cunicu/pkg/device/device_linux.go

package device

import (
	"errors"
	"fmt"
	"math"
	"net"
	"os"

	"github.com/vishvananda/netlink"
	"go.uber.org/zap"
	"golang.org/x/sys/unix"
)

type LinuxKernelDevice struct {
	link netlink.Link

	logger *zap.Logger
}

func NewKernelDevice(name string) (*LinuxKernelDevice, error) {
	link := &netlink.Wireguard{
		LinkAttrs: netlink.NewLinkAttrs(),
	}
	link.LinkAttrs.Name = name

	if err := netlink.LinkAdd(link); err != nil {
		return nil, fmt.Errorf("failed to create WireGuard interface: %w", err)
	}

	return &LinuxKernelDevice{
		link: link,
		logger: zap.L().Named("dev").With(
			zap.String("dev", name),
			zap.String("type", "kernel")),
	}, nil
}

func FindKernelDevice(name string) (Device, error) {
	link, err := netlink.LinkByName(name)
	if err != nil {
		return nil, fmt.Errorf("failed to get link details: %w", err)
	}

	return &LinuxKernelDevice{
		link:   link,
		logger: zap.L().Named("dev").With(zap.String("dev", name)),
	}, nil
}

func (i *LinuxKernelDevice) Close() error {
	i.logger.Debug("Deleting kernel device")

	if err := netlink.LinkDel(i.link); err != nil {
		return fmt.Errorf("failed to delete WireGuard device: %w", err)
	}

	return nil
}

func (i *LinuxKernelDevice) Name() string {
	return i.link.Attrs().Name
}

func (i *LinuxKernelDevice) Index() int {
	return i.link.Attrs().Index
}

func (i *LinuxKernelDevice) MTU() int {
	var err error

	i.link, err = netlink.LinkByIndex(i.Index())
	if err != nil {
		panic(err)
	}

	return i.link.Attrs().MTU
}

func (i *LinuxKernelDevice) SetMTU(mtu int) error {
	i.logger.Debug("Set link MTU", zap.Int("mtu", mtu))
	return netlink.LinkSetMTU(i.link, mtu)
}

func (i *LinuxKernelDevice) SetUp() error {
	i.logger.Debug("Set link up")
	return netlink.LinkSetUp(i.link)
}

func (i *LinuxKernelDevice) SetDown() error {
	i.logger.Debug("Set link down")
	return netlink.LinkSetDown(i.link)
}

func (i *LinuxKernelDevice) AddAddress(ip net.IPNet) error {
	i.logger.Debug("Add address", zap.Any("addr", ip))

	addr := &netlink.Addr{
		IPNet: &ip,
		Flags: unix.IFA_F_PERMANENT,
	}

	if ip.IP.IsLinkLocalUnicast() || ip.IP.IsLinkLocalMulticast() {
		addr.Scope = unix.RT_SCOPE_LINK
	}

	return netlink.AddrAdd(i.link, addr)
}

func (i *LinuxKernelDevice) DeleteAddress(ip net.IPNet) error {
	i.logger.Debug("Delete address", zap.Any("addr", ip))

	addr := &netlink.Addr{
		IPNet: &ip,
	}

	return netlink.AddrDel(i.link, addr)
}

func (i *LinuxKernelDevice) AddRoute(dst net.IPNet, table int) error {
	i.logger.Debug("Add route", zap.Any("dst", dst))

	route := &netlink.Route{
		LinkIndex: i.link.Attrs().Index,
		Dst:       &dst,
		Protocol:  RouteProtocol,
		Table:     table,
	}

	if err := netlink.RouteAdd(route); err != nil && !errors.Is(err, os.ErrExist) {
		return err
	}

	return nil
}

func (i *LinuxKernelDevice) DeleteRoute(dst net.IPNet, table int) error {
	i.logger.Debug("Delete route", zap.Any("dst", dst))

	route := &netlink.Route{
		LinkIndex: i.link.Attrs().Index,
		Dst:       &dst,
		Table:     table,
	}

	return netlink.RouteDel(route)
}

func DetectMTU(ip net.IP) (int, error) {
	// TODO: How do we use the correct fwmark here?
	rts, err := netlink.RouteGet(ip)
	if err != nil {
		return -1, fmt.Errorf("failed to get route: %w", err)
	}

	if len(rts) == 0 {
		return -1, errors.New("no route to destination")
	}

	mtu := math.MaxInt
	for _, rt := range rts {
		if rt.MTU < mtu {
			mtu = rt.MTU
		}
	}

	return mtu, nil
}

func DetectDefaultMTU() (int, error) {
	// TODO: How do we use the correct fwmark here?
	rts, err := netlink.RouteListFiltered(unix.AF_INET, &netlink.Route{
		Dst: nil,
	}, netlink.RT_FILTER_DST)

	if err != nil {
		return -1, fmt.Errorf("failed to get route: %w", err)
	}

	if len(rts) == 0 {
		return -1, errors.New("no route to destination")
	}

	mtu := math.MaxInt
	for _, rt := range rts {
		if rt.MTU < mtu {
			mtu = rt.MTU
		}
	}

	return mtu, nil
}