From 30528049f1d11ea2854a6431e8e8524f83206559 Mon Sep 17 00:00:00 2001
From: Roberto Ierusalimschy <roberto@inf.puc-rio.br>
Date: Mon, 12 Oct 2020 14:51:28 -0300
Subject: [PATCH] 'lua_upvalueid' returns NULL on invalid upvalue index

---
 .gitignore         |  3 +++
 lapi.c             | 19 +++++++++++++------
 ldblib.c           | 24 ++++++++++++++++--------
 testes/closure.lua |  2 +-
 4 files changed, 33 insertions(+), 15 deletions(-)

diff --git a/.gitignore b/.gitignore
index 735661ea..ae2899e0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,6 @@ testes/time.txt
 testes/time-debug.txt
 
 testes/libs/all
+
+temp
+lua
diff --git a/lapi.c b/lapi.c
index 9048245f..c824da27 100644
--- a/lapi.c
+++ b/lapi.c
@@ -1383,13 +1383,16 @@ LUA_API const char *lua_setupvalue (lua_State *L, int funcindex, int n) {
 
 
 static UpVal **getupvalref (lua_State *L, int fidx, int n, LClosure **pf) {
+  static const UpVal *const nullup = NULL;
   LClosure *f;
   TValue *fi = index2value(L, fidx);
   api_check(L, ttisLclosure(fi), "Lua function expected");
   f = clLvalue(fi);
-  api_check(L, (1 <= n && n <= f->p->sizeupvalues), "invalid upvalue index");
   if (pf) *pf = f;
-  return &f->upvals[n - 1];  /* get its upvalue pointer */
+  if (1 <= n && n <= f->p->sizeupvalues)
+    return &f->upvals[n - 1];  /* get its upvalue pointer */
+  else
+    return (UpVal**)&nullup;
 }
 
 
@@ -1401,11 +1404,14 @@ LUA_API void *lua_upvalueid (lua_State *L, int fidx, int n) {
     }
     case LUA_VCCL: {  /* C closure */
       CClosure *f = clCvalue(fi);
-      api_check(L, 1 <= n && n <= f->nupvalues, "invalid upvalue index");
-      return &f->upvalue[n - 1];
-    }
+      if (1 <= n && n <= f->nupvalues)
+        return &f->upvalue[n - 1];
+      /* else */
+    }  /* FALLTHROUGH */
+    case LUA_VLCF:
+      return NULL;  /* light C functions have no upvalues */
     default: {
-      api_check(L, 0, "closure expected");
+      api_check(L, 0, "function expected");
       return NULL;
     }
   }
@@ -1417,6 +1423,7 @@ LUA_API void lua_upvaluejoin (lua_State *L, int fidx1, int n1,
   LClosure *f1;
   UpVal **up1 = getupvalref(L, fidx1, n1, &f1);
   UpVal **up2 = getupvalref(L, fidx2, n2, NULL);
+  api_check(L, *up1 != NULL && *up2 != NULL, "invalid upvalue index");
   *up1 = *up2;
   luaC_objbarrier(L, f1, *up1);
 }
diff --git a/ldblib.c b/ldblib.c
index 26058b50..5a326ade 100644
--- a/ldblib.c
+++ b/ldblib.c
@@ -281,25 +281,33 @@ static int db_setupvalue (lua_State *L) {
 ** Check whether a given upvalue from a given closure exists and
 ** returns its index
 */
-static int checkupval (lua_State *L, int argf, int argnup) {
+static void *checkupval (lua_State *L, int argf, int argnup, int *pnup) {
+  void *id;
   int nup = (int)luaL_checkinteger(L, argnup);  /* upvalue index */
   luaL_checktype(L, argf, LUA_TFUNCTION);  /* closure */
-  luaL_argcheck(L, (lua_getupvalue(L, argf, nup) != NULL), argnup,
-                   "invalid upvalue index");
-  return nup;
+  id = lua_upvalueid(L, argf, nup);
+  if (pnup) {
+    luaL_argcheck(L, id != NULL, argnup, "invalid upvalue index");
+    *pnup = nup;
+  }
+  return id;
 }
 
 
 static int db_upvalueid (lua_State *L) {
-  int n = checkupval(L, 1, 2);
-  lua_pushlightuserdata(L, lua_upvalueid(L, 1, n));
+  void *id = checkupval(L, 1, 2, NULL);
+  if (id != NULL)
+    lua_pushlightuserdata(L, id);
+  else
+    luaL_pushfail(L);
   return 1;
 }
 
 
 static int db_upvaluejoin (lua_State *L) {
-  int n1 = checkupval(L, 1, 2);
-  int n2 = checkupval(L, 3, 4);
+  int n1, n2;
+  checkupval(L, 1, 2, &n1);
+  checkupval(L, 3, 4, &n2);
   luaL_argcheck(L, !lua_iscfunction(L, 1), 1, "Lua function expected");
   luaL_argcheck(L, !lua_iscfunction(L, 3), 3, "Lua function expected");
   lua_upvaluejoin(L, 1, n1, 3, n2);
diff --git a/testes/closure.lua b/testes/closure.lua
index cdeaebaa..c2453677 100644
--- a/testes/closure.lua
+++ b/testes/closure.lua
@@ -242,7 +242,7 @@ end
 
 assert(debug.upvalueid(foo1, 1))
 assert(debug.upvalueid(foo1, 2))
-assert(not pcall(debug.upvalueid, foo1, 3))
+assert(not debug.upvalueid(foo1, 3))
 assert(debug.upvalueid(foo1, 1) == debug.upvalueid(foo2, 2))
 assert(debug.upvalueid(foo1, 2) == debug.upvalueid(foo2, 1))
 assert(debug.upvalueid(foo3, 1))