//go:build darwin || freebsd || linux || openbsd package aghnet import ( "bytes" "fmt" "net" "net/netip" "os" "time" "github.com/AdguardTeam/golibs/errors" "github.com/AdguardTeam/golibs/log" "github.com/AdguardTeam/golibs/netutil" "github.com/insomniacslk/dhcp/dhcpv4" "github.com/insomniacslk/dhcp/dhcpv6" "github.com/insomniacslk/dhcp/dhcpv6/nclient6" "github.com/insomniacslk/dhcp/iana" ) // defaultDiscoverTime is the default timeout of checking another DHCP server // response. const defaultDiscoverTime = 3 * time.Second func checkOtherDHCP(ifaceName string) (ok4, ok6 bool, err4, err6 error) { iface, err := net.InterfaceByName(ifaceName) if err != nil { err = fmt.Errorf("couldn't find interface by name %s: %w", ifaceName, err) err4, err6 = err, err return false, false, err4, err6 } ok4, err4 = checkOtherDHCPv4(iface) ok6, err6 = checkOtherDHCPv6(iface) return ok4, ok6, err4, err6 } // ifaceIPv4Subnet returns the first suitable IPv4 subnetwork iface has. func ifaceIPv4Subnet(iface *net.Interface) (subnet netip.Prefix, err error) { var addrs []net.Addr if addrs, err = iface.Addrs(); err != nil { return netip.Prefix{}, err } for _, a := range addrs { var ip net.IP var maskLen int switch a := a.(type) { case *net.IPAddr: ip = a.IP maskLen, _ = ip.DefaultMask().Size() case *net.IPNet: ip = a.IP maskLen, _ = a.Mask.Size() default: continue } if ip = ip.To4(); ip != nil { return netip.PrefixFrom(netip.AddrFrom4(*(*[4]byte)(ip)), maskLen), nil } } return netip.Prefix{}, fmt.Errorf("interface %s has no ipv4 addresses", iface.Name) } // checkOtherDHCPv4 sends a DHCP request to the specified network interface, and // waits for a response for a period defined by defaultDiscoverTime. func checkOtherDHCPv4(iface *net.Interface) (ok bool, err error) { var subnet netip.Prefix if subnet, err = ifaceIPv4Subnet(iface); err != nil { return false, err } // Resolve broadcast addr. dst := netip.AddrPortFrom(BroadcastFromPref(subnet), 67).String() var dstAddr *net.UDPAddr if dstAddr, err = net.ResolveUDPAddr("udp4", dst); err != nil { return false, fmt.Errorf("couldn't resolve UDP address %s: %w", dst, err) } var hostname string if hostname, err = os.Hostname(); err != nil { return false, fmt.Errorf("couldn't get hostname: %w", err) } return discover4(iface, dstAddr, hostname) } func discover4(iface *net.Interface, dstAddr *net.UDPAddr, hostname string) (ok bool, err error) { var req *dhcpv4.DHCPv4 if req, err = dhcpv4.NewDiscovery(iface.HardwareAddr); err != nil { return false, fmt.Errorf("dhcpv4.NewDiscovery: %w", err) } req.Options.Update(dhcpv4.OptClientIdentifier(iface.HardwareAddr)) req.Options.Update(dhcpv4.OptHostName(hostname)) req.SetBroadcast() // Bind to 0.0.0.0:68. // // On OpenBSD binding to the port 68 competes with dhclient's binding, // so that all incoming packets are ignored and the discovering process // is spoiled. // // It's also known that listening on the specified interface's address // ignores broadcast packets when reading. var c net.PacketConn if c, err = listenPacketReusable(iface.Name, "udp4", ":68"); err != nil { return false, fmt.Errorf("couldn't listen on :68: %w", err) } defer func() { err = errors.WithDeferred(err, c.Close()) }() // Send to broadcast. if _, err = c.WriteTo(req.ToBytes(), dstAddr); err != nil { return false, fmt.Errorf("couldn't send a packet to %s: %w", dstAddr, err) } for { if err = c.SetDeadline(time.Now().Add(defaultDiscoverTime)); err != nil { return false, fmt.Errorf("setting deadline: %w", err) } 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) n, _, err := c.ReadFrom(b) if err != nil { if errors.Is(err, os.ErrDeadlineExceeded) { 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()) switch { case response.OpCode != dhcpv4.OpcodeBootReply, response.HWType != iana.HWTypeEthernet, !bytes.Equal(response.ClientHWAddr, iface.HardwareAddr), response.TransactionID != req.TransactionID, !response.Options.Has(dhcpv4.OptionDHCPMessageType): log.Debug("dhcpv4: received response doesn't match the request") return false, true, nil default: log.Tracef("dhcpv4: the packet is from an active dhcp server") return true, false, nil } } // checkOtherDHCPv6 sends a DHCP request to the specified network interface, and // waits for a response for a period defined by defaultDiscoverTime. func checkOtherDHCPv6(iface *net.Interface) (ok bool, err error) { ifaceIPNet, err := IfaceIPAddrs(iface, IPVersion6) if err != nil { return false, fmt.Errorf("getting ipv6 addrs for iface %s: %w", iface.Name, err) } if len(ifaceIPNet) == 0 { return false, fmt.Errorf("interface %s has no ipv6 addresses", iface.Name) } srcIP := ifaceIPNet[0] src := netutil.JoinHostPort(srcIP.String(), 546) dst := "[ff02::1:2]:547" 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) } return discover6(iface, udpAddr, dstAddr) } func discover6(iface *net.Interface, udpAddr, dstAddr *net.UDPAddr) (ok bool, err error) { req, err := dhcpv6.NewSolicit(iface.HardwareAddr) if err != nil { return false, fmt.Errorf("dhcpv6: dhcpv6.NewSolicit: %w", err) } log.Debug("DHCPv6: Listening to udp6 %+v", udpAddr) c, err := nclient6.NewIPv6UDPConn(iface.Name, dhcpv6.DefaultClientPort) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't listen on :546: %w", err) } defer func() { err = errors.WithDeferred(err, c.Close()) }() _, err = c.WriteTo(req.ToBytes(), dstAddr) if err != nil { return false, fmt.Errorf("dhcpv6: Couldn't send a packet to %s: %w", dstAddr, 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 errors.Is(err, os.ErrDeadlineExceeded) { 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 }