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End-application improvements for the tun library use #139

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2 changes: 2 additions & 0 deletions device/device_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -446,6 +446,8 @@ func (t *fakeTUNDeviceSized) Name() (string, error) { ret
func (t *fakeTUNDeviceSized) Events() <-chan tun.Event { return nil }
func (t *fakeTUNDeviceSized) Close() error { return nil }
func (t *fakeTUNDeviceSized) BatchSize() int { return t.size }
func (t *fakeTUNDeviceSized) MinOffset() int { return 0 }
func (t *fakeTUNDeviceSized) SetCarrier(bool) error { return nil }

func TestBatchSize(t *testing.T) {
d := Device{}
Expand Down
104 changes: 93 additions & 11 deletions tun/checksum.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,8 +5,34 @@ import (
"math/bits"
)

// TODO: Explore SIMD and/or other assembly optimizations.
func checksumNoFold(b []byte, initial uint64) uint64 {
// IP protocol constants
const (
ProtocolICMP4 = 1
ProtocolTCP = 6
ProtocolUDP = 17
ProtocolICMP6 = 58
)

const (
IPv4SrcAddrOffset = 12
IPv6SrcAddrOffset = 8
)

var (
// PseudoHeaderProtocolTCP TCP protocol field of the TCP pseudoheader
PseudoHeaderProtocolTCP = []byte{0, ProtocolTCP}
// PseudoHeaderProtocolUDP UDP protocol field of the UDP pseudoheader
PseudoHeaderProtocolUDP = []byte{0, ProtocolUDP}
// PseudoHeaderProtocolMap provides dispatch for IP protocol to the corresponding protocol pseudo-header field
PseudoHeaderProtocolMap = map[uint8][]byte{
ProtocolTCP: PseudoHeaderProtocolTCP,
ProtocolUDP: PseudoHeaderProtocolUDP,
}
)

// ChecksumNoFold performs intermediate checksum computation per RFC 1071
func ChecksumNoFold(b []byte, initial uint64) uint64 {
// TODO: Explore SIMD and/or other assembly optimizations.
tmp := make([]byte, 8)
binary.NativeEndian.PutUint64(tmp, initial)
ac := binary.BigEndian.Uint64(tmp)
Expand Down Expand Up @@ -83,20 +109,76 @@ func checksumNoFold(b []byte, initial uint64) uint64 {
return binary.BigEndian.Uint64(tmp)
}

func checksum(b []byte, initial uint64) uint16 {
ac := checksumNoFold(b, initial)
// Checksum performs final checksum computation per RFC 1071
func Checksum(b []byte, initial uint64) uint16 {
ac := ChecksumNoFold(b, initial)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
ac = (ac >> 16) + (ac & 0xffff)
return uint16(ac)
}

func pseudoHeaderChecksumNoFold(protocol uint8, srcAddr, dstAddr []byte, totalLen uint16) uint64 {
sum := checksumNoFold(srcAddr, 0)
sum = checksumNoFold(dstAddr, sum)
sum = checksumNoFold([]byte{0, protocol}, sum)
tmp := make([]byte, 2)
binary.BigEndian.PutUint16(tmp, totalLen)
return checksumNoFold(tmp, sum)
// PseudoHeaderChecksumNoFold performs intermediate checksum computation for TCP/UDP pseudoheader values
func PseudoHeaderChecksumNoFold(protocol, srcDstAddr, totalLen []byte) uint64 {
sum := ChecksumNoFold(srcDstAddr, 0)
sum = ChecksumNoFold(protocol, sum)
return ChecksumNoFold(totalLen, sum)
}

// ComputeIPChecksum updates IP and TCP/UDP checksums
func ComputeIPChecksum(pkt []byte) {
ComputeIPChecksumBuffer(pkt, false)
}

// ComputeIPChecksumBuffer updates IP and TCP/UDP checksums using the provided length buffer of size 2
func ComputeIPChecksumBuffer(pkt []byte, partial bool) {
var (
lenbuf [2]byte
addrsum uint64
protocol uint8
headerLen int
totalLen uint16
)

if pkt[0]>>4 == 4 {
pkt[10], pkt[11] = 0, 0 // clear IP header checksum
protocol = pkt[9]
ihl := pkt[0] & 0xF
headerLen = int(ihl * 4)
totalLen = binary.BigEndian.Uint16(pkt[2:])
addrsum = ChecksumNoFold(pkt[IPv4SrcAddrOffset:IPv4SrcAddrOffset+8], 0)
binary.BigEndian.PutUint16(pkt[10:], ^Checksum(pkt[:IPv4SrcAddrOffset], addrsum))
} else {
protocol = pkt[6]
headerLen = 40
totalLen = 40 + binary.BigEndian.Uint16(pkt[4:])
addrsum = ChecksumNoFold(pkt[IPv6SrcAddrOffset:IPv6SrcAddrOffset+32], 0)
}

switch protocol {
case ProtocolTCP:
pkt[headerLen+16], pkt[headerLen+17] = 0, 0
binary.BigEndian.PutUint16(lenbuf[:], totalLen-uint16(headerLen))
tcpCSum := ChecksumNoFold(PseudoHeaderProtocolTCP, addrsum)
tcpCSum = ChecksumNoFold(lenbuf[:], tcpCSum)
if partial {
binary.BigEndian.PutUint16(pkt[headerLen+16:], Checksum([]byte{}, tcpCSum))
} else {
binary.BigEndian.PutUint16(pkt[headerLen+16:], ^Checksum(pkt[headerLen:totalLen], tcpCSum))
}
case ProtocolUDP:
pkt[headerLen+6], pkt[headerLen+7] = 0, 0
binary.BigEndian.PutUint16(lenbuf[:], totalLen-uint16(headerLen))
udpCSum := ChecksumNoFold(PseudoHeaderProtocolUDP, addrsum)
udpCSum = ChecksumNoFold(lenbuf[:], udpCSum)
if partial {
binary.BigEndian.PutUint16(pkt[headerLen+6:], Checksum([]byte{}, udpCSum))
} else {
binary.BigEndian.PutUint16(pkt[headerLen+6:], ^Checksum(pkt[headerLen:totalLen], udpCSum))
}
case ProtocolICMP4, ProtocolICMP6:
pkt[headerLen+2], pkt[headerLen+3] = 0, 0
binary.BigEndian.PutUint16(pkt[headerLen+2:], ^Checksum(pkt[headerLen:totalLen], 0))
}
}
22 changes: 12 additions & 10 deletions tun/checksum_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -40,7 +40,7 @@ func TestChecksum(t *testing.T) {
buf := make([]byte, length)
rng := rand.New(rand.NewSource(1))
rng.Read(buf)
csum := checksum(buf, 0x1234)
csum := Checksum(buf, 0x1234)
csumRef := checksumRef(buf, 0x1234)
if csum != csumRef {
t.Error("Expected checksum", csumRef, "got", csum)
Expand All @@ -49,18 +49,20 @@ func TestChecksum(t *testing.T) {
}

func TestPseudoHeaderChecksum(t *testing.T) {
lenbuf := make([]byte, 2)

for _, addrLen := range []int{4, 16} {
for length := 0; length <= 9001; length++ {
srcAddr := make([]byte, addrLen)
dstAddr := make([]byte, addrLen)
buf := make([]byte, length)
srcDstAddr := make([]byte, addrLen*2)
rng := rand.New(rand.NewSource(1))
rng.Read(srcAddr)
rng.Read(dstAddr)
rng.Read(srcDstAddr)
rng.Read(srcDstAddr[addrLen:])
buf := make([]byte, length)
rng.Read(buf)
phSum := pseudoHeaderChecksumNoFold(unix.IPPROTO_TCP, srcAddr, dstAddr, uint16(length))
csum := checksum(buf, phSum)
phSumRef := pseudoHeaderChecksumRefNoFold(unix.IPPROTO_TCP, srcAddr, dstAddr, uint16(length))
binary.BigEndian.PutUint16(lenbuf, uint16(length))
phSum := PseudoHeaderChecksumNoFold(PseudoHeaderProtocolTCP, srcDstAddr, lenbuf)
csum := Checksum(buf, phSum)
phSumRef := pseudoHeaderChecksumRefNoFold(unix.IPPROTO_TCP, srcDstAddr[:addrLen], srcDstAddr[addrLen:], uint16(length))
csumRef := checksumRef(buf, phSumRef)
if csum != csumRef {
t.Error("Expected checksumRef", csumRef, "got", csum)
Expand Down Expand Up @@ -91,7 +93,7 @@ func BenchmarkChecksum(b *testing.B) {
rng.Read(buf)
b.ResetTimer()
for i := 0; i < b.N; i++ {
checksum(buf, 0)
Checksum(buf, 0)
}
})
}
Expand Down
8 changes: 8 additions & 0 deletions tun/netstack/tun.go
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Original file line number Diff line number Diff line change
Expand Up @@ -191,6 +191,14 @@ func (tun *netTun) BatchSize() int {
return 1
}

func (tun *netTun) MinOffset() int {
return 0
}

func (tun *netTun) SetCarrier(bool) error {
return nil
}

func convertToFullAddr(endpoint netip.AddrPort) (tcpip.FullAddress, tcpip.NetworkProtocolNumber) {
var protoNumber tcpip.NetworkProtocolNumber
if endpoint.Addr().Is4() {
Expand Down
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