137 lines
4.5 KiB
Go
137 lines
4.5 KiB
Go
// Copyright 2018 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package header
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import (
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"encoding/binary"
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"gvisor.dev/gvisor/pkg/tcpip"
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)
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const (
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dstMAC = 0
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srcMAC = 6
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ethType = 12
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)
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// EthernetFields contains the fields of an ethernet frame header. It is used to
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// describe the fields of a frame that needs to be encoded.
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type EthernetFields struct {
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// SrcAddr is the "MAC source" field of an ethernet frame header.
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SrcAddr tcpip.LinkAddress
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// DstAddr is the "MAC destination" field of an ethernet frame header.
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DstAddr tcpip.LinkAddress
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// Type is the "ethertype" field of an ethernet frame header.
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Type tcpip.NetworkProtocolNumber
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}
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// Ethernet represents an ethernet frame header stored in a byte array.
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type Ethernet []byte
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const (
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// EthernetMinimumSize is the minimum size of a valid ethernet frame.
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EthernetMinimumSize = 14
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// EthernetAddressSize is the size, in bytes, of an ethernet address.
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EthernetAddressSize = 6
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// unspecifiedEthernetAddress is the unspecified ethernet address
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// (all bits set to 0).
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unspecifiedEthernetAddress = tcpip.LinkAddress("\x00\x00\x00\x00\x00\x00")
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// unicastMulticastFlagMask is the mask of the least significant bit in
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// the first octet (in network byte order) of an ethernet address that
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// determines whether the ethernet address is a unicast or multicast. If
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// the masked bit is a 1, then the address is a multicast, unicast
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// otherwise.
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//
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// See the IEEE Std 802-2001 document for more details. Specifically,
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// section 9.2.1 of http://ieee802.org/secmail/pdfocSP2xXA6d.pdf:
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// "A 48-bit universal address consists of two parts. The first 24 bits
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// correspond to the OUI as assigned by the IEEE, expect that the
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// assignee may set the LSB of the first octet to 1 for group addresses
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// or set it to 0 for individual addresses."
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unicastMulticastFlagMask = 1
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// unicastMulticastFlagByteIdx is the byte that holds the
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// unicast/multicast flag. See unicastMulticastFlagMask.
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unicastMulticastFlagByteIdx = 0
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)
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const (
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// EthernetProtocolAll is a catch-all for all protocols carried inside
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// an ethernet frame. It is mainly used to create packet sockets that
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// capture all traffic.
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EthernetProtocolAll tcpip.NetworkProtocolNumber = 0x0003
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// EthernetProtocolPUP is the PARC Universial Packet protocol ethertype.
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EthernetProtocolPUP tcpip.NetworkProtocolNumber = 0x0200
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)
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// Ethertypes holds the protocol numbers describing the payload of an ethernet
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// frame. These types aren't necessarily supported by netstack, but can be used
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// to catch all traffic of a type via packet endpoints.
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var Ethertypes = []tcpip.NetworkProtocolNumber{
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EthernetProtocolAll,
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EthernetProtocolPUP,
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}
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// SourceAddress returns the "MAC source" field of the ethernet frame header.
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func (b Ethernet) SourceAddress() tcpip.LinkAddress {
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return tcpip.LinkAddress(b[srcMAC:][:EthernetAddressSize])
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}
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// DestinationAddress returns the "MAC destination" field of the ethernet frame
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// header.
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func (b Ethernet) DestinationAddress() tcpip.LinkAddress {
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return tcpip.LinkAddress(b[dstMAC:][:EthernetAddressSize])
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}
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// Type returns the "ethertype" field of the ethernet frame header.
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func (b Ethernet) Type() tcpip.NetworkProtocolNumber {
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return tcpip.NetworkProtocolNumber(binary.BigEndian.Uint16(b[ethType:]))
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}
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// Encode encodes all the fields of the ethernet frame header.
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func (b Ethernet) Encode(e *EthernetFields) {
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binary.BigEndian.PutUint16(b[ethType:], uint16(e.Type))
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copy(b[srcMAC:][:EthernetAddressSize], e.SrcAddr)
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copy(b[dstMAC:][:EthernetAddressSize], e.DstAddr)
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}
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// IsValidUnicastEthernetAddress returns true if addr is a valid unicast
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// ethernet address.
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func IsValidUnicastEthernetAddress(addr tcpip.LinkAddress) bool {
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// Must be of the right length.
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if len(addr) != EthernetAddressSize {
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return false
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}
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// Must not be unspecified.
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if addr == unspecifiedEthernetAddress {
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return false
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}
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// Must not be a multicast.
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if addr[unicastMulticastFlagByteIdx]&unicastMulticastFlagMask != 0 {
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return false
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}
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// addr is a valid unicast ethernet address.
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return true
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}
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