Move Linux client & common packages into a public repo.
This commit is contained in:
Earl Lee
363
wgengine/packet/packet.go
Normal file
363
wgengine/packet/packet.go
Normal file
@ -0,0 +1,363 @@
|
||||
// Copyright (c) 2020 Tailscale Inc & 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 packet
|
||||
|
||||
import (
|
||||
"encoding/binary"
|
||||
"encoding/json"
|
||||
"fmt"
|
||||
"log"
|
||||
"net"
|
||||
"strings"
|
||||
)
|
||||
|
||||
type IPProto int
|
||||
|
||||
const (
|
||||
Junk IPProto = iota
|
||||
Fragment
|
||||
ICMP
|
||||
UDP
|
||||
TCP
|
||||
)
|
||||
|
||||
// RFC1858: prevent overlapping fragment attacks.
|
||||
const MIN_FRAG = 60 + 20 // max IPv4 header + basic TCP header
|
||||
|
||||
func (p IPProto) String() string {
|
||||
switch p {
|
||||
case Fragment:
|
||||
return "Frag"
|
||||
case ICMP:
|
||||
return "ICMP"
|
||||
case UDP:
|
||||
return "UDP"
|
||||
case TCP:
|
||||
return "TCP"
|
||||
default:
|
||||
return "Junk"
|
||||
}
|
||||
}
|
||||
|
||||
type IP uint32
|
||||
|
||||
const IPAny = IP(0)
|
||||
|
||||
func NewIP(b net.IP) IP {
|
||||
b4 := b.To4()
|
||||
if b4 == nil {
|
||||
panic(fmt.Sprintf("To4(%v) failed", b))
|
||||
}
|
||||
return IP(binary.BigEndian.Uint32(b4))
|
||||
}
|
||||
|
||||
func (ip IP) String() string {
|
||||
if ip == 0 {
|
||||
return "*"
|
||||
}
|
||||
b := make([]byte, 4)
|
||||
binary.BigEndian.PutUint32(b, uint32(ip))
|
||||
return fmt.Sprintf("%d.%d.%d.%d", b[0], b[1], b[2], b[3])
|
||||
}
|
||||
|
||||
func (ipp *IP) MarshalJSON() ([]byte, error) {
|
||||
s := "\"" + (*ipp).String() + "\""
|
||||
return []byte(s), nil
|
||||
}
|
||||
|
||||
func (ipp *IP) UnmarshalJSON(b []byte) error {
|
||||
var hostp *string
|
||||
err := json.Unmarshal(b, &hostp)
|
||||
if err != nil {
|
||||
return err
|
||||
}
|
||||
host := *hostp
|
||||
ip := net.ParseIP(host)
|
||||
if ip != nil && ip.IsUnspecified() {
|
||||
// For clarity, reject 0.0.0.0 as an input
|
||||
return fmt.Errorf("Ports=%#v: to allow all IP addresses, use *:port, not 0.0.0.0:port", host)
|
||||
} else if ip == nil && host == "*" {
|
||||
// User explicitly requested wildcard dst ip
|
||||
*ipp = IPAny
|
||||
} else {
|
||||
if ip != nil {
|
||||
ip = ip.To4()
|
||||
}
|
||||
if ip == nil || len(ip) != 4 {
|
||||
return fmt.Errorf("Ports=%#v: invalid IPv4 address", host)
|
||||
}
|
||||
*ipp = NewIP(ip)
|
||||
}
|
||||
return nil
|
||||
}
|
||||
|
||||
const (
|
||||
EchoReply uint8 = 0x00
|
||||
EchoRequest uint8 = 0x08
|
||||
)
|
||||
|
||||
const (
|
||||
TCPSyn uint8 = 0x02
|
||||
TCPAck uint8 = 0x10
|
||||
TCPSynAck uint8 = TCPSyn | TCPAck
|
||||
)
|
||||
|
||||
type QDecode struct {
|
||||
b []byte // Packet buffer that this decodes
|
||||
subofs int // byte offset of IP subprotocol
|
||||
|
||||
IPProto IPProto // IP subprotocol (UDP, TCP, etc)
|
||||
SrcIP IP // IP source address
|
||||
DstIP IP // IP destination address
|
||||
SrcPort uint16 // TCP/UDP source port
|
||||
DstPort uint16 // TCP/UDP destination port
|
||||
TCPFlags uint8 // TCP flags (SYN, ACK, etc)
|
||||
}
|
||||
|
||||
func (q QDecode) String() string {
|
||||
if q.IPProto == Junk {
|
||||
return "Junk{}"
|
||||
}
|
||||
srcip := make([]byte, 4)
|
||||
dstip := make([]byte, 4)
|
||||
binary.BigEndian.PutUint32(srcip, uint32(q.SrcIP))
|
||||
binary.BigEndian.PutUint32(dstip, uint32(q.DstIP))
|
||||
return fmt.Sprintf("%v{%d.%d.%d.%d:%d > %d.%d.%d.%d:%d}",
|
||||
q.IPProto,
|
||||
srcip[0], srcip[1], srcip[2], srcip[3], q.SrcPort,
|
||||
dstip[0], dstip[1], dstip[2], dstip[3], q.DstPort)
|
||||
}
|
||||
|
||||
// based on https://tools.ietf.org/html/rfc1071
|
||||
func ipChecksum(b []byte) uint16 {
|
||||
var ac uint32
|
||||
i := 0
|
||||
n := len(b)
|
||||
for n >= 2 {
|
||||
ac += uint32(binary.BigEndian.Uint16(b[i : i+2]))
|
||||
n -= 2
|
||||
i += 2
|
||||
}
|
||||
if n == 1 {
|
||||
ac += uint32(b[i]) << 8
|
||||
}
|
||||
for (ac >> 16) > 0 {
|
||||
ac = (ac >> 16) + (ac & 0xffff)
|
||||
}
|
||||
return uint16(^ac)
|
||||
}
|
||||
|
||||
func GenICMP(srcIP, dstIP IP, ipid uint16, icmpType uint8, icmpCode uint8, payload []byte) []byte {
|
||||
if len(payload) < 4 {
|
||||
return nil
|
||||
}
|
||||
if len(payload) > 65535-24 {
|
||||
return nil
|
||||
}
|
||||
|
||||
sz := 24 + len(payload)
|
||||
out := make([]byte, 24+len(payload))
|
||||
out[0] = 0x45 // IPv4, 20-byte header
|
||||
out[1] = 0x00 // DHCP, ECN
|
||||
binary.BigEndian.PutUint16(out[2:4], uint16(sz))
|
||||
binary.BigEndian.PutUint16(out[4:6], ipid)
|
||||
binary.BigEndian.PutUint16(out[6:8], 0) // flags, offset
|
||||
out[8] = 64 // TTL
|
||||
out[9] = 0x01 // ICMPv4
|
||||
// out[10:12] = 0x00 // blank IP header checksum
|
||||
binary.BigEndian.PutUint32(out[12:16], uint32(srcIP))
|
||||
binary.BigEndian.PutUint32(out[16:20], uint32(dstIP))
|
||||
|
||||
out[20] = icmpType
|
||||
out[21] = icmpCode
|
||||
//out[22:24] = 0x00 // blank ICMP checksum
|
||||
copy(out[24:len(out)], payload)
|
||||
|
||||
binary.BigEndian.PutUint16(out[10:12], ipChecksum(out[0:20]))
|
||||
binary.BigEndian.PutUint16(out[22:24], ipChecksum(out))
|
||||
return out
|
||||
}
|
||||
|
||||
// An extremely simple packet decoder for basic IPv4 packet types.
|
||||
// It extracts only the subprotocol id, IP addresses, and (if any) ports,
|
||||
// and shouldn't need any memory allocation.
|
||||
func (q *QDecode) Decode(b []byte) {
|
||||
q.b = nil
|
||||
|
||||
if len(b) < 20 {
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
// Check that it's IPv4.
|
||||
// TODO(apenwarr): consider IPv6 support
|
||||
if ((b[0] & 0xF0) >> 4) != 4 {
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
|
||||
n := int(binary.BigEndian.Uint16(b[2:4]))
|
||||
if len(b) < n {
|
||||
// Packet was cut off before full IPv4 length.
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
|
||||
// If it's valid IPv4, then the IP addresses are valid
|
||||
q.SrcIP = IP(binary.BigEndian.Uint32(b[12:16]))
|
||||
q.DstIP = IP(binary.BigEndian.Uint32(b[16:20]))
|
||||
|
||||
q.subofs = int((b[0] & 0x0F) * 4)
|
||||
sub := b[q.subofs:]
|
||||
|
||||
// We don't care much about IP fragmentation, except insofar as it's
|
||||
// used for firewall bypass attacks. The trick is make the first
|
||||
// fragment of a TCP or UDP packet so short that it doesn't fit
|
||||
// the TCP or UDP header, so we can't read the port, in hope that
|
||||
// it'll sneak past. Then subsequent fragments fill it in, but we're
|
||||
// missing the first part of the header, so we can't read that either.
|
||||
//
|
||||
// A "perfectly correct" implementation would have to reassemble
|
||||
// fragments before deciding what to do. But the truth is there's
|
||||
// zero reason to send such a short first fragment, so we can treat
|
||||
// it as Junk. We can also treat any subsequent fragment that starts
|
||||
// at such a low offset as Junk.
|
||||
fragFlags := binary.BigEndian.Uint16(b[6:8])
|
||||
moreFrags := (fragFlags & 0x20) != 0
|
||||
fragOfs := fragFlags & 0x1FFF
|
||||
if fragOfs == 0 {
|
||||
// This is the first fragment
|
||||
if moreFrags && len(sub) < MIN_FRAG {
|
||||
// Suspiciously short first fragment, dump it.
|
||||
log.Printf("junk1!\n")
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
// otherwise, this is either non-fragmented (the usual case)
|
||||
// or a big enough initial fragment that we can read the
|
||||
// whole subprotocol header.
|
||||
proto := b[9]
|
||||
switch proto {
|
||||
case 1: // ICMPv4
|
||||
if len(sub) < 8 {
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
q.IPProto = ICMP
|
||||
q.SrcPort = 0
|
||||
q.DstPort = 0
|
||||
q.b = b
|
||||
return
|
||||
case 6: // TCP
|
||||
if len(sub) < 20 {
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
q.IPProto = TCP
|
||||
q.SrcPort = binary.BigEndian.Uint16(sub[0:2])
|
||||
q.DstPort = binary.BigEndian.Uint16(sub[2:4])
|
||||
q.TCPFlags = sub[13] & 0x3F
|
||||
q.b = b
|
||||
return
|
||||
case 17: // UDP
|
||||
if len(sub) < 8 {
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
q.IPProto = UDP
|
||||
q.SrcPort = binary.BigEndian.Uint16(sub[0:2])
|
||||
q.DstPort = binary.BigEndian.Uint16(sub[2:4])
|
||||
q.b = b
|
||||
return
|
||||
default:
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
} else {
|
||||
// This is a fragment other than the first one.
|
||||
if fragOfs < MIN_FRAG {
|
||||
// First frag was suspiciously short, so we can't
|
||||
// trust the followup either.
|
||||
q.IPProto = Junk
|
||||
return
|
||||
}
|
||||
// otherwise, we have to permit the fragment to slide through.
|
||||
// Second and later fragments don't have sub-headers.
|
||||
// Ideally, we would drop fragments that we can't identify,
|
||||
// but that would require statefulness. Anyway, receivers'
|
||||
// kernels know to drop fragments where the initial fragment
|
||||
// doesn't arrive.
|
||||
q.IPProto = Fragment
|
||||
return
|
||||
}
|
||||
}
|
||||
|
||||
// Returns a subset of the IP subprotocol section.
|
||||
func (q *QDecode) Sub(begin, n int) []byte {
|
||||
return q.b[q.subofs+begin : q.subofs+begin+n]
|
||||
}
|
||||
|
||||
// For a packet that is known to be IPv4, trim the buffer to its IPv4 length.
|
||||
// Sometimes packets arrive from an interface with extra bytes on the end.
|
||||
// This removes them.
|
||||
func (q *QDecode) Trim() []byte {
|
||||
n := binary.BigEndian.Uint16(q.b[2:4])
|
||||
return q.b[0:n]
|
||||
}
|
||||
|
||||
// For a decoded TCP packet, return true if it's a TCP SYN packet (ie. the
|
||||
// first packet in a new connection).
|
||||
func (q *QDecode) IsTCPSyn() bool {
|
||||
const Syn = 0x02
|
||||
const Ack = 0x10
|
||||
const SynAck = Syn | Ack
|
||||
return (q.TCPFlags & SynAck) == Syn
|
||||
}
|
||||
|
||||
// For a packet that has already been decoded, check if it's an IPv4 ICMP
|
||||
// Echo Request.
|
||||
func (q *QDecode) IsEchoRequest() bool {
|
||||
if q.IPProto == ICMP && len(q.b) >= q.subofs+8 {
|
||||
return q.b[q.subofs] == EchoRequest && q.b[q.subofs+1] == 0
|
||||
}
|
||||
return false
|
||||
}
|
||||
|
||||
func (q *QDecode) EchoRespond() []byte {
|
||||
icmpid := binary.BigEndian.Uint16(q.Sub(4, 2))
|
||||
b := q.Trim()
|
||||
return GenICMP(q.DstIP, q.SrcIP, icmpid, EchoReply, 0, b[q.subofs+4:])
|
||||
}
|
||||
|
||||
func Hexdump(b []byte) string {
|
||||
out := new(strings.Builder)
|
||||
for i := 0; i < len(b); i += 16 {
|
||||
if i > 0 {
|
||||
fmt.Fprintf(out, "\n")
|
||||
}
|
||||
fmt.Fprintf(out, " %04x ", i)
|
||||
j := 0
|
||||
for ; j < 16 && i+j < len(b); j++ {
|
||||
if j == 8 {
|
||||
fmt.Fprintf(out, " ")
|
||||
}
|
||||
fmt.Fprintf(out, "%02x ", b[i+j])
|
||||
}
|
||||
for ; j < 16; j++ {
|
||||
if j == 8 {
|
||||
fmt.Fprintf(out, " ")
|
||||
}
|
||||
fmt.Fprintf(out, " ")
|
||||
}
|
||||
fmt.Fprintf(out, " ")
|
||||
for j = 0; j < 16 && i+j < len(b); j++ {
|
||||
if b[i+j] >= 32 && b[i+j] < 128 {
|
||||
fmt.Fprintf(out, "%c", b[i+j])
|
||||
} else {
|
||||
fmt.Fprintf(out, ".")
|
||||
}
|
||||
}
|
||||
}
|
||||
return out.String()
|
||||
}
|
||||
Reference in New Issue
Block a user