Re: [Bug Report] Use after free in debug.upvaluejoin

[Philippe Verdy <verdy_p@...>]

Do you suggest...

Le jeu. 10 janv. 2019 à 14:49, fady osman <fady.mohamed.osman@gmail.com> a écrit :

Hi there,

I found a heap-user-after-free bug in lua-5.3.5.

The function `lua_upvaluejoin` in file lapi.c at line 1287 suffers from a use after free bug when supplied the same function for parameter f1 and f2 and the same upvalue index, additionally the bug happens only when the upvalue is closed, this happens because the `luaC_upvdeccount` function found in file lgc.c at line 678 will decrement the refcount and then free the upvalue if the refcount is zero and if the upvalue is closed.

--------------

LUA_API void lua_upvaluejoin (lua_State *L, int fidx1, int n1,

                                            int fidx2, int n2) {

  LClosure *f1;

  UpVal **up1 = getupvalref(L, fidx1, n1, &f1);

  UpVal **up2 = getupvalref(L, fidx2, n2, NULL);

 

... moving this line:

  luaC_upvdeccount(L, *up1);      //Will delete up1

... below this: 

  *up1 = *up2;     //up1 is up2 because it's the same upvalue and now it's freed.

  (*up1)->refcount++;   //up1 is freed, yet it's used here.

  if (upisopen(*up1)) (*up1)->u.open.touched = 1; // yet it's also used here

  luaC_upvalbarrier(L, *up1); // used here also???

...i.e. here ?

}