[Tarantool-patches] [PATCH luajit] FFI: Fix __tostring metamethod access to enum cdata value.

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

From: Mike Pall <mike>

Thanks to Sergey Kaplun.

(cherry picked from commit f2a1cd43281361035149b6eedbd267b5e71d64d0)

On a 64-bit host, `*(uint32_t **)p` (in the
`lj_cf_ffi_meta___tostring()`) is the read of 8 bytes, while the size of
the cdata tail for the enum is only 4. This leads to heap-buffer-overflow
during the call of `tostring()` on the corresponding cdata.

This patch fixes the pointer cast to `(uint32_t *)p`, which is correct.

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

Part of tarantool/tarantool#10199
---

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1232-fix-enum-tostring
Related issues:
* https://github.com/LuaJIT/LuaJIT/issues/1232
* https://github.com/tarantool/tarantool/issues/10199

 src/lib_ffi.c                                 |  2 +-
 .../lj-1232-fix-enum-tostring.test.lua        | 21 +++++++++++++++++++
 2 files changed, 22 insertions(+), 1 deletion(-)
 create mode 100644 test/tarantool-tests/lj-1232-fix-enum-tostring.test.lua

diff --git a/src/lib_ffi.c b/src/lib_ffi.c
index 3c8dd77f..7988dab8 100644
--- a/src/lib_ffi.c
+++ b/src/lib_ffi.c
@@ -305,7 +305,7 @@ LJLIB_CF(ffi_meta___tostring)
       p = *(void **)p;
     } else if (ctype_isenum(ct->info)) {
       msg = "cdata<%s>: %d";
-      p = (void *)(uintptr_t)*(uint32_t **)p;
+      p = (void *)(uintptr_t)*(uint32_t *)p;
     } else {
       if (ctype_isptr(ct->info)) {
 	p = cdata_getptr(p, ct->size);
diff --git a/test/tarantool-tests/lj-1232-fix-enum-tostring.test.lua b/test/tarantool-tests/lj-1232-fix-enum-tostring.test.lua
new file mode 100644
index 00000000..073bfcb6
--- /dev/null
+++ b/test/tarantool-tests/lj-1232-fix-enum-tostring.test.lua
@@ -0,0 +1,21 @@
+local tap = require('tap')
+
+-- Test file to demonstrate heap-buffer-overflow in the
+-- `tostring()` call for the enum cdata.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/1232.
+
+local test = tap.test('lj-1232-fix-enum-tostring')
+
+local ffi = require('ffi')
+local ENUM_VAL = 1
+local EXPECTED = 'cdata<enum %d+>: ' .. ENUM_VAL
+
+test:plan(1)
+
+local cdata_enum = ffi.new(('enum {foo = %d}'):format(ENUM_VAL), ENUM_VAL)
+
+-- XXX: The test shows heap-buffer-overflow only under ASAN.
+
+test:like(tostring(cdata_enum), EXPECTED, 'correct tostring result')
+
+test:done(true)
-- 
2.45.2