bitmap-filter.cpp

 
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <map>
#include <memory>
#include <mutex>
 
#include <freerdp/server/proxy/proxy_modules_api.h>
#include <freerdp/server/proxy/proxy_context.h>
 
#include <freerdp/channels/drdynvc.h>
#include <freerdp/channels/rdpgfx.h>
#include <freerdp/utils/gfx.h>
 
#define TAG MODULE_TAG("persist-bitmap-filter")
 
// #define REPLY_WITH_EMPTY_OFFER
 
static constexpr char plugin_name[] = "bitmap-filter";
static constexpr char plugin_desc[] =
    "this plugin deactivates and filters persistent bitmap cache.";
 
static const std::vector<std::string>& plugin_static_intercept()
{
  static std::vector<std::string> vec;
  if (vec.empty())
    vec.emplace_back(DRDYNVC_SVC_CHANNEL_NAME);
  return vec;
}
 
static const std::vector<std::string>& plugin_dyn_intercept()
{
  static std::vector<std::string> vec;
  if (vec.empty())
    vec.emplace_back(RDPGFX_DVC_CHANNEL_NAME);
  return vec;
}
 
class DynChannelState
{
 
  public:
  [[nodiscard]] bool skip() const
  {
    return _toSkip != 0;
  }
 
  [[nodiscard]] bool skip(size_t s)
  {
    if (s > _toSkip)
      _toSkip = 0;
    else
      _toSkip -= s;
    return skip();
  }
 
  [[nodiscard]] size_t remaining() const
  {
    return _toSkip;
  }
 
  [[nodiscard]] size_t total() const
  {
    return _totalSkipSize;
  }
 
  void setSkipSize(size_t len)
  {
    _toSkip = _totalSkipSize = len;
  }
 
  [[nodiscard]] bool drop() const
  {
    return _drop;
  }
 
  void setDrop(bool d)
  {
    _drop = d;
  }
 
  [[nodiscard]] uint32_t channelId() const
  {
    return _channelId;
  }
 
  void setChannelId(uint32_t id)
  {
    _channelId = id;
  }
 
  private:
  size_t _toSkip = 0;
  size_t _totalSkipSize = 0;
  bool _drop = false;
  uint32_t _channelId = 0;
};
 
static BOOL filter_client_pre_connect([[maybe_unused]] proxyPlugin* plugin,
                                      [[maybe_unused]] proxyData* pdata,
                                      [[maybe_unused]] void* custom)
{
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
  WINPR_ASSERT(pdata->pc);
  WINPR_ASSERT(custom);
 
  auto settings = pdata->pc->context.settings;
 
  /* We do not want persistent bitmap cache to be used with proxy */
  return freerdp_settings_set_bool(settings, FreeRDP_BitmapCachePersistEnabled, FALSE);
}
 
static BOOL filter_dyn_channel_intercept_list([[maybe_unused]] proxyPlugin* plugin,
                                              [[maybe_unused]] proxyData* pdata,
                                              [[maybe_unused]] void* arg)
{
  auto data = static_cast<proxyChannelToInterceptData*>(arg);
 
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
  WINPR_ASSERT(data);
 
  auto intercept = std::find(plugin_dyn_intercept().begin(), plugin_dyn_intercept().end(),
                             data->name) != plugin_dyn_intercept().end();
  if (intercept)
    data->intercept = TRUE;
  return TRUE;
}
 
static BOOL filter_static_channel_intercept_list([[maybe_unused]] proxyPlugin* plugin,
                                                 [[maybe_unused]] proxyData* pdata,
                                                 [[maybe_unused]] void* arg)
{
  auto data = static_cast<proxyChannelToInterceptData*>(arg);
 
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
  WINPR_ASSERT(data);
 
  auto intercept = std::find(plugin_static_intercept().begin(), plugin_static_intercept().end(),
                             data->name) != plugin_static_intercept().end();
  if (intercept)
    data->intercept = TRUE;
  return TRUE;
}
 
static size_t drdynvc_cblen_to_bytes(UINT8 cbLen)
{
  switch (cbLen)
  {
    case 0:
      return 1;
 
    case 1:
      return 2;
 
    default:
      return 4;
  }
}
 
static UINT32 drdynvc_read_variable_uint(wStream* s, UINT8 cbLen)
{
  UINT32 val = 0;
 
  switch (cbLen)
  {
    case 0:
      Stream_Read_UINT8(s, val);
      break;
 
    case 1:
      Stream_Read_UINT16(s, val);
      break;
 
    default:
      Stream_Read_UINT32(s, val);
      break;
  }
 
  return val;
}
 
static BOOL drdynvc_try_read_header(wStream* s, uint32_t& channelId, size_t& length)
{
  UINT8 value = 0;
  Stream_SetPosition(s, 0);
  if (Stream_GetRemainingLength(s) < 1)
    return FALSE;
  Stream_Read_UINT8(s, value);
 
  const UINT8 cmd = (value & 0xf0) >> 4;
  const UINT8 Sp = (value & 0x0c) >> 2;
  const UINT8 cbChId = (value & 0x03);
 
  switch (cmd)
  {
    case DATA_PDU:
    case DATA_FIRST_PDU:
      break;
    default:
      return FALSE;
  }
 
  const size_t channelIdLen = drdynvc_cblen_to_bytes(cbChId);
  if (Stream_GetRemainingLength(s) < channelIdLen)
    return FALSE;
 
  channelId = drdynvc_read_variable_uint(s, cbChId);
  length = Stream_Length(s);
  if (cmd == DATA_FIRST_PDU)
  {
    const size_t dataLen = drdynvc_cblen_to_bytes(Sp);
    if (Stream_GetRemainingLength(s) < dataLen)
      return FALSE;
 
    length = drdynvc_read_variable_uint(s, Sp);
  }
 
  return TRUE;
}
 
static DynChannelState* filter_get_plugin_data(proxyPlugin* plugin, proxyData* pdata)
{
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
 
  auto mgr = static_cast<proxyPluginsManager*>(plugin->custom);
  WINPR_ASSERT(mgr);
 
  WINPR_ASSERT(mgr->GetPluginData);
  return static_cast<DynChannelState*>(mgr->GetPluginData(mgr, plugin_name, pdata));
}
 
static BOOL filter_set_plugin_data(proxyPlugin* plugin, proxyData* pdata, DynChannelState* data)
{
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
 
  auto mgr = static_cast<proxyPluginsManager*>(plugin->custom);
  WINPR_ASSERT(mgr);
 
  WINPR_ASSERT(mgr->SetPluginData);
  return mgr->SetPluginData(mgr, plugin_name, pdata, data);
}
 
#if defined(REPLY_WITH_EMPTY_OFFER)
static UINT8 drdynvc_value_to_cblen(UINT32 value)
{
  if (value <= 0xFF)
    return 0;
  if (value <= 0xFFFF)
    return 1;
  return 2;
}
 
static BOOL drdynvc_write_variable_uint(wStream* s, UINT32 value, UINT8 cbLen)
{
  switch (cbLen)
  {
    case 0:
      Stream_Write_UINT8(s, static_cast<UINT8>(value));
      break;
 
    case 1:
      Stream_Write_UINT16(s, static_cast<UINT16>(value));
      break;
 
    default:
      Stream_Write_UINT32(s, value);
      break;
  }
 
  return TRUE;
}
 
static BOOL drdynvc_write_header(wStream* s, UINT32 channelId)
{
  const UINT8 cbChId = drdynvc_value_to_cblen(channelId);
  const UINT8 value = (DATA_PDU << 4) | cbChId;
  const size_t len = drdynvc_cblen_to_bytes(cbChId) + 1;
 
  if (!Stream_EnsureRemainingCapacity(s, len))
    return FALSE;
 
  Stream_Write_UINT8(s, value);
  return drdynvc_write_variable_uint(s, value, cbChId);
}
 
static BOOL filter_forward_empty_offer(const char* sessionID, proxyDynChannelInterceptData* data,
                                       size_t startPosition, UINT32 channelId)
{
  WINPR_ASSERT(data);
 
  Stream_SetPosition(data->data, startPosition);
  if (!drdynvc_write_header(data->data, channelId))
    return FALSE;
 
  if (!Stream_EnsureRemainingCapacity(data->data, sizeof(UINT16)))
    return FALSE;
  Stream_Write_UINT16(data->data, 0);
  Stream_SealLength(data->data);
 
  WLog_INFO(TAG, "[SessionID=%s][%s] forwarding empty %s", sessionID, plugin_name,
            rdpgfx_get_cmd_id_string(RDPGFX_CMDID_CACHEIMPORTOFFER));
  data->rewritten = TRUE;
  return TRUE;
}
#endif
 
static BOOL filter_dyn_channel_intercept(proxyPlugin* plugin, proxyData* pdata, void* arg)
{
  auto data = static_cast<proxyDynChannelInterceptData*>(arg);
 
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
  WINPR_ASSERT(data);
 
  data->result = PF_CHANNEL_RESULT_PASS;
  if (!data->isBackData &&
      (strncmp(data->name, RDPGFX_DVC_CHANNEL_NAME, ARRAYSIZE(RDPGFX_DVC_CHANNEL_NAME)) == 0))
  {
    auto state = filter_get_plugin_data(plugin, pdata);
    if (!state)
    {
      WLog_ERR(TAG, "[SessionID=%s][%s] missing custom data, aborting!", pdata->session_id,
               plugin_name);
      return FALSE;
    }
    const size_t inputDataLength = Stream_Length(data->data);
    UINT16 cmdId = RDPGFX_CMDID_UNUSED_0000;
 
    const auto pos = Stream_GetPosition(data->data);
    if (!state->skip())
    {
      if (data->first)
      {
        uint32_t channelId = 0;
        size_t length = 0;
        if (drdynvc_try_read_header(data->data, channelId, length))
        {
          if (Stream_GetRemainingLength(data->data) >= 2)
          {
            Stream_Read_UINT16(data->data, cmdId);
            state->setSkipSize(length);
            state->setDrop(false);
          }
        }
 
        switch (cmdId)
        {
          case RDPGFX_CMDID_CACHEIMPORTOFFER:
            state->setDrop(true);
            state->setChannelId(channelId);
            break;
          default:
            break;
        }
        Stream_SetPosition(data->data, pos);
      }
    }
 
    if (state->skip())
    {
      if (!state->skip(inputDataLength))
        return FALSE;
 
      if (state->drop())
      {
        WLog_WARN(TAG,
                  "[SessionID=%s][%s] dropping %s packet [total:%" PRIuz ", current:%" PRIuz
                  ", remaining: %" PRIuz "]",
                  pdata->session_id, plugin_name,
                  rdpgfx_get_cmd_id_string(RDPGFX_CMDID_CACHEIMPORTOFFER), state->total(),
                  inputDataLength, state->remaining());
        data->result = PF_CHANNEL_RESULT_DROP;
 
#if defined(REPLY_WITH_EMPTY_OFFER) // TODO: Sending this does screw up some windows RDP server
                                    // versions :/
        if (state->remaining() == 0)
        {
          if (!filter_forward_empty_offer(pdata->session_id, data, pos,
                                          state->channelId()))
            return FALSE;
        }
#endif
      }
    }
  }
 
  return TRUE;
}
 
static BOOL filter_server_session_started(proxyPlugin* plugin, proxyData* pdata, void* /*unused*/)
{
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
 
  auto state = filter_get_plugin_data(plugin, pdata);
  delete state;
 
  auto newstate = new DynChannelState();
  if (!filter_set_plugin_data(plugin, pdata, newstate))
  {
    delete newstate;
    return FALSE;
  }
 
  return TRUE;
}
 
static BOOL filter_server_session_end(proxyPlugin* plugin, proxyData* pdata, void* /*unused*/)
{
  WINPR_ASSERT(plugin);
  WINPR_ASSERT(pdata);
 
  auto state = filter_get_plugin_data(plugin, pdata);
  delete state;
  filter_set_plugin_data(plugin, pdata, nullptr);
  return TRUE;
}
 
#ifdef __cplusplus
extern "C"
{
#endif
  FREERDP_API BOOL proxy_module_entry_point(proxyPluginsManager* plugins_manager, void* userdata);
#ifdef __cplusplus
}
#endif
 
BOOL proxy_module_entry_point(proxyPluginsManager* plugins_manager, void* userdata)
{
  proxyPlugin plugin = {};
 
  plugin.name = plugin_name;
  plugin.description = plugin_desc;
 
  plugin.ServerSessionStarted = filter_server_session_started;
  plugin.ServerSessionEnd = filter_server_session_end;
 
  plugin.ClientPreConnect = filter_client_pre_connect;
 
  plugin.StaticChannelToIntercept = filter_static_channel_intercept_list;
  plugin.DynChannelToIntercept = filter_dyn_channel_intercept_list;
  plugin.DynChannelIntercept = filter_dyn_channel_intercept;
 
  plugin.custom = plugins_manager;
  if (!plugin.custom)
    return FALSE;
  plugin.userdata = userdata;
 
  return plugins_manager->RegisterPlugin(plugins_manager, &plugin);
}