#define MS_CLASS "RTC::StunPacket" // #define MS_LOG_DEV #include "stun_packet.h" #include // std::snprintf() #include // std::memcmp(), std::memcpy() #include "utils.h" namespace RTC { /* Class variables. */ const uint8_t StunPacket::kMagicCookie[] = {0x21, 0x12, 0xA4, 0x42}; /* Class methods. */ StunPacket* StunPacket::Parse(const uint8_t* data, size_t len) { if (!StunPacket::IsStun(data, len)) return nullptr; /* The message type field is decomposed further into the following structure: 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +--+--+-+-+-+-+-+-+-+-+-+-+-+-+ |M |M |M|M|M|C|M|M|M|C|M|M|M|M| |11|10|9|8|7|1|6|5|4|0|3|2|1|0| +--+--+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: Format of STUN Message Type Field Here the bits in the message type field are shown as most significant (M11) through least significant (M0). M11 through M0 represent a 12- bit encoding of the method. C1 and C0 represent a 2-bit encoding of the class. */ // Get type field. uint16_t msgType = Utils::Byte::Get2Bytes(data, 0); // Get length field. uint16_t msgLength = Utils::Byte::Get2Bytes(data, 2); // length field must be total size minus header's 20 bytes, and must be multiple of 4 Bytes. if ((static_cast(msgLength) != len - 20) || ((msgLength & 0x03) != 0)) { ELOG_DEBUG( "length field + 20 does not match total size (or it is not multiple of 4 bytes), " "packet discarded"); return nullptr; } // Get STUN method. uint16_t msgMethod = (msgType & 0x000f) | ((msgType & 0x00e0) >> 1) | ((msgType & 0x3E00) >> 2); // Get STUN class. uint16_t msgClass = ((data[0] & 0x01) << 1) | ((data[1] & 0x10) >> 4); // Create a new StunPacket (data + 8 points to the received TransactionID field). auto packet = new StunPacket(static_cast(msgClass), static_cast(msgMethod), data + 8, data, len); /* STUN Attributes After the STUN header are zero or more attributes. Each attribute MUST be TLV encoded, with a 16-bit type, 16-bit length, and value. Each STUN attribute MUST end on a 32-bit boundary. As mentioned above, all fields in an attribute are transmitted most significant bit first. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value (variable) .... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ */ // Start looking for attributes after STUN header (Byte #20). size_t pos{20}; // Flags (positions) for special MESSAGE-INTEGRITY and FINGERPRINT attributes. bool hasMessageIntegrity{false}; bool hasFingerprint{false}; size_t fingerprintAttrPos; // Will point to the beginning of the attribute. uint32_t fingerprint; // Holds the value of the FINGERPRINT attribute. // Ensure there are at least 4 remaining bytes (attribute with 0 length). while (pos + 4 <= len) { // Get the attribute type. auto attrType = static_cast(Utils::Byte::Get2Bytes(data, pos)); // Get the attribute length. uint16_t attrLength = Utils::Byte::Get2Bytes(data, pos + 2); // Ensure the attribute length is not greater than the remaining size. if ((pos + 4 + attrLength) > len) { ELOG_DEBUG("the attribute length exceeds the remaining size, packet discarded"); delete packet; return nullptr; } // FINGERPRINT must be the last attribute. if (hasFingerprint) { ELOG_DEBUG("attribute after FINGERPRINT is not allowed, packet discarded"); delete packet; return nullptr; } // After a MESSAGE-INTEGRITY attribute just FINGERPRINT is allowed. if (hasMessageIntegrity && attrType != Attribute::FINGERPRINT) { ELOG_DEBUG( "attribute after MESSAGE-INTEGRITY other than FINGERPRINT is not allowed, " "packet discarded"); delete packet; return nullptr; } const uint8_t* attrValuePos = data + pos + 4; switch (attrType) { case Attribute::USERNAME: { packet->SetUsername(reinterpret_cast(attrValuePos), static_cast(attrLength)); break; } case Attribute::PRIORITY: { // Ensure attribute length is 4 bytes. if (attrLength != 4) { ELOG_DEBUG("attribute PRIORITY must be 4 bytes length, packet discarded"); delete packet; return nullptr; } packet->SetPriority(Utils::Byte::Get4Bytes(attrValuePos, 0)); break; } case Attribute::ICE_CONTROLLING: { // Ensure attribute length is 8 bytes. if (attrLength != 8) { ELOG_DEBUG("attribute ICE-CONTROLLING must be 8 bytes length, packet discarded"); delete packet; return nullptr; } packet->SetIceControlling(Utils::Byte::Get8Bytes(attrValuePos, 0)); break; } case Attribute::ICE_CONTROLLED: { // Ensure attribute length is 8 bytes. if (attrLength != 8) { ELOG_DEBUG("attribute ICE-CONTROLLED must be 8 bytes length, packet discarded"); delete packet; return nullptr; } packet->SetIceControlled(Utils::Byte::Get8Bytes(attrValuePos, 0)); break; } case Attribute::USE_CANDIDATE: { // Ensure attribute length is 0 bytes. if (attrLength != 0) { ELOG_DEBUG("attribute USE-CANDIDATE must be 0 bytes length, packet discarded"); delete packet; return nullptr; } packet->SetUseCandidate(); break; } case Attribute::MESSAGE_INTEGRITY: { // Ensure attribute length is 20 bytes. if (attrLength != 20) { ELOG_DEBUG("attribute MESSAGE-INTEGRITY must be 20 bytes length, packet discarded"); delete packet; return nullptr; } hasMessageIntegrity = true; packet->SetMessageIntegrity(attrValuePos); break; } case Attribute::FINGERPRINT: { // Ensure attribute length is 4 bytes. if (attrLength != 4) { ELOG_DEBUG("attribute FINGERPRINT must be 4 bytes length, packet discarded"); delete packet; return nullptr; } hasFingerprint = true; fingerprintAttrPos = pos; fingerprint = Utils::Byte::Get4Bytes(attrValuePos, 0); packet->SetFingerprint(); break; } case Attribute::ERROR_CODE: { // Ensure attribute length >= 4bytes. if (attrLength < 4) { ELOG_DEBUG("attribute ERROR-CODE must be >= 4bytes length, packet discarded"); delete packet; return nullptr; } uint8_t errorClass = Utils::Byte::Get1Byte(attrValuePos, 2); uint8_t errorNumber = Utils::Byte::Get1Byte(attrValuePos, 3); auto errorCode = static_cast(errorClass * 100 + errorNumber); packet->SetErrorCode(errorCode); break; } default:; } // Set next attribute position. pos = static_cast(Utils::Byte::PadTo4Bytes(static_cast(pos + 4 + attrLength))); } // Ensure current position matches the total length. if (pos != len) { ELOG_DEBUG("computed packet size does not match total size, packet discarded"); delete packet; return nullptr; } // If it has FINGERPRINT attribute then verify it. if (hasFingerprint) { // Compute the CRC32 of the received packet up to (but excluding) the // FINGERPRINT attribute and XOR it with 0x5354554e. uint32_t computedFingerprint = Utils::Crypto::GetCRC32(data, fingerprintAttrPos) ^ 0x5354554e; // Compare with the FINGERPRINT value in the packet. if (fingerprint != computedFingerprint) { ELOG_DEBUG( "computed FINGERPRINT value does not match the value in the packet, " "packet discarded"); delete packet; return nullptr; } } return packet; } /* Instance methods. */ StunPacket::StunPacket(Class klass, Method method, const uint8_t* transactionId, const uint8_t* data, size_t size) : klass(klass), method(method), transactionId(transactionId), data(const_cast(data)), size(size) { // MS_TRACE(); } StunPacket::~StunPacket() { // MS_TRACE(); } void StunPacket::Dump() const { // MS_TRACE(); // MS_DUMP(""); std::string klass; switch (this->klass) { case Class::REQUEST: klass = "Request"; break; case Class::INDICATION: klass = "Indication"; break; case Class::SUCCESS_RESPONSE: klass = "SuccessResponse"; break; case Class::ERROR_RESPONSE: klass = "ErrorResponse"; break; } if (this->method == Method::BINDING) { // MS_DUMP(" Binding %s", klass.c_str()); } else { // This prints the unknown method number. Example: TURN Allocate => 0x003. // MS_DUMP(" %s with unknown method %#.3x", klass.c_str(), // static_cast(this->method)); } // MS_DUMP(" size: %zu bytes", this->size); static char transactionId[25]; for (int i{0}; i < 12; ++i) { // NOTE: n must be 3 because snprintf adds a \0 after printed chars. std::snprintf(transactionId + (i * 2), 3, "%.2x", this->transactionId[i]); } // MS_DUMP(" transactionId: %s", transactionId); if (this->errorCode != 0u) // MS_DUMP(" errorCode: %" PRIu16, this->errorCode); if (!this->username.empty()) // MS_DUMP(" username: %s", this->username.c_str()); if (this->priority != 0u) // MS_DUMP(" priority: %" PRIu32, this->priority); if (this->iceControlling != 0u) // MS_DUMP(" iceControlling: %" PRIu64, this->iceControlling); if (this->iceControlled != 0u) // MS_DUMP(" iceControlled: %" PRIu64, this->iceControlled); if (this->hasUseCandidate) // MS_DUMP(" useCandidate"); if (this->xorMappedAddress != nullptr) { int family; uint16_t port; std::string ip; Utils::IP::GetAddressInfo(this->xorMappedAddress, family, ip, port); // MS_DUMP(" xorMappedAddress: %s : %" PRIu16, ip.c_str(), port); } if (this->messageIntegrity != nullptr) { static char messageIntegrity[41]; for (int i{0}; i < 20; ++i) { std::snprintf(messageIntegrity + (i * 2), 3, "%.2x", this->messageIntegrity[i]); } // MS_DUMP(" messageIntegrity: %s", messageIntegrity); } if (this->hasFingerprint) { } // MS_DUMP(" has fingerprint"); // MS_DUMP(""); } StunPacket::Authentication StunPacket::CheckAuthentication(const std::string& localUsername, const std::string& localPassword) { // MS_TRACE(); switch (this->klass) { case Class::REQUEST: case Class::INDICATION: { // Both USERNAME and MESSAGE-INTEGRITY must be present. if (this->messageIntegrity == nullptr || this->username.empty()) return Authentication::BAD_REQUEST; // Check that USERNAME attribute begins with our local username plus ":". size_t localUsernameLen = localUsername.length(); if (this->username.length() <= localUsernameLen || this->username.at(localUsernameLen) != ':' || (this->username.compare(0, localUsernameLen, localUsername) != 0)) { return Authentication::UNAUTHORIZED; } break; } // This method cannot check authentication in received responses (as we // are ICE-Lite and don't generate requests). case Class::SUCCESS_RESPONSE: case Class::ERROR_RESPONSE: { // MS_ERROR("cannot check authentication for a STUN response"); return Authentication::BAD_REQUEST; } } // If there is FINGERPRINT it must be discarded for MESSAGE-INTEGRITY calculation, // so the header length field must be modified (and later restored). if (this->hasFingerprint) // Set the header length field: full size - header length (20) - FINGERPRINT length (8). Utils::Byte::Set2Bytes(this->data, 2, static_cast(this->size - 20 - 8)); // Calculate the HMAC-SHA1 of the message according to MESSAGE-INTEGRITY rules. const uint8_t* computedMessageIntegrity = Utils::Crypto::GetHmacShA1( localPassword, this->data, (this->messageIntegrity - 4) - this->data); Authentication result; // Compare the computed HMAC-SHA1 with the MESSAGE-INTEGRITY in the packet. if (std::memcmp(this->messageIntegrity, computedMessageIntegrity, 20) == 0) result = Authentication::OK; else result = Authentication::UNAUTHORIZED; // Restore the header length field. if (this->hasFingerprint) Utils::Byte::Set2Bytes(this->data, 2, static_cast(this->size - 20)); return result; } StunPacket* StunPacket::CreateSuccessResponse() { // MS_TRACE(); // MS_ASSERT( // this->klass == Class::REQUEST, // "attempt to create a success response for a non Request STUN packet"); return new StunPacket(Class::SUCCESS_RESPONSE, this->method, this->transactionId, nullptr, 0); } StunPacket* StunPacket::CreateErrorResponse(uint16_t errorCode) { // MS_TRACE(); // MS_ASSERT( // this->klass == Class::REQUEST, // "attempt to create an error response for a non Request STUN packet"); auto response = new StunPacket(Class::ERROR_RESPONSE, this->method, this->transactionId, nullptr, 0); response->SetErrorCode(errorCode); return response; } void StunPacket::Authenticate(const std::string& password) { // Just for Request, Indication and SuccessResponse messages. if (this->klass == Class::ERROR_RESPONSE) { // MS_ERROR("cannot set password for ErrorResponse messages"); return; } this->password = password; } void StunPacket::Serialize(uint8_t* buffer) { // MS_TRACE(); // Some useful variables. uint16_t usernamePaddedLen{0}; uint16_t xorMappedAddressPaddedLen{0}; bool addXorMappedAddress = ((this->xorMappedAddress != nullptr) && this->method == StunPacket::Method::BINDING && this->klass == Class::SUCCESS_RESPONSE); bool addErrorCode = ((this->errorCode != 0u) && this->klass == Class::ERROR_RESPONSE); bool addMessageIntegrity = (this->klass != Class::ERROR_RESPONSE && !this->password.empty()); bool addFingerprint{true}; // Do always. // Update data pointer. this->data = buffer; // First calculate the total required size for the entire packet. this->size = 20; // Header. if (!this->username.empty()) { usernamePaddedLen = Utils::Byte::PadTo4Bytes(static_cast(this->username.length())); this->size += 4 + usernamePaddedLen; } if (this->priority != 0u) this->size += 4 + 4; if (this->iceControlling != 0u) this->size += 4 + 8; if (this->iceControlled != 0u) this->size += 4 + 8; if (this->hasUseCandidate) this->size += 4; if (addXorMappedAddress) { switch (this->xorMappedAddress->sa_family) { case AF_INET: { xorMappedAddressPaddedLen = 8; this->size += 4 + 8; break; } case AF_INET6: { xorMappedAddressPaddedLen = 20; this->size += 4 + 20; break; } default: { // MS_ERROR("invalid inet family in XOR-MAPPED-ADDRESS attribute"); addXorMappedAddress = false; } } } if (addErrorCode) this->size += 4 + 4; if (addMessageIntegrity) this->size += 4 + 20; if (addFingerprint) this->size += 4 + 4; // Merge class and method fields into type. uint16_t typeField = (static_cast(this->method) & 0x0f80) << 2; typeField |= (static_cast(this->method) & 0x0070) << 1; typeField |= (static_cast(this->method) & 0x000f); typeField |= (static_cast(this->klass) & 0x02) << 7; typeField |= (static_cast(this->klass) & 0x01) << 4; // Set type field. Utils::Byte::Set2Bytes(buffer, 0, typeField); // Set length field. Utils::Byte::Set2Bytes(buffer, 2, static_cast(this->size) - 20); // Set magic cookie. std::memcpy(buffer + 4, StunPacket::kMagicCookie, 4); // Set TransactionId field. std::memcpy(buffer + 8, this->transactionId, 12); // Update the transaction ID pointer. this->transactionId = buffer + 8; // Add atributes. size_t pos{20}; // Add USERNAME. if (usernamePaddedLen != 0u) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::USERNAME)); Utils::Byte::Set2Bytes(buffer, pos + 2, static_cast(this->username.length())); std::memcpy(buffer + pos + 4, this->username.c_str(), this->username.length()); pos += 4 + usernamePaddedLen; } // Add PRIORITY. if (this->priority != 0u) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::PRIORITY)); Utils::Byte::Set2Bytes(buffer, pos + 2, 4); Utils::Byte::Set4Bytes(buffer, pos + 4, this->priority); pos += 4 + 4; } // Add ICE-CONTROLLING. if (this->iceControlling != 0u) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::ICE_CONTROLLING)); Utils::Byte::Set2Bytes(buffer, pos + 2, 8); Utils::Byte::Set8Bytes(buffer, pos + 4, this->iceControlling); pos += 4 + 8; } // Add ICE-CONTROLLED. if (this->iceControlled != 0u) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::ICE_CONTROLLED)); Utils::Byte::Set2Bytes(buffer, pos + 2, 8); Utils::Byte::Set8Bytes(buffer, pos + 4, this->iceControlled); pos += 4 + 8; } // Add USE-CANDIDATE. if (this->hasUseCandidate) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::USE_CANDIDATE)); Utils::Byte::Set2Bytes(buffer, pos + 2, 0); pos += 4; } // Add XOR-MAPPED-ADDRESS if (addXorMappedAddress) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::XOR_MAPPED_ADDRESS)); Utils::Byte::Set2Bytes(buffer, pos + 2, xorMappedAddressPaddedLen); uint8_t* attrValue = buffer + pos + 4; switch (this->xorMappedAddress->sa_family) { case AF_INET: { // Set first byte to 0. attrValue[0] = 0; // Set inet family. attrValue[1] = 0x01; // Set port and XOR it. std::memcpy(attrValue + 2, &(reinterpret_cast(this->xorMappedAddress))->sin_port, 2); attrValue[2] ^= StunPacket::kMagicCookie[0]; attrValue[3] ^= StunPacket::kMagicCookie[1]; // Set address and XOR it. std::memcpy( attrValue + 4, &(reinterpret_cast(this->xorMappedAddress))->sin_addr.s_addr, 4); attrValue[4] ^= StunPacket::kMagicCookie[0]; attrValue[5] ^= StunPacket::kMagicCookie[1]; attrValue[6] ^= StunPacket::kMagicCookie[2]; attrValue[7] ^= StunPacket::kMagicCookie[3]; pos += 4 + 8; break; } case AF_INET6: { // Set first byte to 0. attrValue[0] = 0; // Set inet family. attrValue[1] = 0x02; // Set port and XOR it. std::memcpy(attrValue + 2, &(reinterpret_cast(this->xorMappedAddress))->sin6_port, 2); attrValue[2] ^= StunPacket::kMagicCookie[0]; attrValue[3] ^= StunPacket::kMagicCookie[1]; // Set address and XOR it. std::memcpy( attrValue + 4, &(reinterpret_cast(this->xorMappedAddress))->sin6_addr.s6_addr, 16); attrValue[4] ^= StunPacket::kMagicCookie[0]; attrValue[5] ^= StunPacket::kMagicCookie[1]; attrValue[6] ^= StunPacket::kMagicCookie[2]; attrValue[7] ^= StunPacket::kMagicCookie[3]; attrValue[8] ^= this->transactionId[0]; attrValue[9] ^= this->transactionId[1]; attrValue[10] ^= this->transactionId[2]; attrValue[11] ^= this->transactionId[3]; attrValue[12] ^= this->transactionId[4]; attrValue[13] ^= this->transactionId[5]; attrValue[14] ^= this->transactionId[6]; attrValue[15] ^= this->transactionId[7]; attrValue[16] ^= this->transactionId[8]; attrValue[17] ^= this->transactionId[9]; attrValue[18] ^= this->transactionId[10]; attrValue[19] ^= this->transactionId[11]; pos += 4 + 20; break; } } } // Add ERROR-CODE. if (addErrorCode) { Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::ERROR_CODE)); Utils::Byte::Set2Bytes(buffer, pos + 2, 4); auto codeClass = static_cast(this->errorCode / 100); uint8_t codeNumber = static_cast(this->errorCode) - (codeClass * 100); Utils::Byte::Set2Bytes(buffer, pos + 4, 0); Utils::Byte::Set1Byte(buffer, pos + 6, codeClass); Utils::Byte::Set1Byte(buffer, pos + 7, codeNumber); pos += 4 + 4; } // Add MESSAGE-INTEGRITY. if (addMessageIntegrity) { // Ignore FINGERPRINT. if (addFingerprint) Utils::Byte::Set2Bytes(buffer, 2, static_cast(this->size - 20 - 8)); // Calculate the HMAC-SHA1 of the packet according to MESSAGE-INTEGRITY rules. const uint8_t* computedMessageIntegrity = Utils::Crypto::GetHmacShA1(this->password, buffer, pos); Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::MESSAGE_INTEGRITY)); Utils::Byte::Set2Bytes(buffer, pos + 2, 20); std::memcpy(buffer + pos + 4, computedMessageIntegrity, 20); // Update the pointer. this->messageIntegrity = buffer + pos + 4; pos += 4 + 20; // Restore length field. if (addFingerprint) Utils::Byte::Set2Bytes(buffer, 2, static_cast(this->size - 20)); } else { // Unset the pointer (if it was set). this->messageIntegrity = nullptr; } // Add FINGERPRINT. if (addFingerprint) { // Compute the CRC32 of the packet up to (but excluding) the FINGERPRINT // attribute and XOR it with 0x5354554e. uint32_t computedFingerprint = Utils::Crypto::GetCRC32(buffer, pos) ^ 0x5354554e; Utils::Byte::Set2Bytes(buffer, pos, static_cast(Attribute::FINGERPRINT)); Utils::Byte::Set2Bytes(buffer, pos + 2, 4); Utils::Byte::Set4Bytes(buffer, pos + 4, computedFingerprint); pos += 4 + 4; // Set flag. this->hasFingerprint = true; } else { this->hasFingerprint = false; } // MS_ASSERT(pos == this->size, "pos != this->size"); } } // namespace RTC