Fixed bug in 'lua_upvaluejoin'

Bug-fix: joining an upvalue with itself could cause a use-after-free
crash.

bugs

@@ -2899,28 +2899,6 @@ patch = [[
 ]]
 }
 
-Bug{
-what = [[Lua does not check memory use when creating error messages]],
-report = [[John Dunn, 2012/09/24]],
-since = [[5.2.0]],
-fix = nil,
-example = [[
-local code = "function test()\n  bob.joe.larry = 23\n end"
-
-load(code)()
-
--- memory will grow steadly 
-for i = 1, math.huge do
-  pcall(test)
-  if i % 100000 == 0 then
-    io.write(collectgarbage'count'*1024, "\n")
-  end
-end
-]],
-patch = [[
-]]
-}
-
 
 
 
@@ -4020,7 +3998,6 @@ patch = [[
 -----------------------------------------------------------------
 -- Lua 5.3.5
 
---[=[
 Bug{
 what = [[Long brackets with a huge number of '=' overflow some
 internal buffer arithmetic]],
@@ -4111,9 +4088,34 @@ patch = [[
        }
 ]]
 }
-]=]
 
 
+Bug{
+what = [[joining an upvalue with itself can cause a use-after-free crash]],
+report = [[Fady Othman, 2019/01/10]],
+since = [[5.3]],
+fix = nil,
+example = [[
+-- the next code may crash the machine
+f=load(function() end)
+interesting={}
+interesting[0]=string.rep("A",512)
+debug.upvaluejoin(f,1,f,1)
+]],
+patch = [[
+--- a/lapi.c
++++ b/lapi.c
+@@ -1289,6 +1289,8 @@ 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);
++  if (*up1 == *up2)
++    return;
+   luaC_upvdeccount(L, *up1);
+   *up1 = *up2;
+   (*up1)->refcount++;
+]]
+}
 
 
 --[=[

lapi.c

@@ -1254,13 +1254,12 @@ 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 UpVal **getupvalref (lua_State *L, int fidx, int n) {
   LClosure *f;
   StkId fi = index2addr(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 */
 }
 
@@ -1269,7 +1268,7 @@ LUA_API void *lua_upvalueid (lua_State *L, int fidx, int n) {
   StkId fi = index2addr(L, fidx);
   switch (ttype(fi)) {
     case LUA_TLCL: {  /* lua closure */
-      return *getupvalref(L, fidx, n, NULL);
+      return *getupvalref(L, fidx, n);
     }
     case LUA_TCCL: {  /* C closure */
       CClosure *f = clCvalue(fi);
@@ -1286,9 +1285,10 @@ LUA_API void *lua_upvalueid (lua_State *L, int fidx, int n) {
 
 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);
+  UpVal **up1 = getupvalref(L, fidx1, n1);
+  UpVal **up2 = getupvalref(L, fidx2, n2);
+  if (*up1 == *up2)
+    return;
   luaC_upvdeccount(L, *up1);
   *up1 = *up2;
   (*up1)->refcount++;

makefile

@@ -58,9 +58,9 @@ MYLDFLAGS= $(LOCAL) -Wl,-E
 MYLIBS= -ldl -lreadline
 
 
-CC= clang-3.8
+CC= gcc
 CFLAGS= -Wall -O2 $(MYCFLAGS)
-AR= ar rcu
+AR= ar rc
 RANLIB= ranlib
 RM= rm -f