[Tarantool-patches] [PATCH luajit] Fix predict_next() in parser (again).

[Sergey Bronnikov via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

From: sergeyb@tarantool.org

Reported by Sergey Bronnikov. #1054

(cherry picked from commit 309fb42b871b6414f53e0e0e708bce0b0d62daff)

The following Lua snippet triggers an out of boundary access to a stack:

```lua
a, b, c = 1, 2, 3
local d
for _ in nil do end
```

With execution snippet by LuaJIT instrumented by ASAN it leads to
a heap-buffer-overflow.

In a function `predict_next` variable `exprpc` looks forward and expects
extra bytecodes on the stack. However, `KPRI` is merged to the `KNIL`
and there is no new bytecode to add, so `exprpc == fs->bclim` and it
leads to out of boundary access.

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

Part of tarantool/tarantool#8825
---

PR: https://github.com/tarantool/tarantool/pull/9054
Branch: https://github.com/tarantool/luajit/tree/ligurio/lj-1054-incorrect-pc-value-predict_next
Related issue:
* https://github.com/LuaJIT/LuaJIT/issues/1054

 src/lj_parse.c                                 |  4 +++-
 ...incorrect-pc-value-in-predict_next.test.lua | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 test/tarantool-tests/lj-1054-incorrect-pc-value-in-predict_next.test.lua

diff --git a/src/lj_parse.c b/src/lj_parse.c
index 343fa797..f1015960 100644
--- a/src/lj_parse.c
+++ b/src/lj_parse.c
@@ -2511,9 +2511,11 @@ static void parse_for_num(LexState *ls, GCstr *varname, BCLine line)
 */
 static int predict_next(LexState *ls, FuncState *fs, BCPos pc)
 {
-  BCIns ins = fs->bcbase[pc].ins;
+  BCIns ins;
   GCstr *name;
   cTValue *o;
+  if (pc >= fs->bclim) return 0;
+  ins = fs->bcbase[pc].ins;
   switch (bc_op(ins)) {
   case BC_MOV:
     name = gco2str(gcref(var_get(ls, fs, bc_d(ins)).name));
diff --git a/test/tarantool-tests/lj-1054-incorrect-pc-value-in-predict_next.test.lua b/test/tarantool-tests/lj-1054-incorrect-pc-value-in-predict_next.test.lua
new file mode 100644
index 00000000..17f1b994
--- /dev/null
+++ b/test/tarantool-tests/lj-1054-incorrect-pc-value-in-predict_next.test.lua
@@ -0,0 +1,18 @@
+local tap = require('tap')
+local test = tap.test('lj-1054-incorrect-pc-value-in-predict_next')
+test:plan(1)
+
+
+-- The test demonstrates a problem with out of boundary access to a stack.
+-- Sample executed in LuaJIT instrumented by ASAN leads to
+-- a heap-buffer-overflow.
+-- See also https://github.com/LuaJIT/LuaJIT/issues/528
+local lua_code = [[
+a, b, c = 1, 2, 3
+local d
+for _ in nil do end
+]]
+
+test:ok(loadstring(lua_code), 'parsing is correct')
+
+test:done(true)
-- 
2.34.1