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// Copyright 2018 Google LLC
//
// 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.
//
// This file contains code taken from gVisor.
// +build go1.12
package nclient4
import (
"encoding/binary"
"net"
"github.com/u-root/u-root/pkg/uio"
)
const (
versIHL = 0
tos = 1
totalLen = 2
id = 4
flagsFO = 6
ttl = 8
protocol = 9
checksum = 10
srcAddr = 12
dstAddr = 16
)
// TransportProtocolNumber is the number of a transport protocol.
type TransportProtocolNumber uint32
// IPv4Fields contains the fields of an IPv4 packet. It is used to describe the
// fields of a packet that needs to be encoded.
type IPv4Fields struct {
// IHL is the "internet header length" field of an IPv4 packet.
IHL uint8
// TOS is the "type of service" field of an IPv4 packet.
TOS uint8
// TotalLength is the "total length" field of an IPv4 packet.
TotalLength uint16
// ID is the "identification" field of an IPv4 packet.
ID uint16
// Flags is the "flags" field of an IPv4 packet.
Flags uint8
// FragmentOffset is the "fragment offset" field of an IPv4 packet.
FragmentOffset uint16
// TTL is the "time to live" field of an IPv4 packet.
TTL uint8
// Protocol is the "protocol" field of an IPv4 packet.
Protocol uint8
// Checksum is the "checksum" field of an IPv4 packet.
Checksum uint16
// SrcAddr is the "source ip address" of an IPv4 packet.
SrcAddr net.IP
// DstAddr is the "destination ip address" of an IPv4 packet.
DstAddr net.IP
}
// IPv4 represents an ipv4 header stored in a byte array.
// Most of the methods of IPv4 access to the underlying slice without
// checking the boundaries and could panic because of 'index out of range'.
// Always call IsValid() to validate an instance of IPv4 before using other methods.
type IPv4 []byte
const (
// IPv4MinimumSize is the minimum size of a valid IPv4 packet.
IPv4MinimumSize = 20
// IPv4MaximumHeaderSize is the maximum size of an IPv4 header. Given
// that there are only 4 bits to represents the header length in 32-bit
// units, the header cannot exceed 15*4 = 60 bytes.
IPv4MaximumHeaderSize = 60
// IPv4AddressSize is the size, in bytes, of an IPv4 address.
IPv4AddressSize = 4
// IPv4Version is the version of the ipv4 protocol.
IPv4Version = 4
)
var (
// IPv4Broadcast is the broadcast address of the IPv4 protocol.
IPv4Broadcast = net.IP{0xff, 0xff, 0xff, 0xff}
// IPv4Any is the non-routable IPv4 "any" meta address.
IPv4Any = net.IP{0, 0, 0, 0}
)
// Flags that may be set in an IPv4 packet.
const (
IPv4FlagMoreFragments = 1 << iota
IPv4FlagDontFragment
)
// HeaderLength returns the value of the "header length" field of the ipv4
// header.
func (b IPv4) HeaderLength() uint8 {
return (b[versIHL] & 0xf) * 4
}
// Protocol returns the value of the protocol field of the ipv4 header.
func (b IPv4) Protocol() uint8 {
return b[protocol]
}
// SourceAddress returns the "source address" field of the ipv4 header.
func (b IPv4) SourceAddress() net.IP {
return net.IP(b[srcAddr : srcAddr+IPv4AddressSize])
}
// DestinationAddress returns the "destination address" field of the ipv4
// header.
func (b IPv4) DestinationAddress() net.IP {
return net.IP(b[dstAddr : dstAddr+IPv4AddressSize])
}
// TransportProtocol implements Network.TransportProtocol.
func (b IPv4) TransportProtocol() TransportProtocolNumber {
return TransportProtocolNumber(b.Protocol())
}
// Payload implements Network.Payload.
func (b IPv4) Payload() []byte {
return b[b.HeaderLength():][:b.PayloadLength()]
}
// PayloadLength returns the length of the payload portion of the ipv4 packet.
func (b IPv4) PayloadLength() uint16 {
return b.TotalLength() - uint16(b.HeaderLength())
}
// TotalLength returns the "total length" field of the ipv4 header.
func (b IPv4) TotalLength() uint16 {
return binary.BigEndian.Uint16(b[totalLen:])
}
// SetTotalLength sets the "total length" field of the ipv4 header.
func (b IPv4) SetTotalLength(totalLength uint16) {
binary.BigEndian.PutUint16(b[totalLen:], totalLength)
}
// SetChecksum sets the checksum field of the ipv4 header.
func (b IPv4) SetChecksum(v uint16) {
binary.BigEndian.PutUint16(b[checksum:], v)
}
// SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the
// ipv4 header.
func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16) {
v := (uint16(flags) << 13) | (offset >> 3)
binary.BigEndian.PutUint16(b[flagsFO:], v)
}
// SetSourceAddress sets the "source address" field of the ipv4 header.
func (b IPv4) SetSourceAddress(addr net.IP) {
copy(b[srcAddr:srcAddr+IPv4AddressSize], addr.To4())
}
// SetDestinationAddress sets the "destination address" field of the ipv4
// header.
func (b IPv4) SetDestinationAddress(addr net.IP) {
copy(b[dstAddr:dstAddr+IPv4AddressSize], addr.To4())
}
// CalculateChecksum calculates the checksum of the ipv4 header.
func (b IPv4) CalculateChecksum() uint16 {
return Checksum(b[:b.HeaderLength()], 0)
}
// Encode encodes all the fields of the ipv4 header.
func (b IPv4) Encode(i *IPv4Fields) {
b[versIHL] = (4 << 4) | ((i.IHL / 4) & 0xf)
b[tos] = i.TOS
b.SetTotalLength(i.TotalLength)
binary.BigEndian.PutUint16(b[id:], i.ID)
b.SetFlagsFragmentOffset(i.Flags, i.FragmentOffset)
b[ttl] = i.TTL
b[protocol] = i.Protocol
b.SetChecksum(i.Checksum)
copy(b[srcAddr:srcAddr+IPv4AddressSize], i.SrcAddr)
copy(b[dstAddr:dstAddr+IPv4AddressSize], i.DstAddr)
}
const (
udpSrcPort = 0
udpDstPort = 2
udpLength = 4
udpChecksum = 6
)
// UDPFields contains the fields of a UDP packet. It is used to describe the
// fields of a packet that needs to be encoded.
type UDPFields struct {
// SrcPort is the "source port" field of a UDP packet.
SrcPort uint16
// DstPort is the "destination port" field of a UDP packet.
DstPort uint16
// Length is the "length" field of a UDP packet.
Length uint16
// Checksum is the "checksum" field of a UDP packet.
Checksum uint16
}
// UDP represents a UDP header stored in a byte array.
type UDP []byte
const (
// UDPMinimumSize is the minimum size of a valid UDP packet.
UDPMinimumSize = 8
// UDPProtocolNumber is UDP's transport protocol number.
UDPProtocolNumber TransportProtocolNumber = 17
)
// SourcePort returns the "source port" field of the udp header.
func (b UDP) SourcePort() uint16 {
return binary.BigEndian.Uint16(b[udpSrcPort:])
}
// DestinationPort returns the "destination port" field of the udp header.
func (b UDP) DestinationPort() uint16 {
return binary.BigEndian.Uint16(b[udpDstPort:])
}
// Length returns the "length" field of the udp header.
func (b UDP) Length() uint16 {
return binary.BigEndian.Uint16(b[udpLength:])
}
// SetSourcePort sets the "source port" field of the udp header.
func (b UDP) SetSourcePort(port uint16) {
binary.BigEndian.PutUint16(b[udpSrcPort:], port)
}
// SetDestinationPort sets the "destination port" field of the udp header.
func (b UDP) SetDestinationPort(port uint16) {
binary.BigEndian.PutUint16(b[udpDstPort:], port)
}
// SetChecksum sets the "checksum" field of the udp header.
func (b UDP) SetChecksum(checksum uint16) {
binary.BigEndian.PutUint16(b[udpChecksum:], checksum)
}
// Payload returns the data contained in the UDP datagram.
func (b UDP) Payload() []byte {
return b[UDPMinimumSize:]
}
// Checksum returns the "checksum" field of the udp header.
func (b UDP) Checksum() uint16 {
return binary.BigEndian.Uint16(b[udpChecksum:])
}
// CalculateChecksum calculates the checksum of the udp packet, given the total
// length of the packet and the checksum of the network-layer pseudo-header
// (excluding the total length) and the checksum of the payload.
func (b UDP) CalculateChecksum(partialChecksum uint16, totalLen uint16) uint16 {
// Add the length portion of the checksum to the pseudo-checksum.
tmp := make([]byte, 2)
binary.BigEndian.PutUint16(tmp, totalLen)
checksum := Checksum(tmp, partialChecksum)
// Calculate the rest of the checksum.
return Checksum(b[:UDPMinimumSize], checksum)
}
// Encode encodes all the fields of the udp header.
func (b UDP) Encode(u *UDPFields) {
binary.BigEndian.PutUint16(b[udpSrcPort:], u.SrcPort)
binary.BigEndian.PutUint16(b[udpDstPort:], u.DstPort)
binary.BigEndian.PutUint16(b[udpLength:], u.Length)
binary.BigEndian.PutUint16(b[udpChecksum:], u.Checksum)
}
func calculateChecksum(buf []byte, initial uint32) uint16 {
v := initial
l := len(buf)
if l&1 != 0 {
l--
v += uint32(buf[l]) << 8
}
for i := 0; i < l; i += 2 {
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
}
return ChecksumCombine(uint16(v), uint16(v>>16))
}
// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
// given byte array.
//
// The initial checksum must have been computed on an even number of bytes.
func Checksum(buf []byte, initial uint16) uint16 {
return calculateChecksum(buf, uint32(initial))
}
// ChecksumCombine combines the two uint16 to form their checksum. This is done
// by adding them and the carry.
//
// Note that checksum a must have been computed on an even number of bytes.
func ChecksumCombine(a, b uint16) uint16 {
v := uint32(a) + uint32(b)
return uint16(v + v>>16)
}
// PseudoHeaderChecksum calculates the pseudo-header checksum for the
// given destination protocol and network address, ignoring the length
// field. Pseudo-headers are needed by transport layers when calculating
// their own checksum.
func PseudoHeaderChecksum(protocol TransportProtocolNumber, srcAddr net.IP, dstAddr net.IP) uint16 {
xsum := Checksum([]byte(srcAddr), 0)
xsum = Checksum([]byte(dstAddr), xsum)
return Checksum([]byte{0, uint8(protocol)}, xsum)
}
func udp4pkt(packet []byte, dest *net.UDPAddr, src *net.UDPAddr) []byte {
ipLen := IPv4MinimumSize
udpLen := UDPMinimumSize
h := make([]byte, 0, ipLen+udpLen+len(packet))
hdr := uio.NewBigEndianBuffer(h)
ipv4fields := &IPv4Fields{
IHL: IPv4MinimumSize,
TotalLength: uint16(ipLen + udpLen + len(packet)),
TTL: 64, // Per RFC 1700's recommendation for IP time to live
Protocol: uint8(UDPProtocolNumber),
SrcAddr: src.IP.To4(),
DstAddr: dest.IP.To4(),
}
ipv4hdr := IPv4(hdr.WriteN(ipLen))
ipv4hdr.Encode(ipv4fields)
ipv4hdr.SetChecksum(^ipv4hdr.CalculateChecksum())
udphdr := UDP(hdr.WriteN(udpLen))
udphdr.Encode(&UDPFields{
SrcPort: uint16(src.Port),
DstPort: uint16(dest.Port),
Length: uint16(udpLen + len(packet)),
})
xsum := Checksum(packet, PseudoHeaderChecksum(
ipv4hdr.TransportProtocol(), ipv4fields.SrcAddr, ipv4fields.DstAddr))
udphdr.SetChecksum(^udphdr.CalculateChecksum(xsum, udphdr.Length()))
hdr.WriteBytes(packet)
return hdr.Data()
}
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