From 3c0d3c6fbeea18f257102c62a01b036c7a5c5161 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Fri, 19 Jul 2019 13:14:06 -0300
Subject: Avoid using addresses of static variables as unique keys

The addresses of static variables may be different for different
instances of Lua, making these instances incompatible if they use
these addresses as unique keys in the registry (or other tables).
---
 ldblib.c      | 18 ++++++++----------
 loadlib.c     | 11 +++++------
 testes/db.lua |  4 ++++
 3 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/ldblib.c b/ldblib.c
index 513a13cb..64158395 100644
--- a/ldblib.c
+++ b/ldblib.c
@@ -21,10 +21,10 @@
 
 
 /*
-** The hook table at registry[&HOOKKEY] maps threads to their current
-** hook function. (We only need the unique address of 'HOOKKEY'.)
+** The hook table at registry[HOOKKEY] maps threads to their current
+** hook function.
 */
-static const int HOOKKEY = 0;
+static const char* HOOKKEY = "_HOOKKEY";
 
 
 /*
@@ -314,7 +314,7 @@ static int db_upvaluejoin (lua_State *L) {
 static void hookf (lua_State *L, lua_Debug *ar) {
   static const char *const hooknames[] =
     {"call", "return", "line", "count", "tail call"};
-  lua_rawgetp(L, LUA_REGISTRYINDEX, &HOOKKEY);
+  lua_getfield(L, LUA_REGISTRYINDEX, HOOKKEY);
   lua_pushthread(L);
   if (lua_rawget(L, -2) == LUA_TFUNCTION) {  /* is there a hook function? */
     lua_pushstring(L, hooknames[(int)ar->event]);  /* push event name */
@@ -367,14 +367,12 @@ static int db_sethook (lua_State *L) {
     count = (int)luaL_optinteger(L, arg + 3, 0);
     func = hookf; mask = makemask(smask, count);
   }
-  if (lua_rawgetp(L, LUA_REGISTRYINDEX, &HOOKKEY) == LUA_TNIL) {
-    lua_createtable(L, 0, 2);  /* create a hook table */
-    lua_pushvalue(L, -1);
-    lua_rawsetp(L, LUA_REGISTRYINDEX, &HOOKKEY);  /* set it in position */
+  if (!luaL_getsubtable(L, LUA_REGISTRYINDEX, HOOKKEY)) {
+    /* table just created; initialize it */
     lua_pushstring(L, "k");
     lua_setfield(L, -2, "__mode");  /** hooktable.__mode = "k" */
     lua_pushvalue(L, -1);
-    lua_setmetatable(L, -2);  /* setmetatable(hooktable) = hooktable */
+    lua_setmetatable(L, -2);  /* metatable(hooktable) = hooktable */
   }
   checkstack(L, L1, 1);
   lua_pushthread(L1); lua_xmove(L1, L, 1);  /* key (thread) */
@@ -396,7 +394,7 @@ static int db_gethook (lua_State *L) {
   else if (hook != hookf)  /* external hook? */
     lua_pushliteral(L, "external hook");
   else {  /* hook table must exist */
-    lua_rawgetp(L, LUA_REGISTRYINDEX, &HOOKKEY);
+    lua_getfield(L, LUA_REGISTRYINDEX, HOOKKEY);
     checkstack(L, L1, 1);
     lua_pushthread(L1); lua_xmove(L1, L, 1);
     lua_rawget(L, -2);   /* 1st result = hooktable[L1] */
diff --git a/loadlib.c b/loadlib.c
index b72dd885..9ef00278 100644
--- a/loadlib.c
+++ b/loadlib.c
@@ -56,10 +56,10 @@
 
 
 /*
-** unique key for table in the registry that keeps handles
+** key for table in the registry that keeps handles
 ** for all loaded C libraries
 */
-static const int CLIBS = 0;
+static const char *CLIBS = "_CLIBS";
 
 #define LIB_FAIL	"open"
 
@@ -327,7 +327,7 @@ static void setpath (lua_State *L, const char *fieldname,
 */
 static void *checkclib (lua_State *L, const char *path) {
   void *plib;
-  lua_rawgetp(L, LUA_REGISTRYINDEX, &CLIBS);
+  lua_getfield(L, LUA_REGISTRYINDEX, CLIBS);
   lua_getfield(L, -1, path);
   plib = lua_touserdata(L, -1);  /* plib = CLIBS[path] */
   lua_pop(L, 2);  /* pop CLIBS table and 'plib' */
@@ -340,7 +340,7 @@ static void *checkclib (lua_State *L, const char *path) {
 ** registry.CLIBS[#CLIBS + 1] = plib  -- also keep a list of all libraries
 */
 static void addtoclib (lua_State *L, const char *path, void *plib) {
-  lua_rawgetp(L, LUA_REGISTRYINDEX, &CLIBS);
+  lua_getfield(L, LUA_REGISTRYINDEX, CLIBS);
   lua_pushlightuserdata(L, plib);
   lua_pushvalue(L, -1);
   lua_setfield(L, -3, path);  /* CLIBS[path] = plib */
@@ -716,12 +716,11 @@ static void createsearcherstable (lua_State *L) {
 ** setting a finalizer to close all libraries when closing state.
 */
 static void createclibstable (lua_State *L) {
-  lua_newtable(L);  /* create CLIBS table */
+  luaL_getsubtable(L, LUA_REGISTRYINDEX, CLIBS);  /* create CLIBS table */
   lua_createtable(L, 0, 1);  /* create metatable for CLIBS */
   lua_pushcfunction(L, gctm);
   lua_setfield(L, -2, "__gc");  /* set finalizer for CLIBS table */
   lua_setmetatable(L, -2);
-  lua_rawsetp(L, LUA_REGISTRYINDEX, &CLIBS);  /* set CLIBS table in registry */
 }
 
 
diff --git a/testes/db.lua b/testes/db.lua
index 3d94f776..a64a1130 100644
--- a/testes/db.lua
+++ b/testes/db.lua
@@ -255,6 +255,10 @@ do   -- test hook presence in debug info
 end
 
 
+-- hook table has weak keys
+assert(getmetatable(debug.getregistry()._HOOKKEY).__mode == 'k')
+
+
 a = {}; L = nil
 local glob = 1
 local oldglob = glob
-- 
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