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