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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
}
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