; then local from_ip= ; fi

	if [[ $3 = "clear" && $4 = "all" ]]
	then
		echo "$from_domain: Clearing Port Forwarding from $1 iptables" >&2
		qvm-run -p -u root "$from_domain" "iptables-save | grep -v 'PortFwd $1' | iptables-restore"

		local nft_cmd="nft list table ip qubes-firewall -a | tr -d '\"' | grep 'iifname $iface accept # handle' | awk '{print \$NF}'"
		local nft_handle=$(qvm-run -p -u root "$from_domain" "$nft_cmd")
		if [[ $nft_handle =~ ^[0-9]+$ ]] ; then qvm-run -p -u root "$from_domain" "nft delete rule ip qubes-firewall forward handle $nft_handle" ; fi
	else
		echo "$from_domain: Forwarding on $iface port $port to $to_domain
			($from_ip -> $to_ip)" >&2
		qvm-run -p -u root "$from_domain" "iptables-save | grep -v 'PortFwd $1>$2:$4$3' | iptables-restore"
		qvm-run -p -u root "$from_domain" "iptables -t nat -A PREROUTING -i $iface -p $type ${from_ip:+-d} $from_ip --dport $port -j DNAT --to-destination $to_ip \
			-m comment --comment 'PortFwd $1>$2:$4$3'"
		qvm-run -p -u root "$from_domain" "iptables -I FORWARD 2 -i $iface -p $type ${to_ip:+-d} $to_ip --dport $port -m conntrack --ctstate NEW -j ACCEPT \
			-m comment --comment 'PortFwd $1>$2:$4$3'"
		qvm-run -p -u root "$from_domain" "nft add rule ip qubes-firewall forward meta iifname $iface accept"
	fi
}

input() {
	local domain=$1
	local port=$2
	local type=$3

	if [[ $2 = "clear" && $3 = "all" ]]
	then
		echo "$domain: Clearing Port Forwarding from $1 iptables" >&2
		qvm-run -p -u root "$domain" "iptables-save | grep -v 'PortFwd $1' | iptables-restore"
	else
		echo "$domain: Allowing input to port $port" >&2
		qvm-run -p -u root "$domain" "iptables-save | grep -v 'PortFwd $1:$3$2' | iptables-restore"
	
		qvm-run -p -u root "$domain" "iptables -I INPUT 5 -p $type --dport $port -m conntrack --ctstate NEW -j ACCEPT \
			-m comment --comment 'PortFwd $1:$3$2'"
	fi
}

recurse_netvms() {
	local this_dom=$1
	local port=$2
	local type=$3

	local outer_dom=$(netvm "$this_dom")
	if [[ -n "$outer_dom" && "$outer_dom" != "None" ]]; then
		forward "$outer_dom" "$this_dom" "$port" "$type"
		recurse_netvms "$outer_dom" "$port" "$type"
	fi
}

usage() {
	echo "Usage: ${0##*/} <vm> <port> <proto> | <vm> clear all" >&2
	exit 1
}

[ $# -eq 3 ] || usage
input "$1" "$2" "$3"
recurse_netvms "$1" "$2" "$3"

Why this double fw thing tho?
nf and ip tables

In case someone wants to test, I improved a little bit the current version (https://gist.github.com/fepitre/941d7161ae1150d90e15f778027e3248), notably by adding option for persistence. I'll do some review again (and from others I hope) and we will probably refactor it a little bit again for putting it in @QubesOS-contrib