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webrtc/net/dcsctp/socket/dcsctp_socket.h
Victor Boivie 63e273ad4b dcsctp: Persist all state in state cookie 
In the example below, the association is being established between peer
A and Z, and A is the initiating party.

Before this CL, when an association was about to be established, Z would
after having received the INIT chunk, persist state in the socket about
which verification tag and initial TSN that was picked. These would be
re-generated on every incoming INIT (that's fine), but when A had
extracted the cookie from INIT_ACK and sent a reply (COOKIE_ECHO) with
the state cookie, that could fail validation when it's received by Z, if
the sent cookie was not the most recent one or if the COOKIE_ECHO had a
verification tag coming not from the most recent INIT_ACK, because Z had
replaced the state in the socket with the one generated when the second
INIT_ACK chunk was generated - state it used for validation of future
received data.

In other words:
A -> INIT 1
<timeout>
A -> INIT 2 (retransmission of INIT 1)
INIT 1 -> Z - sends INIT_ACK 1 with verification_tag=1, initial_tsn=1,
              cookie 1 (and records these to socket state)
INIT 2 -> Z - sends INIT_ACK 2 with verification_tag=2, initial_tsn=2,
              cookie 2 (replaces socket state with the new data)
INIT_ACK 1 -> A -> sends COOKIE_ECHO with verification_tag=1, cookie 1
COOKIE_ECHO (cookie 1) -> Z <FAILS, as the state isn't as expected>.

The solution is really to do what RFC4960 says, to not maintain any
state as the receiving peer until COOKIE_ECHO has been received. This
was initially not done because the underlying reason why this is
important in SCTP is to avoid denial of service, and this is why SCTP
has the four-way handshake. But for Data Channels - SCTP over DTLS -
this attack vector isn't available. So the implementation was
"simplified" by keeping socket state instead of encoding it in the
state cookie, but that obviously had downsides.

So with this CL, the non-initiating peer in connection establishment
doesn't keep any socket state, and puts all that state in the state
cookie instead. This allows any COOKIE_ECHO to be received by Z.

Bug: webrtc:15712
Change-Id: I596c7330ce27292612d3c9f86b21c712f6f4e408
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/330440
Commit-Queue: Victor Boivie <boivie@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#41340}
2023-12-08 10:54:42 +00:00

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/*
* Copyright (c) 2021 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef NET_DCSCTP_SOCKET_DCSCTP_SOCKET_H_
#define NET_DCSCTP_SOCKET_DCSCTP_SOCKET_H_
#include <cstdint>
#include <memory>
#include <string>
#include <utility>
#include "absl/strings/string_view.h"
#include "api/array_view.h"
#include "api/sequence_checker.h"
#include "net/dcsctp/packet/chunk/abort_chunk.h"
#include "net/dcsctp/packet/chunk/chunk.h"
#include "net/dcsctp/packet/chunk/cookie_ack_chunk.h"
#include "net/dcsctp/packet/chunk/cookie_echo_chunk.h"
#include "net/dcsctp/packet/chunk/data_chunk.h"
#include "net/dcsctp/packet/chunk/data_common.h"
#include "net/dcsctp/packet/chunk/error_chunk.h"
#include "net/dcsctp/packet/chunk/forward_tsn_chunk.h"
#include "net/dcsctp/packet/chunk/forward_tsn_common.h"
#include "net/dcsctp/packet/chunk/heartbeat_ack_chunk.h"
#include "net/dcsctp/packet/chunk/heartbeat_request_chunk.h"
#include "net/dcsctp/packet/chunk/idata_chunk.h"
#include "net/dcsctp/packet/chunk/iforward_tsn_chunk.h"
#include "net/dcsctp/packet/chunk/init_ack_chunk.h"
#include "net/dcsctp/packet/chunk/init_chunk.h"
#include "net/dcsctp/packet/chunk/reconfig_chunk.h"
#include "net/dcsctp/packet/chunk/sack_chunk.h"
#include "net/dcsctp/packet/chunk/shutdown_ack_chunk.h"
#include "net/dcsctp/packet/chunk/shutdown_chunk.h"
#include "net/dcsctp/packet/chunk/shutdown_complete_chunk.h"
#include "net/dcsctp/packet/data.h"
#include "net/dcsctp/packet/sctp_packet.h"
#include "net/dcsctp/public/dcsctp_message.h"
#include "net/dcsctp/public/dcsctp_options.h"
#include "net/dcsctp/public/dcsctp_socket.h"
#include "net/dcsctp/public/packet_observer.h"
#include "net/dcsctp/rx/data_tracker.h"
#include "net/dcsctp/rx/reassembly_queue.h"
#include "net/dcsctp/socket/callback_deferrer.h"
#include "net/dcsctp/socket/packet_sender.h"
#include "net/dcsctp/socket/state_cookie.h"
#include "net/dcsctp/socket/transmission_control_block.h"
#include "net/dcsctp/timer/timer.h"
#include "net/dcsctp/tx/retransmission_error_counter.h"
#include "net/dcsctp/tx/retransmission_queue.h"
#include "net/dcsctp/tx/retransmission_timeout.h"
#include "net/dcsctp/tx/rr_send_queue.h"
namespace dcsctp {
// DcSctpSocket represents a single SCTP socket, to be used over DTLS.
//
// Every dcSCTP is completely isolated from any other socket.
//
// This class manages all packet and chunk dispatching and mainly handles the
// connection sequences (connect, close, shutdown, etc) as well as managing
// the Transmission Control Block (tcb).
//
// This class is thread-compatible.
class DcSctpSocket : public DcSctpSocketInterface {
public:
// Instantiates a DcSctpSocket, which interacts with the world through the
// `callbacks` interface and is configured using `options`.
//
// For debugging, `log_prefix` will prefix all debug logs, and a
// `packet_observer` can be attached to e.g. dump sent and received packets.
DcSctpSocket(absl::string_view log_prefix,
DcSctpSocketCallbacks& callbacks,
std::unique_ptr<PacketObserver> packet_observer,
const DcSctpOptions& options);
DcSctpSocket(const DcSctpSocket&) = delete;
DcSctpSocket& operator=(const DcSctpSocket&) = delete;
// Implementation of `DcSctpSocketInterface`.
void ReceivePacket(rtc::ArrayView<const uint8_t> data) override;
void HandleTimeout(TimeoutID timeout_id) override;
void Connect() override;
void RestoreFromState(const DcSctpSocketHandoverState& state) override;
void Shutdown() override;
void Close() override;
SendStatus Send(DcSctpMessage message,
const SendOptions& send_options) override;
ResetStreamsStatus ResetStreams(
rtc::ArrayView<const StreamID> outgoing_streams) override;
SocketState state() const override;
const DcSctpOptions& options() const override { return options_; }
void SetMaxMessageSize(size_t max_message_size) override;
void SetStreamPriority(StreamID stream_id, StreamPriority priority) override;
StreamPriority GetStreamPriority(StreamID stream_id) const override;
size_t buffered_amount(StreamID stream_id) const override;
size_t buffered_amount_low_threshold(StreamID stream_id) const override;
void SetBufferedAmountLowThreshold(StreamID stream_id, size_t bytes) override;
absl::optional<Metrics> GetMetrics() const override;
HandoverReadinessStatus GetHandoverReadiness() const override;
absl::optional<DcSctpSocketHandoverState> GetHandoverStateAndClose() override;
SctpImplementation peer_implementation() const override {
return metrics_.peer_implementation;
}
// Returns this socket's verification tag, or zero if not yet connected.
VerificationTag verification_tag() const {
return tcb_ != nullptr ? tcb_->my_verification_tag() : VerificationTag(0);
}
private:
// Parameter proposals valid during the connect phase.
struct ConnectParameters {
TSN initial_tsn = TSN(0);
VerificationTag verification_tag = VerificationTag(0);
};
// Detailed state (separate from SocketState, which is the public state).
enum class State {
kClosed,
kCookieWait,
// TCB valid in these:
kCookieEchoed,
kEstablished,
kShutdownPending,
kShutdownSent,
kShutdownReceived,
kShutdownAckSent,
};
// Returns the log prefix used for debug logging.
std::string log_prefix() const;
bool IsConsistent() const;
static constexpr absl::string_view ToString(DcSctpSocket::State state);
void CreateTransmissionControlBlock(const Capabilities& capabilities,
VerificationTag my_verification_tag,
TSN my_initial_tsn,
VerificationTag peer_verification_tag,
TSN peer_initial_tsn,
size_t a_rwnd,
TieTag tie_tag);
// Changes the socket state, given a `reason` (for debugging/logging).
void SetState(State state, absl::string_view reason);
// Closes the association. Note that the TCB will not be valid past this call.
void InternalClose(ErrorKind error, absl::string_view message);
// Closes the association, because of too many retransmission errors.
void CloseConnectionBecauseOfTooManyTransmissionErrors();
// Timer expiration handlers
webrtc::TimeDelta OnInitTimerExpiry();
webrtc::TimeDelta OnCookieTimerExpiry();
webrtc::TimeDelta OnShutdownTimerExpiry();
void OnSentPacket(rtc::ArrayView<const uint8_t> packet,
SendPacketStatus status);
// Sends SHUTDOWN or SHUTDOWN-ACK if the socket is shutting down and if all
// outstanding data has been acknowledged.
void MaybeSendShutdownOrAck();
// If the socket is shutting down, responds SHUTDOWN to any incoming DATA.
void MaybeSendShutdownOnPacketReceived(const SctpPacket& packet);
// If there are streams pending to be reset, send a request to reset them.
void MaybeSendResetStreamsRequest();
// Sends a INIT chunk.
void SendInit();
// Sends a SHUTDOWN chunk.
void SendShutdown();
// Sends a SHUTDOWN-ACK chunk.
void SendShutdownAck();
// Validates the SCTP packet, as a whole - not the validity of individual
// chunks within it, as that's done in the different chunk handlers.
bool ValidatePacket(const SctpPacket& packet);
// Parses `payload`, which is a serialized packet that is just going to be
// sent and prints all chunks.
void DebugPrintOutgoing(rtc::ArrayView<const uint8_t> payload);
// Called whenever data has been received, or the cumulative acknowledgment
// TSN has moved, that may result in delivering messages.
void MaybeDeliverMessages();
// Returns true if there is a TCB, and false otherwise (and reports an error).
bool ValidateHasTCB();
// Returns true if the parsing of a chunk of type `T` succeeded. If it didn't,
// it reports an error and returns false.
template <class T>
bool ValidateParseSuccess(const absl::optional<T>& c) {
if (c.has_value()) {
return true;
}
ReportFailedToParseChunk(T::kType);
return false;
}
// Reports failing to have parsed a chunk with the provided `chunk_type`.
void ReportFailedToParseChunk(int chunk_type);
// Called when unknown chunks are received. May report an error.
bool HandleUnrecognizedChunk(const SctpPacket::ChunkDescriptor& descriptor);
// Will dispatch more specific chunk handlers.
bool Dispatch(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming DATA chunks.
void HandleData(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming I-DATA chunks.
void HandleIData(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Common handler for DATA and I-DATA chunks.
void HandleDataCommon(AnyDataChunk& chunk);
// Handles incoming INIT chunks.
void HandleInit(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming INIT-ACK chunks.
void HandleInitAck(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming SACK chunks.
void HandleSack(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming HEARTBEAT chunks.
void HandleHeartbeatRequest(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming HEARTBEAT-ACK chunks.
void HandleHeartbeatAck(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming ABORT chunks.
void HandleAbort(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming ERROR chunks.
void HandleError(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming COOKIE-ECHO chunks.
void HandleCookieEcho(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles receiving COOKIE-ECHO when there already is a TCB. The return value
// indicates if the processing should continue.
bool HandleCookieEchoWithTCB(const CommonHeader& header,
const StateCookie& cookie);
// Handles incoming COOKIE-ACK chunks.
void HandleCookieAck(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming SHUTDOWN chunks.
void HandleShutdown(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming SHUTDOWN-ACK chunks.
void HandleShutdownAck(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming FORWARD-TSN chunks.
void HandleForwardTsn(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming I-FORWARD-TSN chunks.
void HandleIForwardTsn(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Handles incoming RE-CONFIG chunks.
void HandleReconfig(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
// Common handled for FORWARD-TSN/I-FORWARD-TSN.
void HandleForwardTsnCommon(const AnyForwardTsnChunk& chunk);
// Handles incoming SHUTDOWN-COMPLETE chunks
void HandleShutdownComplete(const CommonHeader& header,
const SctpPacket::ChunkDescriptor& descriptor);
const std::string log_prefix_;
const std::unique_ptr<PacketObserver> packet_observer_;
RTC_NO_UNIQUE_ADDRESS webrtc::SequenceChecker thread_checker_;
Metrics metrics_;
DcSctpOptions options_;
// Enqueues callbacks and dispatches them just before returning to the caller.
CallbackDeferrer callbacks_;
TimerManager timer_manager_;
const std::unique_ptr<Timer> t1_init_;
const std::unique_ptr<Timer> t1_cookie_;
const std::unique_ptr<Timer> t2_shutdown_;
// Packets that failed to be sent, but should be retried.
PacketSender packet_sender_;
// The actual SendQueue implementation. As data can be sent on a socket before
// the connection is established, this component is not in the TCB.
RRSendQueue send_queue_;
// Contains verification tag and initial TSN between having sent the INIT
// until the connection is established (there is no TCB at this point).
ConnectParameters connect_params_;
// The socket state.
State state_ = State::kClosed;
// If the connection is established, contains a transmission control block.
std::unique_ptr<TransmissionControlBlock> tcb_;
};
} // namespace dcsctp
#endif // NET_DCSCTP_SOCKET_DCSCTP_SOCKET_H_
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