properly sandbox policy loader global env

gateway/src/apicast/policy_loader.lua

@@ -14,13 +14,13 @@ local insert = table.insert
 local setmetatable = setmetatable
 local concat = table.concat
 
-local _M = { }
+local _G = _G
+local _M = {}
 
 local searchpath = package.searchpath
 local root_loaded = package.loaded
 
 local root_require = require
-local pcall = pcall
 
 local preload = package.preload
 
@@ -129,26 +129,83 @@ local function gen_require(package)
   end
 end
 
+local function export(list, env)
+  assert(env, 'missing env')
+  list:gsub('%S+', function(id)
+    local module, method = id:match('([^%.]+)%.([^%.]+)')
+    if module then
+      env[module]         = env[module] or {}
+      env[module][method] = _G[module][method]
+    else
+      env[id] = _G[id]
+    end
+  end)
+
+  return env
+end
+
 --- this is environment exposed to the policies
 -- that means this is very light sandbox so policies don't mutate global env
 -- and most importantly we replace the require function with our own
-_M.env = {
-  math = math,
-  table = table,
-  string = string,
-  jit = jit,
-  pcall = pcall,
-  getfenv = getfenv, assert = assert, tonumber = tonumber, xpcall = xpcall,
-  select = select, rawset = rawset,
-  io = io, os = os, print = print, type = type,
-  setmetatable = setmetatable,
-  getmetatable = getmetatable,
-  coroutine = coroutine,
-  ipairs = ipairs, pairs = pairs, next = next,
-  ngx = ngx,
-}
+-- The env intentionally does not expose getfenv so sandboxed code can't get top level globals.
+-- And also does not expose functions for loading code from filesystem (loadfile, dofile).
+-- Neither exposes debug functions unless openresty was compiled --with-debug.
+-- But it exposes ngx as the same object, so it can be changed from within the policy.
+_M.env = export([[
+ _VERSION assert print xpcall pcall error
+ unpack next ipairs pairs select
+ collectgarbage gcinfo newproxy loadstring load
+ setmetatable getmetatable
+ tonumber tostring type
+ rawget rawequal rawlen rawset
+
+ bit.arshift bit.band bit.bnot bit.bor bit.bswap bit.bxor
+ bit.lshift bit.rol bit.ror bit.rshift bit.tobit bit.tohex
+
+ coroutine.create coroutine.resume coroutine.running coroutine.status
+ coroutine.wrap   coroutine.yield coroutine.isyieldable
+
+ debug.traceback
+
+ io.open io.close io.flush io.tmpfile io.type
+ io.input io.output io.stderr io.stdin io.stdout
+ io.popen io.read io.lines io.write
+
+ math.abs math.acos math.asin math.atan math.atan2
+ math.ceil math.cos math.cosh math.deg math.exp math.floor
+ math.fmod math.frexp math.ldexp math.log math.pi
+ math.log10 math.max math.min math.modf math.pow
+ math.rad math.random math.randomseed math.huge
+ math.sin math.sinh math.sqrt math.tan math.tanh
+
+ os.clock os.date os.time os.difftime
+ os.execute os.getenv
+ os.rename os.tmpname os.remove
+
+ string.byte string.char string.dump string.find
+ string.format string.lower string.upper string.len
+ string.gmatch string.match string.gsub string.sub
+ string.rep string.reverse
+
+ table.concat table.foreach table.foreachi table.getn
+ table.insert table.maxn table.move table.pack
+ table.remove table.sort table.unpack
+
+ ngx
+]], {})
+
 _M.env._G = _M.env
 
+-- add debug functions only when nginx was compiled --with-debug
+if ngx.config.debug then
+  _M.env = export([[ debug.debug debug.getfenv debug.gethook debug.getinfo
+      debug.getlocal debug.getmetatable debug.getregistry
+      debug.getupvalue debug.getuservalue debug.setfenv
+      debug.sethook debug.setlocal debug.setmetatable
+      debug.setupvalue debug.setuservalue debug.upvalueid debug.upvaluejoin
+  ]], _M.env)
+end
+
 local mt = {
   __call = function(loader, ...) return loader.env.require(...) end
 }