| /* |
| * Copyright (C) 2018 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package android.net.dhcp; |
| |
| import static android.net.NetworkUtils.getBroadcastAddress; |
| import static android.net.NetworkUtils.getPrefixMaskAsInet4Address; |
| import static android.net.TrafficStats.TAG_SYSTEM_DHCP_SERVER; |
| import static android.net.dhcp.DhcpPacket.DHCP_CLIENT; |
| import static android.net.dhcp.DhcpPacket.DHCP_HOST_NAME; |
| import static android.net.dhcp.DhcpPacket.DHCP_SERVER; |
| import static android.net.dhcp.DhcpPacket.ENCAP_BOOTP; |
| import static android.net.dhcp.DhcpPacket.INFINITE_LEASE; |
| import static android.system.OsConstants.AF_INET; |
| import static android.system.OsConstants.IPPROTO_UDP; |
| import static android.system.OsConstants.SOCK_DGRAM; |
| import static android.system.OsConstants.SOL_SOCKET; |
| import static android.system.OsConstants.SO_BINDTODEVICE; |
| import static android.system.OsConstants.SO_BROADCAST; |
| import static android.system.OsConstants.SO_REUSEADDR; |
| |
| import static java.lang.Integer.toUnsignedLong; |
| |
| import android.annotation.NonNull; |
| import android.annotation.Nullable; |
| import android.net.MacAddress; |
| import android.net.NetworkUtils; |
| import android.net.TrafficStats; |
| import android.net.util.InterfaceParams; |
| import android.net.util.SharedLog; |
| import android.os.Handler; |
| import android.os.Looper; |
| import android.os.Message; |
| import android.os.SystemClock; |
| import android.system.ErrnoException; |
| import android.system.Os; |
| import android.text.TextUtils; |
| |
| import com.android.internal.annotations.VisibleForTesting; |
| import com.android.internal.util.HexDump; |
| |
| import java.io.FileDescriptor; |
| import java.io.IOException; |
| import java.net.Inet4Address; |
| import java.net.InetAddress; |
| import java.nio.ByteBuffer; |
| import java.util.ArrayList; |
| |
| /** |
| * A DHCPv4 server. |
| * |
| * <p>This server listens for and responds to packets on a single interface. It considers itself |
| * authoritative for all leases on the subnet, which means that DHCP requests for unknown leases of |
| * unknown hosts receive a reply instead of being ignored. |
| * |
| * <p>The server is single-threaded (including send/receive operations): all internal operations are |
| * done on the provided {@link Looper}. Public methods are thread-safe and will schedule operations |
| * on the looper asynchronously. |
| * @hide |
| */ |
| public class DhcpServer { |
| private static final String REPO_TAG = "Repository"; |
| |
| // Lease time to transmit to client instead of a negative time in case a lease expired before |
| // the server could send it (if the server process is suspended for example). |
| private static final int EXPIRED_FALLBACK_LEASE_TIME_SECS = 120; |
| |
| private static final int CMD_START_DHCP_SERVER = 1; |
| private static final int CMD_STOP_DHCP_SERVER = 2; |
| private static final int CMD_UPDATE_PARAMS = 3; |
| |
| @NonNull |
| private final ServerHandler mHandler; |
| @NonNull |
| private final InterfaceParams mIface; |
| @NonNull |
| private final DhcpLeaseRepository mLeaseRepo; |
| @NonNull |
| private final SharedLog mLog; |
| @NonNull |
| private final Dependencies mDeps; |
| @NonNull |
| private final Clock mClock; |
| @NonNull |
| private final DhcpPacketListener mPacketListener; |
| |
| @Nullable |
| private FileDescriptor mSocket; |
| @NonNull |
| private DhcpServingParams mServingParams; |
| |
| public static class Clock { |
| /** |
| * @see SystemClock#elapsedRealtime() |
| */ |
| public long elapsedRealtime() { |
| return SystemClock.elapsedRealtime(); |
| } |
| } |
| |
| public interface Dependencies { |
| void sendPacket(@NonNull FileDescriptor fd, @NonNull ByteBuffer buffer, |
| @NonNull InetAddress dst) throws ErrnoException, IOException; |
| DhcpLeaseRepository makeLeaseRepository(@NonNull DhcpServingParams servingParams, |
| @NonNull SharedLog log, @NonNull Clock clock); |
| DhcpPacketListener makePacketListener(); |
| Clock makeClock(); |
| void addArpEntry(@NonNull Inet4Address ipv4Addr, @NonNull MacAddress ethAddr, |
| @NonNull String ifname, @NonNull FileDescriptor fd) throws IOException; |
| } |
| |
| private class DependenciesImpl implements Dependencies { |
| @Override |
| public void sendPacket(@NonNull FileDescriptor fd, @NonNull ByteBuffer buffer, |
| @NonNull InetAddress dst) throws ErrnoException, IOException { |
| Os.sendto(fd, buffer, 0, dst, DhcpPacket.DHCP_CLIENT); |
| } |
| |
| @Override |
| public DhcpLeaseRepository makeLeaseRepository(@NonNull DhcpServingParams servingParams, |
| @NonNull SharedLog log, @NonNull Clock clock) { |
| return new DhcpLeaseRepository( |
| DhcpServingParams.makeIpPrefix(servingParams.serverAddr), |
| servingParams.excludedAddrs, |
| servingParams.dhcpLeaseTimeSecs*1000, log.forSubComponent(REPO_TAG), clock); |
| } |
| |
| @Override |
| public DhcpPacketListener makePacketListener() { |
| return new PacketListener(); |
| } |
| |
| @Override |
| public Clock makeClock() { |
| return new Clock(); |
| } |
| |
| @Override |
| public void addArpEntry(@NonNull Inet4Address ipv4Addr, @NonNull MacAddress ethAddr, |
| @NonNull String ifname, @NonNull FileDescriptor fd) throws IOException { |
| NetworkUtils.addArpEntry(ipv4Addr, ethAddr, ifname, fd); |
| } |
| } |
| |
| private static class MalformedPacketException extends Exception { |
| MalformedPacketException(String message, Throwable t) { |
| super(message, t); |
| } |
| } |
| |
| public DhcpServer(@NonNull Looper looper, @NonNull InterfaceParams iface, |
| @NonNull DhcpServingParams params, @NonNull SharedLog log) { |
| this(looper, iface, params, log, null); |
| } |
| |
| @VisibleForTesting |
| DhcpServer(@NonNull Looper looper, @NonNull InterfaceParams iface, |
| @NonNull DhcpServingParams params, @NonNull SharedLog log, |
| @Nullable Dependencies deps) { |
| if (deps == null) { |
| deps = new DependenciesImpl(); |
| } |
| mHandler = new ServerHandler(looper); |
| mIface = iface; |
| mServingParams = params; |
| mLog = log; |
| mDeps = deps; |
| mClock = deps.makeClock(); |
| mPacketListener = deps.makePacketListener(); |
| mLeaseRepo = deps.makeLeaseRepository(mServingParams, mLog, mClock); |
| } |
| |
| /** |
| * Start listening for and responding to packets. |
| */ |
| public void start() { |
| mHandler.sendEmptyMessage(CMD_START_DHCP_SERVER); |
| } |
| |
| /** |
| * Update serving parameters. All subsequently received requests will be handled with the new |
| * parameters, and current leases that are incompatible with the new parameters are dropped. |
| */ |
| public void updateParams(@NonNull DhcpServingParams params) { |
| sendMessage(CMD_UPDATE_PARAMS, params); |
| } |
| |
| /** |
| * Stop listening for packets. |
| * |
| * <p>As the server is stopped asynchronously, some packets may still be processed shortly after |
| * calling this method. |
| */ |
| public void stop() { |
| mHandler.sendEmptyMessage(CMD_STOP_DHCP_SERVER); |
| } |
| |
| private void sendMessage(int what, @Nullable Object obj) { |
| mHandler.sendMessage(mHandler.obtainMessage(what, obj)); |
| } |
| |
| private class ServerHandler extends Handler { |
| public ServerHandler(@NonNull Looper looper) { |
| super(looper); |
| } |
| |
| @Override |
| public void handleMessage(@NonNull Message msg) { |
| switch (msg.what) { |
| case CMD_UPDATE_PARAMS: |
| final DhcpServingParams params = (DhcpServingParams) msg.obj; |
| mServingParams = params; |
| mLeaseRepo.updateParams( |
| DhcpServingParams.makeIpPrefix(mServingParams.serverAddr), |
| params.excludedAddrs, |
| params.dhcpLeaseTimeSecs); |
| break; |
| case CMD_START_DHCP_SERVER: |
| // This is a no-op if the listener is already started |
| mPacketListener.start(); |
| break; |
| case CMD_STOP_DHCP_SERVER: |
| // This is a no-op if the listener was not started |
| mPacketListener.stop(); |
| break; |
| } |
| } |
| } |
| |
| @VisibleForTesting |
| void processPacket(@NonNull DhcpPacket packet, int srcPort) { |
| final String packetType = packet.getClass().getSimpleName(); |
| if (srcPort != DHCP_CLIENT) { |
| mLog.logf("Ignored packet of type %s sent from client port %d", packetType, srcPort); |
| return; |
| } |
| |
| mLog.log("Received packet of type " + packetType); |
| final Inet4Address sid = packet.mServerIdentifier; |
| if (sid != null && !sid.equals(mServingParams.serverAddr.getAddress())) { |
| mLog.log("Packet ignored due to wrong server identifier: " + sid); |
| return; |
| } |
| |
| try { |
| if (packet instanceof DhcpDiscoverPacket) { |
| processDiscover((DhcpDiscoverPacket) packet); |
| } else if (packet instanceof DhcpRequestPacket) { |
| processRequest((DhcpRequestPacket) packet); |
| } else if (packet instanceof DhcpReleasePacket) { |
| processRelease((DhcpReleasePacket) packet); |
| } else { |
| mLog.e("Unknown packet type: " + packet.getClass().getSimpleName()); |
| } |
| } catch (MalformedPacketException e) { |
| // Not an internal error: only logging exception message, not stacktrace |
| mLog.e("Ignored malformed packet: " + e.getMessage()); |
| } |
| } |
| |
| private void logIgnoredPacketInvalidSubnet(DhcpLeaseRepository.InvalidSubnetException e) { |
| // Not an internal error: only logging exception message, not stacktrace |
| mLog.e("Ignored packet from invalid subnet: " + e.getMessage()); |
| } |
| |
| private void processDiscover(@NonNull DhcpDiscoverPacket packet) |
| throws MalformedPacketException { |
| final DhcpLease lease; |
| final MacAddress clientMac = getMacAddr(packet); |
| try { |
| lease = mLeaseRepo.getOffer(packet.getExplicitClientIdOrNull(), clientMac, |
| packet.mRelayIp, packet.mRequestedIp, packet.mHostName); |
| } catch (DhcpLeaseRepository.OutOfAddressesException e) { |
| transmitNak(packet, "Out of addresses to offer"); |
| return; |
| } catch (DhcpLeaseRepository.InvalidSubnetException e) { |
| logIgnoredPacketInvalidSubnet(e); |
| return; |
| } |
| |
| transmitOffer(packet, lease, clientMac); |
| } |
| |
| private void processRequest(@NonNull DhcpRequestPacket packet) throws MalformedPacketException { |
| // If set, packet SID matches with this server's ID as checked in processPacket(). |
| final boolean sidSet = packet.mServerIdentifier != null; |
| final DhcpLease lease; |
| final MacAddress clientMac = getMacAddr(packet); |
| try { |
| lease = mLeaseRepo.requestLease(packet.getExplicitClientIdOrNull(), clientMac, |
| packet.mClientIp, packet.mRelayIp, packet.mRequestedIp, sidSet, |
| packet.mHostName); |
| } catch (DhcpLeaseRepository.InvalidAddressException e) { |
| transmitNak(packet, "Invalid requested address"); |
| return; |
| } catch (DhcpLeaseRepository.InvalidSubnetException e) { |
| logIgnoredPacketInvalidSubnet(e); |
| return; |
| } |
| |
| transmitAck(packet, lease, clientMac); |
| } |
| |
| private void processRelease(@NonNull DhcpReleasePacket packet) |
| throws MalformedPacketException { |
| final byte[] clientId = packet.getExplicitClientIdOrNull(); |
| final MacAddress macAddr = getMacAddr(packet); |
| // Don't care about success (there is no ACK/NAK); logging is already done in the repository |
| mLeaseRepo.releaseLease(clientId, macAddr, packet.mClientIp); |
| } |
| |
| private Inet4Address getAckOrOfferDst(@NonNull DhcpPacket request, @NonNull DhcpLease lease, |
| boolean broadcastFlag) { |
| // Unless relayed or broadcast, send to client IP if already configured on the client, or to |
| // the lease address if the client has no configured address |
| if (!isEmpty(request.mRelayIp)) { |
| return request.mRelayIp; |
| } else if (broadcastFlag) { |
| return (Inet4Address) Inet4Address.ALL; |
| } else if (!isEmpty(request.mClientIp)) { |
| return request.mClientIp; |
| } else { |
| return lease.getNetAddr(); |
| } |
| } |
| |
| /** |
| * Determine whether the broadcast flag should be set in the BOOTP packet flags. This does not |
| * apply to NAK responses, which should always have it set. |
| */ |
| private static boolean getBroadcastFlag(@NonNull DhcpPacket request, @NonNull DhcpLease lease) { |
| // No broadcast flag if the client already has a configured IP to unicast to. RFC2131 #4.1 |
| // has some contradictions regarding broadcast behavior if a client already has an IP |
| // configured and sends a request with both ciaddr (renew/rebind) and the broadcast flag |
| // set. Sending a unicast response to ciaddr matches previous behavior and is more |
| // efficient. |
| // If the client has no configured IP, broadcast if requested by the client or if the lease |
| // address cannot be used to send a unicast reply either. |
| return isEmpty(request.mClientIp) && (request.mBroadcast || isEmpty(lease.getNetAddr())); |
| } |
| |
| /** |
| * Get the hostname from a lease if non-empty and requested in the incoming request. |
| * @param request The incoming request. |
| * @return The hostname, or null if not requested or empty. |
| */ |
| @Nullable |
| private static String getHostnameIfRequested(@NonNull DhcpPacket request, |
| @NonNull DhcpLease lease) { |
| return request.hasRequestedParam(DHCP_HOST_NAME) && !TextUtils.isEmpty(lease.getHostname()) |
| ? lease.getHostname() |
| : null; |
| } |
| |
| private boolean transmitOffer(@NonNull DhcpPacket request, @NonNull DhcpLease lease, |
| @NonNull MacAddress clientMac) { |
| final boolean broadcastFlag = getBroadcastFlag(request, lease); |
| final int timeout = getLeaseTimeout(lease); |
| final Inet4Address prefixMask = |
| getPrefixMaskAsInet4Address(mServingParams.serverAddr.getPrefixLength()); |
| final Inet4Address broadcastAddr = getBroadcastAddress( |
| mServingParams.getServerInet4Addr(), mServingParams.serverAddr.getPrefixLength()); |
| final String hostname = getHostnameIfRequested(request, lease); |
| final ByteBuffer offerPacket = DhcpPacket.buildOfferPacket( |
| ENCAP_BOOTP, request.mTransId, broadcastFlag, mServingParams.getServerInet4Addr(), |
| request.mRelayIp, lease.getNetAddr(), request.mClientMac, timeout, prefixMask, |
| broadcastAddr, new ArrayList<>(mServingParams.defaultRouters), |
| new ArrayList<>(mServingParams.dnsServers), |
| mServingParams.getServerInet4Addr(), null /* domainName */, hostname, |
| mServingParams.metered, (short) mServingParams.linkMtu); |
| |
| return transmitOfferOrAckPacket(offerPacket, request, lease, clientMac, broadcastFlag); |
| } |
| |
| private boolean transmitAck(@NonNull DhcpPacket request, @NonNull DhcpLease lease, |
| @NonNull MacAddress clientMac) { |
| // TODO: replace DhcpPacket's build methods with real builders and use common code with |
| // transmitOffer above |
| final boolean broadcastFlag = getBroadcastFlag(request, lease); |
| final int timeout = getLeaseTimeout(lease); |
| final String hostname = getHostnameIfRequested(request, lease); |
| final ByteBuffer ackPacket = DhcpPacket.buildAckPacket(ENCAP_BOOTP, request.mTransId, |
| broadcastFlag, mServingParams.getServerInet4Addr(), request.mRelayIp, |
| lease.getNetAddr(), request.mClientIp, request.mClientMac, timeout, |
| mServingParams.getPrefixMaskAsAddress(), mServingParams.getBroadcastAddress(), |
| new ArrayList<>(mServingParams.defaultRouters), |
| new ArrayList<>(mServingParams.dnsServers), |
| mServingParams.getServerInet4Addr(), null /* domainName */, hostname, |
| mServingParams.metered, (short) mServingParams.linkMtu); |
| |
| return transmitOfferOrAckPacket(ackPacket, request, lease, clientMac, broadcastFlag); |
| } |
| |
| private boolean transmitNak(DhcpPacket request, String message) { |
| mLog.w("Transmitting NAK: " + message); |
| // Always set broadcast flag for NAK: client may not have a correct IP |
| final ByteBuffer nakPacket = DhcpPacket.buildNakPacket( |
| ENCAP_BOOTP, request.mTransId, mServingParams.getServerInet4Addr(), |
| request.mRelayIp, request.mClientMac, true /* broadcast */, message); |
| |
| final Inet4Address dst = isEmpty(request.mRelayIp) |
| ? (Inet4Address) Inet4Address.ALL |
| : request.mRelayIp; |
| return transmitPacket(nakPacket, DhcpNakPacket.class.getSimpleName(), dst); |
| } |
| |
| private boolean transmitOfferOrAckPacket(@NonNull ByteBuffer buf, @NonNull DhcpPacket request, |
| @NonNull DhcpLease lease, @NonNull MacAddress clientMac, boolean broadcastFlag) { |
| mLog.logf("Transmitting %s with lease %s", request.getClass().getSimpleName(), lease); |
| // Client may not yet respond to ARP for the lease address, which may be the destination |
| // address. Add an entry to the ARP cache to save future ARP probes and make sure the |
| // packet reaches its destination. |
| if (!addArpEntry(clientMac, lease.getNetAddr())) { |
| // Logging for error already done |
| return false; |
| } |
| final Inet4Address dst = getAckOrOfferDst(request, lease, broadcastFlag); |
| return transmitPacket(buf, request.getClass().getSimpleName(), dst); |
| } |
| |
| private boolean transmitPacket(@NonNull ByteBuffer buf, @NonNull String packetTypeTag, |
| @NonNull Inet4Address dst) { |
| try { |
| mDeps.sendPacket(mSocket, buf, dst); |
| } catch (ErrnoException | IOException e) { |
| mLog.e("Can't send packet " + packetTypeTag, e); |
| return false; |
| } |
| return true; |
| } |
| |
| private boolean addArpEntry(@NonNull MacAddress macAddr, @NonNull Inet4Address inetAddr) { |
| try { |
| mDeps.addArpEntry(inetAddr, macAddr, mIface.name, mSocket); |
| return true; |
| } catch (IOException e) { |
| mLog.e("Error adding client to ARP table", e); |
| return false; |
| } |
| } |
| |
| /** |
| * Get the remaining lease time in seconds, starting from {@link Clock#elapsedRealtime()}. |
| * |
| * <p>This is an unsigned 32-bit integer, so it cannot be read as a standard (signed) Java int. |
| * The return value is only intended to be used to populate the lease time field in a DHCP |
| * response, considering that lease time is an unsigned 32-bit integer field in DHCP packets. |
| * |
| * <p>Lease expiration times are tracked internally with millisecond precision: this method |
| * returns a rounded down value. |
| */ |
| private int getLeaseTimeout(@NonNull DhcpLease lease) { |
| final long remainingTimeSecs = (lease.getExpTime() - mClock.elapsedRealtime()) / 1000; |
| if (remainingTimeSecs < 0) { |
| mLog.e("Processing expired lease " + lease); |
| return EXPIRED_FALLBACK_LEASE_TIME_SECS; |
| } |
| |
| if (remainingTimeSecs >= toUnsignedLong(INFINITE_LEASE)) { |
| return INFINITE_LEASE; |
| } |
| |
| return (int) remainingTimeSecs; |
| } |
| |
| /** |
| * Get the client MAC address from a packet. |
| * |
| * @throws MalformedPacketException The address in the packet uses an unsupported format. |
| */ |
| @NonNull |
| private MacAddress getMacAddr(@NonNull DhcpPacket packet) throws MalformedPacketException { |
| try { |
| return MacAddress.fromBytes(packet.getClientMac()); |
| } catch (IllegalArgumentException e) { |
| final String message = "Invalid MAC address in packet: " |
| + HexDump.dumpHexString(packet.getClientMac()); |
| throw new MalformedPacketException(message, e); |
| } |
| } |
| |
| private static boolean isEmpty(@Nullable Inet4Address address) { |
| return address == null || Inet4Address.ANY.equals(address); |
| } |
| |
| private class PacketListener extends DhcpPacketListener { |
| public PacketListener() { |
| super(mHandler); |
| } |
| |
| @Override |
| protected void onReceive(DhcpPacket packet, Inet4Address srcAddr, int srcPort) { |
| processPacket(packet, srcPort); |
| } |
| |
| @Override |
| protected void logError(String msg, Exception e) { |
| mLog.e("Error receiving packet: " + msg, e); |
| } |
| |
| @Override |
| protected void logParseError(byte[] packet, int length, DhcpPacket.ParseException e) { |
| mLog.e("Error parsing packet", e); |
| } |
| |
| @Override |
| protected FileDescriptor createFd() { |
| // TODO: have and use an API to set a socket tag without going through the thread tag |
| final int oldTag = TrafficStats.getAndSetThreadStatsTag(TAG_SYSTEM_DHCP_SERVER); |
| try { |
| mSocket = Os.socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP); |
| Os.setsockoptInt(mSocket, SOL_SOCKET, SO_REUSEADDR, 1); |
| // SO_BINDTODEVICE actually takes a string. This works because the first member |
| // of struct ifreq is a NULL-terminated interface name. |
| // TODO: add a setsockoptString() |
| Os.setsockoptIfreq(mSocket, SOL_SOCKET, SO_BINDTODEVICE, mIface.name); |
| Os.setsockoptInt(mSocket, SOL_SOCKET, SO_BROADCAST, 1); |
| Os.bind(mSocket, Inet4Address.ANY, DHCP_SERVER); |
| NetworkUtils.protectFromVpn(mSocket); |
| |
| return mSocket; |
| } catch (IOException | ErrnoException e) { |
| mLog.e("Error creating UDP socket", e); |
| DhcpServer.this.stop(); |
| return null; |
| } finally { |
| TrafficStats.setThreadStatsTag(oldTag); |
| } |
| } |
| } |
| } |