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Commit 7f7cc611 authored by Lorenzo Colitti's avatar Lorenzo Colitti
Browse files

DHCP: Ethernet/IP packet header changes. 

1. Support L2_ENCAP when building packets as well as when parsing.
2. Skip IP options when parsing DHCP packets.

Bug: 19704592
Change-Id: Ic27a45790ed1cf7cf5b82d63b6c0b64c909a570f
parent 51697eff

services/net/java/android/net/dhcp/DhcpPacket.java

+31 −7
Original line number Diff line number Diff line 
package android.net.dhcp;



import android.system.OsConstants;



import java.net.Inet4Address;

import java.net.UnknownHostException;

import java.nio.ByteBuffer;
@@ -21,6 +23,10 @@ abstract class DhcpPacket { 


    public static final Inet4Address INADDR_ANY = (Inet4Address) Inet4Address.ANY;

    public static final Inet4Address INADDR_BROADCAST = (Inet4Address) Inet4Address.ALL;

    public static final byte[] ETHER_BROADCAST = new byte[] {

            (byte) 0xff, (byte) 0xff, (byte) 0xff,

            (byte) 0xff, (byte) 0xff, (byte) 0xff,

    };



    /**

     * Packet encapsulations.
@@ -246,6 +252,7 @@ abstract class DhcpPacket { 
        byte requestCode, boolean broadcast) {

        byte[] destIpArray = destIp.getAddress();

        byte[] srcIpArray = srcIp.getAddress();

        int ipHeaderOffset = 0;

        int ipLengthOffset = 0;

        int ipChecksumOffset = 0;

        int endIpHeader = 0;
@@ -256,11 +263,17 @@ abstract class DhcpPacket { 
        buf.clear();

        buf.order(ByteOrder.BIG_ENDIAN);



        if (encap == ENCAP_L2) {

            buf.put(ETHER_BROADCAST);

            buf.put(mClientMac);

            buf.putShort((short) OsConstants.ETH_P_IP);

        }



        // if a full IP packet needs to be generated, put the IP & UDP

        // headers in place, and pre-populate with artificial values

        // needed to seed the IP checksum.

        if (encap == ENCAP_L3) {

            // fake IP header, used in the IP-header checksum

        if (encap <= ENCAP_L3) {

            ipHeaderOffset = buf.position();

            buf.put(IP_VERSION_HEADER_LEN);

            buf.put(IP_TOS_LOWDELAY);    // tos: IPTOS_LOWDELAY

            ipLengthOffset = buf.position();
@@ -319,7 +332,7 @@ abstract class DhcpPacket { 


        // If an IP packet is being built, the IP & UDP checksums must be

        // computed.

        if (encap == ENCAP_L3) {

        if (encap <= ENCAP_L3) {

            // fix UDP header: insert length

            short udpLen = (short)(buf.position() - udpHeaderOffset);

            buf.putShort(udpLengthOffset, udpLen);
@@ -342,10 +355,10 @@ abstract class DhcpPacket { 
                                                             udpHeaderOffset,

                                                             buf.position()));

            // fix IP header: insert length

            buf.putShort(ipLengthOffset, (short)buf.position());

            buf.putShort(ipLengthOffset, (short)(buf.position() - ipHeaderOffset));

            // fixup IP-header checksum

            buf.putShort(ipChecksumOffset,

                         (short) checksum(buf, 0, 0, endIpHeader));

                         (short) checksum(buf, 0, ipHeaderOffset, endIpHeader));

        }

    }
@@ -586,13 +599,18 @@ abstract class DhcpPacket { 


            short l2type = packet.getShort();



            if (l2type != 0x0800)

            if (l2type != OsConstants.ETH_P_IP)

                return null;

        }



        if ((pktType == ENCAP_L2) || (pktType == ENCAP_L3)) {

            // assume l2type is 0x0800, i.e. IP

            byte ipType = packet.get();

            byte ipTypeAndLength = packet.get();

            int ipVersion = (ipTypeAndLength & 0xf0) >> 4;

            if (ipVersion != 4) {

                return null;

            }



            // System.out.println("ipType is " + ipType);

            byte ipDiffServicesField = packet.get();

            short ipTotalLength = packet.getShort();
@@ -609,6 +627,12 @@ abstract class DhcpPacket { 
            if (ipProto != IP_TYPE_UDP) // UDP

                return null;



            // Skip options.

            int optionWords = ((ipTypeAndLength & 0x0f) - 5);

            for (int i = 0; i < optionWords; i++) {

                packet.getInt();

            }



            // assume UDP

            short udpSrcPort = packet.getShort();

            short udpDstPort = packet.getShort();