plugins/main/bridge/bridge.go

// Copyright 2014 CNI authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"os"
	"runtime"
	"sort"
	"syscall"
	"time"

	"github.com/vishvananda/netlink"

	"github.com/containernetworking/cni/pkg/skel"
	"github.com/containernetworking/cni/pkg/types"
	current "github.com/containernetworking/cni/pkg/types/100"
	"github.com/containernetworking/cni/pkg/version"
	"github.com/containernetworking/plugins/pkg/ip"
	"github.com/containernetworking/plugins/pkg/ipam"
	"github.com/containernetworking/plugins/pkg/link"
	"github.com/containernetworking/plugins/pkg/netlinksafe"
	"github.com/containernetworking/plugins/pkg/ns"
	bv "github.com/containernetworking/plugins/pkg/utils/buildversion"
	"github.com/containernetworking/plugins/pkg/utils/sysctl"
)

// For testcases to force an error after IPAM has been performed
var debugPostIPAMError error

const defaultBrName = "cni0"

type NetConf struct {
	types.NetConf
	BrName                    string       `json:"bridge"`
	IsGW                      bool         `json:"isGateway"`
	IsDefaultGW               bool         `json:"isDefaultGateway"`
	ForceAddress              bool         `json:"forceAddress"`
	IPMasq                    bool         `json:"ipMasq"`
	IPMasqBackend             *string      `json:"ipMasqBackend,omitempty"`
	MTU                       int          `json:"mtu"`
	HairpinMode               bool         `json:"hairpinMode"`
	PromiscMode               bool         `json:"promiscMode"`
	Vlan                      int          `json:"vlan"`
	VlanTrunk                 []*VlanTrunk `json:"vlanTrunk,omitempty"`
	PreserveDefaultVlan       bool         `json:"preserveDefaultVlan"`
	MacSpoofChk               bool         `json:"macspoofchk,omitempty"`
	EnableDad                 bool         `json:"enabledad,omitempty"`
	DisableContainerInterface bool         `json:"disableContainerInterface,omitempty"`
	PortIsolation             bool         `json:"portIsolation,omitempty"`

	Args struct {
		Cni BridgeArgs `json:"cni,omitempty"`
	} `json:"args,omitempty"`
	RuntimeConfig struct {
		Mac string `json:"mac,omitempty"`
	} `json:"runtimeConfig,omitempty"`

	mac   string
	vlans []int
}

type VlanTrunk struct {
	MinID *int `json:"minID,omitempty"`
	MaxID *int `json:"maxID,omitempty"`
	ID    *int `json:"id,omitempty"`
}

type BridgeArgs struct {
	Mac string `json:"mac,omitempty"`
}

// MacEnvArgs represents CNI_ARGS
type MacEnvArgs struct {
	types.CommonArgs
	MAC types.UnmarshallableString `json:"mac,omitempty"`
}

type gwInfo struct {
	gws               []net.IPNet
	family            int
	defaultRouteFound bool
}

func init() {
	// this ensures that main runs only on main thread (thread group leader).
	// since namespace ops (unshare, setns) are done for a single thread, we
	// must ensure that the goroutine does not jump from OS thread to thread
	runtime.LockOSThread()
}

func loadNetConf(bytes []byte, envArgs string) (*NetConf, string, error) {
	n := &NetConf{
		BrName: defaultBrName,
	}
	if err := json.Unmarshal(bytes, n); err != nil {
		return nil, "", fmt.Errorf("failed to load netconf: %v", err)
	}
	if n.Vlan < 0 || n.Vlan > 4094 {
		return nil, "", fmt.Errorf("invalid VLAN ID %d (must be between 0 and 4094)", n.Vlan)
	}
	var err error
	n.vlans, err = collectVlanTrunk(n.VlanTrunk)
	if err != nil {
		// fail to parsing
		return nil, "", err
	}

	if envArgs != "" {
		e := MacEnvArgs{}
		if err := types.LoadArgs(envArgs, &e); err != nil {
			return nil, "", err
		}

		if e.MAC != "" {
			n.mac = string(e.MAC)
		}
	}

	if mac := n.Args.Cni.Mac; mac != "" {
		n.mac = mac
	}

	if mac := n.RuntimeConfig.Mac; mac != "" {
		n.mac = mac
	}

	return n, n.CNIVersion, nil
}

// This method is copied from https://github.com/k8snetworkplumbingwg/ovs-cni/blob/v0.27.2/pkg/plugin/plugin.go
func collectVlanTrunk(vlanTrunk []*VlanTrunk) ([]int, error) {
	if vlanTrunk == nil {
		return nil, nil
	}

	vlanMap := make(map[int]struct{})
	for _, item := range vlanTrunk {
		var minID int
		var maxID int
		var ID int

		switch {
		case item.MinID != nil && item.MaxID != nil:
			minID = *item.MinID
			if minID <= 0 || minID > 4094 {
				return nil, errors.New("incorrect trunk minID parameter")
			}
			maxID = *item.MaxID
			if maxID <= 0 || maxID > 4094 {
				return nil, errors.New("incorrect trunk maxID parameter")
			}
			if maxID < minID {
				return nil, errors.New("minID is greater than maxID in trunk parameter")
			}
			for v := minID; v <= maxID; v++ {
				vlanMap[v] = struct{}{}
			}
		case item.MinID == nil && item.MaxID != nil:
			return nil, errors.New("minID and maxID should be configured simultaneously, minID is missing")
		case item.MinID != nil && item.MaxID == nil:
			return nil, errors.New("minID and maxID should be configured simultaneously, maxID is missing")
		}

		// single vid
		if item.ID != nil {
			ID = *item.ID
			if ID <= 0 || ID > 4094 {
				return nil, errors.New("incorrect trunk id parameter")
			}
			vlanMap[ID] = struct{}{}
		}
	}

	if len(vlanMap) == 0 {
		return nil, nil
	}
	vlans := make([]int, 0, len(vlanMap))
	for k := range vlanMap {
		vlans = append(vlans, k)
	}
	sort.Slice(vlans, func(i int, j int) bool { return vlans[i] < vlans[j] })
	return vlans, nil
}

// calcGateways processes the results from the IPAM plugin and does the
// following for each IP family:
//   - Calculates and compiles a list of gateway addresses
//   - Adds a default route if needed
func calcGateways(result *current.Result, n *NetConf) (*gwInfo, *gwInfo, error) {
	gwsV4 := &gwInfo{}
	gwsV6 := &gwInfo{}

	for _, ipc := range result.IPs {

		// Determine if this config is IPv4 or IPv6
		var gws *gwInfo
		defaultNet := &net.IPNet{}
		switch {
		case ipc.Address.IP.To4() != nil:
			gws = gwsV4
			gws.family = netlink.FAMILY_V4
			defaultNet.IP = net.IPv4zero
		case len(ipc.Address.IP) == net.IPv6len:
			gws = gwsV6
			gws.family = netlink.FAMILY_V6
			defaultNet.IP = net.IPv6zero
		default:
			return nil, nil, fmt.Errorf("Unknown IP object: %v", ipc)
		}
		defaultNet.Mask = net.IPMask(defaultNet.IP)

		// All IPs currently refer to the container interface
		ipc.Interface = current.Int(2)

		// If not provided, calculate the gateway address corresponding
		// to the selected IP address
		if ipc.Gateway == nil && n.IsGW {
			ipc.Gateway = calcGatewayIP(&ipc.Address)
		}

		// Add a default route for this family using the current
		// gateway address if necessary.
		if n.IsDefaultGW && !gws.defaultRouteFound {
			for _, route := range result.Routes {
				if route.GW != nil && defaultNet.String() == route.Dst.String() {
					gws.defaultRouteFound = true
					break
				}
			}
			if !gws.defaultRouteFound {
				result.Routes = append(
					result.Routes,
					&types.Route{Dst: *defaultNet, GW: ipc.Gateway},
				)
				gws.defaultRouteFound = true
			}
		}

		// Append this gateway address to the list of gateways
		if n.IsGW {
			gw := net.IPNet{
				IP:   ipc.Gateway,
				Mask: ipc.Address.Mask,
			}
			gws.gws = append(gws.gws, gw)
		}
	}
	return gwsV4, gwsV6, nil
}

func ensureAddr(br netlink.Link, family int, ipn *net.IPNet, forceAddress bool) error {
	addrs, err := netlinksafe.AddrList(br, family)
	if err != nil && err != syscall.ENOENT {
		return fmt.Errorf("could not get list of IP addresses: %v", err)
	}

	ipnStr := ipn.String()
	for _, a := range addrs {

		// string comp is actually easiest for doing IPNet comps
		if a.IPNet.String() == ipnStr {
			return nil
		}

		// Multiple IPv6 addresses are allowed on the bridge if the
		// corresponding subnets do not overlap. For IPv4 or for
		// overlapping IPv6 subnets, reconfigure the IP address if
		// forceAddress is true, otherwise throw an error.
		if family == netlink.FAMILY_V4 || a.IPNet.Contains(ipn.IP) || ipn.Contains(a.IPNet.IP) {
			if forceAddress {
				if err = deleteAddr(br, a.IPNet); err != nil {
					return err
				}
			} else {
				return fmt.Errorf("%q already has an IP address different from %v", br.Attrs().Name, ipnStr)
			}
		}
	}

	addr := &netlink.Addr{IPNet: ipn, Label: ""}
	if err := netlink.AddrAdd(br, addr); err != nil && err != syscall.EEXIST {
		return fmt.Errorf("could not add IP address %s to %q: %v", ipnStr, br.Attrs().Name, err)
	}

	// Set the bridge's MAC to itself. Otherwise, the bridge will take the
	// lowest-numbered mac on the bridge, and will change as ifs churn
	if err := netlink.LinkSetHardwareAddr(br, br.Attrs().HardwareAddr); err != nil {
		return fmt.Errorf("could not set bridge's mac: %v", err)
	}

	return nil
}

func deleteAddr(br netlink.Link, ipn *net.IPNet) error {
	addr := &netlink.Addr{IPNet: ipn, Label: ""}

	if err := netlink.AddrDel(br, addr); err != nil {
		return fmt.Errorf("could not remove IP address from %q: %v", br.Attrs().Name, err)
	}

	return nil
}

func bridgeByName(name string) (*netlink.Bridge, error) {
	l, err := netlinksafe.LinkByName(name)
	if err != nil {
		return nil, fmt.Errorf("could not lookup %q: %v", name, err)
	}
	br, ok := l.(*netlink.Bridge)
	if !ok {
		return nil, fmt.Errorf("%q already exists but is not a bridge", name)
	}
	return br, nil
}

func ensureBridge(brName string, mtu int, promiscMode, vlanFiltering bool) (*netlink.Bridge, error) {
	linkAttrs := netlink.NewLinkAttrs()
	linkAttrs.Name = brName
	linkAttrs.MTU = mtu
	br := &netlink.Bridge{
		LinkAttrs: linkAttrs,
	}
	if vlanFiltering {
		br.VlanFiltering = &vlanFiltering
	}

	err := netlink.LinkAdd(br)
	if err != nil && err != syscall.EEXIST {
		return nil, fmt.Errorf("could not add %q: %v", brName, err)
	}

	if promiscMode {
		if err := netlink.SetPromiscOn(br); err != nil {
			return nil, fmt.Errorf("could not set promiscuous mode on %q: %v", brName, err)
		}
	}

	// Re-fetch link to read all attributes and if it already existed,
	// ensure it's really a bridge with similar configuration
	br, err = bridgeByName(brName)
	if err != nil {
		return nil, err
	}

	// we want to own the routes for this interface
	_, _ = sysctl.Sysctl(fmt.Sprintf("net/ipv6/conf/%s/accept_ra", brName), "0")

	if err := netlink.LinkSetUp(br); err != nil {
		return nil, err
	}

	return br, nil
}

func ensureVlanInterface(br *netlink.Bridge, vlanID int, preserveDefaultVlan bool) (netlink.Link, error) {
	name := fmt.Sprintf("%s.%d", br.Name, vlanID)

	brGatewayVeth, err := netlinksafe.LinkByName(name)
	if err != nil {
		if err.Error() != "Link not found" {
			return nil, fmt.Errorf("failed to find interface %q: %v", name, err)
		}

		hostNS, err := ns.GetCurrentNS()
		if err != nil {
			return nil, fmt.Errorf("faild to find host namespace: %v", err)
		}

		_, brGatewayIface, err := setupVeth(hostNS, br, name, br.MTU, false, vlanID, nil, preserveDefaultVlan, "", false)
		if err != nil {
			return nil, fmt.Errorf("faild to create vlan gateway %q: %v", name, err)
		}

		brGatewayVeth, err = netlinksafe.LinkByName(brGatewayIface.Name)
		if err != nil {
			return nil, fmt.Errorf("failed to lookup %q: %v", brGatewayIface.Name, err)
		}

		err = netlink.LinkSetUp(brGatewayVeth)
		if err != nil {
			return nil, fmt.Errorf("failed to up %q: %v", brGatewayIface.Name, err)
		}
	}

	return brGatewayVeth, nil
}

func setupVeth(
	netns ns.NetNS,
	br *netlink.Bridge,
	ifName string,
	mtu int,
	hairpinMode bool,
	vlanID int,
	vlans []int,
	preserveDefaultVlan bool,
	mac string,
	portIsolation bool,
) (*current.Interface, *current.Interface, error) {
	contIface := &current.Interface{}
	hostIface := &current.Interface{}

	err := netns.Do(func(hostNS ns.NetNS) error {
		// create the veth pair in the container and move host end into host netns
		hostVeth, containerVeth, err := ip.SetupVeth(ifName, mtu, mac, hostNS)
		if err != nil {
			return err
		}
		contIface.Name = containerVeth.Name
		contIface.Mac = containerVeth.HardwareAddr.String()
		contIface.Sandbox = netns.Path()
		hostIface.Name = hostVeth.Name
		return nil
	})
	if err != nil {
		return nil, nil, err
	}

	// need to lookup hostVeth again as its index has changed during ns move
	hostVeth, err := netlinksafe.LinkByName(hostIface.Name)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to lookup %q: %v", hostIface.Name, err)
	}
	hostIface.Mac = hostVeth.Attrs().HardwareAddr.String()

	// connect host veth end to the bridge
	if err := netlink.LinkSetMaster(hostVeth, br); err != nil {
		return nil, nil, fmt.Errorf("failed to connect %q to bridge %v: %v", hostVeth.Attrs().Name, br.Attrs().Name, err)
	}

	// set hairpin mode
	if err = netlink.LinkSetHairpin(hostVeth, hairpinMode); err != nil {
		return nil, nil, fmt.Errorf("failed to setup hairpin mode for %v: %v", hostVeth.Attrs().Name, err)
	}

	// set isolation mode
	if err = netlink.LinkSetIsolated(hostVeth, portIsolation); err != nil {
		return nil, nil, fmt.Errorf("failed to set isolated on for %v: %v", hostVeth.Attrs().Name, err)
	}

	if (vlanID != 0 || len(vlans) > 0) && !preserveDefaultVlan {
		err = removeDefaultVlan(hostVeth)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to remove default vlan on interface %q: %v", hostIface.Name, err)
		}
	}

	if vlanID != 0 {
		err = netlink.BridgeVlanAdd(hostVeth, uint16(vlanID), true, true, false, true)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to setup vlan tag on interface %q: %v", hostIface.Name, err)
		}
	}

	for _, v := range vlans {
		err = netlink.BridgeVlanAdd(hostVeth, uint16(v), false, false, false, true)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to setup vlan tag on interface %q: %w", hostIface.Name, err)
		}
	}

	// Backwards compatibility with users that did not specify a vlanID
	if vlanID == 0 && len(vlans) > 0 {
		// If no vlan is specified, we set the native vlan on the trunk equal to 1
		err = netlink.BridgeVlanAdd(hostVeth, 1, true, true, false, true)
		if err != nil {
			return nil, nil, fmt.Errorf("failed to setup default native vlan tag on interface %q: %v", hostIface.Name, err)
		}
	}

	return hostIface, contIface, nil
}

func removeDefaultVlan(hostVeth netlink.Link) error {
	vlanInfo, err := netlinksafe.BridgeVlanList()
	if err != nil {
		return err
	}

	brVlanInfo, ok := vlanInfo[int32(hostVeth.Attrs().Index)]
	if ok {
		for _, info := range brVlanInfo {
			err = netlink.BridgeVlanDel(hostVeth, info.Vid, false, false, false, true)
			if err != nil {
				return err
			}
		}
	}

	return nil
}

func calcGatewayIP(ipn *net.IPNet) net.IP {
	nid := ipn.IP.Mask(ipn.Mask)
	return ip.NextIP(nid)
}

func setupBridge(n *NetConf) (*netlink.Bridge, *current.Interface, error) {
	vlanFiltering := n.Vlan != 0 || n.VlanTrunk != nil
	// create bridge if necessary
	br, err := ensureBridge(n.BrName, n.MTU, n.PromiscMode, vlanFiltering)
	if err != nil {
		return nil, nil, fmt.Errorf("failed to create bridge %q: %v", n.BrName, err)
	}

	return br, &current.Interface{
		Name: br.Attrs().Name,
		Mac:  br.Attrs().HardwareAddr.String(),
	}, nil
}

func enableIPForward(family int) error {
	if family == netlink.FAMILY_V4 {
		return ip.EnableIP4Forward()
	}
	return ip.EnableIP6Forward()
}

func cmdAdd(args *skel.CmdArgs) error {
	success := false

	n, cniVersion, err := loadNetConf(args.StdinData, args.Args)
	if err != nil {
		return err
	}

	isLayer3 := n.IPAM.Type != ""

	if isLayer3 && n.DisableContainerInterface {
		return fmt.Errorf("cannot use IPAM when DisableContainerInterface flag is set")
	}

	if n.IsDefaultGW {
		n.IsGW = true
	}

	if n.HairpinMode && n.PromiscMode {
		return fmt.Errorf("cannot set hairpin mode and promiscuous mode at the same time")
	}

	br, brInterface, err := setupBridge(n)
	if err != nil {
		return err
	}

	netns, err := ns.GetNS(args.Netns)
	if err != nil {
		return fmt.Errorf("failed to open netns %q: %v", args.Netns, err)
	}
	defer netns.Close()

	hostInterface, containerInterface, err := setupVeth(netns, br, args.IfName, n.MTU, n.HairpinMode, n.Vlan, n.vlans, n.PreserveDefaultVlan, n.mac, n.PortIsolation)
	if err != nil {
		return err
	}

	// Assume L2 interface only
	result := &current.Result{
		CNIVersion: current.ImplementedSpecVersion,
		Interfaces: []*current.Interface{
			brInterface,
			hostInterface,
			containerInterface,
		},
	}

	if n.MacSpoofChk {
		sc := link.NewSpoofChecker(hostInterface.Name, containerInterface.Mac, uniqueID(args.ContainerID, args.IfName))
		if err := sc.Setup(); err != nil {
			return err
		}
		defer func() {
			if !success {
				if err := sc.Teardown(); err != nil {
					fmt.Fprintf(os.Stderr, "%v", err)
				}
			}
		}()
	}

	if isLayer3 {
		// run the IPAM plugin and get back the config to apply
		r, err := ipam.ExecAdd(n.IPAM.Type, args.StdinData)
		if err != nil {
			return err
		}

		// release IP in case of failure
		defer func() {
			if !success {
				ipam.ExecDel(n.IPAM.Type, args.StdinData)
			}
		}()

		// Convert whatever the IPAM result was into the current Result type
		ipamResult, err := current.NewResultFromResult(r)
		if err != nil {
			return err
		}

		result.IPs = ipamResult.IPs
		result.Routes = ipamResult.Routes
		result.DNS = ipamResult.DNS

		if len(result.IPs) == 0 {
			return errors.New("IPAM plugin returned missing IP config")
		}

		// Gather gateway information for each IP family
		gwsV4, gwsV6, err := calcGateways(result, n)
		if err != nil {
			return err
		}

		// Configure the container hardware address and IP address(es)
		if err := netns.Do(func(_ ns.NetNS) error {
			if n.EnableDad {
				_, _ = sysctl.Sysctl(fmt.Sprintf("/net/ipv6/conf/%s/enhanced_dad", args.IfName), "1")
				_, _ = sysctl.Sysctl(fmt.Sprintf("net/ipv6/conf/%s/accept_dad", args.IfName), "1")
			} else {
				_, _ = sysctl.Sysctl(fmt.Sprintf("net/ipv6/conf/%s/accept_dad", args.IfName), "0")
			}
			_, _ = sysctl.Sysctl(fmt.Sprintf("net/ipv4/conf/%s/arp_notify", args.IfName), "1")

			// Add the IP to the interface
			return ipam.ConfigureIface(args.IfName, result)
		}); err != nil {
			return err
		}

		if n.IsGW {
			var vlanInterface *current.Interface
			// Set the IP address(es) on the bridge and enable forwarding
			for _, gws := range []*gwInfo{gwsV4, gwsV6} {
				for _, gw := range gws.gws {
					if n.Vlan != 0 {
						vlanIface, err := ensureVlanInterface(br, n.Vlan, n.PreserveDefaultVlan)
						if err != nil {
							return fmt.Errorf("failed to create vlan interface: %v", err)
						}

						if vlanInterface == nil {
							vlanInterface = &current.Interface{
								Name: vlanIface.Attrs().Name,
								Mac:  vlanIface.Attrs().HardwareAddr.String(),
							}
							result.Interfaces = append(result.Interfaces, vlanInterface)
						}

						err = ensureAddr(vlanIface, gws.family, &gw, n.ForceAddress)
						if err != nil {
							return fmt.Errorf("failed to set vlan interface for bridge with addr: %v", err)
						}
					} else {
						err = ensureAddr(br, gws.family, &gw, n.ForceAddress)
						if err != nil {
							return fmt.Errorf("failed to set bridge addr: %v", err)
						}
					}
				}

				if gws.gws != nil {
					if err = enableIPForward(gws.family); err != nil {
						return fmt.Errorf("failed to enable forwarding: %v", err)
					}
				}
			}
		}

		if n.IPMasq {
			ipns := []*net.IPNet{}
			for _, ipc := range result.IPs {
				ipns = append(ipns, &ipc.Address)
			}
			if err = ip.SetupIPMasqForNetworks(n.IPMasqBackend, ipns, n.Name, args.IfName, args.ContainerID); err != nil {
				return err
			}
		}
	} else if !n.DisableContainerInterface {
		if err := netns.Do(func(_ ns.NetNS) error {
			link, err := netlinksafe.LinkByName(args.IfName)
			if err != nil {
				return fmt.Errorf("failed to retrieve link: %v", err)
			}

			// If layer 2 we still need to set the container veth to up
			if err = netlink.LinkSetUp(link); err != nil {
				return fmt.Errorf("failed to set %q up: %v", args.IfName, err)
			}
			return nil
		}); err != nil {
			return err
		}
	}

	hostVeth, err := netlinksafe.LinkByName(hostInterface.Name)
	if err != nil {
		return err
	}

	if !n.DisableContainerInterface {
		// check bridge port state
		retries := []int{0, 50, 500, 1000, 1000}
		for idx, sleep := range retries {
			time.Sleep(time.Duration(sleep) * time.Millisecond)

			hostVeth, err = netlinksafe.LinkByName(hostInterface.Name)
			if err != nil {
				return err
			}
			if hostVeth.Attrs().OperState == netlink.OperUp {
				break
			}

			if idx == len(retries)-1 {
				return fmt.Errorf("bridge port in error state: %s", hostVeth.Attrs().OperState)
			}
		}
	}

	// In certain circumstances, the host-side of the veth may change addrs
	hostInterface.Mac = hostVeth.Attrs().HardwareAddr.String()

	// Refetch the bridge since its MAC address may change when the first
	// veth is added or after its IP address is set
	br, err = bridgeByName(n.BrName)
	if err != nil {
		return err
	}
	brInterface.Mac = br.Attrs().HardwareAddr.String()

	// Return an error requested by testcases, if any
	if debugPostIPAMError != nil {
		return debugPostIPAMError
	}

	// Use incoming DNS settings if provided, otherwise use the
	// settings that were already configured by the IPAM plugin
	if dnsConfSet(n.DNS) {
		result.DNS = n.DNS
	}

	success = true

	return types.PrintResult(result, cniVersion)
}

func dnsConfSet(dnsConf types.DNS) bool {
	return dnsConf.Nameservers != nil ||
		dnsConf.Search != nil ||
		dnsConf.Options != nil ||
		dnsConf.Domain != ""
}

func cmdDel(args *skel.CmdArgs) error {
	n, _, err := loadNetConf(args.StdinData, args.Args)
	if err != nil {
		return err
	}

	isLayer3 := n.IPAM.Type != ""

	ipamDel := func() error {
		if isLayer3 {
			if err := ipam.ExecDel(n.IPAM.Type, args.StdinData); err != nil {
				return err
			}
		}
		return nil
	}

	if args.Netns == "" {
		return ipamDel()
	}

	// There is a netns so try to clean up. Delete can be called multiple times
	// so don't return an error if the device is already removed.
	// If the device isn't there then don't try to clean up IP masq either.
	var ipnets []*net.IPNet
	err = ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
		var err error
		ipnets, err = ip.DelLinkByNameAddr(args.IfName)
		if err != nil && err == ip.ErrLinkNotFound {
			return nil
		}
		return err
	})
	if err != nil {
		//  if NetNs is passed down by the Cloud Orchestration Engine, or if it called multiple times
		// so don't return an error if the device is already removed.
		// https://github.com/kubernetes/kubernetes/issues/43014#issuecomment-287164444
		_, ok := err.(ns.NSPathNotExistErr)
		if ok {
			return ipamDel()
		}
		return err
	}

	// call ipam.ExecDel after clean up device in netns
	if err := ipamDel(); err != nil {
		return err
	}

	if n.MacSpoofChk {
		sc := link.NewSpoofChecker("", "", uniqueID(args.ContainerID, args.IfName))
		if err := sc.Teardown(); err != nil {
			fmt.Fprintf(os.Stderr, "%v", err)
		}
	}

	if isLayer3 && n.IPMasq {
		if err := ip.TeardownIPMasqForNetworks(ipnets, n.Name, args.IfName, args.ContainerID); err != nil {
			return err
		}
	}

	return err
}

func main() {
	skel.PluginMainFuncs(skel.CNIFuncs{
		Add:    cmdAdd,
		Check:  cmdCheck,
		Del:    cmdDel,
		Status: cmdStatus,
		/* FIXME GC */
	}, version.All, bv.BuildString("bridge"))
}

type cniBridgeIf struct {
	Name        string
	ifIndex     int
	peerIndex   int
	masterIndex int
	found       bool
}

func validateInterface(intf current.Interface, expectInSb bool) (cniBridgeIf, netlink.Link, error) {
	ifFound := cniBridgeIf{found: false}
	if intf.Name == "" {
		return ifFound, nil, fmt.Errorf("Interface name missing ")
	}

	link, err := netlinksafe.LinkByName(intf.Name)
	if err != nil {
		return ifFound, nil, fmt.Errorf("Interface name %s not found", intf.Name)
	}

	if expectInSb {
		if intf.Sandbox == "" {
			return ifFound, nil, fmt.Errorf("Interface %s is expected to be in a sandbox", intf.Name)
		}
	} else {
		if intf.Sandbox != "" {
			return ifFound, nil, fmt.Errorf("Interface %s should not be in sandbox", intf.Name)
		}
	}

	return ifFound, link, err
}

func validateCniBrInterface(intf current.Interface, n *NetConf) (cniBridgeIf, error) {
	brFound, link, err := validateInterface(intf, false)
	if err != nil {
		return brFound, err
	}

	_, isBridge := link.(*netlink.Bridge)
	if !isBridge {
		return brFound, fmt.Errorf("Interface %s does not have link type of bridge", intf.Name)
	}

	if intf.Mac != "" {
		if intf.Mac != link.Attrs().HardwareAddr.String() {
			return brFound, fmt.Errorf("Bridge interface %s Mac doesn't match: %s", intf.Name, intf.Mac)
		}
	}

	linkPromisc := link.Attrs().Promisc != 0
	if linkPromisc != n.PromiscMode {
		return brFound, fmt.Errorf("Bridge interface %s configured Promisc Mode %v doesn't match current state: %v ",
			intf.Name, n.PromiscMode, linkPromisc)
	}

	brFound.found = true
	brFound.Name = link.Attrs().Name
	brFound.ifIndex = link.Attrs().Index
	brFound.masterIndex = link.Attrs().MasterIndex

	return brFound, nil
}

func validateCniVethInterface(intf *current.Interface, brIf cniBridgeIf, contIf cniBridgeIf) (cniBridgeIf, error) {
	vethFound, link, err := validateInterface(*intf, false)
	if err != nil {
		return vethFound, err
	}

	_, isVeth := link.(*netlink.Veth)
	if !isVeth {
		// just skip it, it's not what CNI created
		return vethFound, nil
	}

	_, vethFound.peerIndex, err = ip.GetVethPeerIfindex(link.Attrs().Name)
	if err != nil {
		return vethFound, fmt.Errorf("Unable to obtain veth peer index for veth %s", link.Attrs().Name)
	}
	vethFound.ifIndex = link.Attrs().Index
	vethFound.masterIndex = link.Attrs().MasterIndex

	if vethFound.ifIndex != contIf.peerIndex {
		return vethFound, nil
	}

	if contIf.ifIndex != vethFound.peerIndex {
		return vethFound, nil
	}

	if vethFound.masterIndex != brIf.ifIndex {
		return vethFound, nil
	}

	if intf.Mac != "" {
		if intf.Mac != link.Attrs().HardwareAddr.String() {
			return vethFound, fmt.Errorf("Interface %s Mac doesn't match: %s not found", intf.Name, intf.Mac)
		}
	}

	vethFound.found = true
	vethFound.Name = link.Attrs().Name

	return vethFound, nil
}

func validateCniContainerInterface(intf current.Interface) (cniBridgeIf, error) {
	vethFound, link, err := validateInterface(intf, true)
	if err != nil {
		return vethFound, err
	}

	_, isVeth := link.(*netlink.Veth)
	if !isVeth {
		return vethFound, fmt.Errorf("Error: Container interface %s not of type veth", link.Attrs().Name)
	}
	_, vethFound.peerIndex, err = ip.GetVethPeerIfindex(link.Attrs().Name)
	if err != nil {
		return vethFound, fmt.Errorf("Unable to obtain veth peer index for veth %s", link.Attrs().Name)
	}
	vethFound.ifIndex = link.Attrs().Index

	if intf.Mac != "" {
		if intf.Mac != link.Attrs().HardwareAddr.String() {
			return vethFound, fmt.Errorf("Interface %s Mac %s doesn't match container Mac: %s", intf.Name, intf.Mac, link.Attrs().HardwareAddr)
		}
	}

	vethFound.found = true
	vethFound.Name = link.Attrs().Name

	return vethFound, nil
}

func cmdCheck(args *skel.CmdArgs) error {
	n, _, err := loadNetConf(args.StdinData, args.Args)
	if err != nil {
		return err
	}
	netns, err := ns.GetNS(args.Netns)
	if err != nil {
		return fmt.Errorf("failed to open netns %q: %v", args.Netns, err)
	}
	defer netns.Close()

	// run the IPAM plugin and get back the config to apply
	err = ipam.ExecCheck(n.IPAM.Type, args.StdinData)
	if err != nil {
		return err
	}

	// Parse previous result.
	if n.NetConf.RawPrevResult == nil {
		return fmt.Errorf("Required prevResult missing")
	}

	if err := version.ParsePrevResult(&n.NetConf); err != nil {
		return err
	}

	result, err := current.NewResultFromResult(n.PrevResult)
	if err != nil {
		return err
	}

	var errLink error
	var contCNI, vethCNI cniBridgeIf
	var brMap, contMap current.Interface

	// Find interfaces for names whe know, CNI Bridge and container
	for _, intf := range result.Interfaces {
		if n.BrName == intf.Name {
			brMap = *intf
			continue
		} else if args.IfName == intf.Name {
			if args.Netns == intf.Sandbox {
				contMap = *intf
				continue
			}
		}
	}

	brCNI, err := validateCniBrInterface(brMap, n)
	if err != nil {
		return err
	}

	// The namespace must be the same as what was configured
	if args.Netns != contMap.Sandbox {
		return fmt.Errorf("Sandbox in prevResult %s doesn't match configured netns: %s",
			contMap.Sandbox, args.Netns)
	}

	// Check interface against values found in the container
	if err := netns.Do(func(_ ns.NetNS) error {
		contCNI, errLink = validateCniContainerInterface(contMap)
		if errLink != nil {
			return errLink
		}
		return nil
	}); err != nil {
		return err
	}

	// Now look for veth that is peer with container interface.
	// Anything else wasn't created by CNI, skip it
	for _, intf := range result.Interfaces {
		// Skip this result if name is the same as cni bridge
		// It's either the cni bridge we dealt with above, or something with the
		// same name in a different namespace.  We just skip since it's not ours
		if brMap.Name == intf.Name {
			continue
		}

		// same here for container name
		if contMap.Name == intf.Name {
			continue
		}

		vethCNI, errLink = validateCniVethInterface(intf, brCNI, contCNI)
		if errLink != nil {
			return errLink
		}

		if vethCNI.found {
			// veth with container interface as peer and bridge as master found
			break
		}
	}

	if !brCNI.found {
		return fmt.Errorf("CNI created bridge %s in host namespace was not found", n.BrName)
	}
	if !contCNI.found {
		return fmt.Errorf("CNI created interface in container %s not found", args.IfName)
	}
	if !vethCNI.found {
		return fmt.Errorf("CNI veth created for bridge %s was not found", n.BrName)
	}

	// Check prevResults for ips, routes and dns against values found in the container
	return netns.Do(func(_ ns.NetNS) error {
		err = ip.ValidateExpectedInterfaceIPs(args.IfName, result.IPs)
		if err != nil {
			return err
		}

		err = ip.ValidateExpectedRoute(result.Routes)
		if err != nil {
			return err
		}
		return nil
	})
}

func uniqueID(containerID, cniIface string) string {
	return containerID + "-" + cniIface
}

func cmdStatus(args *skel.CmdArgs) error {
	conf := NetConf{}
	if err := json.Unmarshal(args.StdinData, &conf); err != nil {
		return fmt.Errorf("failed to load netconf: %w", err)
	}

	if conf.IPAM.Type != "" {
		if err := ipam.ExecStatus(conf.IPAM.Type, args.StdinData); err != nil {
			return err
		}
	}

	return nil
}