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Commit a12bde35 authored by Lorenzo Colitti's avatar Lorenzo Colitti
Browse files

Deal with null characters in string options. 

This currently truncates all strings at the first NULL character,
except for vendorInfo, which is an opaque string.

Bug: 19985674
Change-Id: Ie53b2c55eb8a5204d7b2c7e2d8587743d923647a
parent aa2609aa

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

+18 −6
Original line number Diff line number Diff line
@@ -611,10 +611,22 @@ abstract class DhcpPacket { 
    /**

     * Reads a string of specified length from the buffer.

     */

    private static String readAsciiString(ByteBuffer buf, int byteCount) {

    private static String readAsciiString(ByteBuffer buf, int byteCount, boolean nullOk) {

        byte[] bytes = new byte[byteCount];

        buf.get(bytes);

        return new String(bytes, 0, bytes.length, StandardCharsets.US_ASCII);

        int length = bytes.length;

        if (!nullOk) {

            // Stop at the first null byte. This is because some DHCP options (e.g., the domain

            // name) are passed to netd via FrameworkListener, which refuses arguments containing

            // null bytes. We don't do this by default because vendorInfo is an opaque string which

            // could in theory contain null bytes.

            for (length = 0; length < bytes.length; length++) {

                if (bytes[length] == 0) {

                    break;

                }

            }

        }

        return new String(bytes, 0, length, StandardCharsets.US_ASCII);

    }



    /**
@@ -797,7 +809,7 @@ abstract class DhcpPacket { 
                            break;

                        case DHCP_HOST_NAME:

                            expectedLen = optionLen;

                            hostName = readAsciiString(packet, optionLen);

                            hostName = readAsciiString(packet, optionLen, false);

                            break;

                        case DHCP_MTU:

                            expectedLen = 2;
@@ -805,7 +817,7 @@ abstract class DhcpPacket { 
                            break;

                        case DHCP_DOMAIN_NAME:

                            expectedLen = optionLen;

                            domainName = readAsciiString(packet, optionLen);

                            domainName = readAsciiString(packet, optionLen, false);

                            break;

                        case DHCP_BROADCAST_ADDRESS:

                            bcAddr = readIpAddress(packet);
@@ -834,7 +846,7 @@ abstract class DhcpPacket { 
                            break;

                        case DHCP_MESSAGE:

                            expectedLen = optionLen;

                            message = readAsciiString(packet, optionLen);

                            message = readAsciiString(packet, optionLen, false);

                            break;

                        case DHCP_MAX_MESSAGE_SIZE:

                            expectedLen = 2;
@@ -850,7 +862,7 @@ abstract class DhcpPacket { 
                            break;

                        case DHCP_VENDOR_CLASS_ID:

                            expectedLen = optionLen;

                            vendorId = readAsciiString(packet, optionLen);

                            vendorId = readAsciiString(packet, optionLen, true);

                            break;

                        case DHCP_CLIENT_IDENTIFIER: { // Client identifier

                            byte[] id = new byte[optionLen];

services/tests/servicestests/Android.mk

+1 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ LOCAL_SRC_FILES := $(call all-java-files-under, src) 
LOCAL_STATIC_JAVA_LIBRARIES := \

    services.core \

    services.devicepolicy \

    services.net \

    easymocklib \

    guava \

    mockito-target

services/tests/servicestests/src/android/net/dhcp/DhcpPacketTest.java

0 → 100644
+116 −0
Original line number Diff line number Diff line 
/*

 * Copyright (C) 2015 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 android.net.NetworkUtils;

import android.system.OsConstants;

import android.test.suitebuilder.annotation.SmallTest;

import junit.framework.TestCase;



import java.net.Inet4Address;

import java.nio.ByteBuffer;



import static android.net.dhcp.DhcpPacket.*;





public class DhcpPacketTest extends TestCase {



    private static Inet4Address SERVER_ADDR =

            (Inet4Address) NetworkUtils.numericToInetAddress("192.0.2.1");

    private static Inet4Address CLIENT_ADDR =

            (Inet4Address) NetworkUtils.numericToInetAddress("192.0.2.234");

    private static byte[] CLIENT_MAC = new byte[] { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 };



    class TestDhcpPacket extends DhcpPacket {

        private byte mType;

        // TODO: Make this a map of option numbers to bytes instead.

        private byte[] mDomainBytes, mVendorInfoBytes;



        public TestDhcpPacket(byte type, byte[] domainBytes, byte[] vendorInfoBytes) {

            super(0xdeadbeef, INADDR_ANY, CLIENT_ADDR, INADDR_ANY, INADDR_ANY, CLIENT_MAC, true);

            mType = type;

            mDomainBytes = domainBytes;

            mVendorInfoBytes = vendorInfoBytes;

        }



        public ByteBuffer buildPacket(int encap, short unusedDestUdp, short unusedSrcUdp) {

            ByteBuffer result = ByteBuffer.allocate(MAX_LENGTH);

            fillInPacket(encap, CLIENT_ADDR, SERVER_ADDR,

                         DHCP_CLIENT, DHCP_SERVER, result, DHCP_BOOTREPLY, false);

            return result;

        }



        public void finishPacket(ByteBuffer buffer) {

            addTlv(buffer, DHCP_MESSAGE_TYPE, mType);

            if (mDomainBytes != null) {

                addTlv(buffer, DHCP_DOMAIN_NAME, mDomainBytes);

            }

            if (mVendorInfoBytes != null) {

                addTlv(buffer, DHCP_VENDOR_CLASS_ID, mVendorInfoBytes);

            }

            addTlvEnd(buffer);

        }



        // Convenience method.

        public ByteBuffer build() {

            // ENCAP_BOOTP packets don't contain ports, so just pass in 0.

            ByteBuffer pkt = buildPacket(ENCAP_BOOTP, (short) 0, (short) 0);

            pkt.flip();

            return pkt;

        }

    }



    private void assertDomainAndVendorInfoParses(

            String expectedDomain, byte[] domainBytes,

            String expectedVendorInfo, byte[] vendorInfoBytes) {

        ByteBuffer packet = new TestDhcpPacket(DHCP_MESSAGE_TYPE_OFFER,

                domainBytes, vendorInfoBytes).build();

        DhcpPacket offerPacket = DhcpPacket.decodeFullPacket(packet, ENCAP_BOOTP);

        assertEquals(expectedDomain, offerPacket.mDomainName);

        assertEquals(expectedVendorInfo, offerPacket.mVendorId);

    }



    @SmallTest

    public void testDomainName() throws Exception {

        byte[] nullByte = new byte[] { 0x00 };

        byte[] twoNullBytes = new byte[] { 0x00, 0x00 };

        byte[] nonNullDomain = new byte[] {

            (byte) 'g', (byte) 'o', (byte) 'o', (byte) '.', (byte) 'g', (byte) 'l'

        };

        byte[] trailingNullDomain = new byte[] {

            (byte) 'g', (byte) 'o', (byte) 'o', (byte) '.', (byte) 'g', (byte) 'l', 0x00

        };

        byte[] embeddedNullsDomain = new byte[] {

            (byte) 'g', (byte) 'o', (byte) 'o', 0x00, 0x00, (byte) 'g', (byte) 'l'

        };

        byte[] metered = "ANDROID_METERED".getBytes("US-ASCII");



        byte[] meteredEmbeddedNull = metered.clone();

        meteredEmbeddedNull[7] = (char) 0;



        byte[] meteredTrailingNull = metered.clone();

        meteredTrailingNull[meteredTrailingNull.length - 1] = (char) 0;



        assertDomainAndVendorInfoParses("", nullByte, "\u0000", nullByte);

        assertDomainAndVendorInfoParses("", twoNullBytes, "\u0000\u0000", twoNullBytes);

        assertDomainAndVendorInfoParses("goo.gl", nonNullDomain, "ANDROID_METERED", metered);

        assertDomainAndVendorInfoParses("goo", embeddedNullsDomain,

                                        "ANDROID\u0000METERED", meteredEmbeddedNull);

        assertDomainAndVendorInfoParses("goo.gl", trailingNullDomain,

                                        "ANDROID_METERE\u0000", meteredTrailingNull);

    }

}