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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 provides the implementation of the encoding and decoding of
// network protocol headers.
package header
import (
"encoding/binary"
"fmt"
"gvisor.dev/gvisor/pkg/tcpip"
"gvisor.dev/gvisor/pkg/tcpip/buffer"
)
func calculateChecksum(buf []byte, odd bool, initial uint32) (uint16, bool) {
v := initial
if odd {
v += uint32(buf[0])
buf = buf[1:]
}
l := len(buf)
odd = l&1 != 0
if odd {
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)), odd
}
func unrolledCalculateChecksum(buf []byte, odd bool, initial uint32) (uint16, bool) {
v := initial
if odd {
v += uint32(buf[0])
buf = buf[1:]
}
l := len(buf)
odd = l&1 != 0
if odd {
l--
v += uint32(buf[l]) << 8
}
for (l - 64) >= 0 {
i := 0
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
i += 16
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
i += 16
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
i += 16
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
buf = buf[64:]
l = l - 64
}
if (l - 32) >= 0 {
i := 0
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
i += 16
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
buf = buf[32:]
l = l - 32
}
if (l - 16) >= 0 {
i := 0
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
v += (uint32(buf[i+8]) << 8) + uint32(buf[i+9])
v += (uint32(buf[i+10]) << 8) + uint32(buf[i+11])
v += (uint32(buf[i+12]) << 8) + uint32(buf[i+13])
v += (uint32(buf[i+14]) << 8) + uint32(buf[i+15])
buf = buf[16:]
l = l - 16
}
if (l - 8) >= 0 {
i := 0
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
v += (uint32(buf[i+4]) << 8) + uint32(buf[i+5])
v += (uint32(buf[i+6]) << 8) + uint32(buf[i+7])
buf = buf[8:]
l = l - 8
}
if (l - 4) >= 0 {
i := 0
v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
v += (uint32(buf[i+2]) << 8) + uint32(buf[i+3])
buf = buf[4:]
l = l - 4
}
// At this point since l was even before we started unrolling
// there can be only two bytes left to add.
if l != 0 {
v += (uint32(buf[0]) << 8) + uint32(buf[1])
}
return ChecksumCombine(uint16(v), uint16(v>>16)), odd
}
// ChecksumOld calculates the checksum (as defined in RFC 1071) of the bytes in
// the given byte array. This function uses a non-optimized implementation. Its
// only retained for reference and to use as a benchmark/test. Most code should
// use the header.Checksum function.
//
// The initial checksum must have been computed on an even number of bytes.
func ChecksumOld(buf []byte, initial uint16) uint16 {
s, _ := calculateChecksum(buf, false, uint32(initial))
return s
}
// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
// given byte array. This function uses an optimized unrolled version of the
// checksum algorithm.
//
// The initial checksum must have been computed on an even number of bytes.
func Checksum(buf []byte, initial uint16) uint16 {
s, _ := unrolledCalculateChecksum(buf, false, uint32(initial))
return s
}
// ChecksumVV calculates the checksum (as defined in RFC 1071) of the bytes in
// the given VectorizedView.
//
// The initial checksum must have been computed on an even number of bytes.
func ChecksumVV(vv buffer.VectorisedView, initial uint16) uint16 {
var c Checksumer
for _, v := range vv.Views() {
c.Add([]byte(v))
}
return ChecksumCombine(initial, c.Checksum())
}
// Checksumer calculates checksum defined in RFC 1071.
type Checksumer struct {
sum uint16
odd bool
}
// Add adds b to checksum.
func (c *Checksumer) Add(b []byte) {
if len(b) > 0 {
c.sum, c.odd = unrolledCalculateChecksum(b, c.odd, uint32(c.sum))
}
}
// Checksum returns the latest checksum value.
func (c *Checksumer) Checksum() uint16 {
return c.sum
}
// 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. Pseudo-headers are needed by
// transport layers when calculating their own checksum.
func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address, totalLen uint16) uint16 {
xsum := Checksum([]byte(srcAddr), 0)
xsum = Checksum([]byte(dstAddr), xsum)
// Add the length portion of the checksum to the pseudo-checksum.
tmp := make([]byte, 2)
binary.BigEndian.PutUint16(tmp, totalLen)
xsum = Checksum(tmp, xsum)
return Checksum([]byte{0, uint8(protocol)}, xsum)
}
// checksumUpdate2ByteAlignedUint16 updates a uint16 value in a calculated
// checksum.
//
// The value MUST begin at a 2-byte boundary in the original buffer.
func checksumUpdate2ByteAlignedUint16(xsum, old, new uint16) uint16 {
// As per RFC 1071 page 4,
// (4) Incremental Update
//
// ...
//
// To update the checksum, simply add the differences of the
// sixteen bit integers that have been changed. To see why this
// works, observe that every 16-bit integer has an additive inverse
// and that addition is associative. From this it follows that
// given the original value m, the new value m', and the old
// checksum C, the new checksum C' is:
//
// C' = C + (-m) + m' = C + (m' - m)
return ChecksumCombine(xsum, ChecksumCombine(new, ^old))
}
// checksumUpdate2ByteAlignedAddress updates an address in a calculated
// checksum.
//
// The addresses must have the same length and must contain an even number
// of bytes. The address MUST begin at a 2-byte boundary in the original buffer.
func checksumUpdate2ByteAlignedAddress(xsum uint16, old, new tcpip.Address) uint16 {
const uint16Bytes = 2
if len(old) != len(new) {
panic(fmt.Sprintf("buffer lengths are different; old = %d, new = %d", len(old), len(new)))
}
if len(old)%uint16Bytes != 0 {
panic(fmt.Sprintf("buffer has an odd number of bytes; got = %d", len(old)))
}
// As per RFC 1071 page 4,
// (4) Incremental Update
//
// ...
//
// To update the checksum, simply add the differences of the
// sixteen bit integers that have been changed. To see why this
// works, observe that every 16-bit integer has an additive inverse
// and that addition is associative. From this it follows that
// given the original value m, the new value m', and the old
// checksum C, the new checksum C' is:
//
// C' = C + (-m) + m' = C + (m' - m)
for len(old) != 0 {
// Convert the 2 byte sequences to uint16 values then apply the increment
// update.
xsum = checksumUpdate2ByteAlignedUint16(xsum, (uint16(old[0])<<8)+uint16(old[1]), (uint16(new[0])<<8)+uint16(new[1]))
old = old[uint16Bytes:]
new = new[uint16Bytes:]
}
return xsum
}
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