Check in gVisor.

PiperOrigin-RevId: 194583126
Change-Id: Ica1d8821a90f74e7e745962d71801c598c652463

1 files changed, 251 insertions, 0 deletions

diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go
new file mode 100644
index 000000000..cb0d42093
--- /dev/null
+++ b/pkg/tcpip/header/ipv4.go
@@ -0,0 +1,251 @@
+// Copyright 2016 The Netstack Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package header
+
+import (
+	"encoding/binary"
+
+	"gvisor.googlesource.com/gvisor/pkg/tcpip"
+)
+
+const (
+	versIHL  = 0
+	tos      = 1
+	totalLen = 2
+	id       = 4
+	flagsFO  = 6
+	ttl      = 8
+	protocol = 9
+	checksum = 10
+	srcAddr  = 12
+	dstAddr  = 16
+)
+
+// IPv4Fields contains the fields of an IPv4 packet. It is used to describe the
+// fields of a packet that needs to be encoded.
+type IPv4Fields struct {
+	// IHL is the "internet header length" field of an IPv4 packet.
+	IHL uint8
+
+	// TOS is the "type of service" field of an IPv4 packet.
+	TOS uint8
+
+	// TotalLength is the "total length" field of an IPv4 packet.
+	TotalLength uint16
+
+	// ID is the "identification" field of an IPv4 packet.
+	ID uint16
+
+	// Flags is the "flags" field of an IPv4 packet.
+	Flags uint8
+
+	// FragmentOffset is the "fragment offset" field of an IPv4 packet.
+	FragmentOffset uint16
+
+	// TTL is the "time to live" field of an IPv4 packet.
+	TTL uint8
+
+	// Protocol is the "protocol" field of an IPv4 packet.
+	Protocol uint8
+
+	// Checksum is the "checksum" field of an IPv4 packet.
+	Checksum uint16
+
+	// SrcAddr is the "source ip address" of an IPv4 packet.
+	SrcAddr tcpip.Address
+
+	// DstAddr is the "destination ip address" of an IPv4 packet.
+	DstAddr tcpip.Address
+}
+
+// IPv4 represents an ipv4 header stored in a byte array.
+// Most of the methods of IPv4 access to the underlying slice without
+// checking the boundaries and could panic because of 'index out of range'.
+// Always call IsValid() to validate an instance of IPv4 before using other methods.
+type IPv4 []byte
+
+const (
+	// IPv4MinimumSize is the minimum size of a valid IPv4 packet.
+	IPv4MinimumSize = 20
+
+	// IPv4MaximumHeaderSize is the maximum size of an IPv4 header. Given
+	// that there are only 4 bits to represents the header length in 32-bit
+	// units, the header cannot exceed 15*4 = 60 bytes.
+	IPv4MaximumHeaderSize = 60
+
+	// IPv4AddressSize is the size, in bytes, of an IPv4 address.
+	IPv4AddressSize = 4
+
+	// IPv4ProtocolNumber is IPv4's network protocol number.
+	IPv4ProtocolNumber tcpip.NetworkProtocolNumber = 0x0800
+
+	// IPv4Version is the version of the ipv4 procotol.
+	IPv4Version = 4
+)
+
+// Flags that may be set in an IPv4 packet.
+const (
+	IPv4FlagMoreFragments = 1 << iota
+	IPv4FlagDontFragment
+)
+
+// IPVersion returns the version of IP used in the given packet. It returns -1
+// if the packet is not large enough to contain the version field.
+func IPVersion(b []byte) int {
+	// Length must be at least offset+length of version field.
+	if len(b) < versIHL+1 {
+		return -1
+	}
+	return int(b[versIHL] >> 4)
+}
+
+// HeaderLength returns the value of the "header length" field of the ipv4
+// header.
+func (b IPv4) HeaderLength() uint8 {
+	return (b[versIHL] & 0xf) * 4
+}
+
+// ID returns the value of the identifier field of the ipv4 header.
+func (b IPv4) ID() uint16 {
+	return binary.BigEndian.Uint16(b[id:])
+}
+
+// Protocol returns the value of the protocol field of the ipv4 header.
+func (b IPv4) Protocol() uint8 {
+	return b[protocol]
+}
+
+// Flags returns the "flags" field of the ipv4 header.
+func (b IPv4) Flags() uint8 {
+	return uint8(binary.BigEndian.Uint16(b[flagsFO:]) >> 13)
+}
+
+// TTL returns the "TTL" field of the ipv4 header.
+func (b IPv4) TTL() uint8 {
+	return b[ttl]
+}
+
+// FragmentOffset returns the "fragment offset" field of the ipv4 header.
+func (b IPv4) FragmentOffset() uint16 {
+	return binary.BigEndian.Uint16(b[flagsFO:]) << 3
+}
+
+// TotalLength returns the "total length" field of the ipv4 header.
+func (b IPv4) TotalLength() uint16 {
+	return binary.BigEndian.Uint16(b[totalLen:])
+}
+
+// Checksum returns the checksum field of the ipv4 header.
+func (b IPv4) Checksum() uint16 {
+	return binary.BigEndian.Uint16(b[checksum:])
+}
+
+// SourceAddress returns the "source address" field of the ipv4 header.
+func (b IPv4) SourceAddress() tcpip.Address {
+	return tcpip.Address(b[srcAddr : srcAddr+IPv4AddressSize])
+}
+
+// DestinationAddress returns the "destination address" field of the ipv4
+// header.
+func (b IPv4) DestinationAddress() tcpip.Address {
+	return tcpip.Address(b[dstAddr : dstAddr+IPv4AddressSize])
+}
+
+// TransportProtocol implements Network.TransportProtocol.
+func (b IPv4) TransportProtocol() tcpip.TransportProtocolNumber {
+	return tcpip.TransportProtocolNumber(b.Protocol())
+}
+
+// Payload implements Network.Payload.
+func (b IPv4) Payload() []byte {
+	return b[b.HeaderLength():][:b.PayloadLength()]
+}
+
+// PayloadLength returns the length of the payload portion of the ipv4 packet.
+func (b IPv4) PayloadLength() uint16 {
+	return b.TotalLength() - uint16(b.HeaderLength())
+}
+
+// TOS returns the "type of service" field of the ipv4 header.
+func (b IPv4) TOS() (uint8, uint32) {
+	return b[tos], 0
+}
+
+// SetTOS sets the "type of service" field of the ipv4 header.
+func (b IPv4) SetTOS(v uint8, _ uint32) {
+	b[tos] = v
+}
+
+// SetTotalLength sets the "total length" field of the ipv4 header.
+func (b IPv4) SetTotalLength(totalLength uint16) {
+	binary.BigEndian.PutUint16(b[totalLen:], totalLength)
+}
+
+// SetChecksum sets the checksum field of the ipv4 header.
+func (b IPv4) SetChecksum(v uint16) {
+	binary.BigEndian.PutUint16(b[checksum:], v)
+}
+
+// SetFlagsFragmentOffset sets the "flags" and "fragment offset" fields of the
+// ipv4 header.
+func (b IPv4) SetFlagsFragmentOffset(flags uint8, offset uint16) {
+	v := (uint16(flags) << 13) | (offset >> 3)
+	binary.BigEndian.PutUint16(b[flagsFO:], v)
+}
+
+// SetSourceAddress sets the "source address" field of the ipv4 header.
+func (b IPv4) SetSourceAddress(addr tcpip.Address) {
+	copy(b[srcAddr:srcAddr+IPv4AddressSize], addr)
+}
+
+// SetDestinationAddress sets the "destination address" field of the ipv4
+// header.
+func (b IPv4) SetDestinationAddress(addr tcpip.Address) {
+	copy(b[dstAddr:dstAddr+IPv4AddressSize], addr)
+}
+
+// CalculateChecksum calculates the checksum of the ipv4 header.
+func (b IPv4) CalculateChecksum() uint16 {
+	return Checksum(b[:b.HeaderLength()], 0)
+}
+
+// Encode encodes all the fields of the ipv4 header.
+func (b IPv4) Encode(i *IPv4Fields) {
+	b[versIHL] = (4 << 4) | ((i.IHL / 4) & 0xf)
+	b[tos] = i.TOS
+	b.SetTotalLength(i.TotalLength)
+	binary.BigEndian.PutUint16(b[id:], i.ID)
+	b.SetFlagsFragmentOffset(i.Flags, i.FragmentOffset)
+	b[ttl] = i.TTL
+	b[protocol] = i.Protocol
+	b.SetChecksum(i.Checksum)
+	copy(b[srcAddr:srcAddr+IPv4AddressSize], i.SrcAddr)
+	copy(b[dstAddr:dstAddr+IPv4AddressSize], i.DstAddr)
+}
+
+// EncodePartial updates the total length and checksum fields of ipv4 header,
+// taking in the partial checksum, which is the checksum of the header without
+// the total length and checksum fields. It is useful in cases when similar
+// packets are produced.
+func (b IPv4) EncodePartial(partialChecksum, totalLength uint16) {
+	b.SetTotalLength(totalLength)
+	checksum := Checksum(b[totalLen:totalLen+2], partialChecksum)
+	b.SetChecksum(^checksum)
+}
+
+// IsValid performs basic validation on the packet.
+func (b IPv4) IsValid(pktSize int) bool {
+	if len(b) < IPv4MinimumSize {
+		return false
+	}
+
+	hlen := int(b.HeaderLength())
+	tlen := int(b.TotalLength())
+	if hlen > tlen || tlen > pktSize {
+		return false
+	}
+
+	return true
+}