Re: [Tarantool-patches] [PATCH luajit] Fix overflow check in unpack().

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

Hi Sergey!

Thanks for the patch, LGTM.

Sergos.


> On 23 Aug 2022, at 11:06, Sergey Kaplun <skaplun@tarantool.org> wrote:
> 
> From: Mike Pall <mike>
> 
> Thanks to HybridDog.
> 
> When build with optimization compiler may throw away overflow check in
> `unpack()` base library function.
> 
> This patch prevents aforementioned error by comparing the unsigned
> amount of values to unpack with `LUAI_MAXCSTACK` instead of 0.
> 
> Sergey Kaplun:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#7230
> ---
> 
> Issue/PR:
> * https://github.com/LuaJIT/LuaJIT/pull/574
> * https://github.com/tarantool/tarantool/issues/7230
> Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-574-overflow-unpack-full-ci
> PR: https://github.com/tarantool/tarantool/pull/7596
> 
> src/lib_base.c                                       |  6 ++++--
> test/tarantool-tests/lj-574-overflow-unpack.test.lua | 12 ++++++++++++
> 2 files changed, 16 insertions(+), 2 deletions(-)
> create mode 100644 test/tarantool-tests/lj-574-overflow-unpack.test.lua
> 
> diff --git a/src/lib_base.c b/src/lib_base.c
> index 613a1859..cf57b4f2 100644
> --- a/src/lib_base.c
> +++ b/src/lib_base.c
> @@ -224,9 +224,11 @@ LJLIB_CF(unpack)
>   int32_t n, i = lj_lib_optint(L, 2, 1);
>   int32_t e = (L->base+3-1 < L->top && !tvisnil(L->base+3-1)) ?
> 	      lj_lib_checkint(L, 3) : (int32_t)lj_tab_len(t);
> +  uint32_t nu;
>   if (i > e) return 0;
> -  n = e - i + 1;
> -  if (n <= 0 || !lua_checkstack(L, n))
> +  nu = (uint32_t)e - (uint32_t)i;
> +  n = (int32_t)(nu+1);
> +  if (nu >= LUAI_MAXCSTACK || !lua_checkstack(L, n))
>     lj_err_caller(L, LJ_ERR_UNPACK);
>   do {
>     cTValue *tv = lj_tab_getint(t, i);
> diff --git a/test/tarantool-tests/lj-574-overflow-unpack.test.lua b/test/tarantool-tests/lj-574-overflow-unpack.test.lua
> new file mode 100644
> index 00000000..6715d947
> --- /dev/null
> +++ b/test/tarantool-tests/lj-574-overflow-unpack.test.lua
> @@ -0,0 +1,12 @@
> +local tap = require('tap')
> +
> +-- Test file to demonstrate integer overflow in the `unpack()`
> +-- function due to compiler optimization.
> +-- See also https://github.com/LuaJIT/LuaJIT/pull/574.
> +local test = tap.test('lj-574-overflow-unpack')
> +test:plan(1)
> +
> +local r, e = pcall(unpack, {}, 0, 2^31 - 1)
> +test:ok(not r and e == 'too many results to unpack', 'overflow check in unpack')
> +
> +os.exit(test:check() and 0 or 1)
> -- 
> 2.34.1
>