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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.
*/
#include "net/dcsctp/packet/sctp_packet.h"
#include <stddef.h>
#include <cstdint>
#include <optional>
#include <string>
#include <utility>
#include <vector>
#include "absl/memory/memory.h"
#include "api/array_view.h"
#include "net/dcsctp/common/math.h"
#include "net/dcsctp/packet/bounded_byte_reader.h"
#include "net/dcsctp/packet/bounded_byte_writer.h"
#include "net/dcsctp/packet/chunk/chunk.h"
#include "net/dcsctp/packet/crc32c.h"
#include "net/dcsctp/public/dcsctp_options.h"
#include "rtc_base/logging.h"
#include "rtc_base/strings/string_format.h"
namespace dcsctp {
namespace {
constexpr size_t kMaxUdpPacketSize = 65535;
constexpr size_t kChunkTlvHeaderSize = 4;
constexpr size_t kExpectedDescriptorCount = 4;
} // namespace
/*
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port Number | Destination Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Verification Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
SctpPacket::Builder::Builder(VerificationTag verification_tag,
const DcSctpOptions& options)
: verification_tag_(verification_tag),
source_port_(options.local_port),
dest_port_(options.remote_port),
max_packet_size_(RoundDownTo4(options.mtu)) {}
SctpPacket::Builder& SctpPacket::Builder::Add(const Chunk& chunk) {
if (out_.empty()) {
out_.reserve(max_packet_size_);
out_.resize(SctpPacket::kHeaderSize);
BoundedByteWriter<kHeaderSize> buffer(out_);
buffer.Store16<0>(source_port_);
buffer.Store16<2>(dest_port_);
buffer.Store32<4>(*verification_tag_);
// Checksum is at offset 8 - written when calling Build(), if configured.
}
RTC_DCHECK(IsDivisibleBy4(out_.size()));
chunk.SerializeTo(out_);
if (out_.size() % 4 != 0) {
out_.resize(RoundUpTo4(out_.size()));
}
RTC_DCHECK(out_.size() <= max_packet_size_)
<< "Exceeded max size, data=" << out_.size()
<< ", max_size=" << max_packet_size_;
return *this;
}
size_t SctpPacket::Builder::bytes_remaining() const {
if (out_.empty()) {
// The packet header (CommonHeader) hasn't been written yet:
return max_packet_size_ - kHeaderSize;
} else if (out_.size() > max_packet_size_) {
RTC_DCHECK_NOTREACHED() << "Exceeded max size, data=" << out_.size()
<< ", max_size=" << max_packet_size_;
return 0;
}
return max_packet_size_ - out_.size();
}
std::vector<uint8_t> SctpPacket::Builder::Build(bool write_checksum) {
std::vector<uint8_t> out;
out_.swap(out);
if (!out.empty() && write_checksum) {
uint32_t crc = GenerateCrc32C(out);
BoundedByteWriter<kHeaderSize>(out).Store32<8>(crc);
}
RTC_DCHECK(out.size() <= max_packet_size_)
<< "Exceeded max size, data=" << out.size()
<< ", max_size=" << max_packet_size_;
return out;
}
std::optional<SctpPacket> SctpPacket::Parse(
webrtc::ArrayView<const uint8_t> data,
const DcSctpOptions& options) {
if (data.size() < kHeaderSize + kChunkTlvHeaderSize ||
data.size() > kMaxUdpPacketSize) {
RTC_DLOG(LS_WARNING) << "Invalid packet size";
return std::nullopt;
}
BoundedByteReader<kHeaderSize> reader(data);
CommonHeader common_header;
common_header.source_port = reader.Load16<0>();
common_header.destination_port = reader.Load16<2>();
common_header.verification_tag = VerificationTag(reader.Load32<4>());
common_header.checksum = reader.Load32<8>();
// Create a copy of the packet, which will be held by this object.
std::vector<uint8_t> data_copy =
std::vector<uint8_t>(data.begin(), data.end());
if (options.disable_checksum_verification ||
(options.zero_checksum_alternate_error_detection_method !=
ZeroChecksumAlternateErrorDetectionMethod::None() &&
common_header.checksum == 0u)) {
// https://www.ietf.org/archive/id/draft-tuexen-tsvwg-sctp-zero-checksum-01.html#section-4.3:
// If an end point has sent the Zero Checksum Acceptable Chunk Parameter in
// an INIT or INIT ACK chunk, it MUST accept SCTP packets using an incorrect
// checksum value of zero in addition to SCTP packets containing the correct
// CRC32c checksum value for this association.
} else {
// Verify the checksum. The checksum field must be zero when that's done.
BoundedByteWriter<kHeaderSize>(data_copy).Store32<8>(0);
uint32_t calculated_checksum = GenerateCrc32C(data_copy);
if (calculated_checksum != common_header.checksum) {
RTC_DLOG(LS_WARNING) << webrtc::StringFormat(
"Invalid packet checksum, packet_checksum=0x%08x, "
"calculated_checksum=0x%08x",
common_header.checksum, calculated_checksum);
return std::nullopt;
}
// Restore the checksum in the header.
BoundedByteWriter<kHeaderSize>(data_copy).Store32<8>(
common_header.checksum);
}
// Validate and parse the chunk headers in the message.
/*
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Chunk Type | Chunk Flags | Chunk Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
std::vector<ChunkDescriptor> descriptors;
descriptors.reserve(kExpectedDescriptorCount);
webrtc::ArrayView<const uint8_t> descriptor_data =
webrtc::ArrayView<const uint8_t>(data_copy).subview(kHeaderSize);
while (!descriptor_data.empty()) {
if (descriptor_data.size() < kChunkTlvHeaderSize) {
RTC_DLOG(LS_WARNING) << "Too small chunk";
return std::nullopt;
}
BoundedByteReader<kChunkTlvHeaderSize> chunk_header(descriptor_data);
uint8_t type = chunk_header.Load8<0>();
uint8_t flags = chunk_header.Load8<1>();
uint16_t length = chunk_header.Load16<2>();
uint16_t padded_length = RoundUpTo4(length);
if (padded_length > descriptor_data.size()) {
RTC_DLOG(LS_WARNING) << "Too large chunk. length=" << length
<< ", remaining=" << descriptor_data.size();
return std::nullopt;
} else if (padded_length < kChunkTlvHeaderSize) {
RTC_DLOG(LS_WARNING) << "Too small chunk. length=" << length;
return std::nullopt;
}
descriptors.emplace_back(type, flags,
descriptor_data.subview(0, padded_length));
descriptor_data = descriptor_data.subview(padded_length);
}
// Note that iterators (and pointer) are guaranteed to be stable when moving a
// std::vector, and `descriptors` have pointers to within `data_copy`.
return SctpPacket(common_header, std::move(data_copy),
std::move(descriptors));
}
} // namespace dcsctp
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