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 dstMAC = 0
25 srcMAC = 6
26 ethType = 12
27 )
28 29 // EthernetFields contains the fields of an ethernet frame header. It is used to
30 // describe the fields of a frame that needs to be encoded.
31 type EthernetFields struct {
32 // SrcAddr is the "MAC source" field of an ethernet frame header.
33 SrcAddr tcpip.LinkAddress
34 35 // DstAddr is the "MAC destination" field of an ethernet frame header.
36 DstAddr tcpip.LinkAddress
37 38 // Type is the "ethertype" field of an ethernet frame header.
39 Type tcpip.NetworkProtocolNumber
40 }
41 42 // Ethernet represents an ethernet frame header stored in a byte array.
43 type Ethernet []byte
44 45 const (
46 // EthernetMinimumSize is the minimum size of a valid ethernet frame.
47 EthernetMinimumSize = 14
48 49 // EthernetMaximumSize is the maximum size of a valid ethernet frame.
50 EthernetMaximumSize = 18
51 52 // EthernetAddressSize is the size, in bytes, of an ethernet address.
53 EthernetAddressSize = 6
54 55 // UnspecifiedEthernetAddress is the unspecified ethernet address
56 // (all bits set to 0).
57 UnspecifiedEthernetAddress = tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00")
58 59 // EthernetBroadcastAddress is an ethernet address that addresses every node
60 // on a local link.
61 EthernetBroadcastAddress = tcpip.LinkAddress("\xff\xff\xff\xff\xff\xff")
62 63 // unicastMulticastFlagMask is the mask of the least significant bit in
64 // the first octet (in network byte order) of an ethernet address that
65 // determines whether the ethernet address is a unicast or multicast. If
66 // the masked bit is a 1, then the address is a multicast, unicast
67 // otherwise.
68 //
69 // See the IEEE Std 802-2001 document for more details. Specifically,
70 // section 9.2.1 of http://ieee802.org/secmail/pdfocSP2xXA6d.pdf:
71 // "A 48-bit universal address consists of two parts. The first 24 bits
72 // correspond to the OUI as assigned by the IEEE, expect that the
73 // assignee may set the LSB of the first octet to 1 for group addresses
74 // or set it to 0 for individual addresses."
75 unicastMulticastFlagMask = 1
76 77 // unicastMulticastFlagByteIdx is the byte that holds the
78 // unicast/multicast flag. See unicastMulticastFlagMask.
79 unicastMulticastFlagByteIdx = 0
80 )
81 82 const (
83 // EthernetProtocolAll is a catch-all for all protocols carried inside
84 // an ethernet frame. It is mainly used to create packet sockets that
85 // capture all traffic.
86 EthernetProtocolAll tcpip.NetworkProtocolNumber = 0x0003
87 88 // EthernetProtocolPUP is the PARC Universal Packet protocol ethertype.
89 EthernetProtocolPUP tcpip.NetworkProtocolNumber = 0x0200
90 )
91 92 // Ethertypes holds the protocol numbers describing the payload of an ethernet
93 // frame. These types aren't necessarily supported by netstack, but can be used
94 // to catch all traffic of a type via packet endpoints.
95 var Ethertypes = []tcpip.NetworkProtocolNumber{
96 EthernetProtocolAll,
97 EthernetProtocolPUP,
98 }
99 100 // SourceAddress returns the "MAC source" field of the ethernet frame header.
101 func (b Ethernet) SourceAddress() tcpip.LinkAddress {
102 return tcpip.LinkAddress(b[srcMAC:][:EthernetAddressSize])
103 }
104 105 // DestinationAddress returns the "MAC destination" field of the ethernet frame
106 // header.
107 func (b Ethernet) DestinationAddress() tcpip.LinkAddress {
108 return tcpip.LinkAddress(b[dstMAC:][:EthernetAddressSize])
109 }
110 111 // Type returns the "ethertype" field of the ethernet frame header.
112 func (b Ethernet) Type() tcpip.NetworkProtocolNumber {
113 return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(b[ethType:]))
114 }
115 116 // Encode encodes all the fields of the ethernet frame header.
117 func (b Ethernet) Encode(e *EthernetFields) {
118 binary.BigEndian.PutUint16(b[ethType:], uint16(e.Type))
119 copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr)
120 copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr)
121 }
122 123 // IsMulticastEthernetAddress returns true if the address is a multicast
124 // ethernet address.
125 func IsMulticastEthernetAddress(addr tcpip.LinkAddress) bool {
126 if len(addr) != EthernetAddressSize {
127 return false
128 }
129 130 return addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0
131 }
132 133 // IsValidUnicastEthernetAddress returns true if the address is a unicast
134 // ethernet address.
135 func IsValidUnicastEthernetAddress(addr tcpip.LinkAddress) bool {
136 if len(addr) != EthernetAddressSize {
137 return false
138 }
139 140 if addr == UnspecifiedEthernetAddress {
141 return false
142 }
143 144 if addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0 {
145 return false
146 }
147 148 return true
149 }
150 151 // EthernetAddressFromMulticastIPv4Address returns a multicast Ethernet address
152 // for a multicast IPv4 address.
153 //
154 // addr MUST be a multicast IPv4 address.
155 func EthernetAddressFromMulticastIPv4Address(addr tcpip.Address) tcpip.LinkAddress {
156 var linkAddrBytes [EthernetAddressSize]byte
157 // RFC 1112 Host Extensions for IP Multicasting
158 //
159 // 6.4. Extensions to an Ethernet Local Network Module:
160 //
161 // An IP host group address is mapped to an Ethernet multicast
162 // address by placing the low-order 23-bits of the IP address
163 // into the low-order 23 bits of the Ethernet multicast address
164 // 01-00-5E-00-00-00 (hex).
165 addrBytes := addr.As4()
166 linkAddrBytes[0] = 0x1
167 linkAddrBytes[2] = 0x5e
168 linkAddrBytes[3] = addrBytes[1] & 0x7F
169 copy(linkAddrBytes[4:], addrBytes[IPv4AddressSize-2:])
170 return tcpip.LinkAddress(linkAddrBytes[:])
171 }
172 173 // EthernetAddressFromMulticastIPv6Address returns a multicast Ethernet address
174 // for a multicast IPv6 address.
175 //
176 // addr MUST be a multicast IPv6 address.
177 func EthernetAddressFromMulticastIPv6Address(addr tcpip.Address) tcpip.LinkAddress {
178 // RFC 2464 Transmission of IPv6 Packets over Ethernet Networks
179 //
180 // 7. Address Mapping -- Multicast
181 //
182 // An IPv6 packet with a multicast destination address DST,
183 // consisting of the sixteen octets DST[1] through DST[16], is
184 // transmitted to the Ethernet multicast address whose first
185 // two octets are the value 3333 hexadecimal and whose last
186 // four octets are the last four octets of DST.
187 addrBytes := addr.As16()
188 linkAddrBytes := []byte(addrBytes[IPv6AddressSize-EthernetAddressSize:])
189 linkAddrBytes[0] = 0x33
190 linkAddrBytes[1] = 0x33
191 return tcpip.LinkAddress(linkAddrBytes[:])
192 }
193