linux-hardening - [PATCH 1/2] stddef: Allow attributes to be used when creating flex arrays

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Date: Fri,  9 Feb 2024 17:16:41 -0800
From: Kees Cook <keescook@...omium.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	"Gustavo A . R . Silva" <gustavoars@...nel.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Dan Williams <dan.j.williams@...el.com>,
	Keith Packard <keithp@...thp.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Dmitry Antipov <dmantipov@...dex.ru>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>,
	Nathan Chancellor <nathan@...nel.org>,
	kernel test robot <lkp@...el.com>,
	linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [PATCH 1/2] stddef: Allow attributes to be used when creating flex arrays

With the coming support for the __counted_by struct member attribute, we
will need a way to add such annotations to the places where
DECLARE_FLEX_ARRAY() is used. Introduce DECLARE_FLEX_ARRAY_ATTR() which
takes a third argument: the attributes to apply to the flexible array.

Cc: Gustavo A. R. Silva <gustavoars@...nel.org>
Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Keith Packard <keithp@...thp.com>
Cc: Miguel Ojeda <ojeda@...nel.org>
Cc: Alexey Dobriyan <adobriyan@...il.com>
Cc: Dmitry Antipov <dmantipov@...dex.ru>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/stddef.h      | 16 ++++++++++++++--
 include/uapi/linux/stddef.h | 25 +++++++++++++++++++------
 2 files changed, 33 insertions(+), 8 deletions(-)

diff --git a/include/linux/stddef.h b/include/linux/stddef.h
index 929d67710cc5..eb51f6727ecf 100644
--- a/include/linux/stddef.h
+++ b/include/linux/stddef.h
@@ -81,8 +81,20 @@ enum {
 	__struct_group(TAG, NAME, /* no attrs */, MEMBERS)
 
 /**
- * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ * DECLARE_FLEX_ARRAY_ATTR() - Declare a flexible array usable in a union
+ * @TYPE: The type of each flexible array element
+ * @NAME: The name of the flexible array member
+ * @ATTRS: The list of member attributes to apply
  *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS) \
+	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)
+
+/**
+ * DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
  * @TYPE: The type of each flexible array element
  * @NAME: The name of the flexible array member
  *
@@ -91,6 +103,6 @@ enum {
  * named member, but that member can be empty.
  */
 #define DECLARE_FLEX_ARRAY(TYPE, NAME) \
-	__DECLARE_FLEX_ARRAY(TYPE, NAME)
+	DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
 
 #endif
diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h
index 2ec6f35cda32..5499c08ad011 100644
--- a/include/uapi/linux/stddef.h
+++ b/include/uapi/linux/stddef.h
@@ -31,24 +31,37 @@
 
 #ifdef __cplusplus
 /* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */
-#define __DECLARE_FLEX_ARRAY(T, member)	\
-	T member[0]
+#define __DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)	\
+	TYPE NAME[0] ATTRS
+#define __DECLARE_FLEX_ARRAY(TYPE, NAME)		\
+	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
 #else
 /**
- * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
- *
+ * __DECLARE_FLEX_ARRAY_ATTR() - Declare a flexible array usable in a union
  * @TYPE: The type of each flexible array element
  * @NAME: The name of the flexible array member
+ * @ATTRS: The list of member attributes to apply
  *
  * In order to have a flexible array member in a union or alone in a
  * struct, it needs to be wrapped in an anonymous struct with at least 1
  * named member, but that member can be empty.
  */
-#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
+#define __DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, ATTRS)	\
 	struct { \
 		struct { } __empty_ ## NAME; \
-		TYPE NAME[]; \
+		TYPE NAME[] ATTRS; \
 	}
+/**
+ * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union
+ * @TYPE: The type of each flexible array element
+ * @NAME: The name of the flexible array member
+ *
+ * In order to have a flexible array member in a union or alone in a
+ * struct, it needs to be wrapped in an anonymous struct with at least 1
+ * named member, but that member can be empty.
+ */
+#define __DECLARE_FLEX_ARRAY(TYPE, NAME)	\
+	__DECLARE_FLEX_ARRAY_ATTR(TYPE, NAME, /* no attributes */)
 #endif
 
 #ifndef __counted_by
-- 
2.34.1