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layer_dhcp4.go
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package packet
import (
"encoding/binary"
"net"
"net/netip"
"time"
"github.com/irai/packet/fastlog"
)
// DHCP4 port numbers
const (
DHCP4ServerPort = 67
DHCP4ClientPort = 68
)
type DHCP4OpCode byte
// OpCodes
const (
DHCP4BootRequest DHCP4OpCode = 1 // From Client
DHCP4BootReply DHCP4OpCode = 2 // From Server
)
type DHCP4MessageType byte
// DHCP Message Type 53
const (
DHCP4Discover DHCP4MessageType = 1
DHCP4Offer DHCP4MessageType = 2
DHCP4Request DHCP4MessageType = 3
DHCP4Decline DHCP4MessageType = 4
DHCP4ACK DHCP4MessageType = 5
DHCP4NAK DHCP4MessageType = 6
DHCP4Release DHCP4MessageType = 7
DHCP4Inform DHCP4MessageType = 8
)
type DHCP4OptionCode byte
// DHCP Options
// see complete list here: https://www.iana.org/assignments/bootp-dhcp-parameters/bootp-dhcp-parameters.xhtml
const (
DHCP4End DHCP4OptionCode = 255
DHCP4Pad DHCP4OptionCode = 0
DHCP4OptionSubnetMask DHCP4OptionCode = 1
DHCP4OptionTimeOffset DHCP4OptionCode = 2
DHCP4OptionRouter DHCP4OptionCode = 3
DHCP4OptionTimeServer DHCP4OptionCode = 4
DHCP4OptionNameServer DHCP4OptionCode = 5
DHCP4OptionDomainNameServer DHCP4OptionCode = 6
DHCP4OptionLogServer DHCP4OptionCode = 7
DHCP4OptionCookieServer DHCP4OptionCode = 8
DHCP4OptionLPRServer DHCP4OptionCode = 9
DHCP4OptionImpressServer DHCP4OptionCode = 10
DHCP4OptionResourceLocationServer DHCP4OptionCode = 11
DHCP4OptionHostName DHCP4OptionCode = 12
DHCP4OptionBootFileSize DHCP4OptionCode = 13
DHCP4OptionMeritDumpFile DHCP4OptionCode = 14
DHCP4OptionDomainName DHCP4OptionCode = 15
DHCP4OptionSwapServer DHCP4OptionCode = 16
DHCP4OptionRootPath DHCP4OptionCode = 17
DHCP4OptionExtensionsPath DHCP4OptionCode = 18
DHCP4OptionIPForwardingEnableDisable DHCP4OptionCode = 19 // IP Layer Parameters per Host
DHCP4OptionNonLocalSourceRoutingEnableDisable DHCP4OptionCode = 20
DHCP4OptionPolicyFilter DHCP4OptionCode = 21
DHCP4OptionMaximumDatagramReassemblySize DHCP4OptionCode = 22
DHCP4OptionDefaultIPTimeToLive DHCP4OptionCode = 23
DHCP4OptionPathMTUAgingTimeout DHCP4OptionCode = 24
DHCP4OptionPathMTUPlateauTable DHCP4OptionCode = 25
DHCP4OptionInterfaceMTU DHCP4OptionCode = 26 // IP Layer Parameters per Interface
DHCP4OptionAllSubnetsAreLocal DHCP4OptionCode = 27
DHCP4OptionBroadcastAddress DHCP4OptionCode = 28
DHCP4OptionPerformMaskDiscovery DHCP4OptionCode = 29
DHCP4OptionMaskSupplier DHCP4OptionCode = 30
DHCP4OptionPerformRouterDiscovery DHCP4OptionCode = 31
DHCP4OptionRouterSolicitationAddress DHCP4OptionCode = 32
DHCP4OptionStaticRoute DHCP4OptionCode = 33
DHCP4OptionTrailerEncapsulation DHCP4OptionCode = 34
DHCP4OptionARPCacheTimeout DHCP4OptionCode = 35
DHCP4OptionEthernetEncapsulation DHCP4OptionCode = 36
DHCP4OptionRequestedIPAddress DHCP4OptionCode = 50 // DHCP Extensions
DHCP4OptionIPAddressLeaseTime DHCP4OptionCode = 51
DHCP4OptionOverload DHCP4OptionCode = 52
DHCP4OptionDHCPMessageType DHCP4OptionCode = 53
DHCP4OptionServerIdentifier DHCP4OptionCode = 54
DHCP4OptionParameterRequestList DHCP4OptionCode = 55
DHCP4OptionMessage DHCP4OptionCode = 56
DHCP4OptionMaximumDHCPMessageSize DHCP4OptionCode = 57
DHCP4OptionRenewalTimeValue DHCP4OptionCode = 58
DHCP4OptionRebindingTimeValue DHCP4OptionCode = 59
DHCP4OptionVendorClassIdentifier DHCP4OptionCode = 60
DHCP4OptionClientIdentifier DHCP4OptionCode = 61
DHCP4OptionClasslessRouteFormat DHCP4OptionCode = 121
)
// DHCP4 represents a dhcp version 4 packet.
type DHCP4 []byte
// DHCPv4 frame format
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | op (1) | htype (1) | hlen (1) | hops (1) |
// +---------------+---------------+---------------+---------------+
// | xid (4) |
// +-------------------------------+-------------------------------+
// | secs (2) | flags (2) |
// +-------------------------------+-------------------------------+
// | ciaddr (4) |
// +---------------------------------------------------------------+
// | yiaddr (4) |
// +---------------------------------------------------------------+
// | siaddr (4) |
// +---------------------------------------------------------------+
// | giaddr (4) |
// +---------------------------------------------------------------+
// | |
// | chaddr (16) |
// | |
// | |
// +---------------------------------------------------------------+
// | |
// | sname (64) |
// +---------------------------------------------------------------+
// | |
// | file (128) |
// +---------------------------------------------------------------+
// |cookie(4bytes) |
// | options (variable) |
// +---------------------------------------------------------------+
func (p DHCP4) OpCode() DHCP4OpCode { return DHCP4OpCode(p[0]) }
func (p DHCP4) HType() byte { return p[1] }
func (p DHCP4) HLen() byte { return p[2] }
func (p DHCP4) Hops() byte { return p[3] }
func (p DHCP4) XId() []byte { return p[4:8] }
func (p DHCP4) Secs() uint16 { return binary.BigEndian.Uint16(p[8:10]) }
func (p DHCP4) Flags() uint16 { return binary.BigEndian.Uint16(p[10:12]) }
func (p DHCP4) CIAddr() netip.Addr { return netip.AddrFrom4(*(*[4]byte)(p[12:16])) }
func (p DHCP4) YIAddr() netip.Addr { return netip.AddrFrom4(*(*[4]byte)(p[16:20])) }
func (p DHCP4) SIAddr() netip.Addr { return netip.AddrFrom4(*(*[4]byte)(p[20:24])) }
func (p DHCP4) GIAddr() netip.Addr { return netip.AddrFrom4(*(*[4]byte)(p[24:28])) }
func (p DHCP4) CHAddr() net.HardwareAddr { return net.HardwareAddr(p[28 : 28+6]) }
func (p DHCP4) SName() []byte { return trimNull(p[44 : 44+64]) } // BOOTP legacy
func (p DHCP4) File() []byte { return trimNull(p[108 : 108+128]) } // BOOTP legacy
func (p DHCP4) Cookie() []byte { return p[236:240] }
func (p DHCP4) Options() []byte {
if len(p) > 240 {
return p[240:]
}
return nil
}
func (p DHCP4) IsValid() error {
if len(p) < 240 { // Invalid size
return ErrFrameLen
}
if p.OpCode() != DHCP4BootRequest && p.OpCode() != DHCP4BootReply {
return ErrParseFrame
}
if p.HLen() != 6 { // Invalid frame - we only accept ethernet hardware addr
return ErrInvalidMAC
}
if err := p.validateOptions(); err != nil {
return err
}
return nil
}
func (p DHCP4) String() string {
l := Logger.Msg("")
return p.FastLog(l).ToString()
}
func (p DHCP4) FastLog(line *fastlog.Line) *fastlog.Line {
line.ByteArray("xid", p.XId())
line.Uint8("opcode", uint8(p.OpCode()))
line.MAC("chaddr", p.CHAddr())
line.IP("ciaddr", p.CIAddr())
line.IP("yiaddr", p.YIAddr())
line.Int("len", len(p))
return line
}
func trimNull(d []byte) []byte {
for i, v := range d {
if v == 0 {
return d[:i]
}
}
return d
}
func (p DHCP4) Broadcast() bool { return (p.Flags() & 0x8000) == 0x8000 }
func (p DHCP4) SetBroadcast(broadcast bool) {
if p.Broadcast() != broadcast {
p[10] ^= 128
}
}
func (p DHCP4) SetOpCode(c DHCP4OpCode) { p[0] = byte(c) }
func (p DHCP4) SetCHAddr(a net.HardwareAddr) {
copy(p[28:44], a)
p[2] = byte(len(a))
}
func (p DHCP4) SetHType(hType byte) { p[1] = hType }
func (p DHCP4) SetHLen(hLen byte) { p[2] = hLen }
func (p DHCP4) SetCookie(cookie []byte) { copy(p.Cookie(), cookie) }
func (p DHCP4) SetHops(hops byte) { p[3] = hops }
func (p DHCP4) SetXId(xId []byte) { copy(p.XId(), xId) }
func (p DHCP4) SetSecs(secs uint16) { binary.BigEndian.PutUint16(p[8:10], secs) }
func (p DHCP4) SetFlags(flags uint16) { binary.BigEndian.PutUint16(p[10:12], flags) }
func (p DHCP4) SetCIAddr(ip netip.Addr) { copy(p[12:16], ip.AsSlice()) }
func (p DHCP4) SetYIAddr(ip netip.Addr) { copy(p[16:20], ip.AsSlice()) }
func (p DHCP4) SetSIAddr(ip netip.Addr) { copy(p[20:24], ip.AsSlice()) }
func (p DHCP4) SetGIAddr(ip netip.Addr) { copy(p[24:28], ip.AsSlice()) }
// BOOTP legacy
func (p DHCP4) SetSName(sName []byte) {
copy(p[44:108], sName)
if len(sName) < 64 {
p[44+len(sName)] = 0
}
}
// BOOTP legacy
func (p DHCP4) SetFile(file []byte) {
copy(p[108:236], file)
if len(file) < 128 {
p[108+len(file)] = 0
}
}
// Map of DHCP options
type DHCP4Options map[DHCP4OptionCode][]byte
func (o DHCP4Options) HostName() string {
return string(o[DHCP4OptionHostName])
}
func (o DHCP4Options) RequestedIPAddress() net.IP {
if tmp, ok := o[DHCP4OptionRequestedIPAddress]; ok {
return net.IP(tmp).To4()
}
return nil
}
func (o DHCP4Options) ServerID() netip.Addr {
if tmp, ok := o[DHCP4OptionServerIdentifier]; ok {
if ip, ok := netip.AddrFromSlice(tmp); ok && ip.Is4() && !ip.IsUnspecified() {
return ip
}
}
return netip.Addr{}
}
func (p DHCP4) validateOptions() error {
opts := p.Options()
if len(opts) < 2 {
return ErrParseFrame
}
for len(opts) >= 2 && DHCP4OptionCode(opts[0]) != DHCP4End {
if DHCP4OptionCode(opts[0]) == DHCP4Pad {
opts = opts[1:]
continue
}
size := int(opts[1])
if len(opts) < 2+size {
return ErrParseFrame
}
opts = opts[2+size:]
}
return nil
}
// Parses the packet's options into an Options map
// Caution: we return slices to the underlying byte array
func (p DHCP4) ParseOptions() DHCP4Options {
opts := p.Options()
options := make(DHCP4Options, 10)
for len(opts) >= 2 && DHCP4OptionCode(opts[0]) != DHCP4End {
if DHCP4OptionCode(opts[0]) == DHCP4Pad {
opts = opts[1:]
continue
}
size := int(opts[1])
if len(opts) < 2+size {
break
}
options[DHCP4OptionCode(opts[0])] = opts[2 : 2+size]
opts = opts[2+size:]
}
return options
}
func (p DHCP4) AppendOptions(options DHCP4Options, order []byte) int {
if cap(p) < 240 {
return 0
}
pos := 0
buffer := make([]byte, 1024) // use a tmp buffer in case options point to the underlying array
var optionsReplyParametersList = []byte{
byte(DHCP4OptionSubnetMask), // must appear before router options
byte(DHCP4OptionStaticRoute),
byte(DHCP4OptionRouter),
}
order = append(order, optionsReplyParametersList...)
// first copy parameters in order
for _, code := range order {
if value, ok := options[DHCP4OptionCode(code)]; ok {
buffer[pos] = byte(code)
buffer[pos+1] = byte(len(value))
pos = pos + 2
pos = pos + copy(buffer[pos:], value)
delete(options, DHCP4OptionCode(code))
}
}
// second, copy any remaining options
for code, value := range options {
buffer[pos] = byte(code)
buffer[pos+1] = byte(len(value))
pos = pos + 2
pos = pos + copy(buffer[pos:], value)
}
copy(p[240:cap(p)], buffer[:pos])
return pos
}
// optionsLeaseTime - converts a time.Duration to a 4 byte slice, compatible
// with OptionIPAddressLeaseTime.
func OptionsLeaseTime(d time.Duration) []byte {
leaseBytes := make([]byte, 4)
binary.BigEndian.PutUint32(leaseBytes, uint32(d/time.Second))
return leaseBytes
}
func zeroes(b []byte) {
for i := 0; i < len(b); i++ {
b[i] = 0x00
}
}
// EncodeDHCP4 returns the underlying slice as a DHCP4 frame. The returned slice is adjusted to the length of the DHCP frame.
// When replying to a DHCP request, you can pass nil to chaddr, ciaddr, yiadd, and xid to keep the underlying values.
func EncodeDHCP4(b []byte, opcode DHCP4OpCode, mt DHCP4MessageType, chaddr net.HardwareAddr, ciaddr netip.Addr, yiaddr netip.Addr, xid []byte, broadcast bool, options DHCP4Options, order []byte) DHCP4 {
if cap(b) < 300 { // minimum packet size
return nil
}
p := DHCP4(b[:cap(b)])
zeroes(p[28+6 : 236]) // zero from chaddr (but keep first 6b of existing mac) , fname, file
p.SetOpCode(opcode)
p.SetHType(1) // Ethernet
p.SetHLen(6) // Ethernet mac len
p.SetHops(0)
if xid != nil {
p.SetXId(xid)
}
p.SetSecs(0)
p.SetFlags(0)
p.SetCookie([]byte{99, 130, 83, 99})
if ciaddr.Is4() {
p.SetCIAddr(ciaddr)
}
if yiaddr.Is4() {
p.SetYIAddr(yiaddr)
}
p.SetSIAddr(IPv4zero)
p.SetGIAddr(IPv4zero)
if chaddr != nil {
p.SetCHAddr(chaddr)
}
p.SetBroadcast(broadcast)
if options == nil {
options = DHCP4Options{}
}
options[DHCP4OptionCode(DHCP4OptionDHCPMessageType)] = []byte{byte(mt)}
n := 240 + p.AppendOptions(options, order)
p[n] = byte(DHCP4End)
n++
// PadToMinSize pads a packet so that when sent over UDP, the entire packet,
// is 300 bytes (BOOTP min), to be compatible with really old devices.
for ; n < 300; n++ {
p[n] = 0x00
}
return p[:n]
}