From 906ff82cd82dd3f8946bfe43605d981d99391207 Mon Sep 17 00:00:00 2001
From: Reinder Feenstra <reinderfeenstra@gmail.com>
Date: Sat, 13 Nov 2021 00:39:45 +0100
Subject: [PATCH] lua: made built-in globals read only

---
 server/src/lua/error.hpp   |  4 ++-
 server/src/lua/sandbox.cpp | 69 +++++++++++++++++++++++++++++++++++---
 server/src/lua/sandbox.hpp |  2 ++
 3 files changed, 69 insertions(+), 6 deletions(-)

diff --git a/server/src/lua/error.hpp b/server/src/lua/error.hpp
index 17c12e7c..bb9268c6 100644
--- a/server/src/lua/error.hpp
+++ b/server/src/lua/error.hpp
@@ -42,7 +42,9 @@ namespace Lua {
 
 [[noreturn]] inline void errorExpectedNArgumentsGotN(lua_State* L, int expected, int got) { luaL_error(L, "expected %d arguments, got %d", expected, got); abort(); }
 
-[[noreturn]] inline void errorException(lua_State* L, const std::exception& e) { luaL_error(L, "exceptiop: %s", e.what()); abort(); }
+[[noreturn]] inline void errorException(lua_State* L, const std::exception& e) { luaL_error(L, "exception: %s", e.what()); abort(); }
+
+[[noreturn]] inline void errorGlobalNIsReadOnly(lua_State* L, const char* name) { luaL_error(L, "global %s is readonly", name); abort(); }
 
 [[noreturn]] inline void errorInternal(lua_State* L) { luaL_error(L, "internal error"); abort(); }
 
diff --git a/server/src/lua/sandbox.cpp b/server/src/lua/sandbox.cpp
index 0ddd0170..1d1d6716 100644
--- a/server/src/lua/sandbox.cpp
+++ b/server/src/lua/sandbox.cpp
@@ -26,6 +26,7 @@
 #include "method.hpp"
 #include "log.hpp"
 #include "class.hpp"
+#include "to.hpp"
 #include <version.hpp>
 #include <traintastic/utils/str.hpp>
 #include <traintastic/codename.hpp>
@@ -37,12 +38,38 @@
 #include "../set/worldstate.hpp"
 
 #define LUA_SANDBOX "_sandbox"
+#define LUA_SANDBOX_GLOBALS "_sandbox_globals"
 
 #define ADD_GLOBAL_TO_SANDBOX(x) \
   lua_pushliteral(L, x); \
   lua_getglobal(L, x); \
   lua_settable(L, -3);
 
+constexpr std::array<std::string_view, 17> readOnlyGlobals = {{
+  // Lua baselib:
+  "assert",
+  "type",
+  "pairs",
+  "ipairs",
+  "_G",
+  // Constants:
+  "VERSION",
+  "VERSION_MAJOR",
+  "VERSION_MINOR",
+  "VERSION_PATCH",
+  "CODENAME",
+  "LUA_VERSION",
+  // Objects:
+  "world",
+  "log",
+  // Functions:
+  "is_instance",
+  // Type info:
+  "class",
+  "enum",
+  "set",
+}};
+
 namespace Lua {
 
 void Sandbox::close(lua_State* L)
@@ -51,6 +78,29 @@ void Sandbox::close(lua_State* L)
   lua_close(L);
 }
 
+int Sandbox::__index(lua_State* L)
+{
+  lua_getglobal(L, LUA_SANDBOX_GLOBALS);
+  lua_replace(L, 1);
+
+  lua_rawget(L, 1);
+
+  return 1;
+}
+
+int Sandbox::__newindex(lua_State* L)
+{
+  if(std::find(readOnlyGlobals.begin(), readOnlyGlobals.end(), to<std::string_view>(L, 2)) != readOnlyGlobals.end())
+    errorGlobalNIsReadOnly(L, lua_tostring(L, 2));
+
+  lua_getglobal(L, LUA_SANDBOX_GLOBALS);
+  lua_replace(L, 1);
+
+  lua_rawset(L, 1);
+
+  return 0;
+}
+
 SandboxPtr Sandbox::create(Script& script)
 {
   lua_State* L = luaL_newstate();
@@ -74,6 +124,16 @@ SandboxPtr Sandbox::create(Script& script)
 
   // setup sandbox:
   lua_newtable(L);
+  luaL_newmetatable(L, LUA_SANDBOX);
+  lua_pushcfunction(L, __index);
+  lua_setfield(L, -2, "__index");
+  lua_pushcfunction(L, __newindex);
+  lua_setfield(L, -2, "__newindex");
+  lua_setmetatable(L, -2);
+  lua_setglobal(L, LUA_SANDBOX);
+
+  // setup globals:
+  lua_newtable(L);
 
   // add some Lua baselib functions to the sandbox:
   ADD_GLOBAL_TO_SANDBOX("assert")
@@ -133,12 +193,11 @@ SandboxPtr Sandbox::create(Script& script)
   ReadOnlyTable::wrap(L, -1);
   lua_setfield(L, -2, "set");
 
-  // let global _G point to itself:
-  lua_pushliteral(L, "_G");
-  lua_pushvalue(L, -2);
-  lua_settable(L, -3);
+  // let global _G point to the sandbox:
+  lua_getglobal(L, LUA_SANDBOX);
+  lua_setfield(L, -2, "_G");
 
-  lua_setglobal(L, LUA_SANDBOX);
+  lua_setglobal(L, LUA_SANDBOX_GLOBALS);
 
   return SandboxPtr(L, close);
 }
diff --git a/server/src/lua/sandbox.hpp b/server/src/lua/sandbox.hpp
index 4155222d..13e6ee56 100644
--- a/server/src/lua/sandbox.hpp
+++ b/server/src/lua/sandbox.hpp
@@ -36,6 +36,8 @@ class Sandbox
 {
   private:
     static void close(lua_State* L);
+    static int __index(lua_State* L);
+    static int __newindex(lua_State* L);
 
   public:
     class StateData