1 package edu.uci.iotproject.trafficreassembly.layer3;
3 import org.pcap4j.core.PacketListener;
4 import org.pcap4j.core.PcapPacket;
5 import org.pcap4j.packet.*;
10 * Reassembles TCP conversations (streams).
11 * <b>Note: current version only supports TCP over IPv4.</b>
13 * @author Janus Varmarken {@literal <jvarmark@uci.edu>}
14 * @author Rahmadi Trimananda {@literal <rtrimana@uci.edu>}
16 public class TcpReassembler implements PacketListener {
19 * Holds <em>open</em> {@link Conversation}s, i.e., {@code Conversation}s that have <em>not</em> been detected as
20 * (gracefully) terminated based on the set of packets observed thus far.
21 * A {@link Conversation} is moved to {@link #mTerminatedConversations} if it can be determined that it is has
22 * terminated. Termination can be detected by a) observing two {@link FinAckPair}s, one in each direction, (graceful
23 * termination, see {@link Conversation#isGracefullyShutdown()}) or b) by observing a SYN packet that matches the
24 * four tuple of an existing {@code Conversation}, but which holds a <em>different</em> sequence number than the
25 * same-direction SYN packet recorded for the {@code Conversation}.
27 * Note that due to limitations of the {@link Set} interface (specifically, there is no {@code get(T t)} method),
28 * we have to resort to a {@link Map} (in which keys map to themselves) to "mimic" a set with {@code get(T t)}
31 * @see <a href="https://stackoverflow.com/questions/7283338/getting-an-element-from-a-set">this question on StackOverflow.com</a>
33 private final Map<Conversation, Conversation> mOpenConversations = new HashMap<>();
36 * Holds <em>terminated</em> {@link Conversation}s.
38 private final List<Conversation> mTerminatedConversations = new ArrayList<>();
41 * IP of the router's WAN port (if analyzed traffic is captured at the ISP's point of view).
43 private final String mRouterWanIp;
44 private static final String ROUTER_WAN_IP = "128.195.205.105";
46 public TcpReassembler() {
47 mRouterWanIp = ROUTER_WAN_IP;
50 public TcpReassembler(String routerWanIp) {
51 mRouterWanIp = routerWanIp;
55 public void gotPacket(PcapPacket pcapPacket) {
56 IpV4Packet ipPacket = pcapPacket.get(IpV4Packet.class);
57 TcpPacket tcpPacket = pcapPacket.get(TcpPacket.class);
59 if (ipPacket == null || tcpPacket == null) {
63 processPacket(pcapPacket);
64 // Class clazz = pcapPacket.getClass();
65 // RadiotapPacket radiotapPacket = pcapPacket.get(RadiotapPacket.class);
66 // Dot11ManagementPacket dot11ManagementPacket = pcapPacket.get(Dot11ManagementPacket.class);
67 // if (dot11ManagementPacket != null) {
70 // if (radiotapPacket != null) {
71 // processRadiotapPacket(pcapPacket);
76 * Get the reassembled TCP connections. Note that if this is called while packets are still being processed (by
77 * calls to {@link #gotPacket(PcapPacket)}), the behavior is undefined and the returned list may be inconsistent.
78 * @return The reassembled TCP connections.
80 public List<Conversation> getTcpConversations() {
81 ArrayList<Conversation> combined = new ArrayList<>();
82 combined.addAll(mTerminatedConversations);
83 combined.addAll(mOpenConversations.values());
87 private void processRadiotapPacket(PcapPacket pcapPacket) {
88 RadiotapPacket radiotapPacket = pcapPacket.get(RadiotapPacket.class);
90 RadiotapPacket.RadiotapHeader header = radiotapPacket.getHeader();
91 short length = header.getLength();
92 ArrayList<RadiotapPacket.RadiotapData> radiotapData = header.getDataFields();
93 // TODO: We can handle this 802.11 QoS data by creating our own class
94 // TODO: We only need to handle the first few bytes for source, destination, receiver, and transmitter
96 Packet dataPacket = radiotapPacket.getPayload();
97 int dataLength = dataPacket.length();
100 private void processPacket(PcapPacket pcapPacket) {
101 TcpPacket tcpPacket = pcapPacket.get(TcpPacket.class);
102 // Handle client connection initiation attempts.
103 if (tcpPacket.getHeader().getSyn() && !tcpPacket.getHeader().getAck()) {
104 // A segment with the SYN flag set, but no ACK flag indicates that a client is attempting to initiate a new
106 processNewConnectionRequest(pcapPacket);
109 // Handle server connection initiation acknowledgement
110 if (tcpPacket.getHeader().getSyn() && tcpPacket.getHeader().getAck()) {
111 // A segment with both the SYN and ACK flags set indicates that the server has accepted the client's request
112 // to initiate a new connection.
113 processNewConnectionAck(pcapPacket);
117 if (tcpPacket.getHeader().getRst()) {
118 processRstPacket(pcapPacket);
122 if (tcpPacket.getHeader().getFin()) {
123 // Handle FIN packet.
124 processFinPacket(pcapPacket);
126 // Handle ACKs (currently only ACKs of FINS)
127 if (tcpPacket.getHeader().getAck()) {
128 processAck(pcapPacket);
130 // Handle packets that carry payload (application data).
131 if (tcpPacket.getPayload() != null) {
132 processPayloadPacket(pcapPacket);
136 private void processNewConnectionRequest(PcapPacket clientSynPacket) {
137 // A SYN w/o ACK always originates from the client.
138 Conversation conv = Conversation.fromPcapPacket(clientSynPacket, true);
139 conv.addSynPacket(clientSynPacket);
140 // Is there an ongoing conversation for the same four tuple (clientIp, clientPort, serverIp, serverPort) as
141 // found in the new SYN packet?
142 Conversation ongoingConv = mOpenConversations.get(conv);
143 if (ongoingConv != null) {
144 if (ongoingConv.isRetransmission(clientSynPacket)) {
145 // SYN retransmission detected, do nothing.
147 // TODO: the way retransmission detection is implemented may cause a bug for connections where we have
148 // not recorded the initial SYN, but only the SYN ACK, as retransmission is determined by comparing the
149 // sequence numbers of initial SYNs -- and if no initial SYN is present for the Conversation, the new
150 // SYN will be interpreted as a retransmission. Possible fix: let isRentransmission ALWAYS return false
151 // when presented with a SYN packet when the Conversation already holds a SYN ACK packet?
153 // New SYN has different sequence number than SYN recorded for ongoingConv, so this must be an attempt
154 // to establish a new conversation with the same four tuple as ongoingConv.
155 // Mark existing connection as terminated.
156 // TODO: is this 100% theoretically correct, e.g., if many connection attempts are made back to back? And RST packets?
157 mTerminatedConversations.add(ongoingConv);
158 mOpenConversations.remove(ongoingConv);
161 // Finally, update the map of open connections with the new connection.
162 mOpenConversations.put(conv, conv);
167 * TODO a problem across the board for all processXPacket methods below:
168 * if we start the capture in the middle of a TCP connection, we will not have an entry for the conversation in the
169 * map as we have not seen the initial SYN packet.
170 * Two ways we can address this:
171 * a) Perform null-checks and ignore packets for which we have not seen SYN
172 * + easy to get correct
173 * - we discard data (issue for long-lived connections!)
174 * b) Add a corresponding conversation entry whenever we encounter a packet that does not map to a conversation
175 * + we consider all data
176 * - not immediately clear if this will introduce bugs (incorrectly mapping packets to wrong conversations?)
178 * [[[ I went with option b) for now; see getOngoingConversationOrCreateNew(PcapPacket pcapPacket). ]]]
181 private void processNewConnectionAck(PcapPacket srvSynPacket) {
182 // Find the corresponding ongoing connection, if any (if we start the capture just *after* the initial SYN, no
183 // ongoing conversation entry will exist, so it must be created in that case).
184 // Conversation conv = mOpenConversations.get(Conversation.fromPcapPacket(srvSynPacket, false));
185 Conversation conv = getOngoingConversationOrCreateNew(srvSynPacket);
186 // Note: exploits &&'s short-circuit operation: only attempts to add non-retransmissions.
187 if (!conv.isRetransmission(srvSynPacket) && !conv.addSynPacket(srvSynPacket)) {
188 // For safety/debugging: if NOT a retransmission and add fails,
189 // something has gone terribly wrong/invariant is broken.
190 // throw new AssertionError("Attempt to add SYN ACK packet that was NOT a retransmission failed." +
191 // Conversation.class.getSimpleName() + " invariant broken.");
195 private void processRstPacket(PcapPacket rstPacket) {
196 Conversation conv = getOngoingConversationOrCreateNew(rstPacket);
197 // Add RST packet to conversation.
198 conv.addRstPacket(rstPacket);
199 // Move conversation to set of terminated conversations.
200 mTerminatedConversations.add(conv);
201 mOpenConversations.remove(conv, conv);
204 private void processFinPacket(PcapPacket finPacket) {
205 // getOngoingConversationForPacket(finPacket).addFinPacket(finPacket);
206 getOngoingConversationOrCreateNew(finPacket).addFinPacket(finPacket);
209 private void processAck(PcapPacket ackPacket) {
210 // getOngoingConversationForPacket(ackPacket).attemptAcknowledgementOfFin(ackPacket);
211 // Note that unlike the style for SYN, FIN, and payload packets, for "ACK only" packets, we want to avoid
212 // creating a new conversation.
213 Conversation conv = getOngoingConversationForPacket(ackPacket);
215 // The ACK may be an ACK of a FIN, so attempt to mark the FIN as ack'ed.
216 conv.attemptAcknowledgementOfFin(ackPacket);
217 if (conv.isGracefullyShutdown()) {
218 // Move conversation to set of terminated conversations.
219 mTerminatedConversations.add(conv);
220 mOpenConversations.remove(conv);
223 // Note: add (additional) processing of ACKs (that are not ACKs of FINs) as necessary here...
226 private void processPayloadPacket(PcapPacket pcapPacket) {
227 // getOngoingConversationForPacket(pcapPacket).addPacket(pcapPacket, true);
228 getOngoingConversationOrCreateNew(pcapPacket).addPacket(pcapPacket, true);
232 * Locates an ongoing conversation (if any) that {@code pcapPacket} pertains to.
233 * @param pcapPacket The packet that is to be mapped to an ongoing {@code Conversation}.
234 * @return The {@code Conversation} matching {@code pcapPacket} or {@code null} if there is no match.
236 private Conversation getOngoingConversationForPacket(PcapPacket pcapPacket) {
237 // We cannot know if this is a client-to-server or server-to-client packet without trying both options...
238 Conversation conv = mOpenConversations.get(Conversation.fromPcapPacket(pcapPacket, true));
240 conv = mOpenConversations.get(Conversation.fromPcapPacket(pcapPacket, false));
246 * Like {@link #getOngoingConversationForPacket(PcapPacket)}, but creates and inserts a new {@code Conversation}
247 * into {@link #mOpenConversations} if no open conversation is found (i.e., in the case that
248 * {@link #getOngoingConversationForPacket(PcapPacket)} returns {@code null}).
250 * @param pcapPacket The packet that is to be mapped to an ongoing {@code Conversation}.
251 * @return The existing, ongoing {@code Conversation} matching {@code pcapPacket} or the newly created one in case
252 * no match was found.
254 private Conversation getOngoingConversationOrCreateNew(PcapPacket pcapPacket) {
255 Conversation conv = getOngoingConversationForPacket(pcapPacket);
257 TcpPacket tcpPacket = pcapPacket.get(TcpPacket.class);
258 if (tcpPacket.getHeader().getSyn() && tcpPacket.getHeader().getAck()) {
259 // A SYN ACK packet always originates from the server (it is a reply to the initial SYN packet from the client)
260 conv = Conversation.fromPcapPacket(pcapPacket, false);
262 // TODO: can we do anything else but arbitrarily select who is designated as the server in this case?
263 // We can check if the IP prefix matches a local IP when handling traffic observed inside the local
264 // network, but that obviously won't be a useful strategy for an observer at the WAN port.
265 String srcIp = pcapPacket.get(IpV4Packet.class).getHeader().getSrcAddr().getHostAddress();
266 // TODO: REPLACE THE ROUTER'S IP WITH A PARAMETER!!!
267 boolean clientIsSrc = srcIp.startsWith("10.") || srcIp.startsWith("192.168.") || srcIp.equals(mRouterWanIp);
268 conv = Conversation.fromPcapPacket(pcapPacket, clientIsSrc);
270 mOpenConversations.put(conv, conv);