// +build aix darwin dragonfly freebsd linux netbsd openbsd solaris package dhcpd import ( "bytes" "fmt" "net" "os" "runtime" "time" "github.com/AdguardTeam/golibs/log" "github.com/insomniacslk/dhcp/dhcpv4" "github.com/insomniacslk/dhcp/dhcpv4/nclient4" "github.com/insomniacslk/dhcp/dhcpv6" "github.com/insomniacslk/dhcp/dhcpv6/nclient6" "github.com/insomniacslk/dhcp/iana" ) // CheckIfOtherDHCPServersPresentV4 sends a DHCP request to the specified network interface, // and waits for a response for a period defined by defaultDiscoverTime func CheckIfOtherDHCPServersPresentV4(ifaceName string) (ok bool, err error) { iface, err := net.InterfaceByName(ifaceName) if err != nil { return false, fmt.Errorf("couldn't find interface by name %s: %w", ifaceName, err) } ifaceIPNet, err := ifaceIPAddrs(iface, ipVersion4) if err != nil { return false, fmt.Errorf("getting ipv4 addrs for iface %s: %w", ifaceName, err) } if len(ifaceIPNet) == 0 { return false, fmt.Errorf("interface %s has no ipv4 addresses", ifaceName) } // TODO(a.garipov): Find out what this is about. Perhaps this // information is outdated or at least incomplete. if runtime.GOOS == "darwin" { return false, fmt.Errorf("can't find DHCP server: not supported on macOS") } srcIP := ifaceIPNet[0] src := net.JoinHostPort(srcIP.String(), "68") dst := "255.255.255.255:67" hostname, _ := os.Hostname() req, err := dhcpv4.NewDiscovery(iface.HardwareAddr) if err != nil { return false, fmt.Errorf("dhcpv4.NewDiscovery: %w", err) } req.Options.Update(dhcpv4.OptClientIdentifier(iface.HardwareAddr)) req.Options.Update(dhcpv4.OptHostName(hostname)) // resolve 0.0.0.0:68 udpAddr, err := net.ResolveUDPAddr("udp4", src) if err != nil { return false, fmt.Errorf("couldn't resolve UDP address %s: %w", src, err) } if !udpAddr.IP.To4().Equal(srcIP) { return false, fmt.Errorf("resolved UDP address is not %s: %w", src, err) } // resolve 255.255.255.255:67 dstAddr, err := net.ResolveUDPAddr("udp4", dst) if err != nil { return false, fmt.Errorf("couldn't resolve UDP address %s: %w", dst, err) } // bind to 0.0.0.0:68 log.Tracef("Listening to udp4 %+v", udpAddr) c, err := nclient4.NewRawUDPConn(ifaceName, 68) if err != nil { return false, fmt.Errorf("couldn't listen on :68: %w", err) } if c != nil { defer c.Close() } // send to 255.255.255.255:67 _, err = c.WriteTo(req.ToBytes(), dstAddr) if err != nil { return false, fmt.Errorf("couldn't send a packet to %s: %w", dst, err) } for { var next bool ok, next, err = tryConn4(req, c, iface) if next { if err != nil { log.Debug("dhcpv4: trying a connection: %s", err) } continue } if err != nil { return false, err } return ok, nil } } // TODO(a.garipov): Refactor further. Inspect error handling, remove parameter // next, address the TODO, merge with tryConn6, etc. func tryConn4(req *dhcpv4.DHCPv4, c net.PacketConn, iface *net.Interface) (ok, next bool, err error) { // TODO: replicate dhclient's behavior of retrying several times with // progressively longer timeouts. log.Tracef("dhcpv4: waiting %v for an answer", defaultDiscoverTime) b := make([]byte, 1500) err = c.SetDeadline(time.Now().Add(defaultDiscoverTime)) if err != nil { return false, false, fmt.Errorf("setting deadline: %w", err) } n, _, err := c.ReadFrom(b) if err != nil { if isTimeout(err) { log.Debug("dhcpv4: didn't receive dhcp response") return false, false, nil } return false, false, fmt.Errorf("receiving packet: %w", err) } log.Tracef("dhcpv4: received packet, %d bytes", n) response, err := dhcpv4.FromBytes(b[:n]) if err != nil { log.Debug("dhcpv4: encoding: %s", err) return false, true, err } log.Debug("dhcpv4: received message from server: %s", response.Summary()) if !(response.OpCode == dhcpv4.OpcodeBootReply && response.HWType == iana.HWTypeEthernet && bytes.Equal(response.ClientHWAddr, iface.HardwareAddr) && bytes.Equal(response.TransactionID[:], req.TransactionID[:]) && response.Options.Has(dhcpv4.OptionDHCPMessageType)) { log.Debug("dhcpv4: received message from server doesn't match our request") return false, true, nil } log.Tracef("dhcpv4: the packet is from an active dhcp server") return true, false, nil } // CheckIfOtherDHCPServersPresentV6 sends a DHCP request to the specified network interface, // and waits for a response for a period defined by defaultDiscoverTime func CheckIfOtherDHCPServersPresentV6(ifaceName string) (ok bool, err error) { iface, err := net.InterfaceByName(ifaceName) if err != nil { return false, fmt.Errorf("dhcpv6: net.InterfaceByName: %s: %w", ifaceName, err) } ifaceIPNet, err := ifaceIPAddrs(iface, ipVersion6) if err != nil { return false, fmt.Errorf("getting ipv6 addrs for iface %s: %w", ifaceName, err) } if len(ifaceIPNet) == 0 { return false, fmt.Errorf("interface %s has no ipv6 addresses", ifaceName) } srcIP := ifaceIPNet[0] src := net.JoinHostPort(srcIP.String(), "546") dst := "[ff02::1:2]:547" req, err := dhcpv6.NewSolicit(iface.HardwareAddr) if err != nil { return false, fmt.Errorf("dhcpv6: dhcpv6.NewSolicit: %w", err) } udpAddr, err := net.ResolveUDPAddr("udp6", src) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't resolve UDP address %s: %w", src, err) } if !udpAddr.IP.To16().Equal(srcIP) { return false, fmt.Errorf("dhcpv6: Resolved UDP address is not %s: %w", src, err) } dstAddr, err := net.ResolveUDPAddr("udp6", dst) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't resolve UDP address %s: %w", dst, err) } log.Debug("DHCPv6: Listening to udp6 %+v", udpAddr) c, err := nclient6.NewIPv6UDPConn(ifaceName, dhcpv6.DefaultClientPort) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't listen on :546: %w", err) } if c != nil { defer c.Close() } _, err = c.WriteTo(req.ToBytes(), dstAddr) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't send a packet to %s: %w", dst, err) } for { var next bool ok, next, err = tryConn6(req, c) if next { if err != nil { log.Debug("dhcpv6: trying a connection: %s", err) } continue } if err != nil { return false, err } return ok, nil } } // TODO(a.garipov): See the comment on tryConn4. Sigh… func tryConn6(req *dhcpv6.Message, c net.PacketConn) (ok, next bool, err error) { // TODO: replicate dhclient's behavior of retrying several times with // progressively longer timeouts. log.Tracef("dhcpv6: waiting %v for an answer", defaultDiscoverTime) b := make([]byte, 4096) err = c.SetDeadline(time.Now().Add(defaultDiscoverTime)) if err != nil { return false, false, fmt.Errorf("setting deadline: %w", err) } n, _, err := c.ReadFrom(b) if err != nil { if isTimeout(err) { log.Debug("dhcpv6: didn't receive dhcp response") return false, false, nil } return false, false, fmt.Errorf("receiving packet: %w", err) } log.Tracef("dhcpv6: received packet, %d bytes", n) response, err := dhcpv6.FromBytes(b[:n]) if err != nil { log.Debug("dhcpv6: encoding: %s", err) return false, true, err } log.Debug("dhcpv6: received message from server: %s", response.Summary()) cid := req.Options.ClientID() msg, err := response.GetInnerMessage() if err != nil { log.Debug("dhcpv6: resp.GetInnerMessage(): %s", err) return false, true, err } rcid := msg.Options.ClientID() if !(response.Type() == dhcpv6.MessageTypeAdvertise && msg.TransactionID == req.TransactionID && rcid != nil && cid.Equal(*rcid)) { log.Debug("dhcpv6: received message from server doesn't match our request") return false, true, nil } log.Tracef("dhcpv6: the packet is from an active dhcp server") return true, false, nil }