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Implement NTP server from DHCP

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This commit is contained in:
lordwelch 2020-08-22 10:36:12 -07:00
parent f60299f3ca
commit 69200acf90
6 changed files with 152 additions and 4 deletions
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44
cmd/dhcp/dhcp.go
View File

@ -9,6 +9,7 @@ package main
import (
"bytes"
"encoding/json"
"flag"
"fmt"
"io/ioutil"
@ -20,8 +21,11 @@ import (
"syscall"
"time"
"internal/notify"
"github.com/gokrazy/gokrazy/internal/iface"
"github.com/google/gopacket/layers"
"github.com/google/renameio"
"github.com/mdlayher/raw"
"github.com/rtr7/dhcp4"
"golang.org/x/sys/unix"
@ -64,7 +68,9 @@ func (c *client) discover() (*layers.DHCPv4, error) {
layers.DHCPOptDNS,
layers.DHCPOptRouter,
layers.DHCPOptSubnetMask,
layers.DHCPOptDomainName),
layers.DHCPOptDomainName,
layers.DHCPOptNTPServers,
),
})
if err := dhcp4.Write(c.conn, discover); err != nil {
return nil, err
@ -101,7 +107,9 @@ func (c *client) request(last *layers.DHCPv4) (*layers.DHCPv4, error) {
layers.DHCPOptDNS,
layers.DHCPOptRouter,
layers.DHCPOptSubnetMask,
layers.DHCPOptDomainName),
layers.DHCPOptDomainName,
layers.DHCPOptNTPServers,
),
}, dhcp4.ServerID(last.Options)...))
if err := dhcp4.Write(c.conn, request); err != nil {
return nil, err
@ -127,6 +135,11 @@ func (c *client) request(last *layers.DHCPv4) (*layers.DHCPv4, error) {
}
}
var permDir = flag.String(
"perm",
"/perm",
"path to replace /perm")
func main() {
log.SetFlags(log.LstdFlags | log.Lshortfile)
var (
@ -137,6 +150,10 @@ func main() {
)
flag.Parse()
if err := os.MkdirAll(filepath.Join(*permDir, "dhcp4"), 0755); err != nil {
log.Println(err)
}
// NOTE: cannot gokrazy.WaitForClock() here, since the clock can only be
// initialized once the network is up.
@ -197,6 +214,7 @@ func main() {
}
lease := dhcp4.LeaseFromACK(last)
saveLease(lease)
// Log the received DHCPACK packet:
details := []string{
@ -218,6 +236,9 @@ func main() {
if len(lease.Broadcast) > 0 {
details = append(details, fmt.Sprintf("broadcast %v", lease.Broadcast))
}
if len(lease.NTP) > 0 {
details = append(details, fmt.Sprintf("NTP %v", lease.NTP))
}
log.Printf("DHCPACK: %v", strings.Join(details, ", "))
@ -286,3 +307,22 @@ func main() {
time.Sleep(lease.RenewalTime)
}
}
func saveLease(lease dhcp4.Lease) {
b, err := json.Marshal(lease)
if err != nil {
log.Println(err)
return
}
var out bytes.Buffer
if err := json.Indent(&out, b, "", "\t"); err == nil {
b = out.Bytes()
}
if err := renameio.WriteFile(filepath.Join(*permDir, "dhcp4/lease.json"), b, 0644); err != nil {
log.Println(err)
return
}
if err := notify.Process(filepath.Join(filepath.Dir(os.Args[0]), "/ntp"), syscall.SIGUSR1); err != nil {
log.Printf("notifying ntp: %v", err)
}
}

43
cmd/ntp/ntp.go
View File

@ -2,17 +2,28 @@
package main
import (
"encoding/json"
"flag"
"io/ioutil"
"log"
"math/rand"
"net"
"os"
"os/signal"
"path/filepath"
"syscall"
"time"
"github.com/beevik/ntp"
"github.com/rtr7/dhcp4"
)
var server = "0.gokrazy.pool.ntp.org"
var permDir = flag.String("perm", "/perm", "path to replace /perm")
func set(rtc *os.File) error {
r, err := ntp.Query("0.gokrazy.pool.ntp.org")
r, err := ntp.Query(server)
if err != nil {
return err
}
@ -21,7 +32,7 @@ func set(rtc *os.File) error {
if err := syscall.Settimeofday(&tv); err != nil {
return err
}
log.Printf("clock set to %v", r.Time)
log.Printf("clock set to %v using %v", r.Time, server)
if rtc == nil {
return nil
@ -30,6 +41,7 @@ func set(rtc *os.File) error {
}
func main() {
flag.Parse()
log.SetFlags(log.LstdFlags | log.Lshortfile)
var rtc *os.File
@ -47,6 +59,15 @@ func main() {
mustDropPrivileges(rtc)
go func() {
ch := make(chan os.Signal, 1)
signal.Notify(ch, syscall.SIGUSR1)
for range ch {
loadNTPServer()
}
}()
loadNTPServer()
for {
if err := set(rtc); err != nil {
log.Fatalf("setting time failed: %v", err)
@ -54,3 +75,21 @@ func main() {
time.Sleep(1*time.Hour + time.Duration(rand.Int63n(250))*time.Millisecond)
}
}
func loadNTPServer() {
var lease dhcp4.Lease
file, err := ioutil.ReadFile(filepath.Join(*permDir, "dhcp4/lease.json"))
if err != nil {
log.Println(err)
return
}
err = json.Unmarshal(file, &lease)
if err != nil {
log.Println(err)
return
}
if len(lease.DNS) > 0 && !lease.DNS[0].To4().Equal(net.IPv4zero) {
server = lease.DNS[0].String()
log.Printf("Setting ntp server to: %s", server)
}
}

10
cmd/ntp/privdrop.go
View File

@ -7,6 +7,7 @@ import (
"log"
"os"
"os/exec"
"os/signal"
"syscall"
"unsafe"
)
@ -84,5 +85,14 @@ func mustDropPrivileges(rtc *os.File) {
},
AmbientCaps: []uintptr{CAP_SYS_TIME},
}
go func() {
ch := make(chan os.Signal, 1)
signal.Notify(ch)
for sig := range ch {
cmd.Process.Signal(sig)
}
}()
log.Fatal(cmd.Run())
}

1
go.mod
View File

@ -7,6 +7,7 @@ require (
github.com/gokrazy/internal v0.0.0-20200531194636-d96421c60091
github.com/google/go-cmp v0.4.0 // indirect
github.com/google/gopacket v1.1.16
github.com/google/renameio v0.1.0
github.com/mdlayher/raw v0.0.0-20190303161257-764d452d77af
github.com/mdlayher/watchdog v0.0.0-20201005150459-8bdc4f41966b
github.com/rtr7/dhcp4 v0.0.0-20181120124042-778e8c2e24a5

2
go.sum
View File

@ -8,6 +8,8 @@ github.com/google/go-cmp v0.4.0 h1:xsAVV57WRhGj6kEIi8ReJzQlHHqcBYCElAvkovg3B/4=
github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/google/gopacket v1.1.16 h1:u6Afvia5C5srlLcbTwpHaFW918asLYPxieziOaWwz8M=
github.com/google/gopacket v1.1.16/go.mod h1:UCLx9mCmAwsVbn6qQl1WIEt2SO7Nd2fD0th1TBAsqBw=
github.com/google/renameio v0.1.0 h1:GOZbcHa3HfsPKPlmyPyN2KEohoMXOhdMbHrvbpl2QaA=
github.com/google/renameio v0.1.0/go.mod h1:KWCgfxg9yswjAJkECMjeO8J8rahYeXnNhOm40UhjYkI=
github.com/mdlayher/raw v0.0.0-20190303161257-764d452d77af h1:20h/EjkLGn9mV5nX9MFnGhbbeEhIGnOKPShJfBtVkVQ=
github.com/mdlayher/raw v0.0.0-20190303161257-764d452d77af/go.mod h1:rC/yE65s/DoHB6BzVOUBNYBGTg772JVytyAytffIZkY=
github.com/mdlayher/watchdog v0.0.0-20201005150459-8bdc4f41966b h1:7tUBfsEEBWfFeHOB7CUfoOamak+Gx/BlirfXyPk1WjI=

56
internal/notify/notify.go Normal file
View File

@ -0,0 +1,56 @@
// Copyright 2018 Google 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 notify implements sending signals (such as SIGUSR1) to processes.
package notify
import (
"io/ioutil"
"os"
"path/filepath"
"regexp"
"strconv"
"strings"
)
var numericRe = regexp.MustCompile(`^[0-9]+$`)
func Process(name string, sig os.Signal) error {
fis, err := ioutil.ReadDir("/proc")
if err != nil {
return err
}
for _, fi := range fis {
if !fi.IsDir() {
continue
}
if !numericRe.MatchString(fi.Name()) {
continue
}
b, err := ioutil.ReadFile(filepath.Join("/proc", fi.Name(), "cmdline"))
if err != nil {
if os.IsNotExist(err) {
continue // process vanished
}
return err
}
if !strings.Contains(string(b), name) {
continue
}
pid, _ := strconv.Atoi(fi.Name()) // already verified to be numeric
p, _ := os.FindProcess(pid)
return p.Signal(sig)
}
return nil
}