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dnsmasq.go
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dnsmasq.go
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// Copyright 2021 Kinvolk GmbH
// Copyright 2015 CoreOS, Inc.
//
// 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 local
import (
"encoding/binary"
"errors"
"fmt"
"net"
"strconv"
"strings"
"text/template"
"github.com/coreos/go-iptables/iptables"
"github.com/coreos/pkg/capnslog"
"github.com/vishvananda/netlink"
"github.com/vishvananda/netns"
"github.com/flatcar/mantle/system/exec"
"github.com/flatcar/mantle/system/ns"
"github.com/flatcar/mantle/util"
)
var (
// ErrIPClash is raised when a generated IP lives in an existing
// root network namespace
ErrIPClash = errors.New("IP lives in a host network")
// ErrIncorrectSeed is raised when the seed used to generate veth pair
// is in an incorrect format
ErrIncorrectSeed = errors.New("seed must be a positive 2 bytes value")
)
type Interface struct {
HardwareAddr net.HardwareAddr
DHCPv4 []net.IPNet
DHCPv6 []net.IPNet
//SLAAC net.IPAddr
}
type Segment struct {
BridgeName string
BridgeIf *Interface
Interfaces []*Interface
nextIf int
// Listener holds the unique TCP socket
// created to ensure uniqueness of IP
// it has to be closed once the kola instance
// has terminated
Listener net.Listener
}
type Dnsmasq struct {
Segments []*Segment
dnsmasq *exec.ExecCmd
}
const (
numInterfaces = 500 // affects dnsmasq startup time
numSegments = 1
debugConfig = `
log-queries
log-dhcp
`
quietConfig = `
quiet-dhcp
quiet-dhcp6
quiet-ra
`
commonConfig = `
keep-in-foreground
leasefile-ro
log-facility=-
pid-file=
# hardcode DNS servers to avoid using systemd-resolved on the unreachable 127.0.0.53
dhcp-option=6,1.1.1.1,1.0.0.1,8.8.8.8
no-resolv
no-hosts
enable-ra
# point NTP at this host (0.0.0.0 and :: are special)
dhcp-option=option:ntp-server,0.0.0.0
dhcp-option=option6:ntp-server,[::]
{{range .Segments}}
domain={{.BridgeName}}.local
{{range .BridgeIf.DHCPv4}}
dhcp-range={{.IP}},static
{{end}}
{{range .BridgeIf.DHCPv6}}
dhcp-range={{.IP}},ra-names,slaac
{{end}}
{{range .Interfaces}}
dhcp-host={{.HardwareAddr}}{{template "ips" .DHCPv4}}{{template "ips" .DHCPv6}}
{{end}}
{{end}}
{{define "ips"}}{{range .}}{{printf ",%s" .IP}}{{end}}{{end}}
`
)
var plog = capnslog.NewPackageLogger("github.com/flatcar/mantle", "platform/local")
func newInterface(s byte, i uint16) *Interface {
return &Interface{
HardwareAddr: net.HardwareAddr{0x02, s, 0, 0, byte(i / 256), byte(i % 256)},
DHCPv4: []net.IPNet{{
IP: net.IP{10, s, byte(i / 256), byte(i % 256)},
Mask: net.CIDRMask(16, 32)}},
DHCPv6: []net.IPNet{{
IP: net.IP{0xfd, s, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, byte(i / 256), byte(i % 256)},
Mask: net.CIDRMask(64, 128)}},
}
}
// configureNAT creates and append a NAT rule
// using the interface i as output
func configureNAT(i string) error {
table, err := iptables.New()
if err != nil {
return fmt.Errorf("unable to get iptables: %w", err)
}
if err := table.AppendUnique("nat", "POSTROUTING", "-j", "MASQUERADE", "-o", i); err != nil {
return fmt.Errorf("unable to append rule: %w", err)
}
return nil
}
// generateVethPair creates and returns a map holding
// a pair of veth based on a seed
// where:
// [0] is the network namespace veth
// [1] is the host namespace veth
// [2] is the next hop for adding route
func generateVethPair(seed int, hostNetworks []*net.IPNet) ([]string, error) {
if seed < 0 || seed > 0xFFFF {
return nil, ErrIncorrectSeed
}
// we basically use each single bit of the seed
// to generate an unique IP range
host := 0b10101100000100000000000000000000 // 172.16.0.0/12
// 20 bits are free: 16 are used for the seed, 1 for the network
// we can shift 1-4 as needed to minimize clashes (and could insert 3 static bits)
seed <<= 4
host |= seed
ns := host | 1
hostIP := make(net.IP, 4)
nsIP := make(net.IP, 4)
binary.BigEndian.PutUint32(hostIP, uint32(host))
binary.BigEndian.PutUint32(nsIP, uint32(ns))
for _, network := range hostNetworks {
if network.Contains(hostIP) {
return nil, ErrIPClash
}
}
topology := make([]string, 3)
topology[0] = fmt.Sprintf("%s|%s", fmt.Sprintf("kola-%d%d%d", nsIP[1], nsIP[2], nsIP[3]), fmt.Sprintf("%s/31", nsIP.String()))
topology[1] = fmt.Sprintf("%s|%s", fmt.Sprintf("kola-%d%d%d", hostIP[1], hostIP[2], hostIP[3]), fmt.Sprintf("%s/31", hostIP.String()))
topology[2] = fmt.Sprintf("%s/32", hostIP.String())
return topology, nil
}
// setupLink creates a new network device, assigns it
// an address and finally set it up
func setupLink(l netlink.Link, addr string, add bool) error {
if add {
if err := netlink.LinkAdd(l); err != nil {
return fmt.Errorf("unable to add link: %w", err)
}
}
ad, err := netlink.ParseAddr(addr)
if err != nil {
return fmt.Errorf("unable to parse addr: %w", err)
}
if err := netlink.AddrAdd(l, ad); err != nil {
return fmt.Errorf("unable to add address: %w", err)
}
if err := netlink.LinkSetUp(l); err != nil {
return fmt.Errorf("unable to set link up: %w", err)
}
return nil
}
func newSegment(s byte) (*Segment, error) {
seg := &Segment{
BridgeName: fmt.Sprintf("br%d", s),
BridgeIf: newInterface(s, 1),
}
for i := uint16(2); i < 2+numInterfaces; i++ {
seg.Interfaces = append(seg.Interfaces, newInterface(s, i))
}
br := netlink.Bridge{
LinkAttrs: netlink.LinkAttrs{
Name: seg.BridgeName,
HardwareAddr: seg.BridgeIf.HardwareAddr,
},
}
if err := netlink.LinkAdd(&br); err != nil {
return nil, fmt.Errorf("LinkAdd() failed: %v", err)
}
for _, addr := range seg.BridgeIf.DHCPv4 {
nladdr := netlink.Addr{IPNet: &addr}
if err := netlink.AddrAdd(&br, &nladdr); err != nil {
return nil, fmt.Errorf("DHCPv4 AddrAdd() failed: %v", err)
}
}
for _, addr := range seg.BridgeIf.DHCPv6 {
nladdr := netlink.Addr{IPNet: &addr}
if err := netlink.AddrAdd(&br, &nladdr); err != nil {
return nil, fmt.Errorf("DHCPv6 AddrAdd() failed: %v", err)
}
}
if err := netlink.LinkSetUp(&br); err != nil {
return nil, fmt.Errorf("LinkSetUp() failed: %v", err)
}
// we first create an unique virtual ethernet pair in the root network namespace
// we use linux network random port attribution to assert the uniqueness of the IP range in order to avoid IP
// range clashes
root, err := netns.GetFromPid(1)
if err != nil {
return nil, fmt.Errorf("unable to get NS from PID 1: %w", err)
}
rootExit, err := ns.Enter(root)
if err != nil {
return nil, fmt.Errorf("unable to enter root namespace: %w", err)
}
var (
listener net.Listener
// isValid indicates whether or not the generated IP
// is valid - meaning no conflict with existing
// IP network
isValid bool
pair []string
)
for !isValid {
listener, err = net.Listen("tcp", ":0")
if err != nil {
return nil, fmt.Errorf("unable to listen on random port: %w", err)
}
_, port, err := net.SplitHostPort(listener.Addr().String())
if err != nil {
return nil, fmt.Errorf("unable to split address: %w", err)
}
p, err := strconv.Atoi(port)
if err != nil {
return nil, fmt.Errorf("unable to convert port to int: %w", err)
}
ips := make([]*net.IPNet, 0)
links, err := netlink.LinkList()
if err != nil {
return nil, fmt.Errorf("unable to fetch network link list: %w", err)
}
for _, link := range links {
addresses, err := netlink.AddrList(link, netlink.FAMILY_V4)
if err != nil {
return nil, fmt.Errorf("unable to list addresses for device: %w", err)
}
for _, address := range addresses {
ips = append(ips, address.IPNet)
}
}
pair, err = generateVethPair(p, ips)
if err != nil {
if errors.Is(err, ErrIPClash) {
isValid = false
plog.Debugf("failed to use port %d as unique seed for the veth pair due to address clash, retrying", p)
if err := listener.Close(); err != nil {
return nil, fmt.Errorf("unable to close TCP listener: %w", err)
}
continue
} else {
return nil, fmt.Errorf("unable to generate veth pair: %w", err)
}
}
isValid = true
}
if err := rootExit(); err != nil {
return nil, fmt.Errorf("unable to exit root namespace: %w", err)
}
// keep the created listener for destroying later
seg.Listener = listener
peer0 := strings.Split(pair[0], "|")
peer1 := strings.Split(pair[1], "|")
attr := netlink.NewLinkAttrs()
attr.Name = peer0[0]
veth := &netlink.Veth{
PeerName: peer1[0],
LinkAttrs: attr,
}
if err := setupLink(veth, peer0[1], true); err != nil {
return nil, fmt.Errorf("unable to set up link: %w", err)
}
peer, err := netlink.LinkByName(peer1[0])
if err != nil {
return nil, fmt.Errorf("unable to get link by name: %w", err)
}
// move to root network namespace
if err := netlink.LinkSetNsPid(peer, 1); err != nil {
return nil, fmt.Errorf("unable to set link into a new ns: %w\n", err)
}
gtw, _, err := net.ParseCIDR(pair[2])
if err != nil {
return nil, fmt.Errorf("unable to parse CIDR address: %w", err)
}
_, dst, err := net.ParseCIDR("0.0.0.0/0")
if err != nil {
return nil, fmt.Errorf("unable to parse CIDR address: %w", err)
}
if err := netlink.RouteAdd(&netlink.Route{
Scope: netlink.SCOPE_UNIVERSE,
Dst: dst,
LinkIndex: veth.Attrs().Index,
Gw: gtw,
}); err != nil {
return nil, fmt.Errorf("unable to add default route: %w", err)
}
if err := configureNAT(peer0[0]); err != nil {
return nil, fmt.Errorf("unable to configure NAT: %w", err)
}
root, err = netns.GetFromPid(1)
if err != nil {
return nil, fmt.Errorf("unable to get NS from PID 1: %w", err)
}
rootExit, err = ns.Enter(root)
if err != nil {
return nil, fmt.Errorf("unable to enter root namespace: %w", err)
}
peer, err = netlink.LinkByName(peer1[0])
if err != nil {
return nil, fmt.Errorf("unable to get link by name: %w", err)
}
if err := setupLink(peer, peer1[1], false); err != nil {
return nil, fmt.Errorf("unable to set up link: %w", err)
}
// `ip route get 1.0.0.0` in order to get device to configure NAT on
d := net.IPv4(1, 0, 0, 0)
routes, err := netlink.RouteGet(d)
if err != nil {
return nil, fmt.Errorf("unable to get routes: %w", err)
}
if len(routes) < 0 {
return nil, fmt.Errorf("at least one default route is required")
}
route := routes[0]
l, err := netlink.LinkByIndex(route.LinkIndex)
if err != nil {
return nil, fmt.Errorf("unable to get link by index: %w", err)
}
if err := configureNAT(l.Attrs().Name); err != nil {
return nil, fmt.Errorf("unable to configure NAT: %w", err)
}
if err := rootExit(); err != nil {
return nil, fmt.Errorf("unable to exit root namespace: %w", err)
}
return seg, nil
}
func NewDnsmasq() (*Dnsmasq, error) {
dm := &Dnsmasq{}
for s := byte(0); s < numSegments; s++ {
seg, err := newSegment(s)
if err != nil {
return nil, fmt.Errorf("Network setup failed: %v", err)
}
dm.Segments = append(dm.Segments, seg)
}
// setup lo
lo, err := netlink.LinkByName("lo")
if err != nil {
return nil, fmt.Errorf("Network loopback setup failed: %v", err)
}
err = netlink.LinkSetUp(lo)
if err != nil {
return nil, fmt.Errorf("Network loopback setup failed: %v", err)
}
dm.dnsmasq = exec.Command("dnsmasq", "--conf-file=-")
cfg, err := dm.dnsmasq.StdinPipe()
if err != nil {
return nil, err
}
out, err := dm.dnsmasq.StdoutPipe()
if err != nil {
return nil, err
}
dm.dnsmasq.Stderr = dm.dnsmasq.Stdout
go util.LogFrom(capnslog.INFO, out)
if err = dm.dnsmasq.Start(); err != nil {
cfg.Close()
return nil, err
}
plog.Debugf("dnsmasq PID (manual cleanup needed if --remove=false): %v", dm.dnsmasq.Pid())
var configTemplate *template.Template
if plog.LevelAt(capnslog.DEBUG) {
configTemplate = template.Must(
template.New("dnsmasq").Parse(debugConfig + commonConfig))
} else {
configTemplate = template.Must(
template.New("dnsmasq").Parse(quietConfig + commonConfig))
}
if err = configTemplate.Execute(cfg, dm); err != nil {
cfg.Close()
dm.Destroy()
return nil, err
}
cfg.Close()
return dm, nil
}
func (dm *Dnsmasq) GetInterface(bridge string) (in *Interface) {
for _, seg := range dm.Segments {
if bridge == seg.BridgeName {
if seg.nextIf >= len(seg.Interfaces) {
panic("Not enough interfaces!")
}
in = seg.Interfaces[seg.nextIf]
seg.nextIf++
return
}
}
panic("Not a valid bridge!")
}
func (dm *Dnsmasq) Destroy() {
if err := dm.dnsmasq.Kill(); err != nil {
plog.Errorf("Error killing dnsmasq: %v", err)
}
for _, seg := range dm.Segments {
if err := seg.Listener.Close(); err != nil {
plog.Errorf("unable to close segment listener: %v", err)
}
}
}