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overflow: Match arithmetic in both parts of __builtin_choose_expr

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The two parts of '__builtin_choose_expr()' had different arithmetic
expressions. This patch corrects it so that both parts calculate:

  COUNT * sizeof(*MEMBER) + __must_be_array(MEMBER)

In practice, '__must_be_array' is meant to assert if 'MEMBER' isn't an
array and return '0' otherwise. However, symmetry is less prone to
subtle errors (and far more satisfying).

Signed-off-by: Bill Wendling <morbo@google.com>
Link: https://patch.msgid.link/20261013203146.387344-1-morbo@google.com
Signed-off-by: Kees Cook <kees@kernel.org>
This commit is contained in:
Bill Wendling 2026-10-13 20:31:46 +00:00 committed by Kees Cook
parent e2cd253cb3
commit 2f70a9b7e9
1 changed files with 1 additions and 1 deletions
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2
include/linux/overflow.h
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@ -418,7 +418,7 @@ static __always_inline size_t __must_check size_sub(size_t minuend, size_t subtr
#define flex_array_size(p, member, count) \
__builtin_choose_expr(__is_constexpr(count), \
(count) * sizeof(*(p)->member) + __must_be_array((p)->member), \
size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member)))
size_mul(count, sizeof(*(p)->member)) + __must_be_array((p)->member))
/**
* struct_size() - Calculate size of structure with trailing flexible array.