Add a new Sandbox Lua module to the luaintf framework.

share/luaintf/modules/sandbox.lua

+--[==========================================================================[
+ sandbox.lua: Lua sandboxing facilities
+--[==========================================================================[
+ Copyright (C) 2007 the VideoLAN team
+ $Id$
+
+ Authors: Antoine Cellerier <dionoea at videolan dot org>
+
+ This program is free software; you can redistribute it and/or modify
+ it under the terms of the GNU General Public License as published by
+ the Free Software Foundation; either version 2 of the License, or
+ (at your option) any later version.
+
+ This program is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License
+ along with this program; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+--]==========================================================================]
+
+module("sandbox",package.seeall)
+
+-- See Programming in Lua (second edition) for sandbox examples
+-- See http://lua-users.org/wiki/SandBoxes for a list of SAFE/UNSAFE variables
+
+local sandbox_blacklist = {
+    collectgarbage = true,
+    dofile = true,
+    _G = true,
+    getfenv = true,
+    getmetatable = true,
+    load = true, -- Can be protected I guess
+    loadfile = true, -- Can be protected I guess
+    loadstring = true, -- Can be protected I guess
+    rawequal = true,
+    rawget = true,
+    rawset = true,
+    setfenv = true,
+    setmetatable = true,
+    module = true,
+    require = true,
+    package = true,
+    debug = true,
+}
+
+function readonly_table_proxy(name,src,blacklist)
+    if type(src)=="nil" then return end
+    if type(src)~="table" then error("2nd argument must be a table (or nil)") end
+    local name = name
+    local t = src
+    local blist = {}
+    if blacklist then
+        for _, v in pairs(blacklist) do
+            blist[v] = true
+        end
+    end
+    local metatable_readonly = {
+        __index = function(self,key)
+            if blist[key] then
+                error("Sandbox: Access to `"..name.."."..key.."' is forbidden.")
+            end
+            return t[key]
+        end,
+        __newindex = function(self,key,value)
+            error("It is forbidden to modify elements of this table.")
+        end,
+    }
+    return setmetatable({},metatable_readonly)
+end
+
+-- Of course, all of this is useless if the sandbox calling code has
+-- another reference to one of these tables in his global environement.
+local sandbox_proxy = {
+    coroutine   = readonly_table_proxy("coroutine",coroutine),
+    string      = readonly_table_proxy("string",string,{"dump"}),
+    table       = readonly_table_proxy("table",table),
+    math        = readonly_table_proxy("math",math),
+    io          = readonly_table_proxy("io",io),
+    os          = readonly_table_proxy("os",os,{"exit","getenv","remove",
+                                                "rename","setlocale"}),
+    sandbox     = readonly_table_proxy("sandbox",sandbox),
+}
+
+function sandbox(func,override)
+    local _G = getfenv(2)
+    local override = override or {}
+    local sandbox_metatable =
+    {
+        __index = function(self,key)
+            if override[key] then
+                return override[key]
+            end
+            if sandbox_blacklist[key] then
+                error( "Sandbox: Access to `"..key.."' is forbidden." )
+            end
+            --print(key,"not found in env. Looking in sandbox_proxy and _G")
+            local value = sandbox_proxy[key] or _G[key]
+            rawset(self,key,value) -- Keep a local copy
+            return value
+        end,
+        __newindex = function(self,key,value)
+            if override and override[key] then
+                error( "Sandbox: Variable `"..key.."' is read only." )
+            end
+            return rawset(self,key,value)
+        end,
+    }
+    local sandbox_env = setmetatable({},sandbox_metatable)
+    return function(...)
+        setfenv(func,sandbox_env)
+        local ret = {func(...)} -- Not perfect (if func returns nil before
+                                -- another return value) ... but it's better
+                                -- than nothing
+        setfenv(func,_G)
+        return unpack(ret)
+    end
+end
\ No newline at end of file