From 1f523638b7ac3f03ea172bb14f702ab472b2062c Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Thu, 1 May 2025 18:44:43 -0600 Subject: overflow: Fix direct struct member initialization in _DEFINE_FLEX() [ Upstream commit 47e36ed7840661a9f7fb53554a1b04a5f8daffea ] Currently, to statically initialize the struct members of the `type` object created by _DEFINE_FLEX(), the internal `obj` member must be explicitly referenced at the call site. See: struct flex { int a; int b; struct foo flex_array[]; }; _DEFINE_FLEX(struct flex, instance, flex_array, FIXED_SIZE, = { .obj = { .a = 0, .b = 1, }, }); This leaks _DEFINE_FLEX() internal implementation details and make the helper harder to use and read. Fix this and allow for a more natural and intuitive C99 init-style: _DEFINE_FLEX(struct flex, instance, flex_array, FIXED_SIZE, = { .a = 0, .b = 1, }); Note that before these changes, the `initializer` argument was optional, but now it's required. Also, update "counter" member initialization in DEFINE_FLEX(). Fixes: 26dd68d293fd ("overflow: add DEFINE_FLEX() for on-stack allocs") Signed-off-by: Gustavo A. R. Silva Link: https://lore.kernel.org/r/aBQVeyKfLOkO9Yss@kspp Signed-off-by: Kees Cook Signed-off-by: Sasha Levin --- include/linux/overflow.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'include/linux/overflow.h') diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 0c7e3dcfe867..823a53cd9a19 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -396,7 +396,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * @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). + * @initializer: Initializer expression (e.g., pass `= { }` at minimum). */ #define _DEFINE_FLEX(type, name, member, count, initializer...) \ _Static_assert(__builtin_constant_p(count), \ @@ -404,7 +404,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) union { \ u8 bytes[struct_size_t(type, member, count)]; \ type obj; \ - } name##_u initializer; \ + } name##_u = { .obj initializer }; \ type *name = (type *)&name##_u /** @@ -438,6 +438,6 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * 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, }) + _DEFINE_FLEX(TYPE, NAME, MEMBER, COUNT, = { .COUNTER = COUNT, }) #endif /* __LINUX_OVERFLOW_H */ -- cgit v1.2.3 From a0c3c47f6b1bb613c74d4d1e64c1dd2d31bb60e5 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Fri, 30 May 2025 12:06:47 -0700 Subject: overflow: Introduce __DEFINE_FLEX for having no initializer 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@intel.com [1] Fixes: 47e36ed78406 ("overflow: Fix direct struct member initialization in _DEFINE_FLEX()") Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman --- include/linux/overflow.h | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) (limited to 'include/linux/overflow.h') diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 823a53cd9a19..89e9d6049883 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -389,24 +389,37 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) 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_sub(size_t minuend, size_t subtrahend) * 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 -- cgit v1.2.3