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overflow: Fix direct struct member initialization in _DEFINE_FLEX()

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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: 26dd68d293 ("overflow: add DEFINE_FLEX() for on-stack allocs")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/aBQVeyKfLOkO9Yss@kspp
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Gustavo A. R. Silva 2025-05-01 18:44:43 -06:00 committed by Kees Cook
parent 6e6500e4e4
commit 47e36ed784
1 changed files with 3 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

6
include/linux/overflow.h
View file

@ -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
/**
@ -444,7 +444,7 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
* elements in array @member.
*/
#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, })
/**
* STACK_FLEX_ARRAY_SIZE() - helper macro for DEFINE_FLEX() family.