Kong serverless plugin Lua implementation

Question

I am attempting to use Kong's API Gateway, however, I want to use its serverless plugin to add some custom implementation before Kong processes the request. I basically want to read in a JSON file volume mapped in the Kong container and do some stuff with it before it processes the request.

When I follow their example I am able to see the logs printed. However, when I start adding Lua code (in custom-auth.lua) it seems to complain. A simple print("hello world") statement on the top of the file gives me the following error.

2021/02/05 02:00:19 [error] 22#0: *8042 [kong] init.lua:270 [pre-function] /usr/local/share/lua/5.1/sandbox.lua:170: [string "..."]:3: attempt to index global 'print' (a nil value), client: 172.31.0.1, server: kong, request: "GET /v1/myEndpoint HTTP/2.0", host: "localhost:8443"

Code reference to error:

170 if not t[1] then error(t[2]) end

sandbox.lua:

local sandbox = {
  _VERSION      = "sandbox 0.5",
  _DESCRIPTION  = "A pure-lua solution for running untrusted Lua code.",
  _URL          = "https://github.com/kikito/sandbox.lua",
  _LICENSE      = [[
    MIT LICENSE

    Copyright (c) 2021 Enrique García Cota

    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
  ]],

}

-- quotas don't work in LuaJIT since debug.sethook works differently there
local quota_supported = type(_G.jit) == "nil"
sandbox.quota_supported = quota_supported

-- PUC-Rio Lua 5.1 does not support deactivation of bytecode
local bytecode_blocked = _ENV or type(_G.jit) == "table"
sandbox.bytecode_blocked = bytecode_blocked

-- The base environment is merged with the given env option (or an empty table, if no env provided)
--
local BASE_ENV = {}

-- List of unsafe packages/functions:
--
-- * string.rep: can be used to allocate millions of bytes in 1 operation
-- * {set|get}metatable: can be used to modify the metatable of global objects (strings, integers)
-- * collectgarbage: can affect performance of other systems
-- * dofile: can access the server filesystem
-- * _G: It has access to everything. It can be mocked to other things though.
-- * load{file|string}: All unsafe because they can grant acces to global env
-- * raw{get|set|equal}: Potentially unsafe
-- * module|require|module: Can modify the host settings
-- * string.dump: Can display confidential server info (implementation of functions)
-- * math.randomseed: Can affect the host sytem
-- * io.*, os.*: Most stuff there is unsafe, see below for exceptions


-- Safe packages/functions below
([[

_VERSION assert error    ipairs   next pairs
pcall    select tonumber tostring type unpack xpcall

coroutine.create coroutine.resume coroutine.running coroutine.status
coroutine.wrap   coroutine.yield

math.abs   math.acos math.asin  math.atan math.atan2 math.ceil
math.cos   math.cosh math.deg   math.exp  math.fmod  math.floor
math.frexp math.huge math.ldexp math.log  math.log10 math.max
math.min   math.modf math.pi    math.pow  math.rad   math.random
math.sin   math.sinh math.sqrt  math.tan  math.tanh

os.clock os.difftime os.time

string.byte string.char  string.find  string.format string.gmatch
string.gsub string.len   string.lower string.match  string.reverse
string.sub  string.upper

table.insert table.maxn table.remove table.sort

]]):gsub('%S+', function(id)
  local module, method = id:match('([^%.]+)%.([^%.]+)')
  if module then
    BASE_ENV[module]         = BASE_ENV[module] or {}
    BASE_ENV[module][method] = _G[module][method]
  else
    BASE_ENV[id] = _G[id]
  end
end)

local function protect_module(module, module_name)
  return setmetatable({}, {
    __index = module,
    __newindex = function(_, attr_name, _)
      error('Can not modify ' .. module_name .. '.' .. attr_name .. '. Protected by the sandbox.')
    end
  })
end

('coroutine math os string table'):gsub('%S+', function(module_name)
  BASE_ENV[module_name] = protect_module(BASE_ENV[module_name], module_name)
end)

-- auxiliary functions/variables

local string_rep = string.rep

local function sethook(f, key, quota)
  if type(debug) ~= 'table' or type(debug.sethook) ~= 'function' then return end
  debug.sethook(f, key, quota)
end

local function cleanup()
  sethook()
  string.rep = string_rep -- luacheck: no global
end

-- Public interface: sandbox.protect
function sandbox.protect(code, options)
  options = options or {}

  local quota = false
  if options.quota and not quota_supported then
    error("options.quota is not supported on this environment (usually LuaJIT). Please unset options.quota")
  end
  if options.quota ~= false then
    quota = options.quota or 500000
  end

  assert(type(code) == 'string', "expected a string")

  local passed_env = options.env or {}
  local env = {}
  for k, v in pairs(BASE_ENV) do
    local pv = passed_env[k]
    if pv ~= nil then
      env[k] = pv
    else
      env[k] = v
    end
  end
  setmetatable(env, { __index = options.env })
  env._G = env

  local f
  if bytecode_blocked then
    f = assert(load(code, nil, 't', env))
  else
    f = assert(loadstring(code))
    setfenv(f, env)
  end

  return function(...)

    if quota and quota_supported then
      local timeout = function()
        cleanup()
        error('Quota exceeded: ' .. tostring(quota))
      end
      sethook(timeout, "", quota)
    end

    string.rep = nil -- luacheck: no global

    local t = table.pack(pcall(f, ...))

    cleanup()

    if not t[1] then error(t[2]) end

    return table.unpack(t, 2, t.n)
  end
end

-- Public interface: sandbox.run
function sandbox.run(code, options, ...)
  return sandbox.protect(code, options)(...)
end

-- make sandbox(f) == sandbox.protect(f)
setmetatable(sandbox, {__call = function(_,code,o) return sandbox.protect(code,o) end})

return sandbox

Any help would be appreciated.

question from:https://stackoverflow.com/questions/66056720/kong-serverless-plugin-lua-implementation

Answer 1

Figured it out, Kong defaults the Lua modules to sandbox but can be set when starting Kong as an environment variable KONG_UNTRUSTED_LUA: "on" or in the kong.conf to enable all modules.

untrusted_lua = on
                                 # Accepted values are:
                                 #
                                 # - `off`: disallow any loading of Lua functions
                                 #          from admin supplied sources (such as via the Admin API).
                                 #
                                 #          Note using the `off` option will render plugins such as
                                 #          Serverless Functions unusable.
                                 # - `sandbox`: allow loading of Lua functions from admin
                                 #              supplied sources, but use a sandbox when
                                 #              executing them. The sandboxed
                                 #              function will have restricted access
                                 #              to the global environment and only
                                 #              have access to standard Lua functions
                                 #              that will generally not cause harm to
                                 #              the Kong node.
                                 #
                                 #              In this mode, the `require` function inside
                                 #              the sandbox only allows loading external Lua
                                 #              modules that are explicitly listed in
                                 #              `untrusted_lua_sandbox_requires` below.
                                 #
                                 #              LuaJIT bytecode loading is disabled.
                                 #
                                 #              Warning: LuaJIT is not designed as a secure
                                 #              runtime for running malicious code, therefore,
                                 #              you should properly protect your Admin API endpoint
                                 #              even with sandboxing enabled. The sandbox only
                                 #              provides protection against trivial attackers or
                                 #              unintentional modification of the Kong global
                                 #              environment.
                                 # - `on`: allow loading of Lua functions from admin
                                 #         supplied sources and do not use a sandbox when
                                 #         executing them. Functions will have unrestricted
                                 #         access to global environment and able to load any
                                 #         Lua modules. This is similar to the behavior in Kong
                                 #         prior to 2.3.0.
                                 #
                                 #         LuaJIT bytecode loading is disabled.