| // Copyright 2016 The Netstack Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| package dhcp |
| |
| import ( |
| "context" |
| "fmt" |
| "io" |
| "log" |
| "sync" |
| "time" |
| |
| "github.com/google/netstack/tcpip" |
| "github.com/google/netstack/tcpip/buffer" |
| "github.com/google/netstack/tcpip/network/ipv4" |
| "github.com/google/netstack/tcpip/stack" |
| "github.com/google/netstack/tcpip/transport/udp" |
| "github.com/google/netstack/waiter" |
| ) |
| |
| // Server is a DHCP server. |
| type Server struct { |
| conn conn |
| broadcast tcpip.FullAddress |
| addrs []tcpip.Address // TODO: use a tcpip.AddressMask or range structure |
| cfg Config |
| cfgopts []option // cfg to send to client |
| |
| handlers []chan header |
| |
| mu sync.Mutex |
| leases map[tcpip.LinkAddress]serverLease |
| } |
| |
| // conn is a blocking read/write network endpoint. |
| type conn interface { |
| Read() (buffer.View, tcpip.FullAddress, error) |
| Write([]byte, *tcpip.FullAddress) error |
| } |
| |
| type epConn struct { |
| ctx context.Context |
| wq *waiter.Queue |
| ep tcpip.Endpoint |
| we waiter.Entry |
| inCh chan struct{} |
| } |
| |
| func newEPConn(ctx context.Context, wq *waiter.Queue, ep tcpip.Endpoint) *epConn { |
| c := &epConn{ |
| ctx: ctx, |
| wq: wq, |
| ep: ep, |
| } |
| c.we, c.inCh = waiter.NewChannelEntry(nil) |
| wq.EventRegister(&c.we, waiter.EventIn) |
| |
| go func() { |
| <-ctx.Done() |
| wq.EventUnregister(&c.we) |
| }() |
| |
| return c |
| } |
| |
| func (c *epConn) Read() (buffer.View, tcpip.FullAddress, error) { |
| for { |
| var addr tcpip.FullAddress |
| v, err := c.ep.Read(&addr) |
| if err == tcpip.ErrWouldBlock { |
| select { |
| case <-c.inCh: |
| continue |
| case <-c.ctx.Done(): |
| return nil, tcpip.FullAddress{}, io.EOF |
| } |
| } |
| return v, addr, err |
| } |
| } |
| |
| func (c *epConn) Write(b []byte, addr *tcpip.FullAddress) error { |
| _, err := c.ep.Write(b, addr) |
| return err |
| } |
| |
| // NewServer creates a new DHCP server and begins serving. |
| // The server continues serving until ctx is done. |
| func NewServer(ctx context.Context, stack *stack.Stack, addrs []tcpip.Address, cfg Config) (*Server, error) { |
| wq := new(waiter.Queue) |
| ep, err := stack.NewEndpoint(udp.ProtocolNumber, ipv4.ProtocolNumber, wq) |
| if err != nil { |
| return nil, fmt.Errorf("dhcp: server endpoint: %v", err) |
| } |
| if err := ep.Bind(tcpip.FullAddress{Port: serverPort}, nil); err != nil { |
| return nil, fmt.Errorf("dhcp: server bind: %v", err) |
| } |
| c := newEPConn(ctx, wq, ep) |
| return newServer(ctx, c, addrs, cfg) |
| } |
| |
| func newServer(ctx context.Context, c conn, addrs []tcpip.Address, cfg Config) (*Server, error) { |
| if cfg.ServerAddress == "" { |
| return nil, fmt.Errorf("dhcp: server requires explicit server address") |
| } |
| s := &Server{ |
| conn: c, |
| addrs: addrs, |
| cfg: cfg, |
| cfgopts: cfg.encode(), |
| broadcast: tcpip.FullAddress{ |
| Addr: "\xff\xff\xff\xff", |
| Port: clientPort, |
| }, |
| |
| handlers: make([]chan header, 8), |
| leases: make(map[tcpip.LinkAddress]serverLease), |
| } |
| |
| for i := 0; i < len(s.handlers); i++ { |
| ch := make(chan header, 8) |
| s.handlers[i] = ch |
| go s.handler(ctx, ch) |
| } |
| |
| go s.expirer(ctx) |
| go s.reader(ctx) |
| return s, nil |
| } |
| |
| func (s *Server) expirer(ctx context.Context) { |
| t := time.NewTicker(1 * time.Minute) |
| defer t.Stop() |
| for { |
| select { |
| case <-t.C: |
| s.mu.Lock() |
| for linkAddr, lease := range s.leases { |
| if time.Since(lease.start) > s.cfg.LeaseLength { |
| lease.state = leaseExpired |
| s.leases[linkAddr] = lease |
| } |
| } |
| s.mu.Unlock() |
| case <-ctx.Done(): |
| return |
| } |
| } |
| } |
| |
| // reader listens for all incoming DHCP packets and fans them out to |
| // handling goroutines based on XID as session identifiers. |
| func (s *Server) reader(ctx context.Context) { |
| for { |
| v, _, err := s.conn.Read() |
| if err != nil { |
| return |
| } |
| |
| h := header(v) |
| if !h.isValid() || h.op() != opRequest { |
| continue |
| } |
| xid := h.xid() |
| |
| // Fan out the packet to a handler goroutine. |
| // |
| // Use a consistent handler for a given xid, so that |
| // packets from a particular client are processed |
| // in order. |
| ch := s.handlers[int(xid)%len(s.handlers)] |
| select { |
| case <-ctx.Done(): |
| return |
| case ch <- h: |
| default: |
| // drop the packet |
| } |
| } |
| } |
| |
| func (s *Server) handler(ctx context.Context, ch chan header) { |
| for { |
| select { |
| case h := <-ch: |
| if h == nil { |
| return |
| } |
| opts, err := h.options() |
| if err != nil { |
| continue |
| } |
| // TODO(crawshaw): Handle DHCPRELEASE and DHCPDECLINE. |
| msgtype, err := opts.dhcpMsgType() |
| if err != nil { |
| continue |
| } |
| switch msgtype { |
| case dhcpDISCOVER: |
| s.handleDiscover(h, opts) |
| case dhcpREQUEST: |
| s.handleRequest(h, opts) |
| } |
| case <-ctx.Done(): |
| return |
| } |
| } |
| } |
| |
| func (s *Server) handleDiscover(hreq header, opts options) { |
| linkAddr := tcpip.LinkAddress(hreq.chaddr()[:6]) |
| xid := hreq.xid() |
| |
| s.mu.Lock() |
| lease := s.leases[linkAddr] |
| switch lease.state { |
| case leaseNew: |
| if len(s.leases) < len(s.addrs) { |
| // Find an unused address. |
| // TODO(crawshaw): avoid building this state on each request. |
| alloced := make(map[tcpip.Address]bool) |
| for _, lease := range s.leases { |
| alloced[lease.addr] = true |
| } |
| for _, addr := range s.addrs { |
| if !alloced[addr] { |
| lease = serverLease{ |
| start: time.Now(), |
| addr: addr, |
| xid: xid, |
| state: leaseOffer, |
| } |
| s.leases[linkAddr] = lease |
| break |
| } |
| } |
| } else { |
| // No more addresses, take an expired address. |
| for k, oldLease := range s.leases { |
| if oldLease.state == leaseExpired { |
| delete(s.leases, k) |
| lease = serverLease{ |
| start: time.Now(), |
| addr: lease.addr, |
| xid: xid, |
| state: leaseOffer, |
| } |
| s.leases[linkAddr] = lease |
| break |
| } |
| } |
| log.Printf("server has no more addresses") |
| s.mu.Unlock() |
| return |
| } |
| case leaseOffer, leaseAck, leaseExpired: |
| lease = serverLease{ |
| start: time.Now(), |
| addr: s.leases[linkAddr].addr, |
| xid: xid, |
| state: leaseOffer, |
| } |
| s.leases[linkAddr] = lease |
| } |
| s.mu.Unlock() |
| |
| // DHCPOFFER |
| opts = options{{optDHCPMsgType, []byte{byte(dhcpOFFER)}}} |
| opts = append(opts, s.cfgopts...) |
| h := make(header, headerBaseSize+opts.len()) |
| h.init() |
| h.setOp(opReply) |
| copy(h.xidbytes(), hreq.xidbytes()) |
| copy(h.yiaddr(), lease.addr) |
| copy(h.chaddr(), hreq.chaddr()) |
| h.setOptions(opts) |
| s.conn.Write([]byte(h), &s.broadcast) |
| } |
| |
| func (s *Server) nack(hreq header) { |
| // DHCPNACK |
| opts := options([]option{ |
| {optDHCPMsgType, []byte{byte(dhcpNAK)}}, |
| {optDHCPServer, []byte(s.cfg.ServerAddress)}, |
| }) |
| h := make(header, headerBaseSize+opts.len()) |
| h.init() |
| h.setOp(opReply) |
| copy(h.xidbytes(), hreq.xidbytes()) |
| copy(h.chaddr(), hreq.chaddr()) |
| h.setOptions(opts) |
| s.conn.Write([]byte(h), &s.broadcast) |
| } |
| |
| func (s *Server) handleRequest(hreq header, opts options) { |
| linkAddr := tcpip.LinkAddress(hreq.chaddr()[:6]) |
| xid := hreq.xid() |
| |
| reqopts, err := hreq.options() |
| if err != nil { |
| s.nack(hreq) |
| return |
| } |
| var reqcfg Config |
| if err := reqcfg.decode(reqopts); err != nil { |
| s.nack(hreq) |
| return |
| } |
| if reqcfg.ServerAddress != s.cfg.ServerAddress { |
| // This request is for a different DHCP server. Ignore it. |
| return |
| } |
| |
| s.mu.Lock() |
| lease := s.leases[linkAddr] |
| switch lease.state { |
| case leaseOffer, leaseAck, leaseExpired: |
| lease = serverLease{ |
| start: time.Now(), |
| addr: s.leases[linkAddr].addr, |
| xid: xid, |
| state: leaseAck, |
| } |
| s.leases[linkAddr] = lease |
| } |
| s.mu.Unlock() |
| |
| if lease.state == leaseNew { |
| // TODO(crawshaw): NACK or accept request |
| return |
| } |
| |
| // DHCPACK |
| opts = []option{{optDHCPMsgType, []byte{byte(dhcpACK)}}} |
| opts = append(opts, s.cfgopts...) |
| h := make(header, headerBaseSize+opts.len()) |
| h.init() |
| h.setOp(opReply) |
| copy(h.xidbytes(), hreq.xidbytes()) |
| copy(h.yiaddr(), lease.addr) |
| copy(h.chaddr(), hreq.chaddr()) |
| h.setOptions(opts) |
| s.conn.Write([]byte(h), &s.broadcast) |
| } |
| |
| type leaseState int |
| |
| const ( |
| leaseNew leaseState = iota |
| leaseOffer |
| leaseAck |
| leaseExpired |
| ) |
| |
| type serverLease struct { |
| start time.Time |
| addr tcpip.Address |
| xid xid |
| state leaseState |
| } |