secure farmer lan

cmds/modules/netlightd/main.go

@@ -131,6 +131,10 @@ func action(cli *cli.Context) error {
 		return fmt.Errorf("failed to setup mycelium on host: %w", err)
 	}
 
+	if err := nft.DropTrafficToLAN(); err != nil {
+		return fmt.Errorf("failed to drop traffic to lan: %w", err)
+	}
+
 	mod, err := netlight.NewNetworker()
 	if err != nil {
 		return fmt.Errorf("failed to create Networker: %w", err)

pkg/netlight/nft/nft.go

@@ -1,10 +1,13 @@
 package nft
 
 import (
+	"fmt"
 	"io"
+	"net"
 	"os/exec"
 
 	"github.com/rs/zerolog/log"
+	"github.com/vishvananda/netlink"
 
 	"github.com/pkg/errors"
 )
@@ -32,3 +35,85 @@ func Apply(r io.Reader, ns string) error {
 	}
 	return nil
 }
+
+func applyNftRule(rule []string) error {
+	cmd := exec.Command(rule[0], rule[1:]...)
+
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Error().Err(err).Str("output", string(out)).Msg("error during nft")
+		if eerr, ok := err.(*exec.ExitError); ok {
+			return errors.Wrapf(err, "failed to execute nft: %v", string(eerr.Stderr))
+		}
+		return errors.Wrap(err, "failed to execute nft")
+	}
+	return nil
+}
+
+// DropTrafficToLAN drops all the outgoing traffic to any peers on
+// the same lan network, but allow dicovery port for ygg/myc by accepting
+// traffic to/from dest/src ports.
+func DropTrafficToLAN() error {
+	rules := [][]string{
+		// @th,0,16 and @th,16,16 is raw expression for sport/dport in transport header
+		// used due to limitation on the installed nft v0.9.1
+		{
+			"nft", "add", "rule", "inet", "filter", "forward",
+			"meta", "l4proto", "{tcp, udp}", "@th,0,16", "{9651, 9650}", "accept",
+		},
+		{
+			"nft", "add", "rule", "inet", "filter", "forward",
+			"meta", "l4proto", "{tcp, udp}", "@th,16,16", "{9651, 9650}", "accept",
+		},
+	}
+	mac, err := getDefaultGwMac()
+	log.Debug().Str("mac", mac.String()).Err(err).Msg("default gw return")
+	rules = append(rules, []string{
+		"nft", "add", "rule", "inet", "filter", "forward",
+		"ether", "daddr", "!=", mac.String(), "drop",
+	})
+
+	for _, rule := range rules {
+		if err := applyNftRule(rule); err != nil {
+			return fmt.Errorf("failed to apply nft rule: %w", err)
+		}
+	}
+
+	return nil
+}
+
+func getDefaultGwMac() (net.HardwareAddr, error) {
+	routes, err := netlink.RouteList(nil, netlink.FAMILY_V4)
+	if err != nil {
+		return nil, fmt.Errorf("failed to list routes: %v", err)
+	}
+
+	var defaultRoute *netlink.Route
+	for _, route := range routes {
+		if route.Dst == nil {
+			defaultRoute = &route
+			break
+		}
+	}
+
+	if defaultRoute == nil {
+		return nil, fmt.Errorf("default route not found")
+	}
+
+	if defaultRoute.Gw == nil {
+		return nil, fmt.Errorf("default route has no gateway")
+	}
+
+	neighs, err := netlink.NeighList(0, netlink.FAMILY_V4)
+	if err != nil {
+		return nil, fmt.Errorf("failed to list neighbors: %v", err)
+	}
+
+	for _, neigh := range neighs {
+		if neigh.IP.Equal(defaultRoute.Gw) {
+			return neigh.HardwareAddr, nil
+		}
+	}
+
+	return nil, errors.New("failed to get default gw")
+}