[grilo-plugins] lua-factory: make grl and grl.lua read-only

[Bastien Nocera <hadess src gnome org>]

commit 3b61064b7b2284667d12015ac40c031e76abd43f
Author: Victor Toso <me victortoso com>
Date:   Mon Mar 21 16:47:44 2016 +0100

    lua-factory: make grl and grl.lua read-only
    
    By using the metamethod __new_index to trigger an error in case Lua
    source try to use it.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=763046

 src/lua-factory/grl-lua-library-operations.c |   13 ++++++++++++-
 src/lua-factory/grl-lua-library.c            |    2 ++
 2 files changed, 14 insertions(+), 1 deletions(-)
---
diff --git a/src/lua-factory/grl-lua-library-operations.c b/src/lua-factory/grl-lua-library-operations.c
index 47e256b..0fa6a9d 100644
--- a/src/lua-factory/grl-lua-library-operations.c
+++ b/src/lua-factory/grl-lua-library-operations.c
@@ -102,6 +102,17 @@ proxy_metatable_handle_call (lua_State *L)
   return 0;
 }
 
+/*
+ * proxy handler for __newindex metamethod
+ * This metamethod is called when updating a table with a new key/value.
+ */
+static int
+proxy_metatable_handle_newindex (lua_State *L)
+{
+  luaL_error (L, "Trying to change read-only table");
+  return 0;
+}
+
 /* ============== Private State helpers ==================================== */
 
 /*
@@ -626,7 +637,7 @@ grl_lua_operations_set_proxy_table (lua_State *L,
 
   /* __newindex: triggered when inserting new key/value to given table */
   lua_pushstring (L, "__newindex");
-  lua_pushvalue (L, index - 3);
+  lua_pushcfunction (L, proxy_metatable_handle_newindex);
   lua_settable (L, -3);
 
   /* __call: triggered when using the table as a function */
diff --git a/src/lua-factory/grl-lua-library.c b/src/lua-factory/grl-lua-library.c
index b5345af..1952f15 100644
--- a/src/lua-factory/grl-lua-library.c
+++ b/src/lua-factory/grl-lua-library.c
@@ -1653,6 +1653,7 @@ luaopen_grilo (lua_State *L)
   }
   lua_pop (L, 1);
 
+  /* grl.lua will be read-only from now on for Lua sources */
   grl_lua_operations_set_proxy_table (L, -1);
 
   /* Those modules are called in 'lua' table, inside 'grl' */
@@ -1660,6 +1661,7 @@ luaopen_grilo (lua_State *L)
 
   grl_lua_operations_init_priv_state (L);
 
+  /* grl will be read-only from now on for Lua sources */
   grl_lua_operations_set_proxy_table (L, -1);
 
   return 1;