Hacking Lua - Calling luaL_openlib to register additional functions

[Stefan Falk <falk.stefan@...>]

Hi!

[sorry if this email comes twice but I did not get the last one I sent 6 
hours ago]

I've managed to get control about what's happening as Lua is 
initializing it's baselib. What I do is I hook up in base_open (in 
lbaselib.c) and call one of my functions before base_open it returns.
This is what's happening if I translate my actions in plain C code:


static void base_open (lua_State *L) {
  lua_pushliteral(L, "_G");
  lua_pushvalue(L, LUA_GLOBALSINDEX);
  luaL_openlib(L, NULL, base_funcs, 0);  /* open lib into global table */
  // some more calls
  lua_rawset(L, -3);  /* set global `newproxy' */
  lua_rawset(L, -1);  /* set global _G */

  // The above lines are "original" as is in Lua 5.0.1; Here comes the 
hack:

  // Essentially what I do is stealing the pointer to L, run a function 
in a DLL
  // which I injected first and then use this pointer to call 
luaL_openlib again
  // but this time with extensions_funcs which is just a list of 
"name/address" pairs
  // terminated by {NULL,NULL} as requested which I want to be registered
  luaL_openlib(L, NULL, extension_funcs, 0);
}

I uploaded an image [1] to show you what this part in my DLL looks like.

The problem I am currently facing is that this is crashing in "markroot" 
saying:

Exception thrown: read access violation.
L->l_G->_defaultmeta.value.gc was nullptr.

If you look at the screenshot you see that the luaL_state object 
actually does look a bit strange which might suggest that I push the 
wrong pointer onto the stack for my "initialize" function, however, I've 
checked it multiple times and I am very certain that I am pushing the 
same address that for L that is getting pushed for the "original" calls 
as well.


I don't know if anybody can help me here. Looking at the values of L, 
can anybody tell me if this struct is looking "healthy"? To me it does 
not but I have no idea what I should expect.

An answer to my question could be, that I am actually not allowed to 
call luaL_openlib() at this point and that I might break stuff. If that 
is so: where should I call it?

Or maybe: Am I doing it wrong anyway? All I want to do is register new 
built-in functions for Lua - am I doing it right actually?

I really hope somebody can give some advice - thanks in advance!

[1] https://s24.postimg.org/dr837uead/Capture.png