From 230f6fa2c1db6a3f3e668cfe95995ac8e6eee212 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Wed, 9 Feb 2022 16:40:41 -0800 Subject: overflow: Provide constant expression struct_size There have been cases where struct_size() (or flex_array_size()) needs to be calculated for an initializer, which requires it be a constant expression. This is possible when the "count" argument is a constant expression, so provide this ability for the helpers. Cc: Gustavo A. R. Silva Cc: Nathan Chancellor Cc: Nick Desaulniers Cc: Rasmus Villemoes Signed-off-by: Kees Cook Reviewed-by: Gustavo A. R. Silva Tested-by: Gustavo A. R. Silva Link: https://lore.kernel.org/lkml/20220210010407.GA701603@embeddedor --- include/linux/overflow.h | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) (limited to 'include/linux/overflow.h') diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 59d7228104d0..f1221d11f8e5 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -4,6 +4,7 @@ #include #include +#include /* * We need to compute the minimum and maximum values representable in a given @@ -221,8 +222,9 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * Return: number of bytes needed or SIZE_MAX on overflow. */ #define flex_array_size(p, member, count) \ - size_mul(count, \ - sizeof(*(p)->member) + __must_be_array((p)->member)) + __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))) /** * struct_size() - Calculate size of structure with trailing flexible array. @@ -237,6 +239,8 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) * Return: number of bytes needed or SIZE_MAX on overflow. */ #define struct_size(p, member, count) \ - size_add(sizeof(*(p)), flex_array_size(p, member, count)) + __builtin_choose_expr(__is_constexpr(count), \ + sizeof(*(p)) + flex_array_size(p, member, count), \ + size_add(sizeof(*(p)), flex_array_size(p, member, count))) #endif /* __LINUX_OVERFLOW_H */ -- cgit v1.2.3