netbird/client/internal/routemanager/systemops_linux.go

//go:build !android

package routemanager

import (
	"net"
	"net/netip"
	"os"

	"github.com/vishvananda/netlink"
)

const ipv4ForwardingPath = "/proc/sys/net/ipv4/ip_forward"

func addToRouteTable(prefix netip.Prefix, addr string) error {
	_, ipNet, err := net.ParseCIDR(prefix.String())
	if err != nil {
		return err
	}

	addrMask := "/32"
	if prefix.Addr().Unmap().Is6() {
		addrMask = "/128"
	}

	ip, _, err := net.ParseCIDR(addr + addrMask)
	if err != nil {
		return err
	}

	route := &netlink.Route{
		Scope: netlink.SCOPE_UNIVERSE,
		Dst:   ipNet,
		Gw:    ip,
	}

	err = netlink.RouteAdd(route)
	if err != nil {
		return err
	}

	return nil
}

func removeFromRouteTable(prefix netip.Prefix) error {
	_, ipNet, err := net.ParseCIDR(prefix.String())
	if err != nil {
		return err
	}

	route := &netlink.Route{
		Scope: netlink.SCOPE_UNIVERSE,
		Dst:   ipNet,
	}

	err = netlink.RouteDel(route)
	if err != nil {
		return err
	}

	return nil
}

func enableIPForwarding() error {
	bytes, err := os.ReadFile(ipv4ForwardingPath)
	if err != nil {
		return err
	}

	// check if it is already enabled
	// see more: https://github.com/netbirdio/netbird/issues/872
	if len(bytes) > 0 && bytes[0] == 49 {
		return nil
	}

	return os.WriteFile(ipv4ForwardingPath, []byte("1"), 0644)
}