89b0f2ef71
for (partially) parsing DTLS packets and extracting the msg_seqs BUG=webrtc:367395350 Change-Id: Ieb0fc121c6dc82118ced5939c1a9ebe2d72e3cb3 Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/370181 Commit-Queue: Philipp Hancke <phancke@meta.com> Reviewed-by: Harald Alvestrand <hta@webrtc.org> Reviewed-by: Jonas Oreland <jonaso@webrtc.org> Cr-Commit-Position: refs/heads/main@{#43501}
110 lines
3.7 KiB
C++
110 lines
3.7 KiB
C++
/*
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* Copyright 2024 The WebRTC Project Authors. All rights reserved.
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*
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* Use of this source code is governed by a BSD-style license
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* that can be found in the LICENSE file in the root of the source
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* tree. An additional intellectual property rights grant can be found
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* in the file PATENTS. All contributing project authors may
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* be found in the AUTHORS file in the root of the source tree.
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*/
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#include "p2p/dtls/dtls_utils.h"
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#include <cstdint>
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#include <optional>
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#include <vector>
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#include "api/array_view.h"
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#include "rtc_base/byte_buffer.h"
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#include "rtc_base/checks.h"
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namespace {
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// https://datatracker.ietf.org/doc/html/rfc5246#appendix-A.1
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const uint8_t kDtlsHandshakeRecord = 22;
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const uint8_t kDtlsChangeCipherSpecRecord = 20;
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} // namespace
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namespace cricket {
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bool IsDtlsPacket(rtc::ArrayView<const uint8_t> payload) {
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const uint8_t* u = payload.data();
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return (payload.size() >= kDtlsRecordHeaderLen && (u[0] > 19 && u[0] < 64));
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}
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bool IsDtlsClientHelloPacket(rtc::ArrayView<const uint8_t> payload) {
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if (!IsDtlsPacket(payload)) {
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return false;
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}
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const uint8_t* u = payload.data();
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return payload.size() > 17 && u[0] == kDtlsHandshakeRecord && u[13] == 1;
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}
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bool IsDtlsHandshakePacket(rtc::ArrayView<const uint8_t> payload) {
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if (!IsDtlsPacket(payload)) {
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return false;
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}
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// change cipher spec is not a handshake packet. This used
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// to work because it was aggregated with the session ticket
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// which is no more. It is followed by the encrypted handshake
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// message which starts with a handshake record (22) again.
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return payload.size() > 17 && (payload[0] == kDtlsHandshakeRecord ||
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payload[0] == kDtlsChangeCipherSpecRecord);
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}
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// Returns a (unsorted) list of (msg_seq) received as part of the handshake.
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std::optional<std::vector<uint16_t>> GetDtlsHandshakeAcks(
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rtc::ArrayView<const uint8_t> dtls_packet) {
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std::vector<uint16_t> acks;
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rtc::ByteBufferReader record_buf(dtls_packet);
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// https://datatracker.ietf.org/doc/html/rfc6347#section-4.1
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while (record_buf.Length() >= kDtlsRecordHeaderLen) {
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uint8_t content_type;
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uint64_t epoch_and_seq;
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uint16_t len;
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// Read content_type(1), skip version(2), read epoch+seq(2+6),
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// read len(2)
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if (!(record_buf.ReadUInt8(&content_type) && record_buf.Consume(2) &&
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record_buf.ReadUInt64(&epoch_and_seq) &&
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record_buf.ReadUInt16(&len) && record_buf.Length() >= len)) {
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return std::nullopt;
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}
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if (content_type != kDtlsHandshakeRecord) {
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record_buf.Consume(len);
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continue;
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}
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// Epoch 1+ is encrypted so we can not parse it.
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if (epoch_and_seq >> 6 != 0) {
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record_buf.Consume(len);
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continue;
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}
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// https://www.rfc-editor.org/rfc/rfc6347.html#section-4.2.2
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rtc::ByteBufferReader handshake_buf(record_buf.DataView().subview(0, len));
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while (handshake_buf.Length() > 0) {
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uint16_t msg_seq;
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uint32_t fragment_len;
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uint32_t fragment_offset;
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// Skip msg_type(1) and length(3), read msg_seq(2), skip
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// fragment_offset(3), read fragment_length(3) and consume it.
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if (!(handshake_buf.Consume(1 + 3) &&
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handshake_buf.ReadUInt16(&msg_seq) &&
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handshake_buf.ReadUInt24(&fragment_offset) &&
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handshake_buf.ReadUInt24(&fragment_len) &&
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handshake_buf.Consume(fragment_len))) {
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return std::nullopt;
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}
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acks.push_back(msg_seq);
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// Advance outer buffer.
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record_buf.Consume(12 + fragment_len);
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}
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RTC_DCHECK(handshake_buf.Length() == 0);
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}
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// Should have consumed everything.
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if (record_buf.Length() != 0) {
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return std::nullopt;
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}
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return acks;
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}
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} // namespace cricket
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