1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
|
// 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 (
"errors"
"io"
"net"
"github.com/mdlayher/ethernet"
"github.com/mdlayher/raw"
"github.com/u-root/u-root/pkg/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.
ipHdr := IPv4(buf.Data())
ipHdr = IPv4(buf.Consume(int(ipHdr.HeaderLength())))
if ipHdr.TransportProtocol() != UDPProtocolNumber {
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})
}
|
