Merge "Dropping NAT-T keepalive packet from APF" am: c4104f029f (2493db83) · Commits · e / os / android_frameworks_base

packages/NetworkStack/src/android/net/apf/ApfFilter.java

+216 −71

Original line number	Diff line number	Diff line
		@@ -155,7 +155,9 @@ public class ApfFilter {
		DROPPED_ETHERTYPE_BLACKLISTED,
		DROPPED_ARP_REPLY_SPA_NO_HOST,
		DROPPED_IPV4_KEEPALIVE_ACK,
		DROPPED_IPV6_KEEPALIVE_ACK;
		DROPPED_IPV6_KEEPALIVE_ACK,
		DROPPED_IPV4_NATT_KEEPALIVE,
		DROPPED_IPV6_NATT_KEEPALIVE;

		// Returns the negative byte offset from the end of the APF data segment for
		// a given counter.
		@@ -857,12 +859,129 @@ public class ApfFilter {
		}
		}

		// A class to hold keepalive ack information.
		private abstract static class TcpKeepaliveAck {
		// TODO: Refactor these subclasses to avoid so much repetition.
		private abstract static class KeepalivePacket {
		// Note that the offset starts from IP header.
		// These must be added ether header length when generating program.
		static final int IP_HEADER_OFFSET = 0;
		static final int IPV4_SRC_ADDR_OFFSET = IP_HEADER_OFFSET + 12;

		// Append a filter for this keepalive ack to {@code gen}.
		// Jump to drop if it matches the keepalive ack.
		// Jump to the next filter if packet doesn't match the keepalive ack.
		abstract void generateFilterLocked(ApfGenerator gen) throws IllegalInstructionException;
		}

		// A class to hold NAT-T keepalive ack information.
		private abstract static class NattKeepaliveAck extends KeepalivePacket {
		static final int UDP_LENGTH_OFFSET = 4;
		static final int UDP_HEADER_LEN = 8;

		protected static class NattKeepaliveAckData {
		public final byte[] srcAddress;
		public final int srcPort;
		public final byte[] dstAddress;
		public final int dstPort;

		NattKeepaliveAckData(final NattKeepalivePacketDataParcelable sentKeepalivePacket) {
		srcAddress = sentKeepalivePacket.dstAddress;
		srcPort = sentKeepalivePacket.dstPort;
		dstAddress = sentKeepalivePacket.srcAddress;
		dstPort = sentKeepalivePacket.srcPort;
		}
		}

		protected final NattKeepaliveAckData mPacket;
		protected final byte[] mSrcDstAddr;
		protected final byte[] mPortFingerprint;
		// NAT-T keepalive packet
		protected final byte[] mPayload = {(byte) 0xff};

		NattKeepaliveAck(final NattKeepaliveAckData packet, final byte[] srcDstAddr) {
		mPacket = packet;
		mSrcDstAddr = srcDstAddr;
		mPortFingerprint = generatePortFingerprint(mPacket.srcPort, mPacket.dstPort);
		}

		static byte[] generatePortFingerprint(int srcPort, int dstPort) {
		final ByteBuffer fp = ByteBuffer.allocate(4);
		fp.order(ByteOrder.BIG_ENDIAN);
		fp.putShort((short) srcPort);
		fp.putShort((short) dstPort);
		return fp.array();
		}

		public String toString() {
		try {
		return String.format("%s -> %s",
		NetworkStackUtils.addressAndPortToString(
		InetAddress.getByAddress(mPacket.srcAddress), mPacket.srcPort),
		NetworkStackUtils.addressAndPortToString(
		InetAddress.getByAddress(mPacket.dstAddress), mPacket.dstPort));
		} catch (UnknownHostException e) {
		return "Unknown host";
		}
		}
		}

		private class NattKeepaliveAckV4 extends NattKeepaliveAck {
		NattKeepaliveAckV4(final NattKeepalivePacketDataParcelable sentKeepalivePacket) {
		this(new NattKeepaliveAckData(sentKeepalivePacket));
		}
		NattKeepaliveAckV4(final NattKeepaliveAckData packet) {
		super(packet, concatArrays(packet.srcAddress, packet.dstAddress) /* srcDstAddr */);
		}

		@Override
		void generateFilterLocked(ApfGenerator gen) throws IllegalInstructionException {
		final String nextFilterLabel = "natt_keepalive_filter" + getUniqueNumberLocked();

		gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN + IPV4_SRC_ADDR_OFFSET);
		gen.addJumpIfBytesNotEqual(Register.R0, mSrcDstAddr, nextFilterLabel);

		// A NAT-T keepalive packet contains 1 byte payload with the value 0xff
		// Check payload length is 1
		gen.addLoadFromMemory(Register.R0, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
		gen.addAdd(UDP_HEADER_LEN);
		gen.addSwap();
		gen.addLoad16(Register.R0, IPV4_TOTAL_LENGTH_OFFSET);
		gen.addNeg(Register.R1);
		gen.addAddR1();
		gen.addJumpIfR0NotEquals(1, nextFilterLabel);

		// R0 = R0 + R1 -> R0 contains IP header
		gen.addLoadFromMemory(Register.R1, gen.IPV4_HEADER_SIZE_MEMORY_SLOT);
		gen.addLoadImmediate(Register.R0, ETH_HEADER_LEN);
		gen.addAddR1();
		gen.addJumpIfBytesNotEqual(Register.R0, mPortFingerprint, nextFilterLabel);

		// Payload offset = R0 + UDP header length
		gen.addAdd(UDP_HEADER_LEN);
		gen.addJumpIfBytesNotEqual(Register.R0, mPayload, nextFilterLabel);

		maybeSetupCounter(gen, Counter.DROPPED_IPV4_NATT_KEEPALIVE);
		gen.addJump(mCountAndDropLabel);
		gen.defineLabel(nextFilterLabel);
		}
		}

		private class NattKeepaliveAckV6 extends NattKeepaliveAck {
		NattKeepaliveAckV6(final NattKeepalivePacketDataParcelable sentKeepalivePacket) {
		this(new NattKeepaliveAckData(sentKeepalivePacket));
		}

		NattKeepaliveAckV6(final NattKeepaliveAckData packet) {
		super(packet, concatArrays(packet.srcAddress, packet.dstAddress) /* srcDstAddr */);
		}

		@Override
		void generateFilterLocked(ApfGenerator gen) throws IllegalInstructionException {
		throw new UnsupportedOperationException("IPv6 NAT-T Keepalive is not supported yet");
		}
		}

		// A class to hold TCP keepalive ack information.
		private abstract static class TcpKeepaliveAck extends KeepalivePacket {
		protected static class TcpKeepaliveAckData {
		public final byte[] srcAddress;
		public final int srcPort;
		@@ -870,6 +989,7 @@ public class ApfFilter {
		public final int dstPort;
		public final int seq;
		public final int ack;

		// Create the characteristics of the ack packet from the sent keepalive packet.
		TcpKeepaliveAckData(final TcpKeepalivePacketDataParcelable sentKeepalivePacket) {
		srcAddress = sentKeepalivePacket.dstAddress;
		@@ -902,28 +1022,18 @@ public class ApfFilter {
		return fp.array();
		}

		static byte[] concatArrays(final byte[]... arr) {
		int size = 0;
		for (byte[] a : arr) {
		size += a.length;
		}
		final byte[] result = new byte[size];
		int offset = 0;
		for (byte[] a : arr) {
		System.arraycopy(a, 0, result, offset, a.length);
		offset += a.length;
		}
		return result;
		}

		public String toString() {
		return String.format("%s(%d) -> %s(%d), seq=%d, ack=%d",
		mPacket.srcAddress,
		mPacket.srcPort,
		mPacket.dstAddress,
		mPacket.dstPort,
		mPacket.seq,
		mPacket.ack);
		try {
		return String.format("%s -> %s , seq=%d, ack=%d",
		NetworkStackUtils.addressAndPortToString(
		InetAddress.getByAddress(mPacket.srcAddress), mPacket.srcPort),
		NetworkStackUtils.addressAndPortToString(
		InetAddress.getByAddress(mPacket.dstAddress), mPacket.dstPort),
		Integer.toUnsignedLong(mPacket.seq),
		Integer.toUnsignedLong(mPacket.ack));
		} catch (UnknownHostException e) {
		return "Unknown host";
		}
		}

		// Append a filter for this keepalive ack to {@code gen}.
		@@ -933,7 +1043,6 @@ public class ApfFilter {
		}

		private class TcpKeepaliveAckV4 extends TcpKeepaliveAck {
		private static final int IPV4_SRC_ADDR_OFFSET = IP_HEADER_OFFSET + 12;

		TcpKeepaliveAckV4(final TcpKeepalivePacketDataParcelable sentKeepalivePacket) {
		this(new TcpKeepaliveAckData(sentKeepalivePacket));
		@@ -987,7 +1096,7 @@ public class ApfFilter {

		@Override
		void generateFilterLocked(ApfGenerator gen) throws IllegalInstructionException {
		throw new UnsupportedOperationException("IPv6 Keepalive is not supported yet");
		throw new UnsupportedOperationException("IPv6 TCP Keepalive is not supported yet");
		}
		}

		@@ -997,7 +1106,7 @@ public class ApfFilter {
		@GuardedBy("this")
		private ArrayList<Ra> mRas = new ArrayList<>();
		@GuardedBy("this")
		private SparseArray<TcpKeepaliveAck> mKeepaliveAcks = new SparseArray<>();
		private SparseArray<KeepalivePacket> mKeepalivePackets = new SparseArray<>();

		// There is always some marginal benefit to updating the installed APF program when an RA is
		// seen because we can extend the program's lifetime slightly, but there is some cost to
		@@ -1171,9 +1280,12 @@ public class ApfFilter {
		gen.addJumpIfR0Equals(broadcastAddr, mCountAndDropLabel);
		}

		// If any keepalive filter matches, drop
		// If any TCP keepalive filter matches, drop
		generateV4KeepaliveFilters(gen);

		// If any NAT-T keepalive filter matches, drop
		generateV4NattKeepaliveFilters(gen);

		// Otherwise, this is an IPv4 unicast, pass
		// If L2 broadcast packet, drop.
		// TODO: can we invert this condition to fall through to the common pass case below?
		@@ -1191,25 +1303,36 @@ public class ApfFilter {
		gen.addJump(mCountAndPassLabel);
		}

		private void generateV4KeepaliveFilters(ApfGenerator gen) throws IllegalInstructionException {
		final String skipV4KeepaliveFilter = "skip_v4_keepalive_filter";
		final boolean haveV4KeepaliveAcks = NetworkStackUtils.any(mKeepaliveAcks,
		ack -> ack instanceof TcpKeepaliveAckV4);
		private void generateFilters(ApfGenerator gen, Class<?> filterType, int proto, int offset,
		String label) throws IllegalInstructionException {
		final boolean haveKeepaliveAcks = NetworkStackUtils.any(mKeepalivePackets,
		ack -> filterType.isInstance(ack));

		// If no keepalive acks
		if (!haveV4KeepaliveAcks) return;
		// If no keepalive packets of this type
		if (!haveKeepaliveAcks) return;

		// If not tcp, skip keepalive filters
		gen.addLoad8(Register.R0, IPV4_PROTOCOL_OFFSET);
		gen.addJumpIfR0NotEquals(IPPROTO_TCP, skipV4KeepaliveFilter);
		// If not the right proto, skip keepalive filters
		gen.addLoad8(Register.R0, offset);
		gen.addJumpIfR0NotEquals(proto, label);

		// Drop Keepalive packets
		for (int i = 0; i < mKeepalivePackets.size(); ++i) {
		final KeepalivePacket ack = mKeepalivePackets.valueAt(i);
		if (filterType.isInstance(ack)) ack.generateFilterLocked(gen);
		}

		gen.defineLabel(label);
		}

		// Drop IPv4 Keepalive acks
		for (int i = 0; i < mKeepaliveAcks.size(); ++i) {
		final TcpKeepaliveAck ack = mKeepaliveAcks.valueAt(i);
		if (ack instanceof TcpKeepaliveAckV4) ack.generateFilterLocked(gen);
		private void generateV4KeepaliveFilters(ApfGenerator gen) throws IllegalInstructionException {
		generateFilters(gen, TcpKeepaliveAckV4.class, IPPROTO_TCP, IPV4_PROTOCOL_OFFSET,
		"skip_v4_keepalive_filter");
		}

		gen.defineLabel(skipV4KeepaliveFilter);
		private void generateV4NattKeepaliveFilters(ApfGenerator gen)
		throws IllegalInstructionException {
		generateFilters(gen, NattKeepaliveAckV4.class, IPPROTO_UDP, IPV4_PROTOCOL_OFFSET,
		"skip_v4_nattkeepalive_filter");
		}

		/**
		@@ -1294,24 +1417,8 @@ public class ApfFilter {
		}

		private void generateV6KeepaliveFilters(ApfGenerator gen) throws IllegalInstructionException {
		final String skipV6KeepaliveFilter = "skip_v6_keepalive_filter";
		final boolean haveV6KeepaliveAcks = NetworkStackUtils.any(mKeepaliveAcks,
		ack -> ack instanceof TcpKeepaliveAckV6);

		// If no keepalive acks
		if (!haveV6KeepaliveAcks) return;

		// If not tcp, skip keepalive filters
		gen.addLoad8(Register.R0, IPV6_NEXT_HEADER_OFFSET);
		gen.addJumpIfR0NotEquals(IPPROTO_TCP, skipV6KeepaliveFilter);

		// Drop IPv6 Keepalive acks
		for (int i = 0; i < mKeepaliveAcks.size(); ++i) {
		final TcpKeepaliveAck ack = mKeepaliveAcks.valueAt(i);
		if (ack instanceof TcpKeepaliveAckV6) ack.generateFilterLocked(gen);
		}

		gen.defineLabel(skipV6KeepaliveFilter);
		generateFilters(gen, TcpKeepaliveAckV6.class, IPPROTO_TCP, IPV6_NEXT_HEADER_OFFSET,
		"skip_v6_keepalive_filter");
		}

		/**
		@@ -1701,11 +1808,11 @@ public class ApfFilter {
		public synchronized void addTcpKeepalivePacketFilter(final int slot,
		final TcpKeepalivePacketDataParcelable sentKeepalivePacket) {
		log("Adding keepalive ack(" + slot + ")");
		if (null != mKeepaliveAcks.get(slot)) {
		if (null != mKeepalivePackets.get(slot)) {
		throw new IllegalArgumentException("Keepalive slot " + slot + " is occupied");
		}
		final int ipVersion = sentKeepalivePacket.srcAddress.length == 4 ? 4 : 6;
		mKeepaliveAcks.put(slot, (ipVersion == 4)
		mKeepalivePackets.put(slot, (ipVersion == 4)
		? new TcpKeepaliveAckV4(sentKeepalivePacket)
		: new TcpKeepaliveAckV6(sentKeepalivePacket));
		installNewProgramLocked();
		@@ -1720,7 +1827,15 @@ public class ApfFilter {
		*/
		public synchronized void addNattKeepalivePacketFilter(final int slot,
		final NattKeepalivePacketDataParcelable sentKeepalivePacket) {
		Log.e(TAG, "APF add NATT keepalive filter is not implemented");
		log("Adding NAT-T keepalive packet(" + slot + ")");
		if (null != mKeepalivePackets.get(slot)) {
		throw new IllegalArgumentException("Natt Keepalive slot " + slot + " is occupied");
		}
		final int ipVersion = sentKeepalivePacket.srcAddress.length == 4 ? 4 : 6;
		mKeepalivePackets.put(slot, (ipVersion == 4)
		? new NattKeepaliveAckV4(sentKeepalivePacket)
		: new NattKeepaliveAckV6(sentKeepalivePacket));
		installNewProgramLocked();
		}

		/**
		@@ -1729,7 +1844,8 @@ public class ApfFilter {
		* @param slot The index used to access the filter.
		*/
		public synchronized void removeKeepalivePacketFilter(int slot) {
		mKeepaliveAcks.remove(slot);
		log("Removing keepalive packet(" + slot + ")");
		mKeepalivePackets.remove(slot);
		installNewProgramLocked();
		}

		@@ -1785,14 +1901,29 @@ public class ApfFilter {
		}
		pw.decreaseIndent();

		pw.println("Keepalive filters:");
		pw.println("TCP Keepalive filters:");
		pw.increaseIndent();
		for (int i = 0; i < mKeepaliveAcks.size(); ++i) {
		final TcpKeepaliveAck keepaliveAck = mKeepaliveAcks.valueAt(i);
		for (int i = 0; i < mKeepalivePackets.size(); ++i) {
		final KeepalivePacket keepalivePacket = mKeepalivePackets.valueAt(i);
		if (keepalivePacket instanceof TcpKeepaliveAck) {
		pw.print("Slot ");
		pw.print(mKeepaliveAcks.keyAt(i));
		pw.print(mKeepalivePackets.keyAt(i));
		pw.print(" : ");
		pw.println(keepaliveAck);
		pw.println(keepalivePacket);
		}
		}
		pw.decreaseIndent();

		pw.println("NAT-T Keepalive filters:");
		pw.increaseIndent();
		for (int i = 0; i < mKeepalivePackets.size(); ++i) {
		final KeepalivePacket keepalivePacket = mKeepalivePackets.valueAt(i);
		if (keepalivePacket instanceof NattKeepaliveAck) {
		pw.print("Slot ");
		pw.print(mKeepalivePackets.keyAt(i));
		pw.print(" : ");
		pw.println(keepalivePacket);
		}
		}
		pw.decreaseIndent();

		@@ -1858,4 +1989,18 @@ public class ApfFilter {
		+ (uint8(bytes[2]) << 8)
		+ (uint8(bytes[3]));
		}

		private static byte[] concatArrays(final byte[]... arr) {
		int size = 0;
		for (byte[] a : arr) {
		size += a.length;
		}
		final byte[] result = new byte[size];
		int offset = 0;
		for (byte[] a : arr) {
		System.arraycopy(a, 0, result, offset, a.length);
		offset += a.length;
		}
		return result;
		}
		}

packages/NetworkStack/src/android/net/util/NetworkStackUtils.java

+11 −0

Original line number	Diff line number	Diff line
		@@ -24,6 +24,8 @@ import android.util.SparseArray;
		import java.io.FileDescriptor;
		import java.io.IOException;
		import java.net.Inet4Address;
		import java.net.Inet6Address;
		import java.net.InetAddress;
		import java.net.SocketException;
		import java.util.List;
		import java.util.function.Predicate;
		@@ -228,4 +230,13 @@ public class NetworkStackUtils {

		private static native void addArpEntry(byte[] ethAddr, byte[] netAddr, String ifname,
		FileDescriptor fd) throws IOException;

		/**
		* Return IP address and port in a string format.
		*/
		public static String addressAndPortToString(InetAddress address, int port) {
		return String.format(
		(address instanceof Inet6Address) ? "[%s]:%d" : "%s:%d",
		address.getHostAddress(), port);
		}
		}

packages/NetworkStack/tests/src/android/net/apf/ApfTest.java

+114 −36

Original line number	Diff line number	Diff line
		@@ -40,6 +40,7 @@ import static org.mockito.Mockito.verify;
		import android.content.Context;
		import android.net.LinkAddress;
		import android.net.LinkProperties;
		import android.net.NattKeepalivePacketDataParcelable;
		import android.net.TcpKeepalivePacketDataParcelable;
		import android.net.apf.ApfFilter.ApfConfiguration;
		import android.net.apf.ApfGenerator.IllegalInstructionException;
		@@ -1010,6 +1011,7 @@ public class ApfTest {
		private static final int IPV4_PROTOCOL_OFFSET = ETH_HEADER_LEN + 9;
		private static final int IPV4_SRC_ADDR_OFFSET = ETH_HEADER_LEN + 12;
		private static final int IPV4_DEST_ADDR_OFFSET = ETH_HEADER_LEN + 16;

		private static final int IPV4_TCP_HEADER_LEN = 20;
		private static final int IPV4_TCP_HEADER_OFFSET = ETH_HEADER_LEN + IPV4_HEADER_LEN;
		private static final int IPV4_TCP_SRC_PORT_OFFSET = IPV4_TCP_HEADER_OFFSET + 0;
		@@ -1018,11 +1020,17 @@ public class ApfTest {
		private static final int IPV4_TCP_ACK_NUM_OFFSET = IPV4_TCP_HEADER_OFFSET + 8;
		private static final int IPV4_TCP_HEADER_LENGTH_OFFSET = IPV4_TCP_HEADER_OFFSET + 12;
		private static final int IPV4_TCP_HEADER_FLAG_OFFSET = IPV4_TCP_HEADER_OFFSET + 13;

		private static final int IPV4_UDP_HEADER_OFFSET = ETH_HEADER_LEN + IPV4_HEADER_LEN;;
		private static final int IPV4_UDP_SRC_PORT_OFFSET = IPV4_UDP_HEADER_OFFSET + 0;
		private static final int IPV4_UDP_DEST_PORT_OFFSET = IPV4_UDP_HEADER_OFFSET + 2;
		private static final int IPV4_UDP_LENGTH_OFFSET = IPV4_UDP_HEADER_OFFSET + 4;
		private static final int IPV4_UDP_PAYLOAD_OFFSET = IPV4_UDP_HEADER_OFFSET + 8;
		private static final byte[] IPV4_BROADCAST_ADDRESS =
		{(byte) 255, (byte) 255, (byte) 255, (byte) 255};

		private static final int IPV6_NEXT_HEADER_OFFSET = ETH_HEADER_LEN + 6;
		private static final int IPV6_HEADER_LEN = 40;
		private static final int IPV6_NEXT_HEADER_OFFSET = ETH_HEADER_LEN + 6;
		private static final int IPV6_SRC_ADDR_OFFSET = ETH_HEADER_LEN + 8;
		private static final int IPV6_DEST_ADDR_OFFSET = ETH_HEADER_LEN + 24;
		private static final int IPV6_TCP_HEADER_OFFSET = ETH_HEADER_LEN + IPV6_HEADER_LEN;
		@@ -1714,6 +1722,76 @@ public class ApfTest {
		return packet.array();
		}

		@Test
		public void testApfFilterNattKeepalivePacket() throws Exception {
		final MockIpClientCallback cb = new MockIpClientCallback();
		final ApfConfiguration config = getDefaultConfig();
		config.multicastFilter = DROP_MULTICAST;
		config.ieee802_3Filter = DROP_802_3_FRAMES;
		final TestApfFilter apfFilter = new TestApfFilter(mContext, config, cb, mLog);
		byte[] program;
		final int srcPort = 1024;
		final int dstPort = 4500;
		final int slot1 = 1;
		// NAT-T keepalive
		final byte[] payload = {(byte) 0xff};

		// src: 10.0.0.5, port: 1024
		// dst: 10.0.0.6, port: 4500
		InetAddress srcAddr = InetAddress.getByAddress(IPV4_KEEPALIVE_SRC_ADDR);
		InetAddress dstAddr = InetAddress.getByAddress(IPV4_KEEPALIVE_DST_ADDR);

		final NattKeepalivePacketDataParcelable parcel = new NattKeepalivePacketDataParcelable();
		parcel.srcAddress = srcAddr.getAddress();
		parcel.srcPort = srcPort;
		parcel.dstAddress = dstAddr.getAddress();
		parcel.dstPort = dstPort;

		apfFilter.addNattKeepalivePacketFilter(slot1, parcel);
		program = cb.getApfProgram();

		// Verify IPv4 keepalive packet is dropped
		// src: 10.0.0.6, port: 4500
		// dst: 10.0.0.5, port: 1024
		final byte[] nattKaPkt = ipv4UdpPacket(IPV4_KEEPALIVE_DST_ADDR,
		IPV4_KEEPALIVE_SRC_ADDR, dstPort, srcPort, 1 /* dataLength */);
		System.arraycopy(payload, 0, nattKaPkt, IPV4_UDP_PAYLOAD_OFFSET, payload.length);
		assertDrop(program, nattKaPkt);
		// Verify IPv4 non-keepalive packet from the same source address is passed
		assertPass(program,
		ipv4UdpPacket(IPV4_KEEPALIVE_DST_ADDR, IPV4_KEEPALIVE_SRC_ADDR,
		dstPort, srcPort, 10 /* dataLength */));
		// Verify IPv4 non-keepalive packet from other source address is passed
		assertPass(program,
		ipv4UdpPacket(IPV4_ANOTHER_ADDR, IPV4_KEEPALIVE_SRC_ADDR,
		dstPort, srcPort, 10 /* dataLength */));

		apfFilter.removeKeepalivePacketFilter(slot1);
		apfFilter.shutdown();
		}

		private static byte[] ipv4UdpPacket(byte[] sip, byte[] dip, int sport,
		int dport, int dataLength) {
		final int totalLength = dataLength + IPV4_HEADER_LEN + UDP_HEADER_LEN;
		final int udpLength = UDP_HEADER_LEN + dataLength;
		ByteBuffer packet = ByteBuffer.wrap(new byte[totalLength + ETH_HEADER_LEN]);

		// ether type
		packet.putShort(ETH_ETHERTYPE_OFFSET, (short) ETH_P_IP);

		// IPv4 header
		packet.put(IPV4_VERSION_IHL_OFFSET, (byte) 0x45);
		packet.putShort(IPV4_TOTAL_LENGTH_OFFSET, (short) totalLength);
		packet.put(IPV4_PROTOCOL_OFFSET, (byte) IPPROTO_UDP);
		put(packet, IPV4_SRC_ADDR_OFFSET, sip);
		put(packet, IPV4_DEST_ADDR_OFFSET, dip);
		packet.putShort(IPV4_UDP_SRC_PORT_OFFSET, (short) sport);
		packet.putShort(IPV4_UDP_DEST_PORT_OFFSET, (short) dport);
		packet.putShort(IPV4_UDP_LENGTH_OFFSET, (short) udpLength);

		return packet.array();
		}

		// Verify that the last program pushed to the IpClient.Callback properly filters the
		// given packet for the given lifetime.
		private void verifyRaLifetime(byte[] program, ByteBuffer packet, int lifetime) {