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Diffstat (limited to 'pkg/tcpip/header/checksum.go')
-rw-r--r--pkg/tcpip/header/checksum.go94
1 files changed, 94 insertions, 0 deletions
diff --git a/pkg/tcpip/header/checksum.go b/pkg/tcpip/header/checksum.go
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+++ b/pkg/tcpip/header/checksum.go
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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"
+
+ "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)
+}