tls_session.h

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// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the Apache 2.0 License.
#pragma once
 
#include "ds/internal_logger.h"
#include "ds/messaging.h"
#include "ds/ring_buffer.h"
#include "tcp/msg_types.h"
#include "tls/context.h"
#include "tls/tls.h"
 
#include <exception>
 
namespace ccf
{
  enum SessionStatus : uint8_t
  {
    handshake,
    ready,
    closing,
    closed,
    authfail,
    error
  };
 
  class TLSSession : public std::enable_shared_from_this<TLSSession>
  {
  public:
    using HandshakeErrorCB = std::function<void(std::string&&)>;
 
  protected:
    ringbuffer::WriterPtr to_host;
    ::tcp::ConnID session_id;
 
  private:
    std::vector<uint8_t> pending_write;
    std::vector<uint8_t> pending_read;
    // Decrypted data
    std::vector<uint8_t> read_buffer;
 
    std::unique_ptr<tls::Context> ctx;
    SessionStatus status = handshake;
 
    HandshakeErrorCB handshake_error_cb;
 
    bool can_send()
    {
      // Closing endpoint should still be able to respond to clients (e.g. to
      // report errors)
      return status == ready || status == closing;
    }
 
    bool can_recv()
    {
      return status == ready || status == handshake;
    }
 
  public:
    TLSSession(
      int64_t session_id_,
      ringbuffer::AbstractWriterFactory& writer_factory_,
      std::unique_ptr<tls::Context> ctx_) :
      to_host(writer_factory_.create_writer_to_outside()),
      session_id(session_id_),
      ctx(std::move(ctx_))
    {
      ctx->set_bio(this, send_callback_openssl, recv_callback_openssl);
    }
 
    virtual ~TLSSession()
    {
      RINGBUFFER_WRITE_MESSAGE(::tcp::tcp_closed, to_host, session_id);
    }
 
    SessionStatus get_status() const
    {
      return status;
    }
 
    void on_handshake_error(std::string&& error_msg)
    {
      if (handshake_error_cb)
      {
        handshake_error_cb(std::move(error_msg));
      }
      else
      {
        LOG_TRACE_FMT("{}", error_msg);
      }
    }
 
    void set_handshake_error_cb(HandshakeErrorCB&& cb)
    {
      handshake_error_cb = std::move(cb);
    }
 
    std::string hostname()
    {
      if (status != ready)
      {
        return {};
      }
 
      return ctx->host();
    }
 
    std::vector<uint8_t> peer_cert()
    {
      return ctx->peer_cert();
    }
 
    // Returns count N of bytes read, which will be the first N bytes of data,
    // up to a maximum of size. If exact is true, will only return either size
    // or 0 (when size bytes are not currently available). data may be accessed
    // beyond N during operation, up to size, but only the first N should be
    // used by caller.
    size_t read(uint8_t* data, size_t size, bool exact = false)
    {
      // This will return empty if the connection isn't
      // ready, but it will not block on the handshake.
      do_handshake();
 
      if (status != ready)
      {
        LOG_TRACE_FMT("Not ready to read {} bytes", size);
        return 0;
      }
 
      LOG_TRACE_FMT("Requesting up to {} bytes", size);
 
      // Send pending writes.
      flush();
 
      size_t offset = 0;
 
      if (!read_buffer.empty())
      {
        LOG_TRACE_FMT(
          "Have existing read_buffer of size: {}", read_buffer.size());
        offset = std::min(size, read_buffer.size());
        ::memcpy(data, read_buffer.data(), offset);
 
        if (offset < read_buffer.size())
        {
          read_buffer.erase(read_buffer.begin(), read_buffer.begin() + offset);
        }
        else
        {
          read_buffer.clear();
        }
 
        if (offset == size)
        {
          return size;
        }
 
        // NB: If we continue past here, read_buffer is empty
      }
 
      auto r = ctx->read(data + offset, size - offset);
      LOG_TRACE_FMT("ctx->read returned: {}", r);
 
      switch (r)
      {
        case 0:
        case TLS_ERR_CONN_CLOSE_NOTIFY:
        {
          LOG_TRACE_FMT(
            "TLS {} close on read: {}", session_id, ::tls::error_string(r));
 
          stop(closed);
 
          if (!exact)
          {
            // Hit an error, but may still have some useful data from the
            // previous read_buffer
            return offset;
          }
 
          return 0;
        }
 
        case TLS_ERR_WANT_READ:
        case TLS_ERR_WANT_WRITE:
        {
          if (!exact)
          {
            return offset;
          }
 
          // May have read something but not enough - copy it into read_buffer
          // for next call
          read_buffer.insert(read_buffer.end(), data, data + offset);
          return 0;
        }
 
        default:
        {
        }
      }
 
      if (r < 0)
      {
        LOG_TRACE_FMT(
          "TLS {} error on read: {}", session_id, ::tls::error_string(r));
        stop(error);
        return 0;
      }
 
      auto total = r + offset;
 
      // We read _some_ data but not enough, and didn't get
      // TLS_ERR_WANT_READ. Probably hit an internal size limit - try
      // again
      if (exact && (total < size))
      {
        LOG_TRACE_FMT(
          "Asked for exactly {}, received {}, retrying", size, total);
        read_buffer.insert(read_buffer.end(), data, data + total);
        return read(data, size, exact);
      }
 
      return total;
    }
 
    void recv_buffered(const uint8_t* data, size_t size)
    {
      if (can_recv())
      {
        pending_read.insert(pending_read.end(), data, data + size);
      }
 
      do_handshake();
    }
 
    void close()
    {
      status = closing;
 
      switch (status)
      {
        case handshake:
        {
          LOG_TRACE_FMT("TLS {} closed during handshake", session_id);
          stop(closed);
          break;
        }
 
        case ready:
        case closing:
        {
          int r = ctx->close();
 
          switch (r)
          {
            case TLS_ERR_WANT_READ:
            case TLS_ERR_WANT_WRITE:
            {
              LOG_TRACE_FMT("TLS {} has pending data ({})", session_id, r);
              // FALLTHROUGH
            }
            case 0:
            {
              LOG_TRACE_FMT("TLS {} closed ({})", session_id, r);
              stop(closed);
              break;
            }
 
            default:
            {
              LOG_TRACE_FMT(
                "TLS {} error on_close: {}",
                session_id,
                ::tls::error_string(r));
              stop(error);
              break;
            }
          }
          break;
        }
 
        case closed:
        case authfail:
        case error:
        {
          break;
        }
      }
    }
 
    void send_data(const uint8_t* data, size_t size)
    {
      // Writes as much of the data as possible. If the data cannot all
      // be written now, we store the remainder. We
      // will try to send pending writes again whenever write() is called.
      do_handshake();
 
      if (status == handshake)
      {
        pending_write.insert(pending_write.end(), data, data + size);
        return;
      }
 
      if (!can_send())
      {
        return;
      }
 
      pending_write.insert(pending_write.end(), data, data + size);
 
      flush();
    }
 
  private:
    void send_buffered(const std::vector<uint8_t>& data)
    {
      pending_write.insert(pending_write.end(), data.begin(), data.end());
    }
 
    void flush()
    {
      do_handshake();
 
      if (!can_send())
      {
        return;
      }
 
      while (!pending_write.empty())
      {
        auto r = write_some(pending_write);
 
        if (r > 0)
        {
          pending_write.erase(pending_write.begin(), pending_write.begin() + r);
        }
        else if (r == 0)
        {
          break;
        }
        else
        {
          LOG_TRACE_FMT("TLS session {} error on flush: {}", session_id, -r);
          stop(error);
          break;
        }
      }
    }
 
    void do_handshake()
    {
      // This should be called when additional data is written to the
      // input buffer, until the handshake is complete.
      if (status != handshake)
      {
        return;
      }
 
      auto rc = ctx->handshake();
 
      switch (rc)
      {
        case 0:
        {
          status = ready;
          break;
        }
 
        case TLS_ERR_WANT_READ:
        case TLS_ERR_WANT_WRITE:
          break;
 
        case TLS_ERR_NEED_CERT:
        {
          on_handshake_error(fmt::format(
            "TLS {} verify error on handshake: {}",
            session_id,
            ::tls::error_string(rc)));
          stop(authfail);
          break;
        }
 
        case TLS_ERR_CONN_CLOSE_NOTIFY:
        {
          LOG_TRACE_FMT(
            "TLS {} closed on handshake: {}",
            session_id,
            ::tls::error_string(rc));
          stop(closed);
          break;
        }
 
        case TLS_ERR_X509_VERIFY:
        {
          auto err = ctx->get_verify_error();
          on_handshake_error(fmt::format(
            "TLS {} invalid cert on handshake: {} [{}]",
            session_id,
            err,
            ::tls::error_string(rc)));
          stop(authfail);
          return;
        }
 
        default:
        {
          on_handshake_error(fmt::format(
            "TLS {} error on handshake: {}",
            session_id,
            ::tls::error_string(rc)));
          stop(error);
          break;
        }
      }
    }
 
    int write_some(const std::vector<uint8_t>& data)
    {
      auto r = ctx->write(data.data(), data.size());
 
      switch (r)
      {
        case TLS_ERR_WANT_READ:
        case TLS_ERR_WANT_WRITE:
          return 0;
 
        default:
          return r;
      }
    }
 
    void stop(SessionStatus status_)
    {
      switch (status)
      {
        case closed:
        case authfail:
        case error:
          return;
 
        case handshake:
        case ready:
        case closing:
        {
          break;
        }
      }
 
      status = status_;
 
      switch (status)
      {
        case handshake:
        case ready:
        {
          break;
        }
        case closing:
        case closed:
        {
          RINGBUFFER_WRITE_MESSAGE(
            ::tcp::tcp_stop,
            to_host,
            session_id,
            std::string("Session closed"));
          break;
        }
 
        case authfail:
        {
          RINGBUFFER_WRITE_MESSAGE(
            ::tcp::tcp_stop,
            to_host,
            session_id,
            std::string("Authentication failed"));
        }
        case error:
        {
          RINGBUFFER_WRITE_MESSAGE(
            ::tcp::tcp_stop, to_host, session_id, std::string("Error"));
          break;
        }
 
        default:
          throw std::logic_error(
            fmt::format("TLS {} unknown status: {}", session_id, status));
      }
    }
 
    int handle_send(const uint8_t* buf, size_t len)
    {
      // Either write all of the data or none of it.
      auto wrote = RINGBUFFER_TRY_WRITE_MESSAGE(
        ::tcp::tcp_outbound,
        to_host,
        session_id,
        serializer::ByteRange{buf, len});
 
      if (!wrote)
      {
        return TLS_WRITING;
      }
 
      return static_cast<int>(len);
    }
 
    int handle_recv(uint8_t* buf, size_t len)
    {
      if (!pending_read.empty())
      {
        // Use the pending data vector. This is populated when the host
        // writes a chunk larger than the size requested by the enclave.
        size_t rd = std::min(len, pending_read.size());
        ::memcpy(buf, pending_read.data(), rd);
 
        if (rd >= pending_read.size())
        {
          pending_read.clear();
        }
        else
        {
          pending_read.erase(pending_read.begin(), pending_read.begin() + rd);
        }
 
        return (int)rd;
      }
 
      return TLS_READING;
    }
 
    static int send_callback(void* ctx, const unsigned char* buf, size_t len)
    {
      return reinterpret_cast<TLSSession*>(ctx)->handle_send(buf, len);
    }
 
    static int recv_callback(void* ctx, unsigned char* buf, size_t len)
    {
      return reinterpret_cast<TLSSession*>(ctx)->handle_recv(buf, len);
    }
 
    // These callbacks below are complex, using the callbacks above and
    // manipulating OpenSSL's BIO objects accordingly. This is just so we can
    // emulate what MbedTLS used to do.
    // Now that we have removed it from the code, we can move the callbacks
    // above to handle BIOs directly and hopefully remove the complexity below.
    // This work will be carried out in #3429.
    static long send_callback_openssl(
      BIO* b,
      int oper,
      const char* argp,
      size_t len,
      int argi,
      long argl,
      int ret,
      size_t* processed)
    {
      // Unused arguments
      (void)argi;
      (void)argl;
      (void)argp;
 
      if (ret != 0 && len > 0 && oper == (BIO_CB_WRITE | BIO_CB_RETURN))
      {
        // Flush BIO so the "pipe doesn't clog", but we don't use the
        // data here, because 'argp' already has it.
        BIO_flush(b);
        size_t pending = BIO_pending(b);
        if (pending != 0)
        {
          BIO_reset(b);
        }
 
        // Pipe object
        void* ctx = BIO_get_callback_arg(b);
        int put =
          send_callback(ctx, reinterpret_cast<const uint8_t*>(argp), len);
 
        // WANTS_WRITE
        if (put == TLS_WRITING)
        {
          BIO_set_retry_write(b);
          LOG_TRACE_FMT("TLS Session::send_cb() : WANTS_WRITE");
          *processed = 0;
          return -1;
        }
 
        LOG_TRACE_FMT("TLS Session::send_cb() : Put {} bytes", put);
 
        // Update the number of bytes to external users
        *processed = put;
      }
 
      // Unless we detected an error, the return value is always the same as the
      // original operation.
      return ret;
    }
 
    static long recv_callback_openssl(
      BIO* b,
      int oper,
      const char* argp,
      size_t len,
      int argi,
      long argl,
      int ret,
      size_t* processed)
    {
      // Unused arguments
      (void)argi;
      (void)argl;
 
      if (ret == 1 && oper == (BIO_CB_CTRL | BIO_CB_RETURN))
      {
        // This callback may be fired at the end of large batches of TLS frames
        // on OpenSSL 3.x. Note that processed == nullptr in this case, hence
        // the early exit.
        return 0;
      }
 
      if (ret != 0 && (oper == (BIO_CB_READ | BIO_CB_RETURN)))
      {
        // Pipe object
        void* ctx = BIO_get_callback_arg(b);
        // NOLINTNEXTLINE(cppcoreguidelines-pro-type-const-cast)
        int got = recv_callback(
          ctx, reinterpret_cast<uint8_t*>(const_cast<char*>(argp)), len);
 
        // WANTS_READ
        if (got == TLS_READING)
        {
          BIO_set_retry_read(b);
          LOG_TRACE_FMT("TLS Session::recv_cb() : WANTS_READ");
          *processed = 0;
          return -1;
        }
 
        LOG_TRACE_FMT("TLS Session::recv_cb() : Got {} bytes of {}", got, len);
 
        // If got less than requested, return WANT_READ
        if ((size_t)got < len)
        {
          *processed = got;
          return 1;
        }
 
        // Write to the actual BIO so SSL can use it
        BIO_write_ex(b, argp, got, processed);
 
        // The buffer should be enough, we can't return WANT_WRITE here
        if ((size_t)got != *processed)
        {
          LOG_TRACE_FMT("TLS Session::recv_cb() : BIO error");
          *processed = got;
          return -1;
        }
 
        // If original return was -1 because it didn't find anything to read,
        // return 1 to say we actually read something. This is common when the
        // buffer is empty and needs an external read, so let's not log this.
        if (got > 0 && ret < 0)
        {
          return 1;
        }
      }
 
      // Unless we detected an error, the return value is always the same as the
      // original operation.
      return ret;
    }
  };
}