mirror of https://github.com/tailscale/tailscale/
wgengine/packet: refactor and expose UDP header marshaling (#408)
Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>reviewable/pr436/r2
Dmytro Shynkevych
4 years ago
committed by
GitHub
parent
5e0ff494a5
commit
059b1d10bb
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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import (
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"errors"
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"math"
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)
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const tcpHeaderLength = 20
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// maxPacketLength is the largest length that all headers support.
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// IPv4 headers using uint16 for this forces an upper bound of 64KB.
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const maxPacketLength = math.MaxUint16
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var (
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errSmallBuffer = errors.New("buffer too small")
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errLargePacket = errors.New("packet too large")
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)
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// Header is a packet header capable of marshaling itself into a byte buffer.
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type Header interface {
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// Len returns the length of the header after marshaling.
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Len() int
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// Marshal serializes the header into buf in wire format.
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// It clobbers the header region, which is the first h.Length() bytes of buf.
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// It explicitly initializes every byte of the header region,
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// so pre-zeroing it on reuse is not required. It does not allocate memory.
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// It fails if and only if len(buf) < Length().
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Marshal(buf []byte) error
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// ToResponse transforms the header into one for a response packet.
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// For instance, this swaps the source and destination IPs.
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ToResponse()
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}
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// Generate generates a new packet with the given header and payload.
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// Unlike Header.Marshal, this does allocate memory.
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func Generate(h Header, payload []byte) []byte {
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hlen := h.Len()
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buf := make([]byte, hlen+len(payload))
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copy(buf[hlen:], payload)
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h.Marshal(buf)
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return buf
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}
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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type ICMPType uint8
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const (
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ICMPEchoReply ICMPType = 0x00
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ICMPEchoRequest ICMPType = 0x08
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ICMPUnreachable ICMPType = 0x03
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ICMPTimeExceeded ICMPType = 0x0b
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)
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func (t ICMPType) String() string {
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switch t {
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case ICMPEchoReply:
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return "EchoReply"
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case ICMPEchoRequest:
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return "EchoRequest"
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case ICMPUnreachable:
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return "Unreachable"
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case ICMPTimeExceeded:
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return "TimeExceeded"
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default:
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return "Unknown"
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}
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}
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type ICMPCode uint8
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const (
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ICMPNoCode ICMPCode = 0
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)
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// ICMPHeader represents an ICMP packet header.
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type ICMPHeader struct {
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IPHeader
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Type ICMPType
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Code ICMPCode
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}
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const (
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icmpHeaderLength = 4
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// icmpTotalHeaderLength is the length of all headers in a ICMP packet.
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icmpAllHeadersLength = ipHeaderLength + icmpHeaderLength
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)
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func (ICMPHeader) Len() int {
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return icmpAllHeadersLength
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}
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func (h ICMPHeader) Marshal(buf []byte) error {
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if len(buf) < icmpAllHeadersLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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// The caller does not need to set this.
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h.IPProto = ICMP
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buf[20] = uint8(h.Type)
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buf[21] = uint8(h.Code)
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h.IPHeader.Marshal(buf)
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put16(buf[22:24], ipChecksum(buf))
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return nil
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}
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func (h *ICMPHeader) ToResponse() {
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h.Type = ICMPEchoReply
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h.Code = ICMPNoCode
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h.IPHeader.ToResponse()
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}
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@ -0,0 +1,127 @@
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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import (
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"fmt"
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"net"
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)
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// IP is an IPv4 address.
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type IP uint32
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// NewIP converts a standard library IP address into an IP.
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// It panics if b is not an IPv4 address.
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func NewIP(b net.IP) IP {
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b4 := b.To4()
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if b4 == nil {
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panic(fmt.Sprintf("To4(%v) failed", b))
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}
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return IP(get32(b4))
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}
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func (ip IP) String() string {
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return fmt.Sprintf("%d.%d.%d.%d", byte(ip>>24), byte(ip>>16), byte(ip>>8), byte(ip))
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}
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// IPProto is either a real IP protocol (ITCP, UDP, ...) or an special value like Unknown.
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// If it is a real IP protocol, its value corresponds to its IP protocol number.
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type IPProto uint8
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const (
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// Unknown represents an unknown or unsupported protocol; it's deliberately the zero value.
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Unknown IPProto = 0x00
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ICMP IPProto = 0x01
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TCP IPProto = 0x06
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UDP IPProto = 0x11
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// IPv6 and Fragment are special values. They're not really IPProto values
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// so we're using the unassigned 0xFE and 0xFF values for them.
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// TODO(dmytro): special values should be taken out of here.
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IPv6 IPProto = 0xFE
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Fragment IPProto = 0xFF
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)
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func (p IPProto) String() string {
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switch p {
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case Fragment:
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return "Frag"
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case ICMP:
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return "ICMP"
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case UDP:
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return "UDP"
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case TCP:
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return "TCP"
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case IPv6:
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return "IPv6"
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default:
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return "Unknown"
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}
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}
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// IPHeader represents an IP packet header.
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type IPHeader struct {
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IPProto IPProto
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IPID uint16
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SrcIP IP
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DstIP IP
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}
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const ipHeaderLength = 20
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func (IPHeader) Len() int {
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return ipHeaderLength
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}
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func (h IPHeader) Marshal(buf []byte) error {
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if len(buf) < ipHeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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buf[0] = 0x40 | (ipHeaderLength >> 2) // IPv4
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buf[1] = 0x00 // DHCP, ECN
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put16(buf[2:4], uint16(len(buf)))
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put16(buf[4:6], h.IPID)
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put16(buf[6:8], 0) // flags, offset
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buf[8] = 64 // TTL
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buf[9] = uint8(h.IPProto)
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put16(buf[10:12], 0) // blank IP header checksum
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put32(buf[12:16], uint32(h.SrcIP))
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put32(buf[16:20], uint32(h.DstIP))
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put16(buf[10:12], ipChecksum(buf[0:20]))
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return nil
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}
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// MarshalPseudo serializes the header into buf in pseudo format.
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// It clobbers the header region, which is the first h.Length() bytes of buf.
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// It explicitly initializes every byte of the header region,
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// so pre-zeroing it on reuse is not required. It does not allocate memory.
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func (h IPHeader) MarshalPseudo(buf []byte) error {
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if len(buf) < ipHeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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length := len(buf) - ipHeaderLength
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put32(buf[8:12], uint32(h.SrcIP))
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put32(buf[12:16], uint32(h.DstIP))
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buf[16] = 0x0
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buf[17] = uint8(h.IPProto)
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put16(buf[18:20], uint16(length))
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return nil
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}
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func (h *IPHeader) ToResponse() {
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h.SrcIP, h.DstIP = h.DstIP, h.SrcIP
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// Flip the bits in the IPID. If incoming IPIDs are distinct, so are these.
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h.IPID = ^h.IPID
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}
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@ -0,0 +1,53 @@
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// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package packet
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// UDPHeader represents an UDP packet header.
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type UDPHeader struct {
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IPHeader
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SrcPort uint16
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DstPort uint16
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}
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const (
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udpHeaderLength = 8
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// udpTotalHeaderLength is the length of all headers in a UDP packet.
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udpTotalHeaderLength = ipHeaderLength + udpHeaderLength
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)
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func (UDPHeader) Len() int {
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return udpTotalHeaderLength
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}
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func (h UDPHeader) Marshal(buf []byte) error {
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if len(buf) < udpTotalHeaderLength {
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return errSmallBuffer
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}
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if len(buf) > maxPacketLength {
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return errLargePacket
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}
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// The caller does not need to set this.
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h.IPProto = UDP
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length := len(buf) - h.IPHeader.Len()
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put16(buf[20:22], h.SrcPort)
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put16(buf[22:24], h.DstPort)
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put16(buf[24:26], uint16(length))
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put16(buf[26:28], 0) // blank checksum
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h.IPHeader.MarshalPseudo(buf)
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// UDP checksum with IP pseudo header.
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put16(buf[26:28], ipChecksum(buf[8:]))
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h.IPHeader.Marshal(buf)
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return nil
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}
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func (h *UDPHeader) ToResponse() {
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h.SrcPort, h.DstPort = h.DstPort, h.SrcPort
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h.IPHeader.ToResponse()
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}
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