1 // Copyright 2018 The gVisor Authors.
2 //
3 // Licensed under the Apache License, Version 2.0 (the "License");
4 // you may not use this file except in compliance with the License.
5 // You may obtain a copy of the License at
6 //
7 // http://www.apache.org/licenses/LICENSE-2.0
8 //
9 // Unless required by applicable law or agreed to in writing, software
10 // distributed under the License is distributed on an "AS IS" BASIS,
11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12 // See the License for the specific language governing permissions and
13 // limitations under the License.
14 15 package header
16 17 import (
18 "encoding/binary"
19 20 "gvisor.dev/gvisor/pkg/tcpip"
21 )
22 23 const (
24 // ARPProtocolNumber is the ARP network protocol number.
25 ARPProtocolNumber tcpip.NetworkProtocolNumber = 0x0806
26 27 // ARPSize is the size of an IPv4-over-Ethernet ARP packet.
28 ARPSize = 28
29 )
30 31 // ARPHardwareType is the hardware type for LinkEndpoint in an ARP header.
32 type ARPHardwareType uint16
33 34 // Typical ARP HardwareType values. Some of the constants have to be specific
35 // values as they are egressed on the wire in the HTYPE field of an ARP header.
36 const (
37 ARPHardwareNone ARPHardwareType = 0
38 // ARPHardwareEther specifically is the HTYPE for Ethernet as specified
39 // in the IANA list here:
40 //
41 // https://www.iana.org/assignments/arp-parameters/arp-parameters.xhtml#arp-parameters-2
42 ARPHardwareEther ARPHardwareType = 1
43 ARPHardwareLoopback ARPHardwareType = 2
44 )
45 46 // ARPOp is an ARP opcode.
47 type ARPOp uint16
48 49 // Typical ARP opcodes defined in RFC 826.
50 const (
51 ARPRequest ARPOp = 1
52 ARPReply ARPOp = 2
53 )
54 55 // ARP is an ARP packet stored in a byte array as described in RFC 826.
56 type ARP []byte
57 58 const (
59 hTypeOffset = 0
60 protocolOffset = 2
61 haAddressSizeOffset = 4
62 protoAddressSizeOffset = 5
63 opCodeOffset = 6
64 senderHAAddressOffset = 8
65 senderProtocolAddressOffset = senderHAAddressOffset + EthernetAddressSize
66 targetHAAddressOffset = senderProtocolAddressOffset + IPv4AddressSize
67 targetProtocolAddressOffset = targetHAAddressOffset + EthernetAddressSize
68 )
69 70 func (a ARP) hardwareAddressType() ARPHardwareType {
71 return ARPHardwareType(binary.BigEndian.Uint16(a[hTypeOffset:]))
72 }
73 74 func (a ARP) protocolAddressSpace() uint16 { return binary.BigEndian.Uint16(a[protocolOffset:]) }
75 func (a ARP) hardwareAddressSize() int { return int(a[haAddressSizeOffset]) }
76 func (a ARP) protocolAddressSize() int { return int(a[protoAddressSizeOffset]) }
77 78 // Op is the ARP opcode.
79 func (a ARP) Op() ARPOp { return ARPOp(binary.BigEndian.Uint16(a[opCodeOffset:])) }
80 81 // SetOp sets the ARP opcode.
82 func (a ARP) SetOp(op ARPOp) {
83 binary.BigEndian.PutUint16(a[opCodeOffset:], uint16(op))
84 }
85 86 // SetIPv4OverEthernet configures the ARP packet for IPv4-over-Ethernet.
87 func (a ARP) SetIPv4OverEthernet() {
88 binary.BigEndian.PutUint16(a[hTypeOffset:], uint16(ARPHardwareEther))
89 binary.BigEndian.PutUint16(a[protocolOffset:], uint16(IPv4ProtocolNumber))
90 a[haAddressSizeOffset] = EthernetAddressSize
91 a[protoAddressSizeOffset] = uint8(IPv4AddressSize)
92 }
93 94 // HardwareAddressSender is the link address of the sender.
95 // It is a view on to the ARP packet so it can be used to set the value.
96 func (a ARP) HardwareAddressSender() []byte {
97 return a[senderHAAddressOffset : senderHAAddressOffset+EthernetAddressSize]
98 }
99 100 // ProtocolAddressSender is the protocol address of the sender.
101 // It is a view on to the ARP packet so it can be used to set the value.
102 func (a ARP) ProtocolAddressSender() []byte {
103 return a[senderProtocolAddressOffset : senderProtocolAddressOffset+IPv4AddressSize]
104 }
105 106 // HardwareAddressTarget is the link address of the target.
107 // It is a view on to the ARP packet so it can be used to set the value.
108 func (a ARP) HardwareAddressTarget() []byte {
109 return a[targetHAAddressOffset : targetHAAddressOffset+EthernetAddressSize]
110 }
111 112 // ProtocolAddressTarget is the protocol address of the target.
113 // It is a view on to the ARP packet so it can be used to set the value.
114 func (a ARP) ProtocolAddressTarget() []byte {
115 return a[targetProtocolAddressOffset : targetProtocolAddressOffset+IPv4AddressSize]
116 }
117 118 // IsValid reports whether this is an ARP packet for IPv4 over Ethernet.
119 func (a ARP) IsValid() bool {
120 if len(a) < ARPSize {
121 return false
122 }
123 return a.hardwareAddressType() == ARPHardwareEther &&
124 a.protocolAddressSpace() == uint16(IPv4ProtocolNumber) &&
125 a.hardwareAddressSize() == EthernetAddressSize &&
126 a.protocolAddressSize() == IPv4AddressSize
127 }
128