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

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

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Hi, Sergey!
Thanks for the patch!
Please consider my comments below:
  
>from Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>:
> 
>From: Mike Pall <mike>
>
>Thanks to HybridDog.
>
>When build with optimization compiler may throw away overflow check in
>`unpack()` base library function.
Typo: s/build with optimization/built with optimization,
Also,  I think we should mention the specific optimization that causes the mentioned behavior
since it is not mentioned in both the LuaJIT’s issue and the original Lua issue.
>
>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
--
Best regards,
Maxim Kokryashkin

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