--[[
Copyright (c) 2018, Vsevolod Stakhov <vsevolod@highsecure.ru>
Copyright (c) 2018, Carsten Rosenberg <c.rosenberg@heinlein-support.de>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
]]--

--[[[
-- @module oletools
-- This module contains oletools access functions.
-- Olefy is needed: https://github.com/HeinleinSupport/olefy
--]]

local lua_util = require "lua_util"
local tcp = require "rspamd_tcp"
local upstream_list = require "rspamd_upstream_list"
local rspamd_logger = require "rspamd_logger"
local ucl = require "ucl"
local common = require "lua_scanners/common"

local N = 'oletools'

local function oletools_config(opts)

  local oletools_conf = {
    name = N,
    scan_mime_parts = true,
    scan_text_mime = false,
    scan_image_mime = false,
    default_port = 10050,
    timeout = 15.0,
    log_clean = false,
    retransmits = 2,
    cache_expire = 86400, -- expire redis in 1d
    min_size = 500,
    symbol = "OLETOOLS",
    message = '${SCANNER}: Oletools threat message found: "${VIRUS}"',
    detection_category = "office macro",
    default_score = 1,
    action = false,
    extended = false,
    symbol_type = 'postfilter',
    dynamic_scan = true,
  }

  oletools_conf = lua_util.override_defaults(oletools_conf, opts)

  if not oletools_conf.prefix then
    oletools_conf.prefix = 'rs_' .. oletools_conf.name .. '_'
  end

  if not oletools_conf.log_prefix then
    if oletools_conf.name:lower() == oletools_conf.type:lower() then
      oletools_conf.log_prefix = oletools_conf.name
    else
      oletools_conf.log_prefix = oletools_conf.name .. ' (' .. oletools_conf.type .. ')'
    end
  end

  if not oletools_conf.servers then
    rspamd_logger.errx(rspamd_config, 'no servers defined')

    return nil
  end

  oletools_conf.upstreams = upstream_list.create(rspamd_config,
      oletools_conf.servers,
      oletools_conf.default_port)

  if oletools_conf.upstreams then
    lua_util.add_debug_alias('external_services', oletools_conf.name)
    return oletools_conf
  end

  rspamd_logger.errx(rspamd_config, 'cannot parse servers %s',
      oletools_conf.servers)
  return nil
end

local function oletools_check(task, content, digest, rule)
  local function oletools_check_uncached ()
    local upstream = rule.upstreams:get_upstream_round_robin()
    local addr = upstream:get_addr()
    local retransmits = rule.retransmits
    local protocol = 'OLEFY/1.0\nMethod: oletools\nRspamd-ID: ' .. task:get_uid() .. '\n\n'
    local json_response = ""

    local function oletools_callback(err, data, conn)

      local function oletools_requery(error)
        -- set current upstream to fail because an error occurred
        upstream:fail()

        -- retry with another upstream until retransmits exceeds
        if retransmits > 0 then

          retransmits = retransmits - 1

          lua_util.debugm(rule.name, task,
              '%s: Request Error: %s - retries left: %s',
              rule.log_prefix, error, retransmits)

          -- Select a different upstream!
          upstream = rule.upstreams:get_upstream_round_robin()
          addr = upstream:get_addr()

          lua_util.debugm(rule.name, task, '%s: retry IP: %s:%s',
              rule.log_prefix, addr, addr:get_port())

          tcp.request({
            task = task,
            host = addr:to_string(),
            port = addr:get_port(),
            timeout = rule.timeout,
            shutdown = true,
            data = { protocol, content },
            callback = oletools_callback,
          })
        else
          rspamd_logger.errx(task, '%s: failed to scan, maximum retransmits '..
              'exceed - err: %s', rule.log_prefix, error)
          common.yield_result(task, rule, 'failed to scan, maximum retransmits exceed - err: ' .. error, 0.0, 'fail')
        end
      end

      if err then

        oletools_requery(err)

      else
        -- Parse the response
        if upstream then upstream:ok() end

        json_response = json_response .. tostring(data)

	      if not string.find(json_response, '\t\n\n\t') and #data == 8192 then
          lua_util.debugm(rule.name, task, '%s: no stop word: add_read - #json: %s / current packet: %s',
            rule.log_prefix, #json_response, #data)
          conn:add_read(oletools_callback)
        else

          local ucl_parser = ucl.parser()
          local ok, ucl_err = ucl_parser:parse_string(tostring(json_response))
          if not ok then
            rspamd_logger.errx(task, "%s: error parsing json response, retry: %s",
                rule.log_prefix, ucl_err)
            oletools_requery(ucl_err)
            return
          end

          local result = ucl_parser:get_object()

          local oletools_rc = {
            [0] = 'RETURN_OK',
            [1] = 'RETURN_WARNINGS',
            [2] = 'RETURN_WRONG_ARGS',
            [3] = 'RETURN_FILE_NOT_FOUND',
            [4] = 'RETURN_XGLOB_ERR',
            [5] = 'RETURN_OPEN_ERROR',
            [6] = 'RETURN_PARSE_ERROR',
            [7] = 'RETURN_SEVERAL_ERRS',
            [8] = 'RETURN_UNEXPECTED',
            [9] = 'RETURN_ENCRYPTED',
          }

          if result[1].error ~= nil then
            rspamd_logger.errx(task, '%s: ERROR found: %s', rule.log_prefix,
                result[1].error)
            if result[1].error == 'File too small' then
              common.save_cache(task, digest, rule, 'OK')
              common.log_clean(task, rule, 'File too small to be scanned for macros')
            else
              oletools_requery(result[1].error)
            end
          elseif result[3]['return_code'] == 9 then
            rspamd_logger.warnx(task, '%s: File is encrypted.', rule.log_prefix)
            common.yield_result(task, rule, 'failed - err: ' .. oletools_rc[result[3]['return_code']], 0.0, 'encrypted')
            common.save_cache(task, digest, rule, 'encrypted')
          elseif result[3]['return_code'] == 5 then
            rspamd_logger.warnx(task, '%s: olefy could not open the file - error: %s', rule.log_prefix,
                result[2]['message'])
            common.yield_result(task, rule, 'failed - err: ' .. oletools_rc[result[3]['return_code']], 0.0, 'fail')
          elseif result[3]['return_code'] > 6 then
            rspamd_logger.errx(task, '%s: Error Returned: %s',
                rule.log_prefix, oletools_rc[result[3]['return_code']])
            rspamd_logger.errx(task, '%s: Error message: %s',
                rule.log_prefix, result[2]['message'])
            common.yield_result(task, rule, 'failed - err: ' .. oletools_rc[result[3]['return_code']], 0.0, 'fail')
          elseif result[3]['return_code'] > 1 then
            rspamd_logger.errx(task, '%s: Error message: %s',
                rule.log_prefix, result[2]['message'])
            oletools_requery(oletools_rc[result[3]['return_code']])
          elseif type(result[2]['analysis']) == 'table' and #result[2]['analysis'] == 0
              and #result[2]['macros'] == 0 then
            rspamd_logger.warnx(task, '%s: maybe unhandled python or oletools error', rule.log_prefix)
            common.yield_result(task, rule, 'oletools unhandled error', 0.0, 'fail')
          elseif type(result[2]['analysis']) ~= 'table' and #result[2]['macros'] == 0 then
            common.save_cache(task, digest, rule, 'OK')
            common.log_clean(task, rule, 'No macro found')
          elseif #result[2]['macros'] > 0 then
            -- M=Macros, A=Auto-executable, S=Suspicious keywords, I=IOCs,
            -- H=Hex strings, B=Base64 strings, D=Dridex strings, V=VBA strings
            local m_exist = 'M'
            local m_autoexec = '-'
            local m_suspicious = '-'
            local m_iocs = '-'
            local m_hex = '-'
            local m_base64 = '-'
            local m_dridex = '-'
            local m_vba = '-'

            lua_util.debugm(rule.name, task,
                '%s: filename: %s', rule.log_prefix, result[2]['file'])
            lua_util.debugm(rule.name, task,
                '%s: type: %s', rule.log_prefix, result[2]['type'])

            for _,m in ipairs(result[2]['macros']) do
              lua_util.debugm(rule.name, task, '%s: macros found - code: %s, ole_stream: %s, '..
                  'vba_filename: %s', rule.log_prefix, m.code, m.ole_stream, m.vba_filename)
            end

            local analysis_keyword_table = {}

            for _,a in ipairs(result[2]['analysis']) do
              lua_util.debugm(rule.name, task, '%s: threat found - type: %s, keyword: %s, '..
                  'description: %s', rule.log_prefix, a.type, a.keyword, a.description)
              if a.type == 'AutoExec' then
                m_autoexec = 'A'
                table.insert(analysis_keyword_table, a.keyword)
              elseif a.type == 'Suspicious' then
                if rule.extended == true or
                  (a.keyword ~= 'Base64 Strings' and a.keyword ~= 'Hex Strings')
                then
                  m_suspicious = 'S'
                  table.insert(analysis_keyword_table, a.keyword)
                end
              elseif a.type == 'IOC' then
                m_iocs = 'I'
              elseif a.type == 'Hex strings' then
                m_hex = 'H'
              elseif a.type == 'Base64 strings' then
                m_base64 = 'B'
              elseif a.type == 'Dridex strings' then
                m_dridex = 'D'
              elseif a.type == 'VBA strings' then
                m_vba = 'V'
              end
            end

            --lua_util.debugm(N, task, '%s: analysis_keyword_table: %s', rule.log_prefix, analysis_keyword_table)

            if rule.extended == false and m_autoexec == 'A' and m_suspicious == 'S' then
              -- use single string as virus name
              local threat = 'AutoExec + Suspicious (' .. table.concat(analysis_keyword_table, ',') .. ')'
              lua_util.debugm(rule.name, task, '%s: threat result: %s', rule.log_prefix, threat)
              common.yield_result(task, rule, threat, rule.default_score)
              common.save_cache(task, digest, rule, threat, rule.default_score)

            elseif rule.extended == true and #analysis_keyword_table > 0 then
              -- report any flags (types) and any most keywords as individual virus name

              local flags = m_exist ..
                  m_autoexec ..
                  m_suspicious ..
                  m_iocs ..
                  m_hex ..
                  m_base64 ..
                  m_dridex ..
                  m_vba
              table.insert(analysis_keyword_table, 1, flags)

              lua_util.debugm(rule.name, task, '%s: extended threat result: %s',
                  rule.log_prefix, table.concat(analysis_keyword_table, ','))

              common.yield_result(task, rule, analysis_keyword_table, rule.default_score)
              common.save_cache(task, digest, rule, analysis_keyword_table, rule.default_score)
            else
              common.save_cache(task, digest, rule, 'OK')
              common.log_clean(task, rule, 'Scanned Macro is OK')
            end

          else
            rspamd_logger.warnx(task, '%s: unhandled response', rule.log_prefix)
            common.yield_result(task, rule, 'unhandled error', 0.0, 'fail')
          end
        end
      end
    end

    tcp.request({
      task = task,
      host = addr:to_string(),
      port = addr:get_port(),
      timeout = rule.timeout,
      shutdown = true,
      data = { protocol, content },
      callback = oletools_callback,
    })

  end

  if common.condition_check_and_continue(task, content, rule, digest, oletools_check_uncached) then
    return
  else
    oletools_check_uncached()
  end

end

return {
  type = {N, 'attachment scanner', 'hash', 'scanner'},
  description = 'oletools office macro scanner',
  configure = oletools_config,
  check = oletools_check,
  name = N
}