badguardhome/dhcpd/dhcpd.go

392 lines
14 KiB
Go

package dhcpd
import (
"bytes"
"fmt"
"net"
"time"
"github.com/hmage/golibs/log"
"github.com/krolaw/dhcp4"
)
const defaultDiscoverTime = time.Second * 3
// field ordering is important -- yaml fields will mirror ordering from here
type Lease struct {
HWAddr net.HardwareAddr `json:"mac" yaml:"hwaddr"`
IP net.IP `json:"ip"`
Hostname string `json:"hostname"`
Expiry time.Time `json:"expires"`
}
// field ordering is important -- yaml fields will mirror ordering from here
type ServerConfig struct {
Enabled bool `json:"enabled" yaml:"enabled"`
InterfaceName string `json:"interface_name" yaml:"interface_name"` // eth0, en0 and so on
GatewayIP string `json:"gateway_ip" yaml:"gateway_ip"`
SubnetMask string `json:"subnet_mask" yaml:"subnet_mask"`
RangeStart string `json:"range_start" yaml:"range_start"`
RangeEnd string `json:"range_end" yaml:"range_end"`
LeaseDuration uint `json:"lease_duration" yaml:"lease_duration"` // in seconds
}
type Server struct {
conn *filterConn // listening UDP socket
ipnet *net.IPNet // if interface name changes, this needs to be reset
// leases
leases []*Lease
leaseStart net.IP // parsed from config RangeStart
leaseStop net.IP // parsed from config RangeEnd
leaseTime time.Duration // parsed from config LeaseDuration
leaseOptions dhcp4.Options // parsed from config GatewayIP and SubnetMask
// IP address pool -- if entry is in the pool, then it's attached to a lease
IPpool map[[4]byte]net.HardwareAddr
ServerConfig
}
// Start will listen on port 67 and serve DHCP requests.
// Even though config can be nil, it is not optional (at least for now), since there are no default values (yet).
func (s *Server) Start(config *ServerConfig) error {
if config != nil {
s.ServerConfig = *config
}
iface, err := net.InterfaceByName(s.InterfaceName)
if err != nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Couldn't find interface by name %s", s.InterfaceName)
}
// get ipv4 address of an interface
s.ipnet = getIfaceIPv4(iface)
if s.ipnet == nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Couldn't find IPv4 address of interface %s %+v", s.InterfaceName, iface)
}
if s.LeaseDuration == 0 {
s.leaseTime = time.Hour * 2
s.LeaseDuration = uint(s.leaseTime.Seconds())
} else {
s.leaseTime = time.Second * time.Duration(s.LeaseDuration)
}
s.leaseStart, err = parseIPv4(s.RangeStart)
if err != nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Failed to parse range start address %s", s.RangeStart)
}
s.leaseStop, err = parseIPv4(s.RangeEnd)
if err != nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Failed to parse range end address %s", s.RangeEnd)
}
subnet, err := parseIPv4(s.SubnetMask)
if err != nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Failed to parse subnet mask %s", s.SubnetMask)
}
// if !bytes.Equal(subnet, s.ipnet.Mask) {
// s.closeConn() // in case it was already started
// return wrapErrPrint(err, "specified subnet mask %s does not meatch interface %s subnet mask %s", s.SubnetMask, s.InterfaceName, s.ipnet.Mask)
// }
router, err := parseIPv4(s.GatewayIP)
if err != nil {
s.closeConn() // in case it was already started
return wrapErrPrint(err, "Failed to parse gateway IP %s", s.GatewayIP)
}
s.leaseOptions = dhcp4.Options{
dhcp4.OptionSubnetMask: subnet,
dhcp4.OptionRouter: router,
dhcp4.OptionDomainNameServer: s.ipnet.IP,
}
// TODO: don't close if interface and addresses are the same
if s.conn != nil {
s.closeConn()
}
c, err := newFilterConn(*iface, ":67") // it has to be bound to 0.0.0.0:67, otherwise it won't see DHCP discover/request packets
if err != nil {
return wrapErrPrint(err, "Couldn't start listening socket on 0.0.0.0:67")
}
s.conn = c
go func() {
// operate on c instead of c.conn because c.conn can change over time
err := dhcp4.Serve(c, s)
if err != nil {
log.Printf("dhcp4.Serve() returned with error: %s", err)
}
c.Close() // in case Serve() exits for other reason than listening socket closure
}()
return nil
}
func (s *Server) Stop() error {
if s.conn == nil {
// nothing to do, return silently
return nil
}
err := s.closeConn()
if err != nil {
return wrapErrPrint(err, "Couldn't close UDP listening socket")
}
return nil
}
// closeConn will close the connection and set it to zero
func (s *Server) closeConn() error {
if s.conn == nil {
return nil
}
err := s.conn.Close()
s.conn = nil
return err
}
func (s *Server) reserveLease(p dhcp4.Packet) (*Lease, error) {
// WARNING: do not remove copy()
// the given hwaddr by p.CHAddr() in the packet survives only during ServeDHCP() call
// since we need to retain it we need to make our own copy
hwaddrCOW := p.CHAddr()
hwaddr := make(net.HardwareAddr, len(hwaddrCOW))
copy(hwaddr, hwaddrCOW)
foundLease := s.locateLease(p)
if foundLease != nil {
// log.Tracef("found lease for %s: %+v", hwaddr, foundLease)
return foundLease, nil
}
// not assigned a lease, create new one, find IP from LRU
log.Tracef("Lease not found for %s: creating new one", hwaddr)
ip, err := s.findFreeIP(p, hwaddr)
if err != nil {
return nil, wrapErrPrint(err, "Couldn't find free IP for the lease %s", hwaddr.String())
}
log.Tracef("Assigning to %s IP address %s", hwaddr, ip.String())
hostname := p.ParseOptions()[dhcp4.OptionHostName]
lease := &Lease{HWAddr: hwaddr, IP: ip, Hostname: string(hostname)}
s.leases = append(s.leases, lease)
return lease, nil
}
func (s *Server) locateLease(p dhcp4.Packet) *Lease {
hwaddr := p.CHAddr()
for i := range s.leases {
if bytes.Equal([]byte(hwaddr), []byte(s.leases[i].HWAddr)) {
// log.Tracef("bytes.Equal(%s, %s) returned true", hwaddr, s.leases[i].hwaddr)
return s.leases[i]
}
}
return nil
}
func (s *Server) findFreeIP(p dhcp4.Packet, hwaddr net.HardwareAddr) (net.IP, error) {
// if IP pool is nil, lazy initialize it
if s.IPpool == nil {
s.IPpool = make(map[[4]byte]net.HardwareAddr)
}
// go from start to end, find unreserved IP
var foundIP net.IP
for i := 0; i < dhcp4.IPRange(s.leaseStart, s.leaseStop); i++ {
newIP := dhcp4.IPAdd(s.leaseStart, i)
foundHWaddr := s.getIPpool(newIP)
log.Tracef("tried IP %v, got hwaddr %v", newIP, foundHWaddr)
if foundHWaddr != nil && len(foundHWaddr) != 0 {
// if !bytes.Equal(foundHWaddr, hwaddr) {
// log.Tracef("SHOULD NOT HAPPEN: hwaddr in IP pool %s is not equal to hwaddr in lease %s", foundHWaddr, hwaddr)
// }
log.Tracef("will try again")
continue
}
foundIP = newIP
break
}
if foundIP == nil {
// TODO: LRU
return nil, fmt.Errorf("Couldn't find free entry in IP pool")
}
s.reserveIP(foundIP, hwaddr)
return foundIP, nil
}
func (s *Server) getIPpool(ip net.IP) net.HardwareAddr {
rawIP := []byte(ip)
IP4 := [4]byte{rawIP[0], rawIP[1], rawIP[2], rawIP[3]}
return s.IPpool[IP4]
}
func (s *Server) reserveIP(ip net.IP, hwaddr net.HardwareAddr) {
rawIP := []byte(ip)
IP4 := [4]byte{rawIP[0], rawIP[1], rawIP[2], rawIP[3]}
s.IPpool[IP4] = hwaddr
}
func (s *Server) unreserveIP(ip net.IP) {
rawIP := []byte(ip)
IP4 := [4]byte{rawIP[0], rawIP[1], rawIP[2], rawIP[3]}
delete(s.IPpool, IP4)
}
func (s *Server) ServeDHCP(p dhcp4.Packet, msgType dhcp4.MessageType, options dhcp4.Options) dhcp4.Packet {
log.Tracef("Got %v message", msgType)
log.Tracef("Leases:")
for i, lease := range s.leases {
log.Tracef("Lease #%d: hwaddr %s, ip %s, expiry %s", i, lease.HWAddr, lease.IP, lease.Expiry)
}
log.Tracef("IP pool:")
for ip, hwaddr := range s.IPpool {
log.Tracef("IP pool entry %s -> %s", net.IPv4(ip[0], ip[1], ip[2], ip[3]), hwaddr)
}
// spew.Dump(s.leases, s.IPpool)
// log.Printf("Called with msgType = %v, options = %+v", msgType, options)
// spew.Dump(p)
// log.Printf("%14s %v", "p.Broadcast", p.Broadcast()) // false
// log.Printf("%14s %v", "p.CHAddr", p.CHAddr()) // 2c:f0:a2:f2:31:00
// log.Printf("%14s %v", "p.CIAddr", p.CIAddr()) // 0.0.0.0
// log.Printf("%14s %v", "p.Cookie", p.Cookie()) // [99 130 83 99]
// log.Printf("%14s %v", "p.File", p.File()) // []
// log.Printf("%14s %v", "p.Flags", p.Flags()) // [0 0]
// log.Printf("%14s %v", "p.GIAddr", p.GIAddr()) // 0.0.0.0
// log.Printf("%14s %v", "p.HLen", p.HLen()) // 6
// log.Printf("%14s %v", "p.HType", p.HType()) // 1
// log.Printf("%14s %v", "p.Hops", p.Hops()) // 0
// log.Printf("%14s %v", "p.OpCode", p.OpCode()) // BootRequest
// log.Printf("%14s %v", "p.Options", p.Options()) // [53 1 1 55 10 1 121 3 6 15 119 252 95 44 46 57 2 5 220 61 7 1 44 240 162 242 49 0 51 4 0 118 167 0 12 4 119 104 109 100 255 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
// log.Printf("%14s %v", "p.ParseOptions", p.ParseOptions()) // map[OptionParameterRequestList:[1 121 3 6 15 119 252 95 44 46] OptionDHCPMessageType:[1] OptionMaximumDHCPMessageSize:[5 220] OptionClientIdentifier:[1 44 240 162 242 49 0] OptionIPAddressLeaseTime:[0 118 167 0] OptionHostName:[119 104 109 100]]
// log.Printf("%14s %v", "p.SIAddr", p.SIAddr()) // 0.0.0.0
// log.Printf("%14s %v", "p.SName", p.SName()) // []
// log.Printf("%14s %v", "p.Secs", p.Secs()) // [0 8]
// log.Printf("%14s %v", "p.XId", p.XId()) // [211 184 20 44]
// log.Printf("%14s %v", "p.YIAddr", p.YIAddr()) // 0.0.0.0
switch msgType {
case dhcp4.Discover: // Broadcast Packet From Client - Can I have an IP?
// find a lease, but don't update lease time
log.Tracef("Got from client: Discover")
lease, err := s.reserveLease(p)
if err != nil {
log.Tracef("Couldn't find free lease: %s", err)
// couldn't find lease, don't respond
return nil
}
reply := dhcp4.ReplyPacket(p, dhcp4.Offer, s.ipnet.IP, lease.IP, s.leaseTime, s.leaseOptions.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]))
log.Tracef("Replying with offer: offered IP %v for %v with options %+v", lease.IP, s.leaseTime, reply.ParseOptions())
return reply
case dhcp4.Request: // Broadcast From Client - I'll take that IP (Also start for renewals)
// start/renew a lease -- update lease time
// some clients (OSX) just go right ahead and do Request first from previously known IP, if they get NAK, they restart full cycle with Discover then Request
log.Tracef("Got from client: Request")
if server, ok := options[dhcp4.OptionServerIdentifier]; ok && !net.IP(server).Equal(s.ipnet.IP) {
log.Tracef("Request message not for this DHCP server (%v vs %v)", server, s.ipnet.IP)
return nil // Message not for this dhcp server
}
reqIP := net.IP(options[dhcp4.OptionRequestedIPAddress])
if reqIP == nil {
reqIP = net.IP(p.CIAddr())
}
if reqIP.To4() == nil {
log.Tracef("Replying with NAK: request IP isn't valid IPv4: %s", reqIP)
return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil)
}
if reqIP.Equal(net.IPv4zero) {
log.Tracef("Replying with NAK: request IP is 0.0.0.0")
return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil)
}
log.Tracef("requested IP is %s", reqIP)
lease, err := s.reserveLease(p)
if err != nil {
log.Tracef("Couldn't find free lease: %s", err)
// couldn't find lease, don't respond
return nil
}
if lease.IP.Equal(reqIP) {
// IP matches lease IP, nothing else to do
lease.Expiry = time.Now().Add(s.leaseTime)
log.Tracef("Replying with ACK: request IP matches lease IP, nothing else to do. IP %v for %v", lease.IP, p.CHAddr())
return dhcp4.ReplyPacket(p, dhcp4.ACK, s.ipnet.IP, lease.IP, s.leaseTime, s.leaseOptions.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]))
}
//
// requested IP different from lease
//
log.Tracef("lease IP is different from requested IP: %s vs %s", lease.IP, reqIP)
hwaddr := s.getIPpool(reqIP)
if hwaddr == nil {
// not in pool, check if it's in DHCP range
if dhcp4.IPInRange(s.leaseStart, s.leaseStop, reqIP) {
// okay, we can give it to our client -- it's in our DHCP range and not taken, so let them use their IP
log.Tracef("Replying with ACK: request IP %v is not taken, so assigning lease IP %v to it, for %v", reqIP, lease.IP, p.CHAddr())
s.unreserveIP(lease.IP)
lease.IP = reqIP
s.reserveIP(reqIP, p.CHAddr())
lease.Expiry = time.Now().Add(s.leaseTime)
return dhcp4.ReplyPacket(p, dhcp4.ACK, s.ipnet.IP, lease.IP, s.leaseTime, s.leaseOptions.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]))
}
}
if hwaddr != nil && !bytes.Equal(hwaddr, lease.HWAddr) {
log.Printf("SHOULD NOT HAPPEN: IP pool hwaddr does not match lease hwaddr: %s vs %s", hwaddr, lease.HWAddr)
}
// requsted IP is not sufficient, reply with NAK
if hwaddr != nil {
log.Tracef("Replying with NAK: request IP %s is taken, asked by %v", reqIP, p.CHAddr())
return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil)
}
// requested IP is outside of DHCP range
log.Tracef("Replying with NAK: request IP %s is outside of DHCP range [%s, %s], asked by %v", reqIP, s.leaseStart, s.leaseStop, p.CHAddr())
return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil)
case dhcp4.Decline: // Broadcast From Client - Sorry I can't use that IP
log.Tracef("Got from client: Decline")
case dhcp4.Release: // From Client, I don't need that IP anymore
log.Tracef("Got from client: Release")
case dhcp4.Inform: // From Client, I have this IP and there's nothing you can do about it
log.Tracef("Got from client: Inform")
// do nothing
// from server -- ignore those but enumerate just in case
case dhcp4.Offer: // Broadcast From Server - Here's an IP
log.Printf("SHOULD NOT HAPPEN -- FROM ANOTHER DHCP SERVER: Offer")
case dhcp4.ACK: // From Server, Yes you can have that IP
log.Printf("SHOULD NOT HAPPEN -- FROM ANOTHER DHCP SERVER: ACK")
case dhcp4.NAK: // From Server, No you cannot have that IP
log.Printf("SHOULD NOT HAPPEN -- FROM ANOTHER DHCP SERVER: NAK")
default:
log.Printf("Unknown DHCP packet detected, ignoring: %v", msgType)
return nil
}
return nil
}
func (s *Server) Leases() []*Lease {
return s.leases
}