Fix incorrect name encoding/decoding in DNS records
Motivation: - The decoded name should always end with a dot (.), but we currently strip it, which is incorrect. - (O) 0 -> "." - (X) 0 -> "" - (O) 5 netty 2 io 0 -> "netty.io." - (X) 5 netty 2 io 0 -> "netty.io" - The encoded name should end with a null-label, which is a label whose length is 0, but we currently append an extra NUL, causing FORMERR(1) on a strict DNS server: - (O) . -> 0 - (X) . -> 0 0 - (O) netty.io. -> 5 netty 2 io 0 - (X) netty.io. -> 5 netty 2 io 0 0 Modifications: - Make sure to append '.' when decoding a name. - Improve index checks so that the decoder can raise CorruptFrameException instead of IIOBE - Do not encode extra NUL - Add more tests Result: Robustness and correctness
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@ -27,6 +27,8 @@ import io.netty.util.internal.StringUtil;
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*/
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public class DefaultDnsRecordDecoder implements DnsRecordDecoder {
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static final String ROOT = ".";
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/**
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* Creates a new instance.
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*/
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@ -117,16 +119,22 @@ public class DefaultDnsRecordDecoder implements DnsRecordDecoder {
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// - https://github.com/netty/netty/issues/5014
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// - https://www.ietf.org/rfc/rfc1035.txt , Section 3.1
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if (readable == 0) {
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return StringUtil.EMPTY_STRING;
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return ROOT;
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}
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final StringBuilder name = new StringBuilder(readable << 1);
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for (int len = in.readUnsignedByte(); in.isReadable() && len != 0; len = in.readUnsignedByte()) {
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boolean pointer = (len & 0xc0) == 0xc0;
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while (in.isReadable()) {
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final int len = in.readUnsignedByte();
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final boolean pointer = (len & 0xc0) == 0xc0;
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if (pointer) {
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if (position == -1) {
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position = in.readerIndex() + 1;
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}
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if (!in.isReadable()) {
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throw new CorruptedFrameException("truncated pointer in a name");
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}
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final int next = (len & 0x3f) << 8 | in.readUnsignedByte();
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if (next >= end) {
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throw new CorruptedFrameException("name has an out-of-range pointer");
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@ -138,18 +146,29 @@ public class DefaultDnsRecordDecoder implements DnsRecordDecoder {
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if (checked >= end) {
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throw new CorruptedFrameException("name contains a loop.");
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}
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} else {
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} else if (len != 0) {
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if (!in.isReadable(len)) {
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throw new CorruptedFrameException("truncated label in a name");
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}
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name.append(in.toString(in.readerIndex(), len, CharsetUtil.UTF_8)).append('.');
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in.skipBytes(len);
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} else { // len == 0
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break;
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}
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}
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if (position != -1) {
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in.readerIndex(position);
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}
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if (name.length() == 0) {
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return StringUtil.EMPTY_STRING;
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return ROOT;
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}
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return name.substring(0, name.length() - 1);
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if (name.charAt(name.length() - 1) != '.') {
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name.append('.');
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}
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return name.toString();
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}
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}
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@ -20,6 +20,8 @@ import io.netty.buffer.ByteBufUtil;
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import io.netty.handler.codec.UnsupportedMessageTypeException;
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import io.netty.util.internal.StringUtil;
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import static io.netty.handler.codec.dns.DefaultDnsRecordDecoder.ROOT;
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/**
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* The default {@link DnsRecordEncoder} implementation.
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*
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@ -77,19 +79,24 @@ public class DefaultDnsRecordEncoder implements DnsRecordEncoder {
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}
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protected void encodeName(String name, ByteBuf buf) throws Exception {
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String[] parts = StringUtil.split(name, '.');
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for (String part: parts) {
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final int partLen = part.length();
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// We always need to write the length even if its 0.
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// See:
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// - https://github.com/netty/netty/issues/5014
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// - https://www.ietf.org/rfc/rfc1035.txt , Section 3.1
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buf.writeByte(partLen);
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if (partLen == 0) {
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continue;
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if (ROOT.equals(name)) {
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// Root domain
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buf.writeByte(0);
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return;
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}
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ByteBufUtil.writeAscii(buf, part);
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final String[] labels = StringUtil.split(name, '.');
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for (String label : labels) {
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final int labelLen = label.length();
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if (labelLen == 0) {
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// zero-length label means the end of the name.
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break;
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}
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buf.writeByte(labelLen);
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ByteBufUtil.writeAscii(buf, label);
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}
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buf.writeByte(0); // marks end of name field
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}
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}
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@ -24,19 +24,46 @@ import org.junit.Test;
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public class DefaultDnsRecordDecoderTest {
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@Test
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public void testDecodeEmptyName() {
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testDecodeEmptyName0(Unpooled.buffer().writeByte('0'));
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public void testDecodeName() {
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testDecodeName("netty.io.", Unpooled.wrappedBuffer(new byte[] {
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5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o', 0
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}));
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}
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@Test
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public void testDecodeEmptyNameNonRFC() {
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testDecodeEmptyName0(Unpooled.EMPTY_BUFFER);
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public void testDecodeNameWithoutTerminator() {
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testDecodeName("netty.io.", Unpooled.wrappedBuffer(new byte[] {
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5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o'
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}));
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}
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private static void testDecodeEmptyName0(ByteBuf buffer) {
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@Test
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public void testDecodeNameWithExtraTerminator() {
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// Should not be decoded as 'netty.io..'
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testDecodeName("netty.io.", Unpooled.wrappedBuffer(new byte[] {
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5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o', 0, 0
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}));
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}
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@Test
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public void testDecodeEmptyName() {
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testDecodeName(".", Unpooled.buffer().writeByte(0));
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}
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@Test
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public void testDecodeEmptyNameFromEmptyBuffer() {
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testDecodeName(".", Unpooled.EMPTY_BUFFER);
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}
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@Test
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public void testDecodeEmptyNameFromExtraZeroes() {
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testDecodeName(".", Unpooled.wrappedBuffer(new byte[] { 0, 0 }));
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}
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private static void testDecodeName(String expected, ByteBuf buffer) {
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try {
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DefaultDnsRecordDecoder decoder = new DefaultDnsRecordDecoder();
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Assert.assertEquals(StringUtil.EMPTY_STRING, decoder.decodeName(buffer));
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Assert.assertEquals(expected, decoder.decodeName(buffer));
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} finally {
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buffer.release();
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}
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@ -16,6 +16,7 @@
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package io.netty.handler.codec.dns;
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import io.netty.buffer.ByteBuf;
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import io.netty.buffer.ByteBufUtil;
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import io.netty.buffer.Unpooled;
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import io.netty.util.internal.StringUtil;
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import org.junit.Test;
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@ -24,18 +25,42 @@ import static org.junit.Assert.assertEquals;
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public class DefaultDnsRecordEncoderTest {
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@Test
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public void testEncodeName() throws Exception {
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testEncodeName(new byte[] { 5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o', 0 }, "netty.io.");
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}
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@Test
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public void testEncodeNameWithoutTerminator() throws Exception {
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testEncodeName(new byte[] { 5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o', 0 }, "netty.io");
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}
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@Test
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public void testEncodeNameWithExtraTerminator() throws Exception {
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testEncodeName(new byte[] { 5, 'n', 'e', 't', 't', 'y', 2, 'i', 'o', 0 }, "netty.io..");
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}
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// Test for https://github.com/netty/netty/issues/5014
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@Test
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public void testEncodeEmptyName() throws Exception {
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testEncodeName(new byte[] { 0 }, StringUtil.EMPTY_STRING);
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}
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@Test
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public void testEncodeRootName() throws Exception {
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testEncodeName(new byte[] { 0 }, ".");
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}
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private static void testEncodeName(byte[] expected, String name) throws Exception {
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DefaultDnsRecordEncoder encoder = new DefaultDnsRecordEncoder();
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ByteBuf out = Unpooled.buffer();
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ByteBuf expectedBuf = Unpooled.wrappedBuffer(expected);
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try {
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encoder.encodeName(StringUtil.EMPTY_STRING, out);
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assertEquals(2, out.readableBytes());
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assertEquals(0, out.readByte());
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assertEquals(0, out.readByte());
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encoder.encodeName(name, out);
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assertEquals(expectedBuf, out);
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} finally {
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out.release();
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expectedBuf.release();
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}
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}
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}
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