--[[
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_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 function oletools_callback(err, data)

      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

        data = tostring(data)

        local ucl_parser = ucl.parser()
        local ok, ucl_err = ucl_parser:parse_string(tostring(data))
        if not ok then
          rspamd_logger.errx(task, "%s: error parsing json response: %s",
              rule.log_prefix, 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_av_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, '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 #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 result[2]['analysis'] == 'null' and #result[2]['macros'] == 0 then
          common.save_av_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 == 'IOCs' 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_av_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_av_cache(task, digest, rule, analysis_keyword_table, rule.default_score)
          else
            common.save_av_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

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

local function oletools_config(opts)

  local oletools_conf = {
    name = N,
    scan_mime_parts = false,
    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
    symbol = "OLETOOLS",
    message = '${SCANNER}: Oletools threat message found: "${VIRUS}"',
    detection_category = "office macro",
    default_score = 1,
    action = false,
    extended = false,
  }

  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

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