diff options
Diffstat (limited to 'pkg/tcpip/header/checksum.go')
-rw-r--r-- | pkg/tcpip/header/checksum.go | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/pkg/tcpip/header/checksum.go b/pkg/tcpip/header/checksum.go new file mode 100644 index 000000000..2eaa7938a --- /dev/null +++ b/pkg/tcpip/header/checksum.go @@ -0,0 +1,94 @@ +// 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" + + "gvisor.googlesource.com/gvisor/pkg/tcpip" + "gvisor.googlesource.com/gvisor/pkg/tcpip/buffer" +) + +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)) +} + +// 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 odd bool + sum := initial + for _, v := range vv.Views() { + if len(v) == 0 { + continue + } + s := uint32(sum) + if odd { + s += uint32(v[0]) + v = v[1:] + } + odd = len(v)&1 != 0 + sum = calculateChecksum(v, s) + } + return 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) +} |