95 lines
2.7 KiB
Go
95 lines
2.7 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 provides the implementation of the encoding and decoding of
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// network protocol headers.
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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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"gvisor.dev/gvisor/pkg/tcpip/buffer"
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)
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func calculateChecksum(buf []byte, initial uint32) uint16 {
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v := initial
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l := len(buf)
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if l&1 != 0 {
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l--
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v += uint32(buf[l]) << 8
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}
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for i := 0; i < l; i += 2 {
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v += (uint32(buf[i]) << 8) + uint32(buf[i+1])
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}
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return ChecksumCombine(uint16(v), uint16(v>>16))
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}
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// Checksum calculates the checksum (as defined in RFC 1071) of the bytes in the
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// given byte array.
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//
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// The initial checksum must have been computed on an even number of bytes.
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func Checksum(buf []byte, initial uint16) uint16 {
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return calculateChecksum(buf, uint32(initial))
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}
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// ChecksumVV calculates the checksum (as defined in RFC 1071) of the bytes in
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// the given VectorizedView.
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//
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// The initial checksum must have been computed on an even number of bytes.
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func ChecksumVV(vv buffer.VectorisedView, initial uint16) uint16 {
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var odd bool
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sum := initial
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for _, v := range vv.Views() {
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if len(v) == 0 {
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continue
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}
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s := uint32(sum)
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if odd {
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s += uint32(v[0])
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v = v[1:]
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}
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odd = len(v)&1 != 0
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sum = calculateChecksum(v, s)
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}
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return sum
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}
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// ChecksumCombine combines the two uint16 to form their checksum. This is done
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// by adding them and the carry.
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//
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// Note that checksum a must have been computed on an even number of bytes.
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func ChecksumCombine(a, b uint16) uint16 {
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v := uint32(a) + uint32(b)
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return uint16(v + v>>16)
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}
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// PseudoHeaderChecksum calculates the pseudo-header checksum for the given
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// destination protocol and network address. Pseudo-headers are needed by
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// transport layers when calculating their own checksum.
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func PseudoHeaderChecksum(protocol tcpip.TransportProtocolNumber, srcAddr tcpip.Address, dstAddr tcpip.Address, totalLen uint16) uint16 {
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xsum := Checksum([]byte(srcAddr), 0)
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xsum = Checksum([]byte(dstAddr), xsum)
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// Add the length portion of the checksum to the pseudo-checksum.
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tmp := make([]byte, 2)
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binary.BigEndian.PutUint16(tmp, totalLen)
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xsum = Checksum(tmp, xsum)
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return Checksum([]byte{0, uint8(protocol)}, xsum)
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}
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