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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.
// +build go1.12
package nclient4
import (
"fmt"
"io"
"net"
"os"
"github.com/insomniacslk/dhcp/dhcpv4"
"github.com/mdlayher/ethernet"
"github.com/mdlayher/raw"
"github.com/u-root/u-root/pkg/uio"
"golang.org/x/sys/unix"
)
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})
)
// NewIPv4UDPConn returns a UDP connection bound to both the interface and port
// given based on a IPv4 DGRAM socket. The UDP connection allows broadcasting.
//
// The interface must already be configured.
func NewIPv4UDPConn(iface string, port int) (net.PacketConn, error) {
fd, err := unix.Socket(unix.AF_INET, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
if err != nil {
return nil, fmt.Errorf("cannot get a UDP socket: %v", err)
}
f := os.NewFile(uintptr(fd), "")
// net.FilePacketConn dups the FD, so we have to close this in any case.
defer f.Close()
// Allow broadcasting.
if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_BROADCAST, 1); err != nil {
return nil, fmt.Errorf("cannot set broadcasting on socket: %v", err)
}
// Allow reusing the addr to aid debugging.
if err := unix.SetsockoptInt(fd, unix.SOL_SOCKET, unix.SO_REUSEADDR, 1); err != nil {
return nil, fmt.Errorf("cannot set reuseaddr on socket: %v", err)
}
if len(iface) != 0 {
// Bind directly to the interface.
if err := dhcpv4.BindToInterface(fd, iface); err != nil {
return nil, fmt.Errorf("cannot bind to interface %s: %v", iface, err)
}
}
// Bind to the port.
if err := unix.Bind(fd, &unix.SockaddrInet4{Port: port}); err != nil {
return nil, fmt.Errorf("cannot bind to port %d: %v", port, err)
}
return net.FilePacketConn(f)
}
// 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) {
ipLen := IPv4MaximumHeaderSize
udpLen := UDPMinimumSize
for {
pkt := make([]byte, ipLen+udpLen+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.
ipHdr := IPv4(buf.Data())
ipHdr = IPv4(buf.Consume(int(ipHdr.HeaderLength())))
if ipHdr.TransportProtocol() != UDPProtocolNumber {
continue
}
udpHdr := UDP(buf.Consume(udpLen))
addr := &net.UDPAddr{
IP: net.IP(ipHdr.DestinationAddress()),
Port: int(udpHdr.DestinationPort()),
}
if !udpMatch(addr, upc.boundAddr) {
continue
}
srcAddr := &net.UDPAddr{
IP: net.IP(ipHdr.SourceAddress()),
Port: int(udpHdr.SourcePort()),
}
return copy(b, buf.ReadAll()), 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, fmt.Errorf("must supply UDPAddr")
}
// 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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