Make IPv4 firewall nftables ready.

conf/include_functions.conf

@@ -1,5 +1,13 @@
 #!/usr/bin/env bash
 
+# - Set firewall command (either iptables or ip6tables)
+#
+if [[ -x "${ip6t}" ]] ; then
+   fw_command="${ip6t}"
+elif [[ -x "${ipt}" ]] ; then
+   fw_command="${ipt}"
+fi 
+
 # -------------
 # --- Some functions
 # -------------
@@ -82,3 +90,167 @@ trim() {
     echo -n "$var"
 }
 
+
+is_container() {
+  command -v systemd-detect-virt >/dev/null 2>&1 && systemd-detect-virt --container >/dev/null 2>&1
+}
+
+
+# -------------
+# - IPv6 handling
+# -------------
+
+ENABLE_IPV6="auto"   # auto | yes | no
+IPV6_ACTIVE=0
+
+ipv6_sysctl_enabled() {
+  sysctl -n net.ipv6.conf.all.disable_ipv6 2>/dev/null | grep -qx 0
+}
+
+has_ipv6_addr() {
+  ip -6 addr show scope global 2>/dev/null | grep -q "inet6"
+}
+
+detect_ipv6() {
+  case "$ENABLE_IPV6" in
+    yes)  return 0 ;;
+    no)   return 1 ;;
+    auto) ipv6_sysctl_enabled ;;
+    *)    return 1 ;;
+  esac
+}
+
+
+# -------------
+# - Fail2ban
+# -------------
+
+FAIL2BAN_CONFIG_FILE="/etc/fail2ban/jail.local"
+FAIL2BAN_WAS_RUNNING=false
+fail2ban_client="$(command -v fail2ban-client 2>/dev/null)"
+has_fail2ban() {
+   command -v fail2ban-client >/dev/null 2>&1
+}
+
+fail2ban_running() {
+   systemctl is-active --quiet fail2ban >/dev/null 2>&1
+}
+
+# -------------
+# - Debian 12/13 compatibility helpers (best effort)
+# -------------
+ensure_mod() {
+
+   # ---
+   # Load a kernel module if possible (no hard failure).
+   # NOTE: In containers module loading is not possible; modules must be loaded on the host.
+   # ---
+
+   local m="$1"
+
+   # Already loaded?
+   if lsmod 2>/dev/null | awk '{print $1}' | grep -qx "$m" ; then
+      return 0
+   fi
+
+   # Skip in containers/guests without module loading capability
+   #
+   is_container && return 0
+
+   # Best effort modprobe
+   /sbin/modprobe "$m" >/dev/null 2>&1 || warn "Loading module '$m' failed (ok if not needed on this host)."
+}
+
+# --- Feature detection helpers (Debian 12/13 + containers)
+module_loaded() {
+   lsmod 2>/dev/null | awk '{print $1}' | grep -qx "$1"
+}
+
+can_use_recent() {
+   # xt_recent is the kernel module behind "-m recent"
+   # In containers lsmod may be restricted; also accept presence of /proc/net/xt_recent.
+   module_loaded xt_recent && return 0
+   [ -d /proc/net/xt_recent ] && return 0
+   # As a last resort, ask iptables to parse the match (works if userspace has it)
+   "$ipt" -m recent -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_hashlimit() {
+   # xt_hashlimit is the kernel module behind "-m hashlimit"
+   module_loaded xt_hashlimit && return 0
+   [ -d /proc/net/xt_hashlimit ] && return 0
+   "${fw_command}" -m hashlimit -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_connlimit() {
+   # xt_connlimit is the kernel module behind "-m connlimit"
+   module_loaded xt_connlimit && return 0
+   "${fw_command}" -m connlimit -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_owner() {
+   # xt_owner is the kernel module behind "-m owner"
+   module_loaded xt_owner && return 0
+   "${fw_command}" -m owner -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_ct_target() {
+   # Check if iptables CT target exists (iptables-nft should support it when kernel has nf_tables CT support)
+   "${fw_command}" -t raw -j CT -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_helper_match() {
+   # Check if helper match exists
+   "${fw_command}" -m helper -h >/dev/null 2>&1 && return 0
+   return 1
+}
+
+can_use_nft() {
+   command -v nft >/dev/null 2>&1 && return 0
+   return 1
+}
+
+setup_ftp_conntrack_helper_output() {
+   # Prefer explicit helper assignment (safe with nf_conntrack_helper=0)
+   if can_use_ct_target ; then
+      "${fw_command}" -A OUTPUT -t raw -p tcp --dport "$standard_ftp_port" -j CT --helper ftp
+      return 0
+   fi
+
+   # nft fallback (nft-native helper assignment); keeps us "nft-ready"
+   if can_use_nft ; then
+      # Best-effort; may fail in containers without CAP_NET_ADMIN
+      nft add table ip fwhelper >/dev/null 2>&1 || true
+      nft add chain ip fwhelper output '{ type filter hook output priority raw; policy accept; }' >/dev/null 2>&1 || true
+      nft add ct helper ip fwhelper ftp '{ type "ftp" protocol tcp; }' >/dev/null 2>&1 || true
+      nft add rule ip fwhelper output tcp dport "$standard_ftp_port" ct helper set "ftp" >/dev/null 2>&1 && return 0
+   fi
+
+   warn "No CT helper assignment available (iptables CT target and nft fallback both unavailable). FTP active/passive may fail; FTPS workaround relies on recent/port rules."
+   return 1
+}
+
+setup_ftp_conntrack_helper_prerouting() {
+   # Prefer explicit helper assignment (safe with nf_conntrack_helper=0)
+   if can_use_ct_target ; then
+      "$ipt" -A PREROUTING -t raw -p tcp --dport "$standard_ftp_port" -j CT --helper ftp
+      return 0
+   fi
+
+   # nft fallback (nft-native helper assignment); keeps us "nft-ready"
+   if can_use_nft ; then
+      nft add table ip fwhelper >/dev/null 2>&1 || true
+      nft add chain ip fwhelper prerouting '{ type filter hook prerouting priority raw; policy accept; }' >/dev/null 2>&1 || true
+      nft add ct helper ip fwhelper ftp '{ type "ftp" protocol tcp; }' >/dev/null 2>&1 || true
+      nft add rule ip fwhelper prerouting tcp dport "$standard_ftp_port" ct helper set "ftp" >/dev/null 2>&1 && return 0
+   fi
+
+   warn "No CT helper assignment available (iptables CT target and nft fallback both unavailable). FTP server traffic may fail; consider enabling passive port ranges."
+   return 1
+}
+