6.12-stable review patch. If anyone has any objections, please let me know.
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From: Kees Cook kees@kernel.org
commit 5c78e793f78732b60276401f75cc1a101f9ad121 upstream.
While not yet in the tree, there is a proposed patch[1] that was depending on the prior behavior of _DEFINE_FLEX, which did not have an explicit initializer. Provide this via __DEFINE_FLEX now, which can also have attributes applied (e.g. __uninitialized).
Examples of the resulting initializer behaviors can be seen here: https://godbolt.org/z/P7Go8Tr33
Link: https://lore.kernel.org/netdev/20250520205920.2134829-9-anthony.l.nguyen@int... [1] Fixes: 47e36ed78406 ("overflow: Fix direct struct member initialization in _DEFINE_FLEX()") Signed-off-by: Kees Cook kees@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/overflow.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-)
--- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -389,25 +389,38 @@ static inline size_t __must_check size_s struct_size((type *)NULL, member, count)
/** - * _DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. - * Enables caller macro to pass (different) initializer. + * __DEFINE_FLEX() - helper macro for DEFINE_FLEX() family. + * Enables caller macro to pass arbitrary trailing expressions * * @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 (e.g., pass `= { }` at minimum). + * @trailer: Trailing expressions for attributes and/or initializers. */ -#define _DEFINE_FLEX(type, name, member, count, initializer...) \ +#define __DEFINE_FLEX(type, name, member, count, trailer...) \ _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 = { .obj initializer }; \ + } name##_u trailer; \ type *name = (type *)&name##_u
/** + * _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 (e.g., pass `= { }` at minimum). + */ +#define _DEFINE_FLEX(type, name, member, count, initializer...) \ + __DEFINE_FLEX(type, name, member, count, = { .obj initializer }) + +/** * 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. * @@ -421,7 +434,7 @@ static inline size_t __must_check size_s * 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(type, name, member, count, = { })
/** * DEFINE_FLEX() - Define an on-stack instance of structure with a trailing