// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris package dhcpd import ( "bytes" "encoding/binary" "fmt" "net" "sync" "time" "github.com/AdguardTeam/golibs/log" "github.com/insomniacslk/dhcp/dhcpv4" "github.com/insomniacslk/dhcp/dhcpv4/server4" "github.com/sparrc/go-ping" ) // v4Server - DHCPv4 server type v4Server struct { srv *server4.Server leasesLock sync.Mutex leases []*Lease ipAddrs [256]byte conf V4ServerConf } // WriteDiskConfig4 - write configuration func (s *v4Server) WriteDiskConfig4(c *V4ServerConf) { *c = s.conf } // WriteDiskConfig6 - write configuration func (s *v4Server) WriteDiskConfig6(c *V6ServerConf) { } // Return TRUE if IP address is within range [start..stop] func ip4InRange(start, stop, ip net.IP) bool { if len(start) != 4 || len(stop) != 4 { return false } from := binary.BigEndian.Uint32(start) to := binary.BigEndian.Uint32(stop) check := binary.BigEndian.Uint32(ip) return from <= check && check <= to } // ResetLeases - reset leases func (s *v4Server) ResetLeases(leases []*Lease) { s.leases = nil for _, l := range leases { if l.Expiry.Unix() != leaseExpireStatic && !ip4InRange(s.conf.ipStart, s.conf.ipEnd, l.IP) { log.Debug("dhcpv4: skipping a lease with IP %v: not within current IP range", l.IP) continue } s.addLease(l) } } // GetLeasesRef - get leases func (s *v4Server) GetLeasesRef() []*Lease { return s.leases } // Return TRUE if this lease holds a blacklisted IP func (s *v4Server) blacklisted(l *Lease) bool { return l.HWAddr.String() == "00:00:00:00:00:00" } // GetLeases returns the list of current DHCP leases (thread-safe) func (s *v4Server) GetLeases(flags int) []Lease { var result []Lease now := time.Now().Unix() s.leasesLock.Lock() for _, lease := range s.leases { if ((flags&LeasesDynamic) != 0 && lease.Expiry.Unix() > now && !s.blacklisted(lease)) || ((flags&LeasesStatic) != 0 && lease.Expiry.Unix() == leaseExpireStatic) { result = append(result, *lease) } } s.leasesLock.Unlock() return result } // FindMACbyIP - find a MAC address by IP address in the currently active DHCP leases func (s *v4Server) FindMACbyIP(ip net.IP) net.HardwareAddr { now := time.Now().Unix() s.leasesLock.Lock() defer s.leasesLock.Unlock() ip4 := ip.To4() if ip4 == nil { return nil } for _, l := range s.leases { if l.IP.Equal(ip4) { unix := l.Expiry.Unix() if unix > now || unix == leaseExpireStatic { return l.HWAddr } } } return nil } // Add the specified IP to the black list for a time period func (s *v4Server) blacklistLease(lease *Lease) { hw := make(net.HardwareAddr, 6) lease.HWAddr = hw lease.Hostname = "" lease.Expiry = time.Now().Add(s.conf.leaseTime) } // Remove (swap) lease by index func (s *v4Server) leaseRemoveSwapByIndex(i int) { s.ipAddrs[s.leases[i].IP[3]] = 0 log.Debug("dhcpv4: removed lease %s", s.leases[i].HWAddr) n := len(s.leases) if i != n-1 { s.leases[i] = s.leases[n-1] // swap with the last element } s.leases = s.leases[:n-1] } // Remove a dynamic lease with the same properties // Return error if a static lease is found func (s *v4Server) rmDynamicLease(lease Lease) error { for i := 0; i < len(s.leases); i++ { l := s.leases[i] if bytes.Equal(l.HWAddr, lease.HWAddr) { if l.Expiry.Unix() == leaseExpireStatic { return fmt.Errorf("static lease already exists") } s.leaseRemoveSwapByIndex(i) if i == len(s.leases) { break } l = s.leases[i] } if net.IP.Equal(l.IP, lease.IP) { if l.Expiry.Unix() == leaseExpireStatic { return fmt.Errorf("static lease already exists") } s.leaseRemoveSwapByIndex(i) } } return nil } // Add a lease func (s *v4Server) addLease(l *Lease) { s.leases = append(s.leases, l) s.ipAddrs[l.IP[3]] = 1 log.Debug("dhcpv4: added lease %s <-> %s", l.IP, l.HWAddr) } // Remove a lease with the same properties func (s *v4Server) rmLease(lease Lease) error { for i, l := range s.leases { if net.IP.Equal(l.IP, lease.IP) { if !bytes.Equal(l.HWAddr, lease.HWAddr) || l.Hostname != lease.Hostname { return fmt.Errorf("lease not found") } s.leaseRemoveSwapByIndex(i) return nil } } return fmt.Errorf("lease not found") } // AddStaticLease adds a static lease (thread-safe) func (s *v4Server) AddStaticLease(lease Lease) error { if len(lease.IP) != 4 { return fmt.Errorf("invalid IP") } if len(lease.HWAddr) != 6 { return fmt.Errorf("invalid MAC") } lease.Expiry = time.Unix(leaseExpireStatic, 0) s.leasesLock.Lock() err := s.rmDynamicLease(lease) if err != nil { s.leasesLock.Unlock() return err } s.addLease(&lease) s.conf.notify(LeaseChangedDBStore) s.leasesLock.Unlock() s.conf.notify(LeaseChangedAddedStatic) return nil } // RemoveStaticLease removes a static lease (thread-safe) func (s *v4Server) RemoveStaticLease(l Lease) error { if len(l.IP) != 4 { return fmt.Errorf("invalid IP") } if len(l.HWAddr) != 6 { return fmt.Errorf("invalid MAC") } s.leasesLock.Lock() err := s.rmLease(l) if err != nil { s.leasesLock.Unlock() return err } s.conf.notify(LeaseChangedDBStore) s.leasesLock.Unlock() s.conf.notify(LeaseChangedRemovedStatic) 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 *v4Server) 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) { reply = true } log.Debug("dhcpv4: Sending ICMP Echo to %v", target) pinger.Run() if reply { log.Info("dhcpv4: IP conflict: %v is already used by another device", target) return false } log.Debug("dhcpv4: ICMP procedure is complete: %v", target) return true } // Find lease by MAC func (s *v4Server) findLease(mac net.HardwareAddr) *Lease { for i := range s.leases { if bytes.Equal(mac, s.leases[i].HWAddr) { return s.leases[i] } } return nil } // Get next free IP func (s *v4Server) findFreeIP() net.IP { for i := s.conf.ipStart[3]; ; i++ { if s.ipAddrs[i] == 0 { ip := make([]byte, 4) copy(ip, s.conf.ipStart) ip[3] = i return ip } if i == s.conf.ipEnd[3] { break } } return nil } // Find an expired lease and return its index or -1 func (s *v4Server) findExpiredLease() int { now := time.Now().Unix() for i, lease := range s.leases { if lease.Expiry.Unix() != leaseExpireStatic && lease.Expiry.Unix() <= now { return i } } return -1 } // Reserve lease for MAC func (s *v4Server) reserveLease(mac net.HardwareAddr) *Lease { l := Lease{} l.HWAddr = make([]byte, 6) copy(l.HWAddr, mac) l.IP = s.findFreeIP() if l.IP == nil { i := s.findExpiredLease() if i < 0 { return nil } copy(s.leases[i].HWAddr, mac) return s.leases[i] } s.addLease(&l) return &l } func (s *v4Server) commitLease(l *Lease) { l.Expiry = time.Now().Add(s.conf.leaseTime) s.leasesLock.Lock() s.conf.notify(LeaseChangedDBStore) s.leasesLock.Unlock() s.conf.notify(LeaseChangedAdded) } // Process Discover request and return lease func (s *v4Server) processDiscover(req, resp *dhcpv4.DHCPv4) *Lease { mac := req.ClientHWAddr s.leasesLock.Lock() defer s.leasesLock.Unlock() lease := s.findLease(mac) if lease == nil { toStore := false for lease == nil { lease = s.reserveLease(mac) if lease == nil { log.Debug("dhcpv4: No more IP addresses") if toStore { s.conf.notify(LeaseChangedDBStore) } return nil } toStore = true if !s.addrAvailable(lease.IP) { s.blacklistLease(lease) lease = nil continue } break } s.conf.notify(LeaseChangedDBStore) } else { reqIP := req.Options.Get(dhcpv4.OptionRequestedIPAddress) if len(reqIP) != 0 && !bytes.Equal(reqIP, lease.IP) { log.Debug("dhcpv4: different RequestedIP: %v != %v", reqIP, lease.IP) } } resp.UpdateOption(dhcpv4.OptMessageType(dhcpv4.MessageTypeOffer)) return lease } type optFQDN struct { name string } func (o *optFQDN) String() string { return "optFQDN" } // flags[1] // A-RR[1] // PTR-RR[1] // name[] func (o *optFQDN) ToBytes() []byte { b := make([]byte, 3+len(o.name)) i := 0 b[i] = 0x03 // f_server_overrides | f_server i++ b[i] = 255 // A-RR i++ b[i] = 255 // PTR-RR i++ copy(b[i:], []byte(o.name)) return b } // Process Request request and return lease // Return false if we don't need to reply func (s *v4Server) processRequest(req, resp *dhcpv4.DHCPv4) (*Lease, bool) { var lease *Lease mac := req.ClientHWAddr hostname := req.Options.Get(dhcpv4.OptionHostName) reqIP := req.Options.Get(dhcpv4.OptionRequestedIPAddress) if reqIP == nil { reqIP = req.ClientIPAddr } sid := req.Options.Get(dhcpv4.OptionServerIdentifier) if len(sid) != 0 && !bytes.Equal(sid, s.conf.dnsIPAddrs[0]) { log.Debug("dhcpv4: Bad OptionServerIdentifier in Request message for %s", mac) return nil, false } if len(reqIP) != 4 { log.Debug("dhcpv4: Bad OptionRequestedIPAddress in Request message for %s", mac) return nil, false } s.leasesLock.Lock() for _, l := range s.leases { if bytes.Equal(l.HWAddr, mac) { if !bytes.Equal(l.IP, reqIP) { s.leasesLock.Unlock() log.Debug("dhcpv4: Mismatched OptionRequestedIPAddress in Request message for %s", mac) return nil, true } lease = l break } } s.leasesLock.Unlock() if lease == nil { log.Debug("dhcpv4: No lease for %s", mac) return nil, true } if lease.Expiry.Unix() != leaseExpireStatic { lease.Hostname = string(hostname) s.commitLease(lease) } else if len(lease.Hostname) != 0 { o := &optFQDN{ name: lease.Hostname, } fqdn := dhcpv4.Option{ Code: dhcpv4.OptionFQDN, Value: o, } resp.UpdateOption(fqdn) } resp.UpdateOption(dhcpv4.OptMessageType(dhcpv4.MessageTypeAck)) return lease, true } // Find a lease associated with MAC and prepare response // Return 1: OK // Return 0: error; reply with Nak // Return -1: error; don't reply func (s *v4Server) process(req, resp *dhcpv4.DHCPv4) int { var lease *Lease resp.UpdateOption(dhcpv4.OptServerIdentifier(s.conf.dnsIPAddrs[0])) switch req.MessageType() { case dhcpv4.MessageTypeDiscover: lease = s.processDiscover(req, resp) if lease == nil { return 0 } case dhcpv4.MessageTypeRequest: var toReply bool lease, toReply = s.processRequest(req, resp) if lease == nil { if toReply { return 0 } return -1 // drop packet } } resp.YourIPAddr = make([]byte, 4) copy(resp.YourIPAddr, lease.IP) resp.UpdateOption(dhcpv4.OptIPAddressLeaseTime(s.conf.leaseTime)) resp.UpdateOption(dhcpv4.OptRouter(s.conf.routerIP)) resp.UpdateOption(dhcpv4.OptSubnetMask(s.conf.subnetMask)) resp.UpdateOption(dhcpv4.OptDNS(s.conf.dnsIPAddrs...)) for _, opt := range s.conf.options { resp.Options[opt.code] = opt.val } return 1 } // client(0.0.0.0:68) -> (Request:ClientMAC,Type=Discover,ClientID,ReqIP,HostName) -> server(255.255.255.255:67) // client(255.255.255.255:68) <- (Reply:YourIP,ClientMAC,Type=Offer,ServerID,SubnetMask,LeaseTime) <- server(:67) // client(0.0.0.0:68) -> (Request:ClientMAC,Type=Request,ClientID,ReqIP||ClientIP,HostName,ServerID,ParamReqList) -> server(255.255.255.255:67) // client(255.255.255.255:68) <- (Reply:YourIP,ClientMAC,Type=ACK,ServerID,SubnetMask,LeaseTime) <- server(:67) func (s *v4Server) packetHandler(conn net.PacketConn, peer net.Addr, req *dhcpv4.DHCPv4) { log.Debug("dhcpv4: received message: %s", req.Summary()) switch req.MessageType() { case dhcpv4.MessageTypeDiscover, dhcpv4.MessageTypeRequest: // default: log.Debug("dhcpv4: unsupported message type %d", req.MessageType()) return } resp, err := dhcpv4.NewReplyFromRequest(req) if err != nil { log.Debug("dhcpv4: dhcpv4.New: %s", err) return } if len(req.ClientHWAddr) != 6 { log.Debug("dhcpv4: Invalid ClientHWAddr") return } r := s.process(req, resp) if r < 0 { return } else if r == 0 { resp.Options.Update(dhcpv4.OptMessageType(dhcpv4.MessageTypeNak)) } log.Debug("dhcpv4: sending: %s", resp.Summary()) _, err = conn.WriteTo(resp.ToBytes(), peer) if err != nil { log.Error("dhcpv4: conn.Write to %s failed: %s", peer, err) return } } // ifaceIPv4Addrs returns the interface's IPv4 addresses. func ifaceIPv4Addrs(iface *net.Interface) (ips []net.IP, err error) { addrs, err := iface.Addrs() if err != nil { return nil, err } for _, a := range addrs { ipnet, ok := a.(*net.IPNet) if !ok { continue } if ip := ipnet.IP.To4(); ip != nil { ips = append(ips, ip) } } return ips, nil } // Start starts the IPv4 DHCP server. func (s *v4Server) Start() error { if !s.conf.Enabled { return nil } ifaceName := s.conf.InterfaceName iface, err := net.InterfaceByName(ifaceName) if err != nil { return fmt.Errorf("dhcpv4: finding interface %s by name: %w", ifaceName, err) } log.Debug("dhcpv4: starting...") dnsIPAddrs, err := ifaceIPv4Addrs(iface) if err != nil { return fmt.Errorf("dhcpv4: getting ipv4 addrs for iface %s: %w", ifaceName, err) } switch len(dnsIPAddrs) { case 0: log.Debug("dhcpv4: no ipv4 address for interface %s", iface.Name) return nil case 1: // Some Android devices use 8.8.8.8 if there is no secondary DNS // server. Fix that by setting the secondary DNS address to our // address as well. // // See https://github.com/AdguardTeam/AdGuardHome/issues/1708. log.Debug("dhcpv4: setting secondary dns ip to iself for interface %s", iface.Name) dnsIPAddrs = append(dnsIPAddrs, dnsIPAddrs[0]) default: // Go on. } s.conf.dnsIPAddrs = dnsIPAddrs laddr := &net.UDPAddr{ IP: net.ParseIP("0.0.0.0"), Port: dhcpv4.ServerPort, } s.srv, err = server4.NewServer(iface.Name, laddr, s.packetHandler, server4.WithDebugLogger()) if err != nil { return err } log.Info("dhcpv4: listening") go func() { err = s.srv.Serve() log.Debug("dhcpv4: srv.Serve: %s", err) }() return nil } // Stop - stop server func (s *v4Server) Stop() { if s.srv == nil { return } log.Debug("dhcpv4: stopping") err := s.srv.Close() if err != nil { log.Error("dhcpv4: srv.Close: %s", err) } // now s.srv.Serve() will return s.srv = nil } // Create DHCPv4 server func v4Create(conf V4ServerConf) (DHCPServer, error) { s := &v4Server{} s.conf = conf if !conf.Enabled { return s, nil } var err error s.conf.routerIP, err = parseIPv4(s.conf.GatewayIP) if err != nil { return s, fmt.Errorf("dhcpv4: %w", err) } subnet, err := parseIPv4(s.conf.SubnetMask) if err != nil || !isValidSubnetMask(subnet) { return s, fmt.Errorf("dhcpv4: invalid subnet mask: %s", s.conf.SubnetMask) } s.conf.subnetMask = make([]byte, 4) copy(s.conf.subnetMask, subnet) s.conf.ipStart, err = parseIPv4(conf.RangeStart) if s.conf.ipStart == nil { return s, fmt.Errorf("dhcpv4: %w", err) } if s.conf.ipStart[0] == 0 { return s, fmt.Errorf("dhcpv4: invalid range start IP") } s.conf.ipEnd, err = parseIPv4(conf.RangeEnd) if s.conf.ipEnd == nil { return s, fmt.Errorf("dhcpv4: %w", err) } if !net.IP.Equal(s.conf.ipStart[:3], s.conf.ipEnd[:3]) || s.conf.ipStart[3] > s.conf.ipEnd[3] { return s, fmt.Errorf("dhcpv4: range end IP should match range start IP") } if conf.LeaseDuration == 0 { s.conf.leaseTime = time.Hour * 24 s.conf.LeaseDuration = uint32(s.conf.leaseTime.Seconds()) } else { s.conf.leaseTime = time.Second * time.Duration(conf.LeaseDuration) } for _, o := range conf.Options { code, val := parseOptionString(o) if code == 0 { log.Debug("dhcpv4: bad option string: %s", o) continue } opt := dhcpOption{ code: code, val: val, } s.conf.options = append(s.conf.options, opt) } return s, nil }