media/base/turn_utils.cc

/*
 *  Copyright (c) 2016 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 "media/base/turn_utils.h"

#include <cstddef>
#include <cstdint>
#include <span>

#include "api/transport/stun.h"
#include "rtc_base/byte_order.h"

namespace webrtc {

namespace {

const size_t kTurnChannelHeaderLength = 4;

bool IsTurnChannelData(const uint8_t* data, size_t length) {
  return length >= kTurnChannelHeaderLength && ((*data & 0xC0) == 0x40);
}

bool IsTurnSendIndicationPacket(const uint8_t* data, size_t length) {
  if (length < kStunHeaderSize) {
    return false;
  }

  uint16_t type = GetBE16(std::span<const uint8_t>(data, 2));
  return (type == TURN_SEND_INDICATION);
}

}  // namespace

bool UnwrapTurnPacket(const uint8_t* packet,
                      size_t packet_size,
                      size_t* content_position,
                      size_t* content_size) {
  std::span<const uint8_t> data_view(packet, packet_size);
  if (IsTurnChannelData(packet, packet_size)) {
    // Turn Channel Message header format.
    //   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
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    // |         Channel Number        |            Length             |
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    // |                                                               |
    // /                       Application Data                        /
    // /                                                               /
    // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    size_t length = GetBE16(data_view.subspan(2, 2));
    if (length + kTurnChannelHeaderLength > packet_size) {
      return false;
    }

    *content_position = kTurnChannelHeaderLength;
    *content_size = length;
    return true;
  }

  if (IsTurnSendIndicationPacket(packet, packet_size)) {
    // Validate STUN message length.
    const size_t stun_message_length = GetBE16(data_view.subspan(2, 2));
    if (stun_message_length + kStunHeaderSize != packet_size) {
      return false;
    }

    // First skip mandatory stun header which is of 20 bytes.
    size_t pos = kStunHeaderSize;
    // Loop through STUN attributes until we find STUN DATA attribute.
    while (pos < packet_size) {
      // Keep reading STUN attributes until we hit DATA attribute.
      // Attribute will be a TLV structure.
      // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      // |         Type                  |            Length             |
      // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      // |                         Value (variable)                ....
      // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      // The value in the length field MUST contain the length of the Value
      // part of the attribute, prior to padding, measured in bytes.  Since
      // STUN aligns attributes on 32-bit boundaries, attributes whose content
      // is not a multiple of 4 bytes are padded with 1, 2, or 3 bytes of
      // padding so that its value contains a multiple of 4 bytes.  The
      // padding bits are ignored, and may be any value.
      uint16_t attr_type, attr_length;
      const int kAttrHeaderLength = sizeof(attr_type) + sizeof(attr_length);

      if (packet_size < pos + kAttrHeaderLength) {
        return false;
      }

      // Getting attribute type and length.
      attr_type = GetBE16(data_view.subspan(pos, 2));
      attr_length = GetBE16(data_view.subspan(pos + sizeof(attr_type), 2));

      pos += kAttrHeaderLength;  // Skip STUN_DATA_ATTR header.

      // Checking for bogus attribute length.
      if (pos + attr_length > packet_size) {
        return false;
      }

      if (attr_type == STUN_ATTR_DATA) {
        *content_position = pos;
        *content_size = attr_length;
        return true;
      }

      pos += attr_length;
      if ((attr_length % 4) != 0) {
        pos += (4 - (attr_length % 4));
      }
    }

    // There is no data attribute present in the message.
    return false;
  }

  // This is not a TURN packet.
  *content_position = 0;
  *content_size = packet_size;
  return true;
}

}  // namespace webrtc