package dhcpd import ( "bytes" "fmt" "net" "strings" "sync" "time" "github.com/AdguardTeam/golibs/log" "github.com/krolaw/dhcp4" ping "github.com/sparrc/go-ping" ) const defaultDiscoverTime = time.Second * 3 const leaseExpireStatic = 1 // Lease contains the necessary information about a DHCP lease // 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"` // Lease expiration time // 1: static lease Expiry time.Time `json:"expires"` } // ServerConfig - DHCP server configuration // 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 // IP conflict detector: time (ms) to wait for ICMP reply. // 0: disable ICMPTimeout uint `json:"icmp_timeout_msec" yaml:"icmp_timeout_msec"` } // Server - the current state of the DHCP server type Server struct { conn *filterConn // listening UDP socket ipnet *net.IPNet // if interface name changes, this needs to be reset cond *sync.Cond // Synchronize worker thread with main thread mutex sync.Mutex // Mutex for 'cond' running bool // Set if the worker thread is running stopping bool // Set if the worker thread should be stopped // leases leases []*Lease leasesLock sync.RWMutex 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 conf ServerConfig } // Print information about the available network interfaces func printInterfaces() { ifaces, _ := net.Interfaces() var buf strings.Builder for i := range ifaces { buf.WriteString(fmt.Sprintf("\"%s\", ", ifaces[i].Name)) } log.Info("Available network interfaces: %s", buf.String()) } // CheckConfig checks the configuration func (s *Server) CheckConfig(config ServerConfig) error { tmpServer := Server{} return tmpServer.setConfig(config) } // Init checks the configuration and initializes the server func (s *Server) Init(config ServerConfig) error { err := s.setConfig(config) if err != nil { return err } s.dbLoad() return nil } func (s *Server) setConfig(config ServerConfig) error { s.conf = config iface, err := net.InterfaceByName(config.InterfaceName) if err != nil { printInterfaces() return wrapErrPrint(err, "Couldn't find interface by name %s", config.InterfaceName) } // get ipv4 address of an interface s.ipnet = getIfaceIPv4(iface) if s.ipnet == nil { return wrapErrPrint(err, "Couldn't find IPv4 address of interface %s %+v", config.InterfaceName, iface) } if config.LeaseDuration == 0 { s.leaseTime = time.Hour * 2 } else { s.leaseTime = time.Second * time.Duration(config.LeaseDuration) } s.leaseStart, err = parseIPv4(config.RangeStart) if err != nil { return wrapErrPrint(err, "Failed to parse range start address %s", config.RangeStart) } s.leaseStop, err = parseIPv4(config.RangeEnd) if err != nil { return wrapErrPrint(err, "Failed to parse range end address %s", config.RangeEnd) } subnet, err := parseIPv4(config.SubnetMask) if err != nil { return wrapErrPrint(err, "Failed to parse subnet mask %s", config.SubnetMask) } // if !bytes.Equal(subnet, s.ipnet.Mask) { // 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(config.GatewayIP) if err != nil { return wrapErrPrint(err, "Failed to parse gateway IP %s", config.GatewayIP) } s.leaseOptions = dhcp4.Options{ dhcp4.OptionSubnetMask: subnet, dhcp4.OptionRouter: router, dhcp4.OptionDomainNameServer: s.ipnet.IP, } return nil } // Start will listen on port 67 and serve DHCP requests. func (s *Server) Start() error { // TODO: don't close if interface and addresses are the same if s.conn != nil { s.closeConn() } iface, err := net.InterfaceByName(s.conf.InterfaceName) if err != nil { return wrapErrPrint(err, "Couldn't find interface by name %s", s.conf.InterfaceName) } 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") } log.Info("DHCP: listening on 0.0.0.0:67") s.conn = c s.cond = sync.NewCond(&s.mutex) s.running = true go func() { // operate on c instead of c.conn because c.conn can change over time err := dhcp4.Serve(c, s) if err != nil && !s.stopping { log.Printf("dhcp4.Serve() returned with error: %s", err) } c.Close() // in case Serve() exits for other reason than listening socket closure s.running = false s.cond.Signal() }() return nil } // Stop closes the listening UDP socket func (s *Server) Stop() error { if s.conn == nil { // nothing to do, return silently return nil } s.stopping = true err := s.closeConn() if err != nil { return wrapErrPrint(err, "Couldn't close UDP listening socket") } // We've just closed the listening socket. // Worker thread should exit right after it tries to read from the socket. s.mutex.Lock() for s.running { s.cond.Wait() } s.mutex.Unlock() s.dbStore() 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 } // Reserve a lease for the client 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) // not assigned a lease, create new one, find IP from LRU hostname := p.ParseOptions()[dhcp4.OptionHostName] lease := &Lease{HWAddr: hwaddr, Hostname: string(hostname)} log.Tracef("Lease not found for %s: creating new one", hwaddr) ip, err := s.findFreeIP(hwaddr) if err != nil { i := s.findExpiredLease() if i < 0 { return nil, wrapErrPrint(err, "Couldn't find free IP for the lease %s", hwaddr.String()) } log.Tracef("Assigning IP address %s to %s (lease for %s expired at %s)", s.leases[i].IP, hwaddr, s.leases[i].HWAddr, s.leases[i].Expiry) lease.IP = s.leases[i].IP s.leasesLock.Lock() s.leases[i] = lease s.leasesLock.Unlock() s.reserveIP(lease.IP, hwaddr) return lease, nil } log.Tracef("Assigning to %s IP address %s", hwaddr, ip.String()) lease.IP = ip s.leasesLock.Lock() s.leases = append(s.leases, lease) s.leasesLock.Unlock() return lease, nil } // Find a lease for the client func (s *Server) findLease(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 } // Find an expired lease and return its index or -1 func (s *Server) findExpiredLease() int { now := time.Now().Unix() for i, lease := range s.leases { if lease.Expiry.Unix() <= now && lease.Expiry.Unix() != leaseExpireStatic { return i } } return -1 } func (s *Server) findFreeIP(hwaddr net.HardwareAddr) (net.IP, error) { // 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.findReservedHWaddr(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) // } 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) findReservedHWaddr(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) } // ServeDHCP handles an incoming DHCP request func (s *Server) ServeDHCP(p dhcp4.Packet, msgType dhcp4.MessageType, options dhcp4.Options) dhcp4.Packet { s.printLeases() switch msgType { case dhcp4.Discover: // Broadcast Packet From Client - Can I have an IP? return s.handleDiscover(p, options) 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 return s.handleDHCP4Request(p, options) case dhcp4.Decline: // Broadcast From Client - Sorry I can't use that IP return s.handleDecline(p, options) case dhcp4.Release: // From Client, I don't need that IP anymore return s.handleRelease(p, options) case dhcp4.Inform: // From Client, I have this IP and there's nothing you can do about it return s.handleInform(p, options) // from server -- ignore those but enumerate just in case case dhcp4.Offer: // Broadcast From Server - Here's an IP log.Printf("DHCP: received message from %s: Offer", p.CHAddr()) case dhcp4.ACK: // From Server, Yes you can have that IP log.Printf("DHCP: received message from %s: ACK", p.CHAddr()) case dhcp4.NAK: // From Server, No you cannot have that IP log.Printf("DHCP: received message from %s: NAK", p.CHAddr()) default: log.Printf("DHCP: unknown packet %v from %s", msgType, p.CHAddr()) return nil } return nil } // Send ICMP to the specified machine // Return TRUE if it doesn't reply, which probably means that the IP is available func (s *Server) addrAvailable(target net.IP) bool { if s.conf.ICMPTimeout == 0 { return true } pinger, err := ping.NewPinger(target.String()) if err != nil { log.Error("ping.NewPinger(): %v", err) return true } pinger.SetPrivileged(true) pinger.Timeout = time.Duration(s.conf.ICMPTimeout) * time.Millisecond pinger.Count = 1 reply := false pinger.OnRecv = func(pkt *ping.Packet) { // log.Tracef("Received ICMP Reply from %v", target) reply = true } log.Tracef("Sending ICMP Echo to %v", target) pinger.Run() if reply { log.Info("DHCP: IP conflict: %v is already used by another device", target) return false } log.Tracef("ICMP procedure is complete: %v", target) return true } // Add the specified IP to the black list for a time period func (s *Server) blacklistLease(lease *Lease) { hw := make(net.HardwareAddr, 6) s.reserveIP(lease.IP, hw) s.leasesLock.Lock() lease.HWAddr = hw lease.Hostname = "" lease.Expiry = time.Now().Add(s.leaseTime) s.leasesLock.Unlock() } // Return TRUE if DHCP packet is correct func isValidPacket(p dhcp4.Packet) bool { hw := p.CHAddr() zeroes := make([]byte, len(hw)) if bytes.Equal(hw, zeroes) { log.Tracef("Packet has empty CHAddr") return false } return true } func (s *Server) handleDiscover(p dhcp4.Packet, options dhcp4.Options) dhcp4.Packet { // find a lease, but don't update lease time var lease *Lease var err error reqIP := net.IP(options[dhcp4.OptionRequestedIPAddress]) hostname := p.ParseOptions()[dhcp4.OptionHostName] log.Tracef("Message from client: Discover. ReqIP: %s HW: %s Hostname: %s", reqIP, p.CHAddr(), hostname) if !isValidPacket(p) { return nil } lease = s.findLease(p) for lease == nil { lease, err = s.reserveLease(p) if err != nil { log.Error("Couldn't find free lease: %s", err) return nil } if !s.addrAvailable(lease.IP) { s.blacklistLease(lease) lease = nil continue } break } opt := s.leaseOptions.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]) reply := dhcp4.ReplyPacket(p, dhcp4.Offer, s.ipnet.IP, lease.IP, s.leaseTime, opt) log.Tracef("Replying with offer: offered IP %v for %v with options %+v", lease.IP, s.leaseTime, reply.ParseOptions()) return reply } func (s *Server) handleDHCP4Request(p dhcp4.Packet, options dhcp4.Options) dhcp4.Packet { var lease *Lease reqIP := net.IP(options[dhcp4.OptionRequestedIPAddress]) log.Tracef("Message from client: Request. IP: %s ReqIP: %s HW: %s", p.CIAddr(), reqIP, p.CHAddr()) if !isValidPacket(p) { return nil } server := options[dhcp4.OptionServerIdentifier] if server != nil && !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 } if reqIP == nil { reqIP = p.CIAddr() } else if reqIP == nil || reqIP.To4() == nil { log.Tracef("Requested IP isn't a valid IPv4: %s", reqIP) return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil) } lease = s.findLease(p) if lease == nil { log.Tracef("Lease for %s isn't found", p.CHAddr()) return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil) } if !lease.IP.Equal(reqIP) { log.Tracef("Lease for %s doesn't match requested/client IP: %s vs %s", lease.HWAddr, lease.IP, reqIP) return dhcp4.ReplyPacket(p, dhcp4.NAK, s.ipnet.IP, nil, 0, nil) } lease.Expiry = time.Now().Add(s.leaseTime) log.Tracef("Replying with ACK. IP: %s HW: %s Expire: %s", lease.IP, lease.HWAddr, lease.Expiry) opt := s.leaseOptions.SelectOrderOrAll(options[dhcp4.OptionParameterRequestList]) return dhcp4.ReplyPacket(p, dhcp4.ACK, s.ipnet.IP, lease.IP, s.leaseTime, opt) } func (s *Server) handleInform(p dhcp4.Packet, options dhcp4.Options) dhcp4.Packet { log.Tracef("Message from client: Inform. IP: %s HW: %s", p.CIAddr(), p.CHAddr()) return nil } func (s *Server) handleRelease(p dhcp4.Packet, options dhcp4.Options) dhcp4.Packet { log.Tracef("Message from client: Release. IP: %s HW: %s", p.CIAddr(), p.CHAddr()) return nil } func (s *Server) handleDecline(p dhcp4.Packet, options dhcp4.Options) dhcp4.Packet { reqIP := net.IP(options[dhcp4.OptionRequestedIPAddress]) log.Tracef("Message from client: Decline. IP: %s HW: %s", reqIP, p.CHAddr()) return nil } // AddStaticLease adds a static lease (thread-safe) func (s *Server) AddStaticLease(l Lease) error { if s.IPpool == nil { return fmt.Errorf("DHCP server isn't started") } if len(l.IP) != 4 { return fmt.Errorf("Invalid IP") } if len(l.HWAddr) != 6 { return fmt.Errorf("Invalid MAC") } l.Expiry = time.Unix(leaseExpireStatic, 0) s.leasesLock.Lock() defer s.leasesLock.Unlock() if s.findReservedHWaddr(l.IP) != nil { return fmt.Errorf("IP is already used") } s.leases = append(s.leases, &l) s.reserveIP(l.IP, l.HWAddr) s.dbStore() return nil } // RemoveStaticLease removes a static lease (thread-safe) func (s *Server) RemoveStaticLease(l Lease) error { if s.IPpool == nil { return fmt.Errorf("DHCP server isn't started") } if len(l.IP) != 4 { return fmt.Errorf("Invalid IP") } if len(l.HWAddr) != 6 { return fmt.Errorf("Invalid MAC") } s.leasesLock.Lock() defer s.leasesLock.Unlock() if s.findReservedHWaddr(l.IP) == nil { return fmt.Errorf("Lease not found") } var newLeases []*Lease for _, lease := range s.leases { if bytes.Equal(lease.IP.To4(), l.IP) { if !bytes.Equal(lease.HWAddr, l.HWAddr) || lease.Hostname != l.Hostname { return fmt.Errorf("Lease not found") } continue } newLeases = append(newLeases, lease) } s.leases = newLeases s.unreserveIP(l.IP) s.dbStore() return nil } // Leases returns the list of current DHCP leases (thread-safe) func (s *Server) Leases() []Lease { var result []Lease now := time.Now().Unix() s.leasesLock.RLock() for _, lease := range s.leases { if lease.Expiry.Unix() > now { result = append(result, *lease) } } s.leasesLock.RUnlock() return result } // StaticLeases returns the list of statically-configured DHCP leases (thread-safe) func (s *Server) StaticLeases() []Lease { s.leasesLock.Lock() if s.IPpool == nil { s.dbLoad() } s.leasesLock.Unlock() var result []Lease s.leasesLock.RLock() for _, lease := range s.leases { if lease.Expiry.Unix() == 1 { result = append(result, *lease) } } s.leasesLock.RUnlock() return result } // Print information about the current leases func (s *Server) printLeases() { 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) } } // FindIPbyMAC finds an IP address by MAC address in the currently active DHCP leases func (s *Server) FindIPbyMAC(mac net.HardwareAddr) net.IP { now := time.Now().Unix() s.leasesLock.RLock() defer s.leasesLock.RUnlock() for _, l := range s.leases { if l.Expiry.Unix() > now && bytes.Equal(mac, l.HWAddr) { return l.IP } } return nil } // Reset internal state func (s *Server) reset() { s.leasesLock.Lock() s.leases = nil s.leasesLock.Unlock() s.IPpool = make(map[[4]byte]net.HardwareAddr) }