i2pd/tunnel/TunnelEndpoint.cpp

#include "util/I2PEndian.h"
#include <string.h>
#include "util/Log.h"
#include "NetDb.h"
#include "I2NPProtocol.h"
#include "transport/Transports.h"
#include "RouterContext.h"
#include "TunnelEndpoint.h"

namespace i2p
{
namespace tunnel
{
    TunnelEndpoint::~TunnelEndpoint ()
    {
    }   
    
    void TunnelEndpoint::HandleDecryptedTunnelDataMsg (std::shared_ptr<I2NPMessage> msg)
    {
        m_NumReceivedBytes += TUNNEL_DATA_MSG_SIZE;
        
        uint8_t * decrypted = msg->GetPayload () + 20; // 4 + 16
        uint8_t * zero = (uint8_t *)memchr (decrypted + 4, 0, TUNNEL_DATA_ENCRYPTED_SIZE - 4); // witout 4-byte checksum
        if (zero)
        {   
            uint8_t * fragment = zero + 1;
            // verify checksum
            memcpy (msg->GetPayload () + TUNNEL_DATA_MSG_SIZE, msg->GetPayload () + 4, 16); // copy iv to the end
            uint8_t hash[32];
            CryptoPP::SHA256().CalculateDigest (hash, fragment, TUNNEL_DATA_MSG_SIZE -(fragment - msg->GetPayload ()) + 16); // payload + iv
            if (memcmp (hash, decrypted, 4))
            {
                LogPrint (eLogError, "TunnelMessage: checksum verification failed");
                return;
            }   
            // process fragments
            while (fragment < decrypted + TUNNEL_DATA_ENCRYPTED_SIZE)
            {
                uint8_t flag = fragment[0];
                fragment++;
                
                bool isFollowOnFragment = flag & 0x80, isLastFragment = true;       
                uint32_t msgID = 0;
                int fragmentNum = 0;
                TunnelMessageBlockEx m;
                if (!isFollowOnFragment)
                {   
                    // first fragment
                    
                    m.deliveryType = (TunnelDeliveryType)((flag >> 5) & 0x03);
                    switch (m.deliveryType)
                    {
                        case eDeliveryTypeLocal: // 0
                        break;
                        case eDeliveryTypeTunnel: // 1
                            m.tunnelID = bufbe32toh (fragment);
                            fragment += 4; // tunnelID
                            m.hash = i2p::data::IdentHash (fragment);
                            fragment += 32; // hash
                        break;
                        case eDeliveryTypeRouter: // 2
                            m.hash = i2p::data::IdentHash (fragment);   
                            fragment += 32; // to hash
                        break;
                        default:
                            ;
                    }   

                    bool isFragmented = flag & 0x08;
                    if (isFragmented)
                    {
                        // Message ID
                        msgID = bufbe32toh (fragment);  
                        fragment += 4;
                        isLastFragment = false;
                    }   
                }
                else
                {
                    // follow on
                    msgID = bufbe32toh (fragment); // MessageID         
                    fragment += 4; 
                    fragmentNum = (flag >> 1) & 0x3F; // 6 bits
                    isLastFragment = flag & 0x01;
                }   
                
                uint16_t size = bufbe16toh (fragment);
                fragment += 2;

                msg->offset = fragment - msg->buf;
                msg->len = msg->offset + size;
                if (fragment + size < decrypted + TUNNEL_DATA_ENCRYPTED_SIZE)
                {
                    // this is not last message. we have to copy it
                    m.data = ToSharedI2NPMessage (NewI2NPShortMessage ());
                    m.data->offset += TUNNEL_GATEWAY_HEADER_SIZE; // reserve room for TunnelGateway header
                    m.data->len += TUNNEL_GATEWAY_HEADER_SIZE;
                    *(m.data) = *msg;
                }
                else
                    m.data = msg;
                
                if (!isFollowOnFragment && isLastFragment)
                    HandleNextMessage (m);
                else
                {
                    if (msgID) // msgID is presented, assume message is fragmented
                    {
                        if (!isFollowOnFragment) // create new incomlete message
                        {
                            m.nextFragmentNum = 1;
                            auto ret = m_IncompleteMessages.insert (std::pair<uint32_t, TunnelMessageBlockEx>(msgID, m));
                            if (ret.second)
                                HandleOutOfSequenceFragment (msgID, ret.first->second);
                            else
                                LogPrint (eLogError, "Incomplete message ", msgID, "already exists");
                        }
                        else
                        {
                            m.nextFragmentNum = fragmentNum;
                            HandleFollowOnFragment (msgID, isLastFragment, m);
                        }   
                    }
                    else    
                        LogPrint (eLogError, "Message is fragmented, but msgID is not presented");
                }   
                    
                fragment += size;
            }   
        }   
        else
            LogPrint (eLogError, "TunnelMessage: zero not found");
    }   

    void TunnelEndpoint::HandleFollowOnFragment (uint32_t msgID, bool isLastFragment, const TunnelMessageBlockEx& m)
    {
        auto fragment = m.data->GetBuffer ();
        auto size = m.data->GetLength ();
        auto it = m_IncompleteMessages.find (msgID);
        if (it != m_IncompleteMessages.end())
        {
            auto& msg = it->second;
            if (m.nextFragmentNum == msg.nextFragmentNum)
            {
                if (msg.data->len + size < I2NP_MAX_MESSAGE_SIZE) // check if message is not too long
                {   
                    if (msg.data->len + size > msg.data->maxLen)
                    {
                        LogPrint (eLogInfo, "Tunnel endpoint I2NP message size ", msg.data->maxLen, " is not enough");
                        auto newMsg = ToSharedI2NPMessage (NewI2NPMessage ());
                        *newMsg = *(msg.data);
                        msg.data = newMsg;
                    }
                    memcpy (msg.data->buf + msg.data->len, fragment, size); // concatenate fragment
                    msg.data->len += size;
                    if (isLastFragment)
                    {
                        // message complete
                        HandleNextMessage (msg);    
                        m_IncompleteMessages.erase (it); 
                    }   
                    else
                    {   
                        msg.nextFragmentNum++;
                        HandleOutOfSequenceFragment (msgID, msg);
                    }   
                }
                else
                {
                    LogPrint (eLogError, "Fragment ", m.nextFragmentNum, " of message ", msgID, "exceeds max I2NP message size. Message dropped");
                    m_IncompleteMessages.erase (it);
                }
            }
            else
            {   
                LogPrint (eLogInfo, "Unexpected fragment ", (int)m.nextFragmentNum, " instead ", (int)msg.nextFragmentNum, " of message ", msgID, ". Saved");
                AddOutOfSequenceFragment (msgID, m.nextFragmentNum, isLastFragment, m.data);
            }
        }
        else
        {   
            LogPrint (eLogInfo, "First fragment of message ", msgID, " not found. Saved");
            AddOutOfSequenceFragment (msgID, m.nextFragmentNum, isLastFragment, m.data);
        }   
    }   

    void TunnelEndpoint::AddOutOfSequenceFragment (uint32_t msgID, uint8_t fragmentNum, bool isLastFragment, std::shared_ptr<I2NPMessage> data)
    {
        auto it = m_OutOfSequenceFragments.find (msgID);
        if (it == m_OutOfSequenceFragments.end ())
            m_OutOfSequenceFragments.insert (std::pair<uint32_t, Fragment> (msgID, {fragmentNum, isLastFragment, data}));   
    }   

    void TunnelEndpoint::HandleOutOfSequenceFragment (uint32_t msgID, TunnelMessageBlockEx& msg)
    {
        auto it = m_OutOfSequenceFragments.find (msgID);
        if (it != m_OutOfSequenceFragments.end ())
        {
            if (it->second.fragmentNum == msg.nextFragmentNum)
            {
                LogPrint (eLogInfo, "Out-of-sequence fragment ", (int)it->second.fragmentNum, " of message ", msgID, " found");
                auto size = it->second.data->GetLength ();
                if (msg.data->len + size > msg.data->maxLen)
                {
                    LogPrint (eLogInfo, "Tunnel endpoint I2NP message size ", msg.data->maxLen, " is not enough");
                    auto newMsg = ToSharedI2NPMessage (NewI2NPMessage ());
                    *newMsg = *(msg.data);
                    msg.data = newMsg;
                }
                memcpy (msg.data->buf + msg.data->len, it->second.data->GetBuffer (), size); // concatenate out-of-sync fragment
                msg.data->len += size;
                if (it->second.isLastFragment)
                {
                    // message complete
                    HandleNextMessage (msg);    
                    m_IncompleteMessages.erase (msgID); 
                }   
                else
                    msg.nextFragmentNum++;
                m_OutOfSequenceFragments.erase (it);
            }   
        }   
    }   
    
    void TunnelEndpoint::HandleNextMessage (const TunnelMessageBlock& msg)
    {
        LogPrint (eLogInfo, "TunnelMessage: handle fragment of ", msg.data->GetLength ()," bytes. Msg type ", (int)msg.data->GetTypeID ());
        switch (msg.deliveryType)
        {
            case eDeliveryTypeLocal:
                i2p::HandleI2NPMessage (msg.data);
            break;
            case eDeliveryTypeTunnel:
                i2p::transport::transports.SendMessage (msg.hash, i2p::CreateTunnelGatewayMsg (msg.tunnelID, msg.data));
            break;
            case eDeliveryTypeRouter:
                if (msg.hash == i2p::context.GetRouterInfo ().GetIdentHash ()) // check if message is sent to us
                    i2p::HandleI2NPMessage (msg.data);
                else
                {   
                    // to somebody else
                    if (!m_IsInbound) // outbound transit tunnel
                    {
                    /*  auto typeID = msg.data->GetTypeID ();
                        if (typeID == eI2NPDatabaseStore || typeID == eI2NPDatabaseSearchReply )
                            // catch RI or reply with new list of routers
                            i2p::data::netdb.PostI2NPMsg (msg.data);*/
                        i2p::transport::transports.SendMessage (msg.hash, msg.data);
                    }
                    else // we shouldn't send this message. possible leakage 
                        LogPrint (eLogError, "Message to another router arrived from an inbound tunnel. Dropped");
                }
            break;
            default:
                LogPrint (eLogError, "TunnelMessage: Unknown delivery type ", (int)msg.deliveryType);
        };  
    }   
}       
}