mirror of
https://github.com/coredhcp/coredhcp.git
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15f169d55b
When the broadcast bit isn't set in the request, send responses to the L3 address we're assigning, using the peer L2 address, as that's the preferred behavior according to the RFC Signed-off-by: Daniel Zainzinger <dza1@mailbox.org> Co-authored-by: Daniel Zainzinger <dza1@mailbox.org>
97 lines
2.6 KiB
Go
97 lines
2.6 KiB
Go
// Copyright 2018-present the CoreDHCP Authors. All rights reserved
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// This source code is licensed under the MIT license found in the
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// LICENSE file in the root directory of this source tree.
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// +build linux
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package server
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import (
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"fmt"
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"net"
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"syscall"
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"github.com/google/gopacket"
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"github.com/google/gopacket/layers"
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"github.com/insomniacslk/dhcp/dhcpv4"
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)
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//this function sends an unicast to the hardware address defined in resp.ClientHWAddr,
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//the layer3 destination address is still the broadcast address;
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//iface: the interface where the DHCP message should be sent;
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//resp: DHCPv4 struct, which should be sent;
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func sendEthernet(iface net.Interface, resp *dhcpv4.DHCPv4) error {
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eth := layers.Ethernet{
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EthernetType: layers.EthernetTypeIPv4,
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SrcMAC: iface.HardwareAddr,
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DstMAC: resp.ClientHWAddr,
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}
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ip := layers.IPv4{
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Version: 4,
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TTL: 64,
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SrcIP: resp.ServerIPAddr,
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DstIP: resp.YourIPAddr,
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Protocol: layers.IPProtocolUDP,
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Flags: layers.IPv4DontFragment,
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}
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udp := layers.UDP{
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SrcPort: dhcpv4.ServerPort,
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DstPort: dhcpv4.ClientPort,
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}
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err := udp.SetNetworkLayerForChecksum(&ip)
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if err != nil {
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return fmt.Errorf("Send Ethernet: Couldn't set network layer: %v", err)
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}
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buf := gopacket.NewSerializeBuffer()
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opts := gopacket.SerializeOptions{
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ComputeChecksums: true,
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FixLengths: true,
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}
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// Decode a packet
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packet := gopacket.NewPacket(resp.ToBytes(), layers.LayerTypeDHCPv4, gopacket.NoCopy)
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dhcpLayer := packet.Layer(layers.LayerTypeDHCPv4)
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dhcp, ok := dhcpLayer.(gopacket.SerializableLayer)
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if !ok {
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return fmt.Errorf("Layer %s is not serializable", dhcpLayer.LayerType().String())
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}
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err = gopacket.SerializeLayers(buf, opts, ð, &ip, &udp, dhcp)
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if err != nil {
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return fmt.Errorf("Cannot serialize layer: %v", err)
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}
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data := buf.Bytes()
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fd, err := syscall.Socket(syscall.AF_PACKET, syscall.SOCK_RAW, 0)
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if err != nil {
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return fmt.Errorf("Send Ethernet: Cannot open socket: %v", err)
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}
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defer func() {
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err = syscall.Close(fd)
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if err != nil {
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log.Errorf("Send Ethernet: Cannot close socket: %v", err)
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}
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}()
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err = syscall.SetsockoptInt(fd, syscall.SOL_SOCKET, syscall.SO_REUSEADDR, 1)
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if err != nil {
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log.Errorf("Send Ethernet: Cannot set option for socket: %v", err)
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}
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var hwAddr [8]byte
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copy(hwAddr[0:6], resp.ClientHWAddr[0:6])
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ethAddr := syscall.SockaddrLinklayer{
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Protocol: 0,
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Ifindex: iface.Index,
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Halen: 6,
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Addr: hwAddr, //not used
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}
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err = syscall.Sendto(fd, data, 0, ðAddr)
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if err != nil {
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return fmt.Errorf("Cannot send frame via socket: %v", err)
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}
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return nil
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}
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