feat: add native nftables support (#1389)

- Add nftables as a third firewall backend option alongside firewalld
and iptables
- Detection priority: firewalld → nftables → iptables (legacy fallback)
- Uses dedicated `openvpn` and `openvpn-nat` tables for clean isolation
- Integrates with native `nftables.service` via include in
`/etc/nftables.conf`


Closes https://github.com/angristan/openvpn-install/issues/530

test/Dockerfile.server

@@ -7,32 +7,40 @@ FROM ${BASE_IMAGE}
 ARG BASE_IMAGE
 # Set to "y" to install and enable firewalld for testing
 ARG ENABLE_FIREWALLD=n
+# Set to "y" to install and enable nftables for testing
+ARG ENABLE_NFTABLES=n
 ENV DEBIAN_FRONTEND=noninteractive
 ENV ENABLE_FIREWALLD=${ENABLE_FIREWALLD}
+ENV ENABLE_NFTABLES=${ENABLE_NFTABLES}
 
 # Install basic dependencies based on the OS
 # dnsutils/bind-utils provides dig for DNS testing with Unbound
 RUN if command -v apt-get >/dev/null; then \
         apt-get update && apt-get install -y --no-install-recommends \
             iproute2 iptables curl procps systemd systemd-sysv dnsutils \
+        && if [ "$ENABLE_NFTABLES" = "y" ]; then apt-get install -y --no-install-recommends nftables; fi \
         && rm -rf /var/lib/apt/lists/*; \
     elif command -v dnf >/dev/null; then \
         dnf install -y --allowerasing \
             iproute iptables curl procps-ng systemd tar gzip bind-utils \
         && if [ "$ENABLE_FIREWALLD" = "y" ]; then dnf install -y firewalld; fi \
+        && if [ "$ENABLE_NFTABLES" = "y" ]; then dnf install -y nftables; fi \
         && dnf clean all; \
     elif command -v yum >/dev/null; then \
         yum install -y \
             iproute iptables curl procps-ng systemd tar gzip bind-utils \
         && if [ "$ENABLE_FIREWALLD" = "y" ]; then yum install -y firewalld; fi \
+        && if [ "$ENABLE_NFTABLES" = "y" ]; then yum install -y nftables; fi \
         && yum clean all; \
     elif command -v pacman >/dev/null; then \
         pacman -Syu --noconfirm \
             iproute2 iptables curl procps-ng bind \
+        && if [ "$ENABLE_NFTABLES" = "y" ]; then pacman -S --noconfirm nftables; fi \
         && pacman -Scc --noconfirm; \
     elif command -v zypper >/dev/null; then \
         zypper install -y \
             iproute2 iptables curl procps systemd tar gzip bind-utils gawk \
+        && if [ "$ENABLE_NFTABLES" = "y" ]; then zypper install -y nftables; fi \
         && zypper clean -a; \
     fi
 
@@ -41,6 +49,14 @@ RUN if [ "$ENABLE_FIREWALLD" = "y" ] && command -v firewall-cmd >/dev/null; then
         systemctl enable firewalld; \
     fi
 
+# Enable nftables if requested (must be done after systemd is available)
+# Use empty nftables.conf - do NOT flush ruleset as it removes Docker's networking rules
+RUN if [ "$ENABLE_NFTABLES" = "y" ] && command -v nft >/dev/null; then \
+        systemctl enable nftables; \
+        mkdir -p /etc/nftables; \
+        echo '#!/usr/sbin/nft -f' > /etc/nftables.conf; \
+    fi
+
 # Create TUN device (will be mounted at runtime)
 RUN mkdir -p /dev/net
 

test/server-entrypoint.sh

@@ -87,9 +87,11 @@ REQUIRED_FILES=(
 	/etc/openvpn/server/easy-rsa/pki/ca.crt
 	/root/testclient.ovpn
 )
-# Only check for iptables script if firewalld is not active
-if ! systemctl is-active --quiet firewalld; then
+# Only check for iptables script if firewalld and nftables are not active
+if ! systemctl is-active --quiet firewalld && ! systemctl is-active --quiet nftables; then
 	REQUIRED_FILES+=(/etc/iptables/add-openvpn-rules.sh)
+elif systemctl is-active --quiet nftables; then
+	REQUIRED_FILES+=(/etc/nftables/openvpn.nft)
 fi
 
 for f in "${REQUIRED_FILES[@]}"; do
@@ -422,6 +424,46 @@ if systemctl is-active --quiet firewalld; then
 		firewall-cmd --list-rich-rules
 		exit 1
 	fi
+elif systemctl is-active --quiet nftables; then
+	# nftables mode - verify OpenVPN tables exist
+	echo "nftables detected, checking OpenVPN tables..."
+	for _ in $(seq 1 10); do
+		if nft list table inet openvpn >/dev/null 2>&1; then
+			echo "PASS: nftables 'inet openvpn' table exists"
+			break
+		fi
+		sleep 1
+	done
+	if ! nft list table inet openvpn >/dev/null 2>&1; then
+		echo "FAIL: nftables 'inet openvpn' table not found"
+		echo "Current nftables ruleset:"
+		nft list ruleset 2>&1 || true
+		exit 1
+	fi
+	# Verify NAT table exists
+	if nft list table ip openvpn-nat >/dev/null 2>&1; then
+		echo "PASS: nftables 'ip openvpn-nat' table exists"
+	else
+		echo "FAIL: nftables 'ip openvpn-nat' table not found"
+		nft list ruleset 2>&1 || true
+		exit 1
+	fi
+	# Verify masquerade rule exists
+	if nft list table ip openvpn-nat | grep -q "masquerade"; then
+		echo "PASS: nftables masquerade rule exists"
+	else
+		echo "FAIL: nftables masquerade rule not found"
+		nft list table ip openvpn-nat 2>&1 || true
+		exit 1
+	fi
+	# Verify include in nftables.conf
+	if grep -q 'include.*/etc/nftables/openvpn.nft' /etc/nftables.conf; then
+		echo "PASS: OpenVPN rules included in nftables.conf"
+	else
+		echo "FAIL: OpenVPN rules not included in nftables.conf"
+		cat /etc/nftables.conf 2>&1 || true
+		exit 1
+	fi
 else
 	# iptables mode - verify NAT rules
 	echo "iptables mode, checking NAT rules..."