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// Copyright 2018 the u-root Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build go1.12 && (darwin || freebsd || linux || netbsd || openbsd)
// +build go1.12
// +build darwin freebsd linux netbsd openbsd
package nclient4
import (
"errors"
"io"
"net"
"github.com/mdlayher/ethernet"
"github.com/mdlayher/raw"
"github.com/u-root/uio/uio"
)
var (
// BroadcastMac is the broadcast MAC address.
//
// Any UDP packet sent to this address is broadcast on the subnet.
BroadcastMac = net.HardwareAddr([]byte{255, 255, 255, 255, 255, 255})
)
var (
// ErrUDPAddrIsRequired is an error used when a passed argument is not of type "*net.UDPAddr".
ErrUDPAddrIsRequired = errors.New("must supply UDPAddr")
)
// NewRawUDPConn returns a UDP connection bound to the interface and port
// given based on a raw packet socket. All packets are broadcasted.
//
// The interface can be completely unconfigured.
func NewRawUDPConn(iface string, port int) (net.PacketConn, error) {
ifc, err := net.InterfaceByName(iface)
if err != nil {
return nil, err
}
rawConn, err := raw.ListenPacket(ifc, uint16(ethernet.EtherTypeIPv4), &raw.Config{LinuxSockDGRAM: true})
if err != nil {
return nil, err
}
return NewBroadcastUDPConn(rawConn, &net.UDPAddr{Port: port}), nil
}
// BroadcastRawUDPConn uses a raw socket to send UDP packets to the broadcast
// MAC address.
type BroadcastRawUDPConn struct {
// PacketConn is a raw DGRAM socket.
net.PacketConn
// boundAddr is the address this RawUDPConn is "bound" to.
//
// Calls to ReadFrom will only return packets destined to this address.
boundAddr *net.UDPAddr
}
// NewBroadcastUDPConn returns a PacketConn that marshals and unmarshals UDP
// packets, sending them to the broadcast MAC at on rawPacketConn.
//
// Calls to ReadFrom will only return packets destined to boundAddr.
func NewBroadcastUDPConn(rawPacketConn net.PacketConn, boundAddr *net.UDPAddr) net.PacketConn {
return &BroadcastRawUDPConn{
PacketConn: rawPacketConn,
boundAddr: boundAddr,
}
}
func udpMatch(addr *net.UDPAddr, bound *net.UDPAddr) bool {
if bound == nil {
return true
}
if bound.IP != nil && !bound.IP.Equal(addr.IP) {
return false
}
return bound.Port == addr.Port
}
// ReadFrom implements net.PacketConn.ReadFrom.
//
// ReadFrom reads raw IP packets and will try to match them against
// upc.boundAddr. Any matching packets are returned via the given buffer.
func (upc *BroadcastRawUDPConn) ReadFrom(b []byte) (int, net.Addr, error) {
ipHdrMaxLen := ipv4MaximumHeaderSize
udpHdrLen := udpMinimumSize
for {
pkt := make([]byte, ipHdrMaxLen+udpHdrLen+len(b))
n, _, err := upc.PacketConn.ReadFrom(pkt)
if err != nil {
return 0, nil, err
}
if n == 0 {
return 0, nil, io.EOF
}
pkt = pkt[:n]
buf := uio.NewBigEndianBuffer(pkt)
// To read the header length, access data directly.
if !buf.Has(ipv4MinimumSize) {
continue
}
ipHdr := ipv4(buf.Data())
if !buf.Has(int(ipHdr.headerLength())) {
continue
}
ipHdr = ipv4(buf.Consume(int(ipHdr.headerLength())))
if ipHdr.transportProtocol() != udpProtocolNumber {
continue
}
if !buf.Has(udpHdrLen) {
continue
}
udpHdr := udp(buf.Consume(udpHdrLen))
addr := &net.UDPAddr{
IP: ipHdr.destinationAddress(),
Port: int(udpHdr.destinationPort()),
}
if !udpMatch(addr, upc.boundAddr) {
continue
}
srcAddr := &net.UDPAddr{
IP: ipHdr.sourceAddress(),
Port: int(udpHdr.sourcePort()),
}
// Extra padding after end of IP packet should be ignored,
// if not dhcp option parsing will fail.
dhcpLen := int(ipHdr.payloadLength()) - udpHdrLen
return copy(b, buf.Consume(dhcpLen)), srcAddr, nil
}
}
// WriteTo implements net.PacketConn.WriteTo and broadcasts all packets at the
// raw socket level.
//
// WriteTo wraps the given packet in the appropriate UDP and IP header before
// sending it on the packet conn.
func (upc *BroadcastRawUDPConn) WriteTo(b []byte, addr net.Addr) (int, error) {
udpAddr, ok := addr.(*net.UDPAddr)
if !ok {
return 0, ErrUDPAddrIsRequired
}
// Using the boundAddr is not quite right here, but it works.
packet := udp4pkt(b, udpAddr, upc.boundAddr)
// Broadcasting is not always right, but hell, what the ARP do I know.
return upc.PacketConn.WriteTo(packet, &raw.Addr{HardwareAddr: BroadcastMac})
}
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