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moved max packet size evaluation before full read of mqtt message #583

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Merged
merged 1 commit into from
Jun 23, 2025
Merged

moved max packet size evaluation before full read of mqtt message #583

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88 changes: 52 additions & 36 deletions src/main/java/com/hivemq/codec/decoder/MQTTMessageDecoder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -35,10 +35,8 @@
import io.netty.handler.codec.ByteToMessageDecoder;

import java.util.List;
import java.util.Objects;

import static com.hivemq.mqtt.message.MessageType.CONNECT;
import static com.hivemq.mqtt.message.MessageType.PUBLISH;

/**
* @author Dominik Obermaier
Expand All @@ -49,14 +47,16 @@ public class MQTTMessageDecoder extends ByteToMessageDecoder {
private static final int NOT_ENOUGH_BYTES_READABLE = -2;
private static final int MALFORMED_REMAINING_LENGTH = -1;
private static final int MIN_FIXED_HEADER_LENGTH = 2;
private static final int MIN_CONNECT_VAR_HEADER_LENGTH = 7;

private final @NotNull MqttConnectDecoder connectDecoder;
private final @NotNull MqttConnacker mqttConnacker;
private final @NotNull MqttConfigurationService mqttConfig;
private final @NotNull MqttDecoders mqttDecoders;
private final @NotNull MqttServerDisconnector mqttServerDisconnector;
private final @NotNull GlobalMQTTMessageCounter globalMQTTMessageCounter;

private final int maxPacketSize;

public MQTTMessageDecoder(
final @NotNull MqttConnectDecoder connectDecoder,
final @NotNull MqttConnacker mqttConnacker,
Expand All @@ -66,10 +66,10 @@ public MQTTMessageDecoder(
final @NotNull GlobalMQTTMessageCounter globalMQTTMessageCounter) {
this.connectDecoder = connectDecoder;
this.mqttConnacker = mqttConnacker;
this.mqttConfig = mqttConfig;
this.mqttDecoders = mqttDecoders;
this.mqttServerDisconnector = mqttServerDisconnector;
this.globalMQTTMessageCounter = globalMQTTMessageCounter;
this.maxPacketSize = mqttConfig.maxPacketSize();
}

public MQTTMessageDecoder(final ChannelDependencies channelDependencies) {
Expand Down Expand Up @@ -116,15 +116,22 @@ protected void decode(
return;
}

final int fixedHeaderSize = getFixedHeaderSize(remainingLength);
final int packetSize = fixedHeaderSize + remainingLength;

final MessageType messageType = getMessageType(fixedHeader);

//this is the message size HiveMQ allows for incoming messages
if (packetSize > maxPacketSize) {
handlePacketTooLarge(buf, messageType, clientConnectionContext);
return;
}

if (buf.readableBytes() < remainingLength) {
buf.resetReaderIndex();
return;
}

final int fixedHeaderSize = getFixedHeaderSize(remainingLength);
final int packetSize = fixedHeaderSize + remainingLength;

final MessageType messageType = getMessageType(fixedHeader);
final Message message;
if (messageType == CONNECT) {
message = handleConnect(buf, clientConnectionContext, fixedHeader, packetSize, remainingLength);
Expand All @@ -140,25 +147,50 @@ protected void decode(
out.add(message);
}

private @Nullable Message handleConnect(
private void handlePacketTooLarge(
final @NotNull ByteBuf buf,
final @NotNull ClientConnectionContext clientConnectionContext,
final byte fixedHeader,
final int packetSize,
final int remainingLength) {

//this is the message size HiveMQ allows for incoming messages
if (packetSize > mqttConfig.maxPacketSize()) {
//connack with PACKET_TOO_LARGE for Mqtt5
final @NotNull MessageType messageType,
final @NotNull ClientConnectionContext clientConnectionContext) {
//connack with PACKET_TOO_LARGE for Mqtt5
if (messageType == MessageType.CONNECT) {
// Theoretically, remaining length could be too short to read the protocol version.
// But in this case we can never reach a "packet too large" as the minimum configurable max packet size is 15
// while the broker needs only 7 bytes to read the version. Therefore, broker ignores this case and continues reading until
// it has at least 7 bytes of the variable CONNECT header to determine the protocol version,
// see https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901035:~:text=identify%20MQTT%20traffic.-,3.1.2.2%20Protocol%20Version,-Figure%203%E2%80%913
if (buf.readableBytes() < MIN_CONNECT_VAR_HEADER_LENGTH) {
buf.resetReaderIndex();
return;
}
connectDecoder.decodeProtocolVersion(clientConnectionContext, buf);
mqttConnacker.connackError(clientConnectionContext.getChannel(),
"A client (IP: {}) connect packet exceeded the maximum permissible size.",
"A client (ID: {}, IP: {}) connect packet exceeded the maximum permissible size.",
"Sent CONNECT exceeded the maximum permissible size",
Mqtt5ConnAckReasonCode.PACKET_TOO_LARGE,
ReasonStrings.CONNACK_PACKET_TOO_LARGE);

return null;
} else {
final ProtocolVersion protocolVersion = clientConnectionContext.getProtocolVersion();
//force channel close for Mqtt3.1, Mqtt3.1.1 and null (before connect)
final boolean forceClose = protocolVersion != ProtocolVersion.MQTTv5;
mqttServerDisconnector.disconnect(clientConnectionContext.getChannel(),
"A client (ID: {}, IP: {}) sent a message, that was bigger than the maximum message size. Disconnecting client.",
"Sent a message that was bigger than the maximum size",
Mqtt5DisconnectReasonCode.PACKET_TOO_LARGE,
ReasonStrings.DISCONNECT_PACKET_TOO_LARGE_MESSAGE,
Mqtt5UserProperties.NO_USER_PROPERTIES,
false,
forceClose);
}
buf.clear();
}


private @Nullable Message handleConnect(
final @NotNull ByteBuf buf,
final @NotNull ClientConnectionContext clientConnectionContext,
final byte fixedHeader,
final int packetSize,
final int remainingLength) {

// Check if the client is already connected
if (clientConnectionContext.getProtocolVersion() != null) {
Expand Down Expand Up @@ -195,22 +227,6 @@ protected void decode(

final ProtocolVersion protocolVersion = clientConnectionContext.getProtocolVersion();

//this is the message size HiveMQ allows for incoming messages
if (packetSize > mqttConfig.maxPacketSize()) {

//force channel close for Mqtt3.1, Mqtt3.1.1 and null (before connect)
final boolean forceClose = protocolVersion != ProtocolVersion.MQTTv5;
mqttServerDisconnector.disconnect(clientConnectionContext.getChannel(),
"A client (IP: {}) sent a message, that was bigger than the maximum message size. Disconnecting client.",
"Sent a message that was bigger than the maximum size",
Mqtt5DisconnectReasonCode.PACKET_TOO_LARGE,
ReasonStrings.DISCONNECT_PACKET_TOO_LARGE_MESSAGE,
Mqtt5UserProperties.NO_USER_PROPERTIES,
false,
forceClose);
return null;
}

// Check if client is connected
if (protocolVersion == null) {
mqttServerDisconnector.logAndClose(clientConnectionContext.getChannel(),
Expand Down
2 changes: 2 additions & 0 deletions src/test/java/com/hivemq/bootstrap/netty/initializer/TlsTcpChannelInitializerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
import com.hivemq.configuration.service.entity.Listener;
import com.hivemq.configuration.service.entity.Tls;
import com.hivemq.configuration.service.entity.TlsTcpListener;
import com.hivemq.configuration.service.impl.MqttConfigurationServiceImpl;
import com.hivemq.logging.EventLog;
import com.hivemq.mqtt.handler.disconnect.MqttServerDisconnector;
import com.hivemq.mqtt.handler.disconnect.MqttServerDisconnectorImpl;
Expand Down Expand Up @@ -106,6 +107,7 @@ public void before() throws Exception {
when(socketChannel.attr(any(AttributeKey.class))).thenReturn(attribute);
when(socketChannel.isActive()).thenReturn(true);
when(channelDependencies.getConfigurationService()).thenReturn(fullConfigurationService);
when(fullConfigurationService.mqttConfiguration()).thenReturn(new MqttConfigurationServiceImpl());
when(channelDependencies.getRestrictionsConfigurationService()).thenReturn(restrictionsConfigurationService);
when(restrictionsConfigurationService.incomingLimit()).thenReturn(0L);

Expand Down
2 changes: 2 additions & 0 deletions src/test/java/com/hivemq/bootstrap/netty/initializer/TlsWebsocketChannelInitializerTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
import com.hivemq.configuration.service.entity.Listener;
import com.hivemq.configuration.service.entity.Tls;
import com.hivemq.configuration.service.entity.TlsWebsocketListener;
import com.hivemq.configuration.service.impl.MqttConfigurationServiceImpl;
import com.hivemq.logging.EventLog;
import com.hivemq.mqtt.handler.disconnect.MqttServerDisconnector;
import com.hivemq.mqtt.handler.disconnect.MqttServerDisconnectorImpl;
Expand Down Expand Up @@ -110,6 +111,7 @@ public void before() {
when(sslFactory.getSslHandler(any(SocketChannel.class), any(Tls.class), any(SslContext.class))).thenReturn(
sslHandler);
when(channelDependencies.getConfigurationService()).thenReturn(fullConfigurationService);
when(fullConfigurationService.mqttConfiguration()).thenReturn(new MqttConfigurationServiceImpl());
when(mockListener.getTls()).thenReturn(tls);
when(channelDependencies.getConfigurationService()).thenReturn(fullConfigurationService);
when(channelDependencies.getRestrictionsConfigurationService()).thenReturn(restrictionsConfigurationService);
Expand Down
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