[Tarantool-patches] [PATCH luajit] FFI: Shrink container of packed bitfield.

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

From: Mike Pall <mike>

Reported by Huang Haiyang.

(cherry picked from commit e4c7d8b38040518d42599eef8ddb5e67aa967a9c)

The bitfield of packed structure uses the original type size, which
leads to heap-buffer-overflow access on conversions.

This patch fixes it by adjusting the size of the bitfield container when
necessary.

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

Part of tarantool/tarantool#12880
---

Branch: https://github.com/tarantool/luajit/tree/skaplun/lj-1451-ffi-packed-bitfield
Related issues:
* https://github.com/LuaJIT/LuaJIT/issues/1451
* https://github.com/tarantool/tarantool/issues/12880

 src/lj_cparse.c                               |  2 ++
 .../lj-1451-ffi-packed-bitfield.test.lua      | 28 +++++++++++++++++++
 2 files changed, 30 insertions(+)
 create mode 100644 test/tarantool-tests/lj-1451-ffi-packed-bitfield.test.lua

diff --git a/src/lj_cparse.c b/src/lj_cparse.c
index ff23b44b..1b3ce7ec 100644
--- a/src/lj_cparse.c
+++ b/src/lj_cparse.c
@@ -1341,6 +1341,8 @@ static void cp_struct_layout(CPState *cp, CTypeID sid, CTInfo sattr)
 		     CTALIGN(lj_fls(sz));
 	  ct->size = (bofs >> 3);  /* Store field offset. */
 	} else {
+	  if (csz > amask+1 && bsz <= amask+1)
+	    csz = amask+1;  /* Shrink container of packed bitfield. */
 	  ct->info = CTINFO(CT_BITFIELD,
 	    (info & (CTF_QUAL|CTF_UNSIGNED|CTF_BOOL)) +
 	    (csz << (CTSHIFT_BITCSZ-3)) + (bsz << CTSHIFT_BITBSZ));
diff --git a/test/tarantool-tests/lj-1451-ffi-packed-bitfield.test.lua b/test/tarantool-tests/lj-1451-ffi-packed-bitfield.test.lua
new file mode 100644
index 00000000..07e53f76
--- /dev/null
+++ b/test/tarantool-tests/lj-1451-ffi-packed-bitfield.test.lua
@@ -0,0 +1,28 @@
+local tap = require('tap')
+
+-- Test file to demonstrate LuaJIT's incorrect behaviour of the
+-- `#pragma` pack directive for bitfields in structures.
+-- See also: https://github.com/LuaJIT/LuaJIT/issues/1451.
+
+local test = tap.test('lj-1451-ffi-packed-bitfield')
+
+local ffi = require('ffi')
+
+ffi.cdef[[
+#pragma pack(push, 2)
+typedef struct {
+  unsigned int bitfield:1;
+} packed_struct;
+#pragma pack(pop)
+]]
+
+test:plan(2)
+
+local packed = ffi.new('packed_struct')
+
+test:is(packed.bitfield, 0, 'correct 0-initialization')
+
+packed.bitfield = 1
+test:is(packed.bitfield, 1, 'bitfield set correctly')
+
+test:done(true)
-- 
2.55.0