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+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package header
+
+import (
+ "encoding/binary"
+
+ "gvisor.dev/gvisor/pkg/tcpip"
+)
+
+const (
+ dstMAC = 0
+ srcMAC = 6
+ ethType = 12
+)
+
+// EthernetFields contains the fields of an ethernet frame header. It is used to
+// describe the fields of a frame that needs to be encoded.
+type EthernetFields struct {
+ // SrcAddr is the "MAC source" field of an ethernet frame header.
+ SrcAddr tcpip.LinkAddress
+
+ // DstAddr is the "MAC destination" field of an ethernet frame header.
+ DstAddr tcpip.LinkAddress
+
+ // Type is the "ethertype" field of an ethernet frame header.
+ Type tcpip.NetworkProtocolNumber
+}
+
+// Ethernet represents an ethernet frame header stored in a byte array.
+type Ethernet []byte
+
+const (
+ // EthernetMinimumSize is the minimum size of a valid ethernet frame.
+ EthernetMinimumSize = 14
+
+ // EthernetAddressSize is the size, in bytes, of an ethernet address.
+ EthernetAddressSize = 6
+
+ // unspecifiedEthernetAddress is the unspecified ethernet address
+ // (all bits set to 0).
+ unspecifiedEthernetAddress = tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00")
+
+ // unicastMulticastFlagMask is the mask of the least significant bit in
+ // the first octet (in network byte order) of an ethernet address that
+ // determines whether the ethernet address is a unicast or multicast. If
+ // the masked bit is a 1, then the address is a multicast, unicast
+ // otherwise.
+ //
+ // See the IEEE Std 802-2001 document for more details. Specifically,
+ // section 9.2.1 of http://ieee802.org/secmail/pdfocSP2xXA6d.pdf:
+ // "A 48-bit universal address consists of two parts. The first 24 bits
+ // correspond to the OUI as assigned by the IEEE, expect that the
+ // assignee may set the LSB of the first octet to 1 for group addresses
+ // or set it to 0 for individual addresses."
+ unicastMulticastFlagMask = 1
+
+ // unicastMulticastFlagByteIdx is the byte that holds the
+ // unicast/multicast flag. See unicastMulticastFlagMask.
+ unicastMulticastFlagByteIdx = 0
+)
+
+const (
+ // EthernetProtocolAll is a catch-all for all protocols carried inside
+ // an ethernet frame. It is mainly used to create packet sockets that
+ // capture all traffic.
+ EthernetProtocolAll tcpip.NetworkProtocolNumber = 0x0003
+
+ // EthernetProtocolPUP is the PARC Universial Packet protocol ethertype.
+ EthernetProtocolPUP tcpip.NetworkProtocolNumber = 0x0200
+)
+
+// Ethertypes holds the protocol numbers describing the payload of an ethernet
+// frame. These types aren't necessarily supported by netstack, but can be used
+// to catch all traffic of a type via packet endpoints.
+var Ethertypes = []tcpip.NetworkProtocolNumber{
+ EthernetProtocolAll,
+ EthernetProtocolPUP,
+}
+
+// SourceAddress returns the "MAC source" field of the ethernet frame header.
+func (b Ethernet) SourceAddress() tcpip.LinkAddress {
+ return tcpip.LinkAddress(b[srcMAC:][:EthernetAddressSize])
+}
+
+// DestinationAddress returns the "MAC destination" field of the ethernet frame
+// header.
+func (b Ethernet) DestinationAddress() tcpip.LinkAddress {
+ return tcpip.LinkAddress(b[dstMAC:][:EthernetAddressSize])
+}
+
+// Type returns the "ethertype" field of the ethernet frame header.
+func (b Ethernet) Type() tcpip.NetworkProtocolNumber {
+ return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(b[ethType:]))
+}
+
+// Encode encodes all the fields of the ethernet frame header.
+func (b Ethernet) Encode(e *EthernetFields) {
+ binary.BigEndian.PutUint16(b[ethType:], uint16(e.Type))
+ copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr)
+ copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr)
+}
+
+// IsValidUnicastEthernetAddress returns true if addr is a valid unicast
+// ethernet address.
+func IsValidUnicastEthernetAddress(addr tcpip.LinkAddress) bool {
+ // Must be of the right length.
+ if len(addr) != EthernetAddressSize {
+ return false
+ }
+
+ // Must not be unspecified.
+ if addr == unspecifiedEthernetAddress {
+ return false
+ }
+
+ // Must not be a multicast.
+ if addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0 {
+ return false
+ }
+
+ // addr is a valid unicast ethernet address.
+ return true
+}
+
+// EthernetAddressFromMulticastIPv4Address returns a multicast Ethernet address
+// for a multicast IPv4 address.
+//
+// addr MUST be a multicast IPv4 address.
+func EthernetAddressFromMulticastIPv4Address(addr tcpip.Address) tcpip.LinkAddress {
+ var linkAddrBytes [EthernetAddressSize]byte
+ // RFC 1112 Host Extensions for IP Multicasting
+ //
+ // 6.4. Extensions to an Ethernet Local Network Module:
+ //
+ // An IP host group address is mapped to an Ethernet multicast
+ // address by placing the low-order 23-bits of the IP address
+ // into the low-order 23 bits of the Ethernet multicast address
+ // 01-00-5E-00-00-00 (hex).
+ linkAddrBytes[0] = 0x1
+ linkAddrBytes[2] = 0x5e
+ linkAddrBytes[3] = addr[1] & 0x7F
+ copy(linkAddrBytes[4:], addr[IPv4AddressSize-2:])
+ return tcpip.LinkAddress(linkAddrBytes[:])
+}
+
+// EthernetAddressFromMulticastIPv6Address returns a multicast Ethernet address
+// for a multicast IPv6 address.
+//
+// addr MUST be a multicast IPv6 address.
+func EthernetAddressFromMulticastIPv6Address(addr tcpip.Address) tcpip.LinkAddress {
+ // RFC 2464 Transmission of IPv6 Packets over Ethernet Networks
+ //
+ // 7. Address Mapping -- Multicast
+ //
+ // An IPv6 packet with a multicast destination address DST,
+ // consisting of the sixteen octets DST[1] through DST[16], is
+ // transmitted to the Ethernet multicast address whose first
+ // two octets are the value 3333 hexadecimal and whose last
+ // four octets are the last four octets of DST.
+ linkAddrBytes := []byte(addr[IPv6AddressSize-EthernetAddressSize:])
+ linkAddrBytes[0] = 0x33
+ linkAddrBytes[1] = 0x33
+ return tcpip.LinkAddress(linkAddrBytes[:])
+}