[Tarantool-patches] [PATCH luajit 0/2][v2] Fix cdata finalizer table

[Tarantool-patches] [PATCH luajit 0/2][v2] Fix cdata finalizer table

[Sergey Bronnikov via Tarantool-patches]

From: Sergey Bronnikov <sergeyb@tarantool.org>

Branch:
https://github.com/tarantool/luajit/tree/ligurio/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer-nointegration
PR in Tarantool: https://github.com/tarantool/tarantool/pull/9796

NOTE: Jobs with Tarantool integration regression tests has failed
because patch "FFI: Turn FFI finalizer table into a proper GC root."
broke Tarantool build and fix (see below) must be applied before
a bump to LuaJIT version with proposed patches.

Mike Pall (2):
  FFI: Treat cdata finalizer table as a GC root.
  FFI: Turn FFI finalizer table into a proper GC root.

 src/lib_ffi.c                                 |  20 +--
 src/lj_cdata.c                                |   2 +-
 src/lj_ctype.c                                |  12 ++
 src/lj_ctype.h                                |   2 +-
 src/lj_gc.c                                   |  38 +++---
 src/lj_obj.h                                  |   3 +
 src/lj_state.c                                |   3 +
 .../lj-1168-unmarked-finalizer-tab.test.c     | 123 ++++++++++++++++++
 .../lj-1168-unmarked-finalizer-tab.test.lua   |  18 +++
 9 files changed, 180 insertions(+), 41 deletions(-)
 create mode 100644 test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
 create mode 100644 test/tarantool-tests/lj-1168-unmarked-finalizer-tab.test.lua

-- 
2.34.1

[Tarantool-patches] [PATCH luajit 1/2][v2] FFI: Treat cdata finalizer table as a GC root.

[Sergey Bronnikov via Tarantool-patches]

From: Mike Pall <mike>

Thanks to Sergey Bronnikov.

(cherry picked from commit dda1ac273ad946387088d91039a8ae319359903d)

The finalizers table is created on initialization of the `ffi`
module by calling the `ffi_finalizer()` routine in the
`luaopen_ffi()`. `ffi.gc()` is referenced by Lua stack via the
`ffi` library, and the finalizer table is anchored there as well.
If there is no FFI module table anywhere to anchor the `ffi.gc`
itself and the `lua_State` object is marked after the function
`ffi.gc` is removed from it (since we stop the GC before chunk
loading and start after), then the finalizer table isn't marked.
Hence, after the atomic phase, the table is considered dead and
collected. Since the table is collected, the usage of its nodes in
the `lj_gc_finalize_cdata()` leads to heap-use-after-free.

The patch fixes the problem partially by marking the finalizer
table on the start of the GC cycle. The complete fix will be
applied in the next patch by turning the finalizer table into
the proper GC root.

Sergey Bronnikov:
* added the description and the tests for the problem

Part of tarantool/tarantool#10199
---
 src/lj_gc.c                                   |  3 +
 .../lj-1168-unmarked-finalizer-tab.test.c     | 76 +++++++++++++++++++
 .../lj-1168-unmarked-finalizer-tab.test.lua   | 18 +++++
 3 files changed, 97 insertions(+)
 create mode 100644 test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
 create mode 100644 test/tarantool-tests/lj-1168-unmarked-finalizer-tab.test.lua

diff --git a/src/lj_gc.c b/src/lj_gc.c
index 591862b3..42348a34 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -99,6 +99,9 @@ static void gc_mark_start(global_State *g)
   gc_markobj(g, tabref(mainthread(g)->env));
   gc_marktv(g, &g->registrytv);
   gc_mark_gcroot(g);
+#if LJ_HASFFI
+  if (ctype_ctsG(g)) gc_markobj(g, ctype_ctsG(g)->finalizer);
+#endif
   g->gc.state = GCSpropagate;
 }
 
diff --git a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
new file mode 100644
index 00000000..d577b551
--- /dev/null
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -0,0 +1,76 @@
+#include "lua.h"
+#include "lauxlib.h"
+
+#include "test.h"
+
+#define UNUSED(x) ((void)(x))
+
+/*
+ * This test demonstrates LuaJIT's incorrect behaviour on
+ * loading Lua chunk with cdata numbers.
+ * See https://github.com/LuaJIT/LuaJIT/issues/1168 for details.
+ *
+ * The GC is driving forward during parsing of the Lua chunk
+ * (`test_chunk`). The chunk contains a single cdata object with
+ * a number. That leads to the opening of the FFI library
+ * on-demand during the parsing of this number. After the FFI
+ * library is open, `ffi.gc` has the finalizer table as its
+ * environment. But, there is no FFI module table anywhere to
+ * anchor the `ffi.gc` itself, and the `lua_State` object is
+ * marked after the function is removed from it. Hence, after the
+ * atomic phase, the table is considered dead and collected. Since
+ * the table is collected, the usage of its nodes in the
+ * `lj_gc_finalize_cdata` leads to heap-use-after-free.
+ */
+
+const char buff[] = "return 1LL";
+
+/*
+ * lua_close is a part of testcase, so testcase creates
+ * its own Lua state and closes it at the end.
+ */
+static int unmarked_finalizer_tab_gcstart(void *test_state)
+{
+	/* Shared Lua state is not needed. */
+	UNUSED(test_state);
+
+	/* Setup. */
+	lua_State *L = luaL_newstate();
+
+	/* Set GC at the start. */
+	lua_gc(L, LUA_GCCOLLECT, 0);
+
+	/* Not trigger GC during `lua_openffi()`. */
+	lua_gc(L, LUA_GCSTOP, 0);
+
+	/*
+	 * The terminating '\0' is considered by parser as part of
+	 * the input, so we must chomp it.
+	 */
+	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1,
+				   "test_chunk", "t");
+	if (res != LUA_OK) {
+		test_comment("error loading Lua chunk: %s",
+			     lua_tostring(L, -1));
+		bail_out("error loading Lua chunk");
+	}
+
+	/* Finish GC cycle to collect the finalizer table. */
+	while (!lua_gc(L, LUA_GCSTEP, -1));
+
+	/* Teardown. */
+	lua_settop(L, 0);
+	lua_close(L);
+
+	return TEST_EXIT_SUCCESS;
+}
+
+int main(void)
+{
+	const struct test_unit tgroup[] = {
+		test_unit_def(unmarked_finalizer_tab_gcstart),
+	};
+	const int test_result = test_run_group(tgroup, NULL);
+
+	return test_result;
+}
diff --git a/test/tarantool-tests/lj-1168-unmarked-finalizer-tab.test.lua b/test/tarantool-tests/lj-1168-unmarked-finalizer-tab.test.lua
new file mode 100644
index 00000000..4b49e9a1
--- /dev/null
+++ b/test/tarantool-tests/lj-1168-unmarked-finalizer-tab.test.lua
@@ -0,0 +1,18 @@
+local tap = require('tap')
+
+-- This test demonstrates LuaJIT's heap-use-after-free on
+-- cleaning of resources during shutdown. The test simulates
+-- "unloading" of the library, or removing some of its
+-- functionality and then calls `collectgarbage`.
+-- See https://github.com/LuaJIT/LuaJIT/issues/1168 for details.
+local test = tap.test('lj-1168-unmarked-finalizer-tab')
+test:plan(1)
+
+local ffi = require('ffi')
+
+ffi.gc = nil
+collectgarbage()
+
+test:ok(true, 'no heap use after free')
+
+test:done(true)
-- 
2.34.1

[Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Bronnikov via Tarantool-patches]

From: Mike Pall <mike>

Reported by Sergey Bronnikov.

(cherry picked from commit f5affaa6c4e7524e661484f22f24255f9a83eb47)

Previous patch fixes the problem partially because the introduced
GC root may not exist at the start phase of the GC cycle (since it
isn't marked because it is not accessible from any GC root).
In that case, the cdata finalizer table will be collected at the
end of the cycle. Access to the cdata finalizer table exhibits
heap use after free. The patch turns the finalizer table into
a proper GC root. Note, that finalizer table is created on the
initialization of the main Lua State instead of loading the FFI
library.

Sergey Bronnikov:
* added the description and the tests for the problem

Part of tarantool/tarantool#10199
---
 src/lib_ffi.c                                 | 20 +-------
 src/lj_cdata.c                                |  2 +-
 src/lj_ctype.c                                | 12 +++++
 src/lj_ctype.h                                |  2 +-
 src/lj_gc.c                                   | 41 +++++++---------
 src/lj_obj.h                                  |  3 ++
 src/lj_state.c                                |  3 ++
 .../lj-1168-unmarked-finalizer-tab.test.c     | 47 +++++++++++++++++++
 8 files changed, 86 insertions(+), 44 deletions(-)

diff --git a/src/lib_ffi.c b/src/lib_ffi.c
index 7ed6fc78..3c8dd77f 100644
--- a/src/lib_ffi.c
+++ b/src/lib_ffi.c
@@ -513,7 +513,7 @@ LJLIB_CF(ffi_new)	LJLIB_REC(.)
     /* Handle ctype __gc metamethod. Use the fast lookup here. */
     cTValue *tv = lj_tab_getinth(cts->miscmap, -(int32_t)id);
     if (tv && tvistab(tv) && (tv = lj_meta_fast(L, tabV(tv), MM_gc))) {
-      GCtab *t = cts->finalizer;
+      GCtab *t = tabref(G(L)->gcroot[GCROOT_FFI_FIN]);
       if (gcref(t->metatable)) {
 	/* Add to finalizer table, if still enabled. */
 	copyTV(L, lj_tab_set(L, t, o-1), tv);
@@ -762,7 +762,7 @@ LJLIB_CF(ffi_abi)	LJLIB_REC(.)
   return 1;
 }
 
-LJLIB_PUSH(top-8) LJLIB_SET(!)  /* Store reference to miscmap table. */
+LJLIB_PUSH(top-7) LJLIB_SET(!)  /* Store reference to miscmap table. */
 
 LJLIB_CF(ffi_metatype)
 {
@@ -788,8 +788,6 @@ LJLIB_CF(ffi_metatype)
   return 1;
 }
 
-LJLIB_PUSH(top-7) LJLIB_SET(!)  /* Store reference to finalizer table. */
-
 LJLIB_CF(ffi_gc)	LJLIB_REC(.)
 {
   GCcdata *cd = ffi_checkcdata(L, 1);
@@ -822,19 +820,6 @@ LJLIB_PUSH(top-2) LJLIB_SET(arch)
 
 /* ------------------------------------------------------------------------ */
 
-/* Create special weak-keyed finalizer table. */
-static GCtab *ffi_finalizer(lua_State *L)
-{
-  /* NOBARRIER: The table is new (marked white). */
-  GCtab *t = lj_tab_new(L, 0, 1);
-  settabV(L, L->top++, t);
-  setgcref(t->metatable, obj2gco(t));
-  setstrV(L, lj_tab_setstr(L, t, lj_str_newlit(L, "__mode")),
-	  lj_str_newlit(L, "k"));
-  t->nomm = (uint8_t)(~(1u<<MM_mode));
-  return t;
-}
-
 /* Register FFI module as loaded. */
 static void ffi_register_module(lua_State *L)
 {
@@ -850,7 +835,6 @@ LUALIB_API int luaopen_ffi(lua_State *L)
 {
   CTState *cts = lj_ctype_init(L);
   settabV(L, L->top++, (cts->miscmap = lj_tab_new(L, 0, 1)));
-  cts->finalizer = ffi_finalizer(L);
   LJ_LIB_REG(L, NULL, ffi_meta);
   /* NOBARRIER: basemt is a GC root. */
   setgcref(basemt_it(G(L), LJ_TCDATA), obj2gco(tabV(L->top-1)));
diff --git a/src/lj_cdata.c b/src/lj_cdata.c
index 35d0e76a..3d6ff1cc 100644
--- a/src/lj_cdata.c
+++ b/src/lj_cdata.c
@@ -89,7 +89,7 @@ void LJ_FASTCALL lj_cdata_free(global_State *g, GCcdata *cd)
 
 void lj_cdata_setfin(lua_State *L, GCcdata *cd, GCobj *obj, uint32_t it)
 {
-  GCtab *t = ctype_ctsG(G(L))->finalizer;
+  GCtab *t = tabref(G(L)->gcroot[GCROOT_FFI_FIN]);
   if (gcref(t->metatable)) {
     /* Add cdata to finalizer table, if still enabled. */
     TValue *tv, tmp;
diff --git a/src/lj_ctype.c b/src/lj_ctype.c
index 53b83031..c0213629 100644
--- a/src/lj_ctype.c
+++ b/src/lj_ctype.c
@@ -643,6 +643,18 @@ CTState *lj_ctype_init(lua_State *L)
   return cts;
 }
 
+/* Create special weak-keyed finalizer table. */
+void lj_ctype_initfin(lua_State *L)
+{
+  /* NOBARRIER: The table is new (marked white). */
+  GCtab *t = lj_tab_new(L, 0, 1);
+  setgcref(t->metatable, obj2gco(t));
+  setstrV(L, lj_tab_setstr(L, t, lj_str_newlit(L, "__mode")),
+	  lj_str_newlit(L, "k"));
+  t->nomm = (uint8_t)(~(1u<<MM_mode));
+  setgcref(G(L)->gcroot[GCROOT_FFI_FIN], obj2gco(t));
+}
+
 /* Free C type table and state. */
 void lj_ctype_freestate(global_State *g)
 {
diff --git a/src/lj_ctype.h b/src/lj_ctype.h
index 8edbd561..2d393eb9 100644
--- a/src/lj_ctype.h
+++ b/src/lj_ctype.h
@@ -177,7 +177,6 @@ typedef struct CTState {
   MSize sizetab;	/* Size of C type table. */
   lua_State *L;		/* Lua state (needed for errors and allocations). */
   global_State *g;	/* Global state. */
-  GCtab *finalizer;	/* Map of cdata to finalizer. */
   GCtab *miscmap;	/* Map of -CTypeID to metatable and cb slot to func. */
   CCallback cb;		/* Temporary callback state. */
   CTypeID1 hash[CTHASH_SIZE];  /* Hash anchors for C type table. */
@@ -473,6 +472,7 @@ LJ_FUNC GCstr *lj_ctype_repr(lua_State *L, CTypeID id, GCstr *name);
 LJ_FUNC GCstr *lj_ctype_repr_int64(lua_State *L, uint64_t n, int isunsigned);
 LJ_FUNC GCstr *lj_ctype_repr_complex(lua_State *L, void *sp, CTSize size);
 LJ_FUNC CTState *lj_ctype_init(lua_State *L);
+LJ_FUNC void lj_ctype_initfin(lua_State *L);
 LJ_FUNC void lj_ctype_freestate(global_State *g);
 
 #endif
diff --git a/src/lj_gc.c b/src/lj_gc.c
index 42348a34..4c222f21 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -99,9 +99,6 @@ static void gc_mark_start(global_State *g)
   gc_markobj(g, tabref(mainthread(g)->env));
   gc_marktv(g, &g->registrytv);
   gc_mark_gcroot(g);
-#if LJ_HASFFI
-  if (ctype_ctsG(g)) gc_markobj(g, ctype_ctsG(g)->finalizer);
-#endif
   g->gc.state = GCSpropagate;
 }
 
@@ -181,8 +178,7 @@ static int gc_traverse_tab(global_State *g, GCtab *t)
     }
     if (weak) {  /* Weak tables are cleared in the atomic phase. */
 #if LJ_HASFFI
-      CTState *cts = ctype_ctsG(g);
-      if (cts && cts->finalizer == t) {
+      if (gcref(g->gcroot[GCROOT_FFI_FIN]) == obj2gco(t)) {
 	weak = (int)(~0u & ~LJ_GC_WEAKVAL);
       } else
 #endif
@@ -550,7 +546,7 @@ static void gc_finalize(lua_State *L)
     o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
     /* Resolve finalizer. */
     setcdataV(L, &tmp, gco2cd(o));
-    tv = lj_tab_set(L, ctype_ctsG(g)->finalizer, &tmp);
+    tv = lj_tab_set(L, tabref(g->gcroot[GCROOT_FFI_FIN]), &tmp);
     if (!tvisnil(tv)) {
       g->gc.nocdatafin = 0;
       copyTV(L, &tmp, tv);
@@ -582,23 +578,20 @@ void lj_gc_finalize_udata(lua_State *L)
 void lj_gc_finalize_cdata(lua_State *L)
 {
   global_State *g = G(L);
-  CTState *cts = ctype_ctsG(g);
-  if (cts) {
-    GCtab *t = cts->finalizer;
-    Node *node = noderef(t->node);
-    ptrdiff_t i;
-    setgcrefnull(t->metatable);  /* Mark finalizer table as disabled. */
-    for (i = (ptrdiff_t)t->hmask; i >= 0; i--)
-      if (!tvisnil(&node[i].val) && tviscdata(&node[i].key)) {
-	GCobj *o = gcV(&node[i].key);
-	TValue tmp;
-	makewhite(g, o);
-	o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
-	copyTV(L, &tmp, &node[i].val);
-	setnilV(&node[i].val);
-	gc_call_finalizer(g, L, &tmp, o);
-      }
-  }
+  GCtab *t = tabref(g->gcroot[GCROOT_FFI_FIN]);
+  Node *node = noderef(t->node);
+  ptrdiff_t i;
+  setgcrefnull(t->metatable);  /* Mark finalizer table as disabled. */
+  for (i = (ptrdiff_t)t->hmask; i >= 0; i--)
+    if (!tvisnil(&node[i].val) && tviscdata(&node[i].key)) {
+      GCobj *o = gcV(&node[i].key);
+      TValue tmp;
+      makewhite(g, o);
+      o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
+      copyTV(L, &tmp, &node[i].val);
+      setnilV(&node[i].val);
+      gc_call_finalizer(g, L, &tmp, o);
+    }
 }
 #endif
 
@@ -721,7 +714,7 @@ static size_t gc_onestep(lua_State *L)
       return GCFINALIZECOST;
     }
 #if LJ_HASFFI
-    if (!g->gc.nocdatafin) lj_tab_rehash(L, ctype_ctsG(g)->finalizer);
+    if (!g->gc.nocdatafin) lj_tab_rehash(L, tabref(g->gcroot[GCROOT_FFI_FIN]));
 #endif
     g->gc.state = GCSpause;  /* End of GC cycle. */
     g->gc.debt = 0;
diff --git a/src/lj_obj.h b/src/lj_obj.h
index 69e94ff2..06ea0cd0 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -580,6 +580,9 @@ typedef enum {
   GCROOT_BASEMT_NUM = GCROOT_BASEMT + ~LJ_TNUMX,
   GCROOT_IO_INPUT,	/* Userdata for default I/O input file. */
   GCROOT_IO_OUTPUT,	/* Userdata for default I/O output file. */
+#if LJ_HASFFI
+  GCROOT_FFI_FIN,	/* FFI finalizer table. */
+#endif
   GCROOT_MAX
 } GCRootID;
 
diff --git a/src/lj_state.c b/src/lj_state.c
index 01d4901a..5a920102 100644
--- a/src/lj_state.c
+++ b/src/lj_state.c
@@ -180,6 +180,9 @@ static TValue *cpluaopen(lua_State *L, lua_CFunction dummy, void *ud)
   lj_lex_init(L);
   fixstring(lj_err_str(L, LJ_ERR_ERRMEM));  /* Preallocate memory error msg. */
   g->gc.threshold = 4*g->gc.total;
+#if LJ_HASFFI
+  lj_ctype_initfin(L);
+#endif
   lj_trace_initstate(g);
   lj_err_verify();
   return NULL;
diff --git a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
index d577b551..9e57efb8 100644
--- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -65,10 +65,57 @@ static int unmarked_finalizer_tab_gcstart(void *test_state)
 	return TEST_EXIT_SUCCESS;
 }
 
+static int
+unmarked_finalizer_tab_gcmark(void *test_state)
+{
+	/* Shared Lua state is not needed. */
+	UNUSED(test_state);
+
+	/* Setup. */
+	lua_State *L = luaL_newstate();
+
+	/* Set GC at the start. */
+	lua_gc(L, LUA_GCCOLLECT, 0);
+
+	/*
+	 * Default step is too big -- one step ends after the
+	 * atomic phase.
+	 */
+	lua_gc(L, LUA_GCSETSTEPMUL, 1);
+
+	/* Skip marking roots. */
+	lua_gc(L, LUA_GCSTEP, 1);
+
+	/* Not trigger GC during `lua_openffi()`. */
+	lua_gc(L, LUA_GCSTOP, 0);
+
+	/*
+	 * The terminating '\0' is considered by parser as part of
+	 * the input, so we must chomp it.
+	 */
+	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1,
+				   "test_chunk", "t");
+	if (res != LUA_OK) {
+		test_comment("error loading Lua chunk: %s",
+			     lua_tostring(L, -1));
+		bail_out("error loading Lua chunk");
+	}
+
+	/* Finish GC cycle to collect the finalizer table. */
+	while (!lua_gc(L, LUA_GCSTEP, -1));
+
+	/* Teardown. */
+	lua_settop(L, 0);
+	lua_close(L);
+
+	return TEST_EXIT_SUCCESS;
+}
+
 int main(void)
 {
 	const struct test_unit tgroup[] = {
 		test_unit_def(unmarked_finalizer_tab_gcstart),
+		test_unit_def(unmarked_finalizer_tab_gcmark),
 	};
 	const int test_result = test_run_group(tgroup, NULL);
 
-- 
2.34.1

Re: [Tarantool-patches] [PATCH luajit 1/2][v2] FFI: Treat cdata finalizer table as a GC root.

[Maxim Kokryashkin via Tarantool-patches]

Hi, Sergey!
Thanks for the patch!
LGTM.

Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Maxim Kokryashkin via Tarantool-patches]

Hi, Sergey!
Thanks for the patch!
LGTM.

Re: [Tarantool-patches] [PATCH luajit 0/2][v2] Fix cdata finalizer table

[Sergey Kaplun via Tarantool-patches]

Sergey,

I've checked the patchset into all long-term branches in
tarantool/luajit and bumped a new version in master [1], release/3.1 [2]
and release/2.11 [3].

[1]: https://github.com/tarantool/tarantool/pull/10423
[2]: https://github.com/tarantool/tarantool/pull/10424
[3]: https://github.com/tarantool/tarantool/pull/10425

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Kaplun via Tarantool-patches]

Thanks for the fixes!
LGTM!

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Bronnikov via Tarantool-patches]

[-- Attachment #1: Type: text/plain, Size: 947 bytes --]

Hello, Sergey,


On 12.08.2024 16:17, Sergey Kaplun wrote:


<snipped>

>>
>>> Also, please add here comment about `sizeof(buff) - 1` too.
> Please add a comment that the terminating '\0' is considered by parser
> as part of the input, so we must chomp it.

Updated:


--- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -89,6 +89,10 @@ unmarked_finalizer_tab_gcmark(void *test_state)
         /* Not trigger GC during `lua_openffi()`. */
         lua_gc(L, LUA_GCSTOP, 0);

+       /*
+        * The terminating '\0' is considered by parser as part of
+        * the input, so we must chomp it.
+        */
         int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1,
                                    "test_chunk", "t");
         if (res != LUA_OK) {

>
> <snipped>
>

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Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Kaplun via Tarantool-patches]

Hi, Sergey!
Thanks for the fixes!

On 23.07.24, Sergey Bronnikov wrote:
> Hi, Sergey,
> 
> fixes applied and force-pushed.
> 
> Sergey
> 
> On 10.07.2024 17:08, Sergey Kaplun wrote:
> > Hi, Sergey!
> > Thanks for the fixes!
> > LGTM, after fixing minor comments below.
> >
> > On 10.07.24, Sergey Bronnikov wrote:
> >> Hi, Sergey
> >>
> >> thanks for review. Fixes applied and force-pushed.
> >>
> >> Sergey
> >>
> >>
> >> On 09.07.2024 15:14, Sergey Kaplun via Tarantool-patches wrote:
> >>> Hi, Sergey!
> >>> Thanks for the patch!
> >>> Please consider my comments below.
> >>>
> >>> On 09.07.24, Sergey Bronnikov wrote:

<snipped>

> >>>> diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> >>>> index c388c6a7..259528cb 100644
> >>>> --- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> >>>> +++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c

<snipped>

> >>>> +	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
> > I suggest renaming "chunk" to the "test_chunk" here too.
> 
> Fixed, but after this the line becomes longer max length and I need to 
> split it for two lines:
> 
> --- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
> +++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
> @@ -83,7 +83,8 @@ unmarked_finalizer_tab_gcmark(void *test_state)
>          /* Not trigger GC during `lua_openffi()`. */
>          lua_gc(L, LUA_GCSTOP, 0);
> 
> -       int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
> +       int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1,
> +                                  "test_chunk", "t");
>          if (res != LUA_OK) {
>                  test_comment("error loading Lua chunk: %s", 
> lua_tostring(L, -1));
>                  bail_out("error loading Lua chunk");
> 
> I would leave "chunk" due to this. And you?

OK, let's leave it as "chunk" in both places.

> 
> 
> >
> > Also, please add here comment about `sizeof(buff) - 1` too.

Please add a comment that the terminating '\0' is considered by parser
as part of the input, so we must chomp it.

> >

<snipped>

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Bronnikov via Tarantool-patches]

[-- Attachment #1: Type: text/plain, Size: 4466 bytes --]

Hi, Sergey,

fixes applied and force-pushed.

Sergey

On 10.07.2024 17:08, Sergey Kaplun wrote:
> Hi, Sergey!
> Thanks for the fixes!
> LGTM, after fixing minor comments below.
>
> On 10.07.24, Sergey Bronnikov wrote:
>> Hi, Sergey
>>
>> thanks for review. Fixes applied and force-pushed.
>>
>> Sergey
>>
>>
>> On 09.07.2024 15:14, Sergey Kaplun via Tarantool-patches wrote:
>>> Hi, Sergey!
>>> Thanks for the patch!
>>> Please consider my comments below.
>>>
>>> On 09.07.24, Sergey Bronnikov wrote:
>>>> From: Mike Pall <mike>
>>>>
> <snipped>
>
>>> Minor: "will be collected at the end of the cycle if it is created after
>>> the start phase."
>> Updated.
> | Previous patch fixes the problem partially because the introduced
> | GC root may not exist at the start phase of the GC cycle. In that
> | case, the cdata finalizer table will be collected at the end of
> | the cycle.
>
> Minor: "cycle (since it isn't marked because it is not accessible from
> any GC root)."
Updated.
>
> |            Access to the cdata finalizer table exhibits heap use
> | after free. The patch turns the finalizer table into a proper
> <snipped>
>
>>>> diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
>>>> index c388c6a7..259528cb 100644
>>>> --- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
>>>> +++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> <snipped>
>
>>>> +
>>>> +	/* Not trigger GC during `lua_openffi()`. */
>>>> +	lua_gc(L, LUA_GCSTOP, 0);
>>> Maybe it is worth adding this GC stop for the first test case too to
>>> make it more robust.
>> Ok, I'll add.
> Thanks!
>
>>>> +
>>>> +	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
> I suggest renaming "chunk" to the "test_chunk" here too.

Fixed, but after this the line becomes longer max length and I need to 
split it for two lines:

--- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -83,7 +83,8 @@ unmarked_finalizer_tab_gcmark(void *test_state)
         /* Not trigger GC during `lua_openffi()`. */
         lua_gc(L, LUA_GCSTOP, 0);

-       int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
+       int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1,
+                                  "test_chunk", "t");
         if (res != LUA_OK) {
                 test_comment("error loading Lua chunk: %s", 
lua_tostring(L, -1));
                 bail_out("error loading Lua chunk");

I would leave "chunk" due to this. And you?


>
> Also, please add here comment about `sizeof(buff) - 1` too.
>
>
>>>> +	assert_true(res == LUA_OK);
> <snipped>
>
>> --- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
>> +++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
>> @@ -78,7 +78,10 @@ unmarked_finalizer_tab_gcsweep(void *test_state)
>>           lua_gc(L, LUA_GCSTOP, 0);
>>
>>           int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk",
>> "t");
>> -       assert_true(res == LUA_OK);
>> +       if (res != LUA_OK) {
>> +               test_comment("error loading Lua chunk: %s",
>> lua_tostring(L, -1));
> Code line length is more than 80 symbols.
> (Same for the previous commit.)
Fixed for both commits.
>
>
>> +               bail_out("error loading Lua chunk");
>> +       }
>>
>>           /* Finish GC cycle. */
>>           while (!lua_gc(L, LUA_GCSTEP, -1));
>>
>>>> +
>>>> +	/* Finish GC cycle. */
> Let's add "to collect the finalizer table." to be consistent with
> another test.

Fixed:


--- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -93,7 +93,7 @@ unmarked_finalizer_tab_gcmark(void *test_state)
                 bail_out("error loading Lua chunk");
         }

-       /* Finish GC cycle. */
+       /* Finish GC cycle to collect the finalizer table. */
         while (!lua_gc(L, LUA_GCSTEP, -1));

         /* Teardown. */

>
>>>> +	while (!lua_gc(L, LUA_GCSTEP, -1));
>>>> +
> <snipped>
>

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Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Kaplun via Tarantool-patches]

Hi, Sergey!
Thanks for the fixes!
LGTM, after fixing minor comments below.

On 10.07.24, Sergey Bronnikov wrote:
> Hi, Sergey
> 
> thanks for review. Fixes applied and force-pushed.
> 
> Sergey
> 
> 
> On 09.07.2024 15:14, Sergey Kaplun via Tarantool-patches wrote:
> > Hi, Sergey!
> > Thanks for the patch!
> > Please consider my comments below.
> >
> > On 09.07.24, Sergey Bronnikov wrote:
> >> From: Mike Pall <mike>
> >>

<snipped>

> > Minor: "will be collected at the end of the cycle if it is created after
> > the start phase."
> 
> Updated.

| Previous patch fixes the problem partially because the introduced
| GC root may not exist at the start phase of the GC cycle. In that
| case, the cdata finalizer table will be collected at the end of
| the cycle.

Minor: "cycle (since it isn't marked because it is not accessible from
any GC root)."

|            Access to the cdata finalizer table exhibits heap use
| after free. The patch turns the finalizer table into a proper
> 

<snipped>

> >> diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> >> index c388c6a7..259528cb 100644
> >> --- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> >> +++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c

<snipped>

> >> +
> >> +	/* Not trigger GC during `lua_openffi()`. */
> >> +	lua_gc(L, LUA_GCSTOP, 0);
> > Maybe it is worth adding this GC stop for the first test case too to
> > make it more robust.
> Ok, I'll add.

Thanks!

> >
> >> +
> >> +	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");

I suggest renaming "chunk" to the "test_chunk" here too.

Also, please add here comment about `sizeof(buff) - 1` too.


> >> +	assert_true(res == LUA_OK);

<snipped>

> --- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
> +++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
> @@ -78,7 +78,10 @@ unmarked_finalizer_tab_gcsweep(void *test_state)
>          lua_gc(L, LUA_GCSTOP, 0);
> 
>          int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", 
> "t");
> -       assert_true(res == LUA_OK);
> +       if (res != LUA_OK) {
> +               test_comment("error loading Lua chunk: %s", 
> lua_tostring(L, -1));

Code line length is more than 80 symbols.
(Same for the previous commit.)


> +               bail_out("error loading Lua chunk");
> +       }
> 
>          /* Finish GC cycle. */
>          while (!lua_gc(L, LUA_GCSTEP, -1));
> 
> >
> >> +
> >> +	/* Finish GC cycle. */

Let's add "to collect the finalizer table." to be consistent with
another test.

> >> +	while (!lua_gc(L, LUA_GCSTEP, -1));
> >> +

<snipped>

-- 
Best regards,
Sergey Kaplun

Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Bronnikov via Tarantool-patches]

[-- Attachment #1: Type: text/plain, Size: 5685 bytes --]

Hi, Sergey

thanks for review. Fixes applied and force-pushed.

Sergey


On 09.07.2024 15:14, Sergey Kaplun via Tarantool-patches wrote:
> Hi, Sergey!
> Thanks for the patch!
> Please consider my comments below.
>
> On 09.07.24, Sergey Bronnikov wrote:
>> From: Mike Pall <mike>
>>
>> Reported by Sergey Bronnikov.
>>
>> (cherry picked from commit f5affaa6c4e7524e661484f22f24255f9a83eb47)
>>
>> Previous patch fixes the problem partially because the introduced
> Typo: s/Previous/The previous/
> Typo: s/fixes (.*) partially/partially fixes \1/

Fixed.


>
>> GC root may not exist at the start phase of the GC cycle. In that
>> case, the cdata finalizer table will be collected at the end of
>> the cycle. Access to the cdata finalizer table exhibits heap use
> Minor: "will be collected at the end of the cycle if it is created after
> the start phase."

Updated.


>
>> after free. The patch is turned the finalizer table into a proper
> Typo: s/is turned/turns/

Updated.


>> GC root.
> It is worth mentioning that this table is created on the initialization
> of the main Lua State instead of loading the FFI library.
Added.
>> Sergey Bronnikov:
>> * added the description and the tests for the problem
>>
>> Part of tarantool/tarantool#10199
>> ---
>>   src/lib_ffi.c                                 | 20 +--------
>>   src/lj_cdata.c                                |  2 +-
>>   src/lj_ctype.c                                | 12 ++++++
>>   src/lj_ctype.h                                |  2 +-
>>   src/lj_gc.c                                   | 41 ++++++++----------
>>   src/lj_obj.h                                  |  3 ++
>>   src/lj_state.c                                |  3 ++
>>   ...free-on-access-to-CTState-finalizer.test.c | 42 +++++++++++++++++++
>>   8 files changed, 81 insertions(+), 44 deletions(-)
>>
>> diff --git a/src/lib_ffi.c b/src/lib_ffi.c
>> index 7ed6fc78..3c8dd77f 100644
>> --- a/src/lib_ffi.c
>> +++ b/src/lib_ffi.c
> <snipped>
>
>> diff --git a/src/lj_cdata.c b/src/lj_cdata.c
>> index 35d0e76a..3d6ff1cc 100644
>> --- a/src/lj_cdata.c
>> +++ b/src/lj_cdata.c
> <snipped>
>
>> diff --git a/src/lj_ctype.c b/src/lj_ctype.c
>> index 53b83031..c0213629 100644
>> --- a/src/lj_ctype.c
>> +++ b/src/lj_ctype.c
> <snipped>
>
>> diff --git a/src/lj_ctype.h b/src/lj_ctype.h
>> index 8edbd561..2d393eb9 100644
>> --- a/src/lj_ctype.h
>> +++ b/src/lj_ctype.h
> <snipped>
>
>> diff --git a/src/lj_gc.c b/src/lj_gc.c
>> index 42348a34..4c222f21 100644
>> --- a/src/lj_gc.c
>> +++ b/src/lj_gc.c
> <snipped>
>
>> diff --git a/src/lj_obj.h b/src/lj_obj.h
>> index 69e94ff2..06ea0cd0 100644
>> --- a/src/lj_obj.h
>> +++ b/src/lj_obj.h
> <snipped>
>
>> diff --git a/src/lj_state.c b/src/lj_state.c
>> index 01d4901a..5a920102 100644
>> --- a/src/lj_state.c
>> +++ b/src/lj_state.c
> <snipped>
>
>> diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
>> index c388c6a7..259528cb 100644
>> --- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
>> +++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
>> @@ -55,10 +55,52 @@ static int unmarked_finalizer_tab_gcstart(void *test_state)
>>   	return TEST_EXIT_SUCCESS;
>>   }
>>   
>> +static int
>> +unmarked_finalizer_tab_gcsweep(void *test_state)
>> +{
>> +	const char buff[] = "return 1LL";
> Why do we need an additional buffer if the same one already exists?
Left a single buffer.
>
>> +
>> +	/* Shared Lua state is not needed. */
>> +	(void)test_state;
>> +
>> +	/* Setup. */
>> +	lua_State *L = luaL_newstate();
>> +
>> +	/* Set GC at the start. */
>> +	lua_gc(L, LUA_GCCOLLECT, 0);
>> +
>> +	/*
>> +	 * Default step is too big -- one step ends after the
>> +	 * atomic phase.
>> +	 */
>> +	lua_gc(L, LUA_GCSETSTEPMUL, 1);
>> +
>> +	/* Skip marking roots. */
>> +	lua_gc(L, LUA_GCSTEP, 1);
>> +
>> +	/* Not trigger GC during `lua_openffi()`. */
>> +	lua_gc(L, LUA_GCSTOP, 0);
> Maybe it is worth adding this GC stop for the first test case too to
> make it more robust.
Ok, I'll add.
>
>> +
>> +	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
>> +	assert_true(res == LUA_OK);
> I suppose it is better to use not assert_true here but `test_comment()`
> and `bail_out()`, since this is not behaviour that we are testing.

Updated:


--- a/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
+++ b/test/tarantool-c-tests/lj-1168-unmarked-finalizer-tab.test.c
@@ -78,7 +78,10 @@ unmarked_finalizer_tab_gcsweep(void *test_state)
         lua_gc(L, LUA_GCSTOP, 0);

         int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", 
"t");
-       assert_true(res == LUA_OK);
+       if (res != LUA_OK) {
+               test_comment("error loading Lua chunk: %s", 
lua_tostring(L, -1));
+               bail_out("error loading Lua chunk");
+       }

         /* Finish GC cycle. */
         while (!lua_gc(L, LUA_GCSTEP, -1));

>
>> +
>> +	/* Finish GC cycle. */
>> +	while (!lua_gc(L, LUA_GCSTEP, -1));
>> +
>> +	assert_true(lua_gettop(L) == 1);
> Why do we need this assert?

removed


>
>> +
>> +	/* Teardown. */
>> +	lua_settop(L, 0);
>> +	lua_close(L);
>> +
>> +	return TEST_EXIT_SUCCESS;
>> +}
>> +
>>   int main(void)
>>   {
>>   	const struct test_unit tgroup[] = {
>>   		test_unit_def(unmarked_finalizer_tab_gcstart),
>> +		test_unit_def(unmarked_finalizer_tab_gcsweep),
>>   	};
>>   	const int test_result = test_run_group(tgroup, NULL);
>>   
>> -- 
>> 2.34.1
>>

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Re: [Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Kaplun via Tarantool-patches]

Hi, Sergey!
Thanks for the patch!
Please consider my comments below.

On 09.07.24, Sergey Bronnikov wrote:
> From: Mike Pall <mike>
> 
> Reported by Sergey Bronnikov.
> 
> (cherry picked from commit f5affaa6c4e7524e661484f22f24255f9a83eb47)
> 
> Previous patch fixes the problem partially because the introduced

Typo: s/Previous/The previous/
Typo: s/fixes (.*) partially/partially fixes \1/

> GC root may not exist at the start phase of the GC cycle. In that
> case, the cdata finalizer table will be collected at the end of
> the cycle. Access to the cdata finalizer table exhibits heap use

Minor: "will be collected at the end of the cycle if it is created after
the start phase."

> after free. The patch is turned the finalizer table into a proper

Typo: s/is turned/turns/

> GC root.

It is worth mentioning that this table is created on the initialization
of the main Lua State instead of loading the FFI library.

> 
> Sergey Bronnikov:
> * added the description and the tests for the problem
> 
> Part of tarantool/tarantool#10199
> ---
>  src/lib_ffi.c                                 | 20 +--------
>  src/lj_cdata.c                                |  2 +-
>  src/lj_ctype.c                                | 12 ++++++
>  src/lj_ctype.h                                |  2 +-
>  src/lj_gc.c                                   | 41 ++++++++----------
>  src/lj_obj.h                                  |  3 ++
>  src/lj_state.c                                |  3 ++
>  ...free-on-access-to-CTState-finalizer.test.c | 42 +++++++++++++++++++
>  8 files changed, 81 insertions(+), 44 deletions(-)
> 
> diff --git a/src/lib_ffi.c b/src/lib_ffi.c
> index 7ed6fc78..3c8dd77f 100644
> --- a/src/lib_ffi.c
> +++ b/src/lib_ffi.c

<snipped>

> diff --git a/src/lj_cdata.c b/src/lj_cdata.c
> index 35d0e76a..3d6ff1cc 100644
> --- a/src/lj_cdata.c
> +++ b/src/lj_cdata.c

<snipped>

> diff --git a/src/lj_ctype.c b/src/lj_ctype.c
> index 53b83031..c0213629 100644
> --- a/src/lj_ctype.c
> +++ b/src/lj_ctype.c

<snipped>

> diff --git a/src/lj_ctype.h b/src/lj_ctype.h
> index 8edbd561..2d393eb9 100644
> --- a/src/lj_ctype.h
> +++ b/src/lj_ctype.h

<snipped>

> diff --git a/src/lj_gc.c b/src/lj_gc.c
> index 42348a34..4c222f21 100644
> --- a/src/lj_gc.c
> +++ b/src/lj_gc.c

<snipped>

> diff --git a/src/lj_obj.h b/src/lj_obj.h
> index 69e94ff2..06ea0cd0 100644
> --- a/src/lj_obj.h
> +++ b/src/lj_obj.h

<snipped>

> diff --git a/src/lj_state.c b/src/lj_state.c
> index 01d4901a..5a920102 100644
> --- a/src/lj_state.c
> +++ b/src/lj_state.c

<snipped>

> diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> index c388c6a7..259528cb 100644
> --- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> +++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
> @@ -55,10 +55,52 @@ static int unmarked_finalizer_tab_gcstart(void *test_state)
>  	return TEST_EXIT_SUCCESS;
>  }
>  
> +static int
> +unmarked_finalizer_tab_gcsweep(void *test_state)
> +{
> +	const char buff[] = "return 1LL";

Why do we need an additional buffer if the same one already exists?

> +
> +	/* Shared Lua state is not needed. */
> +	(void)test_state;
> +
> +	/* Setup. */
> +	lua_State *L = luaL_newstate();
> +
> +	/* Set GC at the start. */
> +	lua_gc(L, LUA_GCCOLLECT, 0);
> +
> +	/*
> +	 * Default step is too big -- one step ends after the
> +	 * atomic phase.
> +	 */
> +	lua_gc(L, LUA_GCSETSTEPMUL, 1);
> +
> +	/* Skip marking roots. */
> +	lua_gc(L, LUA_GCSTEP, 1);
> +
> +	/* Not trigger GC during `lua_openffi()`. */
> +	lua_gc(L, LUA_GCSTOP, 0);

Maybe it is worth adding this GC stop for the first test case too to
make it more robust.

> +
> +	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
> +	assert_true(res == LUA_OK);

I suppose it is better to use not assert_true here but `test_comment()`
and `bail_out()`, since this is not behaviour that we are testing.

> +
> +	/* Finish GC cycle. */
> +	while (!lua_gc(L, LUA_GCSTEP, -1));
> +
> +	assert_true(lua_gettop(L) == 1);

Why do we need this assert?

> +
> +	/* Teardown. */
> +	lua_settop(L, 0);
> +	lua_close(L);
> +
> +	return TEST_EXIT_SUCCESS;
> +}
> +
>  int main(void)
>  {
>  	const struct test_unit tgroup[] = {
>  		test_unit_def(unmarked_finalizer_tab_gcstart),
> +		test_unit_def(unmarked_finalizer_tab_gcsweep),
>  	};
>  	const int test_result = test_run_group(tgroup, NULL);
>  
> -- 
> 2.34.1
> 

-- 
Best regards,
Sergey Kaplun

[Tarantool-patches] [PATCH luajit 2/2][v2] FFI: Turn FFI finalizer table into a proper GC root.

[Sergey Bronnikov via Tarantool-patches]

From: Mike Pall <mike>

Reported by Sergey Bronnikov.

(cherry picked from commit f5affaa6c4e7524e661484f22f24255f9a83eb47)

Previous patch fixes the problem partially because the introduced
GC root may not exist at the start phase of the GC cycle. In that
case, the cdata finalizer table will be collected at the end of
the cycle. Access to the cdata finalizer table exhibits heap use
after free. The patch is turned the finalizer table into a proper
GC root.

Sergey Bronnikov:
* added the description and the tests for the problem

Part of tarantool/tarantool#10199
---
 src/lib_ffi.c                                 | 20 +--------
 src/lj_cdata.c                                |  2 +-
 src/lj_ctype.c                                | 12 ++++++
 src/lj_ctype.h                                |  2 +-
 src/lj_gc.c                                   | 41 ++++++++----------
 src/lj_obj.h                                  |  3 ++
 src/lj_state.c                                |  3 ++
 ...free-on-access-to-CTState-finalizer.test.c | 42 +++++++++++++++++++
 8 files changed, 81 insertions(+), 44 deletions(-)

diff --git a/src/lib_ffi.c b/src/lib_ffi.c
index 7ed6fc78..3c8dd77f 100644
--- a/src/lib_ffi.c
+++ b/src/lib_ffi.c
@@ -513,7 +513,7 @@ LJLIB_CF(ffi_new)	LJLIB_REC(.)
     /* Handle ctype __gc metamethod. Use the fast lookup here. */
     cTValue *tv = lj_tab_getinth(cts->miscmap, -(int32_t)id);
     if (tv && tvistab(tv) && (tv = lj_meta_fast(L, tabV(tv), MM_gc))) {
-      GCtab *t = cts->finalizer;
+      GCtab *t = tabref(G(L)->gcroot[GCROOT_FFI_FIN]);
       if (gcref(t->metatable)) {
 	/* Add to finalizer table, if still enabled. */
 	copyTV(L, lj_tab_set(L, t, o-1), tv);
@@ -762,7 +762,7 @@ LJLIB_CF(ffi_abi)	LJLIB_REC(.)
   return 1;
 }
 
-LJLIB_PUSH(top-8) LJLIB_SET(!)  /* Store reference to miscmap table. */
+LJLIB_PUSH(top-7) LJLIB_SET(!)  /* Store reference to miscmap table. */
 
 LJLIB_CF(ffi_metatype)
 {
@@ -788,8 +788,6 @@ LJLIB_CF(ffi_metatype)
   return 1;
 }
 
-LJLIB_PUSH(top-7) LJLIB_SET(!)  /* Store reference to finalizer table. */
-
 LJLIB_CF(ffi_gc)	LJLIB_REC(.)
 {
   GCcdata *cd = ffi_checkcdata(L, 1);
@@ -822,19 +820,6 @@ LJLIB_PUSH(top-2) LJLIB_SET(arch)
 
 /* ------------------------------------------------------------------------ */
 
-/* Create special weak-keyed finalizer table. */
-static GCtab *ffi_finalizer(lua_State *L)
-{
-  /* NOBARRIER: The table is new (marked white). */
-  GCtab *t = lj_tab_new(L, 0, 1);
-  settabV(L, L->top++, t);
-  setgcref(t->metatable, obj2gco(t));
-  setstrV(L, lj_tab_setstr(L, t, lj_str_newlit(L, "__mode")),
-	  lj_str_newlit(L, "k"));
-  t->nomm = (uint8_t)(~(1u<<MM_mode));
-  return t;
-}
-
 /* Register FFI module as loaded. */
 static void ffi_register_module(lua_State *L)
 {
@@ -850,7 +835,6 @@ LUALIB_API int luaopen_ffi(lua_State *L)
 {
   CTState *cts = lj_ctype_init(L);
   settabV(L, L->top++, (cts->miscmap = lj_tab_new(L, 0, 1)));
-  cts->finalizer = ffi_finalizer(L);
   LJ_LIB_REG(L, NULL, ffi_meta);
   /* NOBARRIER: basemt is a GC root. */
   setgcref(basemt_it(G(L), LJ_TCDATA), obj2gco(tabV(L->top-1)));
diff --git a/src/lj_cdata.c b/src/lj_cdata.c
index 35d0e76a..3d6ff1cc 100644
--- a/src/lj_cdata.c
+++ b/src/lj_cdata.c
@@ -89,7 +89,7 @@ void LJ_FASTCALL lj_cdata_free(global_State *g, GCcdata *cd)
 
 void lj_cdata_setfin(lua_State *L, GCcdata *cd, GCobj *obj, uint32_t it)
 {
-  GCtab *t = ctype_ctsG(G(L))->finalizer;
+  GCtab *t = tabref(G(L)->gcroot[GCROOT_FFI_FIN]);
   if (gcref(t->metatable)) {
     /* Add cdata to finalizer table, if still enabled. */
     TValue *tv, tmp;
diff --git a/src/lj_ctype.c b/src/lj_ctype.c
index 53b83031..c0213629 100644
--- a/src/lj_ctype.c
+++ b/src/lj_ctype.c
@@ -643,6 +643,18 @@ CTState *lj_ctype_init(lua_State *L)
   return cts;
 }
 
+/* Create special weak-keyed finalizer table. */
+void lj_ctype_initfin(lua_State *L)
+{
+  /* NOBARRIER: The table is new (marked white). */
+  GCtab *t = lj_tab_new(L, 0, 1);
+  setgcref(t->metatable, obj2gco(t));
+  setstrV(L, lj_tab_setstr(L, t, lj_str_newlit(L, "__mode")),
+	  lj_str_newlit(L, "k"));
+  t->nomm = (uint8_t)(~(1u<<MM_mode));
+  setgcref(G(L)->gcroot[GCROOT_FFI_FIN], obj2gco(t));
+}
+
 /* Free C type table and state. */
 void lj_ctype_freestate(global_State *g)
 {
diff --git a/src/lj_ctype.h b/src/lj_ctype.h
index 8edbd561..2d393eb9 100644
--- a/src/lj_ctype.h
+++ b/src/lj_ctype.h
@@ -177,7 +177,6 @@ typedef struct CTState {
   MSize sizetab;	/* Size of C type table. */
   lua_State *L;		/* Lua state (needed for errors and allocations). */
   global_State *g;	/* Global state. */
-  GCtab *finalizer;	/* Map of cdata to finalizer. */
   GCtab *miscmap;	/* Map of -CTypeID to metatable and cb slot to func. */
   CCallback cb;		/* Temporary callback state. */
   CTypeID1 hash[CTHASH_SIZE];  /* Hash anchors for C type table. */
@@ -473,6 +472,7 @@ LJ_FUNC GCstr *lj_ctype_repr(lua_State *L, CTypeID id, GCstr *name);
 LJ_FUNC GCstr *lj_ctype_repr_int64(lua_State *L, uint64_t n, int isunsigned);
 LJ_FUNC GCstr *lj_ctype_repr_complex(lua_State *L, void *sp, CTSize size);
 LJ_FUNC CTState *lj_ctype_init(lua_State *L);
+LJ_FUNC void lj_ctype_initfin(lua_State *L);
 LJ_FUNC void lj_ctype_freestate(global_State *g);
 
 #endif
diff --git a/src/lj_gc.c b/src/lj_gc.c
index 42348a34..4c222f21 100644
--- a/src/lj_gc.c
+++ b/src/lj_gc.c
@@ -99,9 +99,6 @@ static void gc_mark_start(global_State *g)
   gc_markobj(g, tabref(mainthread(g)->env));
   gc_marktv(g, &g->registrytv);
   gc_mark_gcroot(g);
-#if LJ_HASFFI
-  if (ctype_ctsG(g)) gc_markobj(g, ctype_ctsG(g)->finalizer);
-#endif
   g->gc.state = GCSpropagate;
 }
 
@@ -181,8 +178,7 @@ static int gc_traverse_tab(global_State *g, GCtab *t)
     }
     if (weak) {  /* Weak tables are cleared in the atomic phase. */
 #if LJ_HASFFI
-      CTState *cts = ctype_ctsG(g);
-      if (cts && cts->finalizer == t) {
+      if (gcref(g->gcroot[GCROOT_FFI_FIN]) == obj2gco(t)) {
 	weak = (int)(~0u & ~LJ_GC_WEAKVAL);
       } else
 #endif
@@ -550,7 +546,7 @@ static void gc_finalize(lua_State *L)
     o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
     /* Resolve finalizer. */
     setcdataV(L, &tmp, gco2cd(o));
-    tv = lj_tab_set(L, ctype_ctsG(g)->finalizer, &tmp);
+    tv = lj_tab_set(L, tabref(g->gcroot[GCROOT_FFI_FIN]), &tmp);
     if (!tvisnil(tv)) {
       g->gc.nocdatafin = 0;
       copyTV(L, &tmp, tv);
@@ -582,23 +578,20 @@ void lj_gc_finalize_udata(lua_State *L)
 void lj_gc_finalize_cdata(lua_State *L)
 {
   global_State *g = G(L);
-  CTState *cts = ctype_ctsG(g);
-  if (cts) {
-    GCtab *t = cts->finalizer;
-    Node *node = noderef(t->node);
-    ptrdiff_t i;
-    setgcrefnull(t->metatable);  /* Mark finalizer table as disabled. */
-    for (i = (ptrdiff_t)t->hmask; i >= 0; i--)
-      if (!tvisnil(&node[i].val) && tviscdata(&node[i].key)) {
-	GCobj *o = gcV(&node[i].key);
-	TValue tmp;
-	makewhite(g, o);
-	o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
-	copyTV(L, &tmp, &node[i].val);
-	setnilV(&node[i].val);
-	gc_call_finalizer(g, L, &tmp, o);
-      }
-  }
+  GCtab *t = tabref(g->gcroot[GCROOT_FFI_FIN]);
+  Node *node = noderef(t->node);
+  ptrdiff_t i;
+  setgcrefnull(t->metatable);  /* Mark finalizer table as disabled. */
+  for (i = (ptrdiff_t)t->hmask; i >= 0; i--)
+    if (!tvisnil(&node[i].val) && tviscdata(&node[i].key)) {
+      GCobj *o = gcV(&node[i].key);
+      TValue tmp;
+      makewhite(g, o);
+      o->gch.marked &= (uint8_t)~LJ_GC_CDATA_FIN;
+      copyTV(L, &tmp, &node[i].val);
+      setnilV(&node[i].val);
+      gc_call_finalizer(g, L, &tmp, o);
+    }
 }
 #endif
 
@@ -721,7 +714,7 @@ static size_t gc_onestep(lua_State *L)
       return GCFINALIZECOST;
     }
 #if LJ_HASFFI
-    if (!g->gc.nocdatafin) lj_tab_rehash(L, ctype_ctsG(g)->finalizer);
+    if (!g->gc.nocdatafin) lj_tab_rehash(L, tabref(g->gcroot[GCROOT_FFI_FIN]));
 #endif
     g->gc.state = GCSpause;  /* End of GC cycle. */
     g->gc.debt = 0;
diff --git a/src/lj_obj.h b/src/lj_obj.h
index 69e94ff2..06ea0cd0 100644
--- a/src/lj_obj.h
+++ b/src/lj_obj.h
@@ -580,6 +580,9 @@ typedef enum {
   GCROOT_BASEMT_NUM = GCROOT_BASEMT + ~LJ_TNUMX,
   GCROOT_IO_INPUT,	/* Userdata for default I/O input file. */
   GCROOT_IO_OUTPUT,	/* Userdata for default I/O output file. */
+#if LJ_HASFFI
+  GCROOT_FFI_FIN,	/* FFI finalizer table. */
+#endif
   GCROOT_MAX
 } GCRootID;
 
diff --git a/src/lj_state.c b/src/lj_state.c
index 01d4901a..5a920102 100644
--- a/src/lj_state.c
+++ b/src/lj_state.c
@@ -180,6 +180,9 @@ static TValue *cpluaopen(lua_State *L, lua_CFunction dummy, void *ud)
   lj_lex_init(L);
   fixstring(lj_err_str(L, LJ_ERR_ERRMEM));  /* Preallocate memory error msg. */
   g->gc.threshold = 4*g->gc.total;
+#if LJ_HASFFI
+  lj_ctype_initfin(L);
+#endif
   lj_trace_initstate(g);
   lj_err_verify();
   return NULL;
diff --git a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
index c388c6a7..259528cb 100644
--- a/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
+++ b/test/tarantool-c-tests/lj-1168-heap-use-after-free-on-access-to-CTState-finalizer.test.c
@@ -55,10 +55,52 @@ static int unmarked_finalizer_tab_gcstart(void *test_state)
 	return TEST_EXIT_SUCCESS;
 }
 
+static int
+unmarked_finalizer_tab_gcsweep(void *test_state)
+{
+	const char buff[] = "return 1LL";
+
+	/* Shared Lua state is not needed. */
+	(void)test_state;
+
+	/* Setup. */
+	lua_State *L = luaL_newstate();
+
+	/* Set GC at the start. */
+	lua_gc(L, LUA_GCCOLLECT, 0);
+
+	/*
+	 * Default step is too big -- one step ends after the
+	 * atomic phase.
+	 */
+	lua_gc(L, LUA_GCSETSTEPMUL, 1);
+
+	/* Skip marking roots. */
+	lua_gc(L, LUA_GCSTEP, 1);
+
+	/* Not trigger GC during `lua_openffi()`. */
+	lua_gc(L, LUA_GCSTOP, 0);
+
+	int res = luaL_loadbufferx(L, buff, sizeof(buff) - 1, "chunk", "t");
+	assert_true(res == LUA_OK);
+
+	/* Finish GC cycle. */
+	while (!lua_gc(L, LUA_GCSTEP, -1));
+
+	assert_true(lua_gettop(L) == 1);
+
+	/* Teardown. */
+	lua_settop(L, 0);
+	lua_close(L);
+
+	return TEST_EXIT_SUCCESS;
+}
+
 int main(void)
 {
 	const struct test_unit tgroup[] = {
 		test_unit_def(unmarked_finalizer_tab_gcstart),
+		test_unit_def(unmarked_finalizer_tab_gcsweep),
 	};
 	const int test_result = test_run_group(tgroup, NULL);
 
-- 
2.34.1