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      1 /*
      2  * Copyright (C) 2015 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *      http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.server.connectivity;
     18 
     19 import android.system.OsConstants;
     20 import android.net.ConnectivityManager;
     21 import android.net.NetworkUtils;
     22 import android.net.util.IpUtils;
     23 
     24 import java.net.Inet4Address;
     25 import java.net.Inet6Address;
     26 import java.net.InetAddress;
     27 import java.nio.ByteBuffer;
     28 import java.nio.ByteOrder;
     29 
     30 import static android.net.ConnectivityManager.PacketKeepalive.*;
     31 
     32 /**
     33  * Represents the actual packets that are sent by the
     34  * {@link android.net.ConnectivityManager.PacketKeepalive} API.
     35  *
     36  * @hide
     37  */
     38 public class KeepalivePacketData {
     39     /** Protocol of the packet to send; one of the OsConstants.ETH_P_* values. */
     40     public final int protocol;
     41 
     42     /** Source IP address */
     43     public final InetAddress srcAddress;
     44 
     45     /** Destination IP address */
     46     public final InetAddress dstAddress;
     47 
     48     /** Source port */
     49     public final int srcPort;
     50 
     51     /** Destination port */
     52     public final int dstPort;
     53 
     54     /** Destination MAC address. Can change if routing changes. */
     55     public byte[] dstMac;
     56 
     57     /** Packet data. A raw byte string of packet data, not including the link-layer header. */
     58     public final byte[] data;
     59 
     60     private static final int IPV4_HEADER_LENGTH = 20;
     61     private static final int UDP_HEADER_LENGTH = 8;
     62 
     63     protected KeepalivePacketData(InetAddress srcAddress, int srcPort,
     64             InetAddress dstAddress, int dstPort, byte[] data) throws InvalidPacketException {
     65         this.srcAddress = srcAddress;
     66         this.dstAddress = dstAddress;
     67         this.srcPort = srcPort;
     68         this.dstPort = dstPort;
     69         this.data = data;
     70 
     71         // Check we have two IP addresses of the same family.
     72         if (srcAddress == null || dstAddress == null ||
     73                 !srcAddress.getClass().getName().equals(dstAddress.getClass().getName())) {
     74             throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
     75         }
     76 
     77         // Set the protocol.
     78         if (this.dstAddress instanceof Inet4Address) {
     79             this.protocol = OsConstants.ETH_P_IP;
     80         } else if (this.dstAddress instanceof Inet6Address) {
     81             this.protocol = OsConstants.ETH_P_IPV6;
     82         } else {
     83             throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
     84         }
     85 
     86         // Check the ports.
     87         if (!IpUtils.isValidUdpOrTcpPort(srcPort) || !IpUtils.isValidUdpOrTcpPort(dstPort)) {
     88             throw new InvalidPacketException(ERROR_INVALID_PORT);
     89         }
     90     }
     91 
     92     public static class InvalidPacketException extends Exception {
     93         final public int error;
     94         public InvalidPacketException(int error) {
     95             this.error = error;
     96         }
     97     }
     98 
     99     /**
    100      * Creates an IPsec NAT-T keepalive packet with the specified parameters.
    101      */
    102     public static KeepalivePacketData nattKeepalivePacket(
    103             InetAddress srcAddress, int srcPort,
    104             InetAddress dstAddress, int dstPort) throws InvalidPacketException {
    105 
    106         if (!(srcAddress instanceof Inet4Address) || !(dstAddress instanceof Inet4Address)) {
    107             throw new InvalidPacketException(ERROR_INVALID_IP_ADDRESS);
    108         }
    109 
    110         if (dstPort != NATT_PORT) {
    111             throw new InvalidPacketException(ERROR_INVALID_PORT);
    112         }
    113 
    114         int length = IPV4_HEADER_LENGTH + UDP_HEADER_LENGTH + 1;
    115         ByteBuffer buf = ByteBuffer.allocate(length);
    116         buf.order(ByteOrder.BIG_ENDIAN);
    117         buf.putShort((short) 0x4500);             // IP version and TOS
    118         buf.putShort((short) length);
    119         buf.putInt(0);                            // ID, flags, offset
    120         buf.put((byte) 64);                       // TTL
    121         buf.put((byte) OsConstants.IPPROTO_UDP);
    122         int ipChecksumOffset = buf.position();
    123         buf.putShort((short) 0);                  // IP checksum
    124         buf.put(srcAddress.getAddress());
    125         buf.put(dstAddress.getAddress());
    126         buf.putShort((short) srcPort);
    127         buf.putShort((short) dstPort);
    128         buf.putShort((short) (length - 20));      // UDP length
    129         int udpChecksumOffset = buf.position();
    130         buf.putShort((short) 0);                  // UDP checksum
    131         buf.put((byte) 0xff);                     // NAT-T keepalive
    132         buf.putShort(ipChecksumOffset, IpUtils.ipChecksum(buf, 0));
    133         buf.putShort(udpChecksumOffset, IpUtils.udpChecksum(buf, 0, IPV4_HEADER_LENGTH));
    134 
    135         return new KeepalivePacketData(srcAddress, srcPort, dstAddress, dstPort, buf.array());
    136     }
    137 }
    138