From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	"Gustavo A. R. Silva" <gustavoars@kernel.org>,
	Przemek Kitszel <przemyslaw.kitszel@intel.com>,
	Kees Cook <keescook@chromium.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.6 104/166] overflow: Change DEFINE_FLEX to take __counted_by member
Date: Thu, 20 Aug 2026 16:56:03 +0200
Message-ID: <20260820145214.292458934@linuxfoundation.org>
In-Reply-To: <20260820145211.194104353@linuxfoundation.org>
References: <20260820145211.194104353@linuxfoundation.org>
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6.6-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Kees Cook <keescook@chromium.org>

[ Upstream commit d8e45f2929b94099913eb66c3ebb18b5063e9421 ]

The norm should be flexible array structures with __counted_by
annotations, so DEFINE_FLEX() is updated to expect that. Rename
the non-annotated version to DEFINE_RAW_FLEX(), and update the
few existing users. Additionally add selftests for the macros.

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20240306235128.it.933-kees@kernel.org
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Stable-dep-of: cdc36db204ff ("Bluetooth: hci_sync: Fix advertising data UAFs")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/ethernet/intel/ice/ice_switch.c |   10 ++---
 include/linux/overflow.h                    |   52 ++++++++++++++++++++++++++++
 lib/overflow_kunit.c                        |   19 ++++++++++
 3 files changed, 76 insertions(+), 5 deletions(-)

--- a/drivers/net/ethernet/intel/ice/ice_switch.c
+++ b/drivers/net/ethernet/intel/ice/ice_switch.c
@@ -1812,7 +1812,7 @@ ice_aq_alloc_free_vsi_list(struct ice_hw
 			   enum ice_sw_lkup_type lkup_type,
 			   enum ice_adminq_opc opc)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
 	u16 buf_len = __struct_size(sw_buf);
 	struct ice_aqc_res_elem *vsi_ele;
 	int status;
@@ -2082,7 +2082,7 @@ ice_aq_get_recipe_to_profile(struct ice_
  */
 int ice_alloc_recipe(struct ice_hw *hw, u16 *rid)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
 	u16 buf_len = __struct_size(sw_buf);
 	int status;
 
@@ -4425,7 +4425,7 @@ int
 ice_alloc_res_cntr(struct ice_hw *hw, u8 type, u8 alloc_shared, u16 num_items,
 		   u16 *counter_id)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
 	u16 buf_len = __struct_size(buf);
 	int status;
 
@@ -4453,7 +4453,7 @@ int
 ice_free_res_cntr(struct ice_hw *hw, u8 type, u8 alloc_shared, u16 num_items,
 		  u16 counter_id)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
 	u16 buf_len = __struct_size(buf);
 	int status;
 
@@ -4483,7 +4483,7 @@ ice_free_res_cntr(struct ice_hw *hw, u8
  */
 int ice_share_res(struct ice_hw *hw, u16 type, u8 shared, u16 res_id)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, buf, elem, 1);
 	u16 buf_len = __struct_size(buf);
 	int status;
 
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -311,4 +311,56 @@ static inline size_t __must_check size_s
 #define struct_size_t(type, member, count)					\
 	struct_size((type *)NULL, member, count)
 
+/**
+ * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family.
+ * Enables caller macro to pass (different) initializer.
+ *
+ * @type: structure type name, including "struct" keyword.
+ * @name: Name for a variable to define.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ * @initializer: initializer expression (could be empty for no init).
+ */
+#define _DEFINE_FLEX(type, name, member, count, initializer...)			\
+	_Static_assert(__builtin_constant_p(count),				\
+		       "onstack flex array members require compile-time const count"); \
+	union {									\
+		u8 bytes[struct_size_t(type, member, count)];			\
+		type obj;							\
+	} name##_u initializer;							\
+	type *name = (type *)&name##_u
+
+/**
+ * DEFINE_RAW_FLEX() - Define an on-stack instance of structure with a trailing
+ * flexible array member, when it does not have a __counted_by annotation.
+ *
+ * @type: structure type name, including "struct" keyword.
+ * @name: Name for a variable to define.
+ * @member: Name of the array member.
+ * @count: Number of elements in the array; must be compile-time const.
+ *
+ * Define a zeroed, on-stack, instance of @type structure with a trailing
+ * flexible array member.
+ * Use __struct_size(@name) to get compile-time size of it afterwards.
+ */
+#define DEFINE_RAW_FLEX(type, name, member, count)	\
+	_DEFINE_FLEX(type, name, member, count, = {})
+
+/**
+ * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing
+ * flexible array member.
+ *
+ * @TYPE: structure type name, including "struct" keyword.
+ * @NAME: Name for a variable to define.
+ * @MEMBER: Name of the array member.
+ * @COUNTER: Name of the __counted_by member.
+ * @COUNT: Number of elements in the array; must be compile-time const.
+ *
+ * Define a zeroed, on-stack, instance of @TYPE structure with a trailing
+ * flexible array member.
+ * Use __struct_size(@NAME) to get compile-time size of it afterwards.
+ */
+#define DEFINE_FLEX(TYPE, NAME, MEMBER, COUNTER, COUNT)	\
+	_DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .obj.COUNTER = COUNT, })
+
 #endif /* __LINUX_OVERFLOW_H */
--- a/lib/overflow_kunit.c
+++ b/lib/overflow_kunit.c
@@ -1113,6 +1113,24 @@ static void castable_to_type_test(struct
 #undef TEST_CASTABLE_TO_TYPE
 }
 
+struct foo {
+	int a;
+	u32 counter;
+	s16 array[] __counted_by(counter);
+};
+
+static void DEFINE_FLEX_test(struct kunit *test)
+{
+	DEFINE_RAW_FLEX(struct foo, two, array, 2);
+	DEFINE_FLEX(struct foo, eight, array, counter, 8);
+	DEFINE_FLEX(struct foo, empty, array, counter, 0);
+
+	KUNIT_EXPECT_EQ(test, __struct_size(two),
+			sizeof(struct foo) + sizeof(s16) + sizeof(s16));
+	KUNIT_EXPECT_EQ(test, __struct_size(eight), 24);
+	KUNIT_EXPECT_EQ(test, __struct_size(empty), sizeof(struct foo));
+}
+
 static struct kunit_case overflow_test_cases[] = {
 	KUNIT_CASE(u8_u8__u8_overflow_test),
 	KUNIT_CASE(s8_s8__s8_overflow_test),
@@ -1135,6 +1153,7 @@ static struct kunit_case overflow_test_c
 	KUNIT_CASE(overflows_type_test),
 	KUNIT_CASE(same_type_test),
 	KUNIT_CASE(castable_to_type_test),
+	KUNIT_CASE(DEFINE_FLEX_test),
 	{}
 };