6127f9566e
E.g. /etc/kresd/dhcp_host_domain_ng.sh on a turris omnia incorrectly deletes DHCP hostname mappings when more than one client does not send a client id.
275 lines
6.8 KiB
Go
275 lines
6.8 KiB
Go
// Only build for (linux AND (amd64 OR arm64)) due to using
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// linux-specific syscalls with uint64 for “unsigned long”:
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// +build linux
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// +build amd64 arm64
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// dhcp is a minimal DHCP client for gokrazy.
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package main
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import (
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"encoding/binary"
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"fmt"
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"io/ioutil"
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"log"
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"net"
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"os"
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"strings"
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"syscall"
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"time"
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"golang.org/x/sys/unix"
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"github.com/d2g/dhcp4"
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"github.com/d2g/dhcp4client"
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"github.com/gokrazy/gokrazy/internal/iface"
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)
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func parseDHCPDuration(b []byte) time.Duration {
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return time.Duration(binary.BigEndian.Uint32(b)) * time.Second
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}
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var (
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defaultDst = net.IP([]byte{0, 0, 0, 0})
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defaultNetmask = net.IPMask([]byte{0, 0, 0, 0})
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hardwareAddr net.HardwareAddr
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)
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func addHostname(p *dhcp4.Packet) {
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var utsname unix.Utsname
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if err := unix.Uname(&utsname); err != nil {
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log.Fatal(err)
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}
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nnb := make([]byte, 0, len(utsname.Nodename))
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for _, i := range utsname.Nodename {
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if i == 0 {
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break
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}
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nnb = append(nnb, byte(i))
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}
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p.AddOption(dhcp4.OptionHostName, nnb)
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}
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func addClientId(p *dhcp4.Packet) {
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id := make([]byte, len(hardwareAddr)+1)
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id[0] = 1 // hardware type ethernet, https://tools.ietf.org/html/rfc1700
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copy(id[1:], hardwareAddr)
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p.AddOption(dhcp4.OptionClientIdentifier, id)
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}
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// dhcpRequest is a copy of (dhcp4client/Client).Request which
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// includes the hostname.
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func dhcpRequest(c *dhcp4client.Client) (bool, dhcp4.Packet, error) {
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discoveryPacket := c.DiscoverPacket()
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addHostname(&discoveryPacket)
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addClientId(&discoveryPacket)
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discoveryPacket.PadToMinSize()
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if err := c.SendPacket(discoveryPacket); err != nil {
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return false, discoveryPacket, err
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}
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offerPacket, err := c.GetOffer(&discoveryPacket)
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if err != nil {
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return false, offerPacket, err
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}
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requestPacket := c.RequestPacket(&offerPacket)
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addHostname(&requestPacket)
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addClientId(&requestPacket)
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requestPacket.PadToMinSize()
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if err := c.SendPacket(requestPacket); err != nil {
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return false, requestPacket, err
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}
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acknowledgement, err := c.GetAcknowledgement(&requestPacket)
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if err != nil {
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return false, acknowledgement, err
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}
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acknowledgementOptions := acknowledgement.ParseOptions()
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if dhcp4.MessageType(acknowledgementOptions[dhcp4.OptionDHCPMessageType][0]) != dhcp4.ACK {
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return false, acknowledgement, nil
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}
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return true, acknowledgement, nil
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}
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// dhcpRenew is a copy of (dhcp4client/Client).Renew which
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// includes the hostname.
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func dhcpRenew(c *dhcp4client.Client, packet dhcp4.Packet) (bool, dhcp4.Packet, error) {
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addHostname(&packet)
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addClientId(&packet)
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packet.PadToMinSize()
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if err := c.SendPacket(packet); err != nil {
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return false, packet, err
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}
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acknowledgement, err := c.GetAcknowledgement(&packet)
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if err != nil {
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return false, acknowledgement, err
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}
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acknowledgementOptions := acknowledgement.ParseOptions()
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if dhcp4.MessageType(acknowledgementOptions[dhcp4.OptionDHCPMessageType][0]) != dhcp4.ACK {
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return false, acknowledgement, nil
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}
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return true, acknowledgement, nil
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}
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func main() {
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log.SetFlags(log.LstdFlags | log.Lshortfile)
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eth0, err := net.InterfaceByName("eth0")
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if err != nil {
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log.Fatal(err)
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}
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cs, err := iface.NewConfigSocket("eth0")
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if err != nil {
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log.Fatalf("config socket: %v", err)
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}
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defer cs.Close()
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// Ensure the interface is up so that we can send DHCP packets.
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if err := cs.Up(); err != nil {
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log.Fatal(err)
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}
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// Wait for up to 10 seconds for the link to indicate it has a
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// carrier.
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for i := 0; i < 10; i++ {
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b, err := ioutil.ReadFile("/sys/class/net/eth0/carrier")
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if err == nil && strings.TrimSpace(string(b)) == "1" {
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break
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}
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time.Sleep(1 * time.Second)
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}
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hardwareAddr = eth0.HardwareAddr
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pktsock, err := dhcp4client.NewPacketSock(eth0.Index)
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if err != nil {
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log.Fatal(err)
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}
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dhcp, err := dhcp4client.New(
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dhcp4client.HardwareAddr(eth0.HardwareAddr),
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dhcp4client.Timeout(5*time.Second),
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dhcp4client.Broadcast(false),
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dhcp4client.Connection(pktsock),
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)
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if err != nil {
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log.Fatal(err)
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}
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ok, ack, err := dhcpRequest(dhcp)
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for {
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if err != nil {
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log.Fatal(err)
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}
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if !ok {
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log.Fatal("received DHCPNAK")
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}
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opts := ack.ParseOptions()
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// DHCPACK (described in RFC2131 4.3.1)
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// - yiaddr: IP address assigned to client
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details := []string{
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fmt.Sprintf("IP %v", ack.YIAddr()),
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}
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if b, ok := opts[dhcp4.OptionSubnetMask]; ok {
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ipnet := net.IPNet{
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IP: ack.YIAddr(),
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Mask: net.IPMask(b),
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}
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details[0] = fmt.Sprintf("IP %v", ipnet.String())
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}
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if b, ok := opts[dhcp4.OptionBroadcastAddress]; ok {
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details = append(details, fmt.Sprintf("broadcast %v", net.IP(b)))
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}
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if b, ok := opts[dhcp4.OptionRouter]; ok {
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details = append(details, fmt.Sprintf("router %v", net.IP(b)))
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}
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if b, ok := opts[dhcp4.OptionDomainNameServer]; ok {
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details = append(details, fmt.Sprintf("DNS %v", net.IP(b)))
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}
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log.Printf("DHCPACK: %v", strings.Join(details, ", "))
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if err := cs.SetAddress(ack.YIAddr()); err != nil {
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log.Fatal(err)
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}
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if b, ok := opts[dhcp4.OptionSubnetMask]; ok {
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if err := cs.SetNetmask(net.IPMask(b)); err != nil {
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log.Fatalf("setNetmask(%v): %v", net.IPMask(b), err)
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}
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}
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if b, ok := opts[dhcp4.OptionBroadcastAddress]; ok {
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if err := cs.SetBroadcast(net.IP(b)); err != nil {
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log.Fatalf("setBroadcast(%v): %v", net.IP(b), err)
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}
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}
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if err := cs.Up(); err != nil {
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log.Fatal(err)
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}
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if b, ok := opts[dhcp4.OptionRouter]; ok {
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if errno := cs.AddRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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if errno == syscall.EEXIST {
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if errno := cs.DelRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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log.Printf("delRoute(%v): %v", net.IP(b), errno)
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}
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if errno := cs.AddRoute(defaultDst, net.IP(b), defaultNetmask); errno != 0 {
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log.Fatalf("addRoute(%v): %v", net.IP(b), errno)
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}
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} else {
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log.Fatalf("addRoute(%v): %v", net.IP(b), errno)
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}
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}
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}
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if b, ok := opts[dhcp4.OptionDomainNameServer]; ok {
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// Get the symlink out of the way, if any.
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if err := os.Remove("/etc/resolv.conf"); err != nil && !os.IsNotExist(err) {
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log.Fatalf("resolv.conf: %v", err)
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}
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if err := ioutil.WriteFile("/etc/resolv.conf", []byte(fmt.Sprintf("nameserver %v\n", net.IP(b))), 0644); err != nil {
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log.Fatalf("resolv.conf: %v", err)
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}
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}
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// Notify init of new addresses
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p, _ := os.FindProcess(1)
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if err := p.Signal(syscall.SIGHUP); err != nil {
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log.Printf("send SIGHUP to init: %v", err)
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}
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leaseTime := 10 * time.Minute // seems sensible as a fallback
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if b, ok := opts[dhcp4.OptionIPAddressLeaseTime]; ok && len(b) == 4 {
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leaseTime = parseDHCPDuration(b)
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}
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// As per RFC 2131 section 4.4.5:
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// renewal time defaults to 50% of the lease time
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renewalTime := time.Duration(float64(leaseTime) * 0.5)
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if b, ok := opts[dhcp4.OptionRenewalTimeValue]; ok && len(b) == 4 {
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renewalTime = parseDHCPDuration(b)
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}
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time.Sleep(renewalTime)
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ok, ack, err = dhcpRenew(dhcp, dhcp.RenewalRequestPacket(&ack))
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}
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}
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