i2pd/SOCKS.cpp

#include <cstring>
#include <cassert>
#include <string>
#include <atomic>
#include "SOCKS.h"
#include "Identity.h"
#include "Streaming.h"
#include "Destination.h"
#include "ClientContext.h"
#include "I2PEndian.h"
#include "I2PTunnel.h"

namespace i2p
{
namespace proxy
{
    static const size_t socks_buffer_size = 8192;
    static const size_t max_socks_hostname_size = 255; // Limit for socks5 and bad idea to traverse

    struct SOCKSDnsAddress 
    {
        uint8_t size;
        char value[max_socks_hostname_size];
        void FromString (std::string str) 
        {
            size = str.length();
            if (str.length() > max_socks_hostname_size) size = max_socks_hostname_size;
            memcpy(value,str.c_str(),size);
        }
        std::string ToString() { return std::string(value, size); }
        void push_back (char c) { value[size++] = c; }
    };

    class SOCKSServer;
    class SOCKSHandler: public i2p::client::I2PServiceHandler, public std::enable_shared_from_this<SOCKSHandler> 
    {
        private:
            enum state 
            {
                GET_SOCKSV,
                GET_COMMAND,
                GET_PORT,
                GET_IPV4,
                GET4_IDENT,
                GET4A_HOST,
                GET5_AUTHNUM,
                GET5_AUTH,
                GET5_REQUESTV,
                GET5_GETRSV,
                GET5_GETADDRTYPE,
                GET5_IPV6,
                GET5_HOST_SIZE,
                GET5_HOST,
                DONE
            };
            enum authMethods 
            {
                AUTH_NONE = 0, //No authentication, skip to next step
                AUTH_GSSAPI = 1, //GSSAPI authentication
                AUTH_USERPASSWD = 2, //Username and password
                AUTH_UNACCEPTABLE = 0xff //No acceptable method found
            };
            enum addrTypes 
            {
                ADDR_IPV4 = 1, //IPv4 address (4 octets)
                ADDR_DNS = 3, // DNS name (up to 255 octets)
                ADDR_IPV6 = 4 //IPV6 address (16 octets)
            };
            enum errTypes 
            {
                SOCKS5_OK = 0, // No error for SOCKS5
                SOCKS5_GEN_FAIL = 1, // General server failure
                SOCKS5_RULE_DENIED = 2, // Connection disallowed by ruleset
                SOCKS5_NET_UNREACH = 3, // Network unreachable
                SOCKS5_HOST_UNREACH = 4, // Host unreachable
                SOCKS5_CONN_REFUSED = 5, // Connection refused by the peer
                SOCKS5_TTL_EXPIRED = 6, // TTL Expired
                SOCKS5_CMD_UNSUP = 7, // Command unsuported
                SOCKS5_ADDR_UNSUP = 8, // Address type unsuported
                SOCKS4_OK = 90, // No error for SOCKS4
                SOCKS4_FAIL = 91, // Failed establishing connecting or not allowed
                SOCKS4_IDENTD_MISSING = 92, // Couldn't connect to the identd server
                SOCKS4_IDENTD_DIFFER = 93 // The ID reported by the application and by identd differ
            };
            enum cmdTypes 
            {
                CMD_CONNECT = 1, // TCP Connect
                CMD_BIND = 2, // TCP Bind
                CMD_UDP = 3 // UDP associate
            };
            enum socksVersions 
            {
                SOCKS4 = 4, // SOCKS4
                SOCKS5 = 5 // SOCKS5
            };
            union address 
            {
                uint32_t ip;
                SOCKSDnsAddress dns;
                uint8_t ipv6[16];
            };

            void EnterState(state nstate, uint8_t parseleft = 1);
            bool HandleData(uint8_t *sock_buff, std::size_t len);
            bool ValidateSOCKSRequest();
            void HandleSockRecv(const boost::system::error_code & ecode, std::size_t bytes_transfered);
            void Terminate();
            void AsyncSockRead();
            boost::asio::const_buffers_1 GenerateSOCKS5SelectAuth(authMethods method);
            boost::asio::const_buffers_1 GenerateSOCKS4Response(errTypes error, uint32_t ip, uint16_t port);
            boost::asio::const_buffers_1 GenerateSOCKS5Response(errTypes error, addrTypes type, const address &addr, uint16_t port);
            bool Socks5ChooseAuth();
            void SocksRequestFailed(errTypes error);
            void SocksRequestSuccess();
            void SentSocksFailed(const boost::system::error_code & ecode);
            void SentSocksDone(const boost::system::error_code & ecode);
            void SentSocksResponse(const boost::system::error_code & ecode);
            void HandleStreamRequestComplete (std::shared_ptr<i2p::stream::Stream> stream);

            uint8_t m_sock_buff[socks_buffer_size];
            std::shared_ptr<boost::asio::ip::tcp::socket> m_sock;
            std::shared_ptr<i2p::stream::Stream> m_stream;
            uint8_t *m_remaining_data; //Data left to be sent
            uint8_t m_response[7+max_socks_hostname_size];
            address m_address; //Address
            std::size_t m_remaining_data_len; //Size of the data left to be sent
            uint32_t m_4aip; //Used in 4a requests
            uint16_t m_port;
            uint8_t m_command;
            uint8_t m_parseleft; //Octets left to parse
            authMethods m_authchosen; //Authentication chosen
            addrTypes m_addrtype; //Address type chosen
            socksVersions m_socksv; //Socks version
            cmdTypes m_cmd; // Command requested
            state m_state;

        public:
            SOCKSHandler(SOCKSServer * parent, std::shared_ptr<boost::asio::ip::tcp::socket> sock) :
                I2PServiceHandler(parent), m_sock(sock), m_stream(nullptr),
                m_authchosen(AUTH_UNACCEPTABLE), m_addrtype(ADDR_IPV4)
                { m_address.ip = 0; EnterState(GET_SOCKSV); }
            ~SOCKSHandler() { Terminate(); }
            void Handle() { AsyncSockRead(); }
    };

    void SOCKSHandler::AsyncSockRead()
    {
        LogPrint(eLogDebug,"--- SOCKS async sock read");
        if(m_sock)
            m_sock->async_receive(boost::asio::buffer(m_sock_buff, socks_buffer_size),
                        std::bind(&SOCKSHandler::HandleSockRecv, shared_from_this(),
                                std::placeholders::_1, std::placeholders::_2));
        else 
            LogPrint(eLogError,"--- SOCKS no socket for read");
    }

    void SOCKSHandler::Terminate() 
    {
        if (Kill()) return;
        if (m_sock) 
        {
            LogPrint(eLogDebug,"--- SOCKS close sock");
            m_sock->close();
            m_sock = nullptr;
        }
        if (m_stream) 
        {
            LogPrint(eLogDebug,"--- SOCKS close stream");
            m_stream.reset ();
        }
        Done(shared_from_this());
    }

    boost::asio::const_buffers_1 SOCKSHandler::GenerateSOCKS4Response(SOCKSHandler::errTypes error, uint32_t ip, uint16_t port)
    {
        assert(error >= SOCKS4_OK);
        m_response[0] = '\x00'; //Version
        m_response[1] = error; //Response code
        htobe16buf(m_response+2,port); //Port
        htobe32buf(m_response+4,ip); //IP
        return boost::asio::const_buffers_1(m_response,8);
    }

    boost::asio::const_buffers_1 SOCKSHandler::GenerateSOCKS5Response(SOCKSHandler::errTypes error, SOCKSHandler::addrTypes type, const SOCKSHandler::address &addr, uint16_t port)
    {
        size_t size = 6;
        assert(error <= SOCKS5_ADDR_UNSUP);
        m_response[0] = '\x05'; //Version
        m_response[1] = error; //Response code
        m_response[2] = '\x00'; //RSV
        m_response[3] = type; //Address type
        switch (type) 
        {
            case ADDR_IPV4:
                size = 10;
                htobe32buf(m_response+4,addr.ip);
                break;
            case ADDR_IPV6:
                size = 22;
                memcpy(m_response+4,addr.ipv6, 16);
                break;
            case ADDR_DNS:
                size = 7+addr.dns.size;
                m_response[4] = addr.dns.size;
                memcpy(m_response+5,addr.dns.value, addr.dns.size);
                break;
        }
        htobe16buf(m_response+size-2,port); //Port
        return boost::asio::const_buffers_1(m_response,size);
    }

    bool SOCKSHandler::Socks5ChooseAuth()
    {
        m_response[0] = '\x05'; //Version
        m_response[1] = m_authchosen; //Response code
        boost::asio::const_buffers_1 response(m_response,2);
        if (m_authchosen == AUTH_UNACCEPTABLE) 
        {
            LogPrint(eLogWarning,"--- SOCKS5 authentication negotiation failed");
            boost::asio::async_write(*m_sock, response, std::bind(&SOCKSHandler::SentSocksFailed,
                                          shared_from_this(), std::placeholders::_1));
            return false;
        } 
        else 
        {
            LogPrint(eLogDebug,"--- SOCKS5 choosing authentication method: ", m_authchosen);
            boost::asio::async_write(*m_sock, response, std::bind(&SOCKSHandler::SentSocksResponse,
                                          shared_from_this(), std::placeholders::_1));
            return true;
        }
    }

    /* All hope is lost beyond this point */
    void SOCKSHandler::SocksRequestFailed(SOCKSHandler::errTypes error)
    {
        boost::asio::const_buffers_1 response(nullptr,0);
        assert(error != SOCKS4_OK && error != SOCKS5_OK);
        switch (m_socksv) 
        {
            case SOCKS4:
                LogPrint(eLogWarning,"--- SOCKS4 failed: ", error);
                if (error < SOCKS4_OK) error = SOCKS4_FAIL; //Transparently map SOCKS5 errors
                response = GenerateSOCKS4Response(error, m_4aip, m_port);
            break;
            case SOCKS5:
                LogPrint(eLogWarning,"--- SOCKS5 failed: ", error);
                response = GenerateSOCKS5Response(error, m_addrtype, m_address, m_port);
            break;
        }
        boost::asio::async_write(*m_sock, response, std::bind(&SOCKSHandler::SentSocksFailed,
                                      shared_from_this(), std::placeholders::_1));
    }

    void SOCKSHandler::SocksRequestSuccess()
    {
        boost::asio::const_buffers_1 response(nullptr,0);
        //TODO: this should depend on things like the command type and callbacks may change
        switch (m_socksv) 
        {
            case SOCKS4:
                LogPrint(eLogInfo,"--- SOCKS4 connection success");
                response = GenerateSOCKS4Response(SOCKS4_OK, m_4aip, m_port);
            break;
            case SOCKS5:
                LogPrint(eLogInfo,"--- SOCKS5 connection success");
                auto s = i2p::client::context.GetAddressBook().ToAddress(GetOwner()->GetLocalDestination()->GetIdentHash());
                address ad; ad.dns.FromString(s);
                //HACK only 16 bits passed in port as SOCKS5 doesn't allow for more
                response = GenerateSOCKS5Response(SOCKS5_OK, ADDR_DNS, ad, m_stream->GetRecvStreamID());
            break;
        }
        boost::asio::async_write(*m_sock, response, std::bind(&SOCKSHandler::SentSocksDone,
                                      shared_from_this(), std::placeholders::_1));
    }

    void SOCKSHandler::EnterState(SOCKSHandler::state nstate, uint8_t parseleft) {
        switch (nstate) 
        {
            case GET_PORT: parseleft = 2; break;
            case GET_IPV4: m_addrtype = ADDR_IPV4; m_address.ip = 0; parseleft = 4; break;
            case GET4_IDENT: m_4aip = m_address.ip; break;
            case GET4A_HOST:
            case GET5_HOST: m_addrtype = ADDR_DNS; m_address.dns.size = 0; break;
            case GET5_IPV6: m_addrtype = ADDR_IPV6; parseleft = 16; break;
            default:;
        }
        m_parseleft = parseleft;
        m_state = nstate;
    }

    bool SOCKSHandler::ValidateSOCKSRequest() 
    {
        if ( m_cmd != CMD_CONNECT ) 
        {
            //TODO: we need to support binds and other shit!
            LogPrint(eLogError,"--- SOCKS unsupported command: ", m_cmd);
            SocksRequestFailed(SOCKS5_CMD_UNSUP);
            return false;
        }
        //TODO: we may want to support other address types!
        if ( m_addrtype != ADDR_DNS ) 
        {
            switch (m_socksv) 
            {
                case SOCKS5:
                    LogPrint(eLogError,"--- SOCKS5 unsupported address type: ", m_addrtype);
                break;
                case SOCKS4:
                    LogPrint(eLogError,"--- SOCKS4a rejected because it's actually SOCKS4");
                break;
            }
            SocksRequestFailed(SOCKS5_ADDR_UNSUP);
            return false;
        }
        //TODO: we may want to support other domains
        if(m_addrtype == ADDR_DNS && m_address.dns.ToString().find(".i2p") == std::string::npos) 
        {
            LogPrint(eLogError,"--- SOCKS invalid hostname: ", m_address.dns.ToString());
            SocksRequestFailed(SOCKS5_ADDR_UNSUP);
            return false;
        }
        return true;
    }

    bool SOCKSHandler::HandleData(uint8_t *sock_buff, std::size_t len)
    {
        assert(len); // This should always be called with a least a byte left to parse
        while (len > 0) 
        {
            switch (m_state) 
            {
                case GET_SOCKSV:
                    m_socksv = (SOCKSHandler::socksVersions) *sock_buff;
                    switch (*sock_buff) 
                    {
                        case SOCKS4:
                            EnterState(GET_COMMAND); //Initialize the parser at the right position
                        break;
                        case SOCKS5:
                            EnterState(GET5_AUTHNUM); //Initialize the parser at the right position
                        break;
                        default:
                            LogPrint(eLogError,"--- SOCKS rejected invalid version: ", ((int)*sock_buff));
                            Terminate();
                            return false;
                    }
                break;
                case GET5_AUTHNUM:
                    EnterState(GET5_AUTH, *sock_buff);
                break;
                case GET5_AUTH:
                    m_parseleft --;
                    if (*sock_buff == AUTH_NONE)
                        m_authchosen = AUTH_NONE;
                    if ( m_parseleft == 0 ) 
                    {
                        if (!Socks5ChooseAuth()) return false;
                        EnterState(GET5_REQUESTV);
                    }
                break;
                case GET_COMMAND:
                    switch (*sock_buff) 
                    {
                        case CMD_CONNECT:
                        case CMD_BIND:
                        break;
                        case CMD_UDP:
                            if (m_socksv == SOCKS5) break;
                        default:
                            LogPrint(eLogError,"--- SOCKS invalid command: ", ((int)*sock_buff));
                            SocksRequestFailed(SOCKS5_GEN_FAIL);
                            return false;
                    }
                    m_cmd = (SOCKSHandler::cmdTypes)*sock_buff;
                    switch (m_socksv) 
                    {
                        case SOCKS5: EnterState(GET5_GETRSV); break;
                        case SOCKS4: EnterState(GET_PORT); break;
                    }
                break;
                case GET_PORT:
                    m_port = (m_port << 8)|((uint16_t)*sock_buff);
                    m_parseleft--;
                    if (m_parseleft == 0) 
                    {
                        switch (m_socksv) 
                        {
                            case SOCKS5: EnterState(DONE); break;
                            case SOCKS4: EnterState(GET_IPV4); break;
                        }
                    }
                break;
                case GET_IPV4:
                    m_address.ip = (m_address.ip << 8)|((uint32_t)*sock_buff);
                    m_parseleft--;
                    if (m_parseleft == 0) 
                    {
                        switch (m_socksv) 
                        {
                            case SOCKS5: EnterState(GET_PORT); break;
                            case SOCKS4: EnterState(GET4_IDENT); m_4aip = m_address.ip; break;
                        }
                    }
                break;
                case GET4_IDENT:
                    if (!*sock_buff) 
                    {
                        if( m_4aip == 0 || m_4aip > 255 )
                            EnterState(DONE);
                        else
                            EnterState(GET4A_HOST);
                    }
                break;
                case GET4A_HOST:
                    if (!*sock_buff) 
                    {
                        EnterState(DONE);
                        break;
                    }
                    if (m_address.dns.size >= max_socks_hostname_size) 
                    {
                        LogPrint(eLogError,"--- SOCKS4a destination is too large");
                        SocksRequestFailed(SOCKS4_FAIL);
                        return false;
                    }
                    m_address.dns.push_back(*sock_buff);
                break;
                case GET5_REQUESTV:
                    if (*sock_buff != SOCKS5) 
                    {
                        LogPrint(eLogError,"--- SOCKS5 rejected unknown request version: ", ((int)*sock_buff));
                        SocksRequestFailed(SOCKS5_GEN_FAIL);
                        return false;
                    }
                    EnterState(GET_COMMAND);
                break;
                case GET5_GETRSV:
                    if ( *sock_buff != 0 ) 
                    {
                        LogPrint(eLogError,"--- SOCKS5 unknown reserved field: ", ((int)*sock_buff));
                        SocksRequestFailed(SOCKS5_GEN_FAIL);
                        return false;
                    }
                    EnterState(GET5_GETADDRTYPE);
                break;
                case GET5_GETADDRTYPE:
                    switch (*sock_buff) 
                    {
                        case ADDR_IPV4: EnterState(GET_IPV4); break;
                        case ADDR_IPV6: EnterState(GET5_IPV6); break;
                        case ADDR_DNS : EnterState(GET5_HOST_SIZE); break;
                        default:
                            LogPrint(eLogError,"--- SOCKS5 unknown address type: ", ((int)*sock_buff));
                            SocksRequestFailed(SOCKS5_GEN_FAIL);
                            return false;
                    }
                break;
                case GET5_IPV6:
                    m_address.ipv6[16-m_parseleft] = *sock_buff;
                    m_parseleft--;
                    if (m_parseleft == 0) EnterState(GET_PORT);
                break;
                case GET5_HOST_SIZE:
                    EnterState(GET5_HOST, *sock_buff);
                break;
                case GET5_HOST:
                    m_address.dns.push_back(*sock_buff);
                    m_parseleft--;
                    if (m_parseleft == 0) EnterState(GET_PORT);
                break;
                default:
                    LogPrint(eLogError,"--- SOCKS parse state?? ", m_state);
                    Terminate();
                    return false;
            }
            sock_buff++;
            len--;
            if (m_state == DONE) 
            {
                m_remaining_data_len = len;
                m_remaining_data = sock_buff;
                return ValidateSOCKSRequest();
            }
        }
        return true;
    }

    void SOCKSHandler::HandleSockRecv(const boost::system::error_code & ecode, std::size_t len)
    {
        LogPrint(eLogDebug,"--- SOCKS sock recv: ", len);
        if(ecode) 
        {
            LogPrint(eLogWarning," --- SOCKS sock recv got error: ", ecode);
            Terminate();
            return;
        }

        if (HandleData(m_sock_buff, len)) 
        {
            if (m_state == DONE) 
            {
                LogPrint(eLogInfo,"--- SOCKS requested ", m_address.dns.ToString(), ":" , m_port);
                GetOwner()->CreateStream ( std::bind (&SOCKSHandler::HandleStreamRequestComplete,
                        shared_from_this(), std::placeholders::_1), m_address.dns.ToString(), m_port);
            } 
            else
                AsyncSockRead();
        }
    }

    void SOCKSHandler::SentSocksFailed(const boost::system::error_code & ecode)
    {
        if (!ecode) 
            Terminate();
        else 
        {
            LogPrint (eLogError,"--- SOCKS Closing socket after sending failure because: ", ecode.message ());
            Terminate();
        }
    }

    void SOCKSHandler::SentSocksDone(const boost::system::error_code & ecode)
    {
        if (!ecode) 
        {
            if (Kill()) return;
            LogPrint (eLogInfo,"--- SOCKS New I2PTunnel connection");
            auto connection = std::make_shared<i2p::client::I2PTunnelConnection>(GetOwner(), m_sock, m_stream);
            GetOwner()->AddHandler (connection);
            connection->I2PConnect (m_remaining_data,m_remaining_data_len);
            Done(shared_from_this());
        }
        else
        {
            LogPrint (eLogError,"--- SOCKS Closing socket after completion reply because: ", ecode.message ());
            Terminate();
        }
    }

    void SOCKSHandler::SentSocksResponse(const boost::system::error_code & ecode)
    {
        if (ecode) 
        {
            LogPrint (eLogError,"--- SOCKS Closing socket after sending reply because: ", ecode.message ());
            Terminate();
        }
    }

    void SOCKSHandler::HandleStreamRequestComplete (std::shared_ptr<i2p::stream::Stream> stream)
    {
        if (stream) 
        {
            m_stream = stream;
            SocksRequestSuccess();
        } 
        else 
        {
            LogPrint (eLogError,"--- SOCKS Issue when creating the stream, check the previous warnings for more info.");
            SocksRequestFailed(SOCKS5_HOST_UNREACH);
        }
    }

    SOCKSServer::SOCKSServer(const std::string& address, int port, std::shared_ptr<i2p::client::ClientDestination> localDestination)
        : TCPIPAcceptor(
            address, port,
            localDestination ? localDestination : i2p::client::context.GetSharedLocalDestination()
        ) 
    {
    }
    
    std::shared_ptr<i2p::client::I2PServiceHandler> SOCKSServer::CreateHandler(std::shared_ptr<boost::asio::ip::tcp::socket> socket)
    {
        return std::make_shared<SOCKSHandler> (this, socket);
    }

}
}