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overflow: Provide constant expression struct_size

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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 <gustavoars@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Tested-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/lkml/20220210010407.GA701603@embeddedor
This commit is contained in:
Kees Cook 2022-02-09 16:40:41 -08:00
parent e1be43d9b5
commit 230f6fa2c1
2 changed files with 24 additions and 12 deletions
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10
include/linux/overflow.h
View File

@ -4,6 +4,7 @@
#include <linux/compiler.h>
#include <linux/limits.h>
#include <linux/const.h>
/*
* 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 */

26
lib/test_overflow.c
View File

@ -602,10 +602,18 @@ struct __test_flex_array {
static int __init test_overflow_size_helpers(void)
{
/* Make sure struct_size() can be used in a constant expression. */
u8 ce_array[struct_size((struct __test_flex_array *)0, data, 55)];
struct __test_flex_array *obj;
int count = 0;
int err = 0;
int var;
volatile int unconst = 0;
/* Verify constant expression against runtime version. */
var = 55;
OPTIMIZER_HIDE_VAR(var);
err |= sizeof(ce_array) != struct_size(obj, data, var);
#define check_one_size_helper(expected, func, args...) ({ \
bool __failure = false; \
@ -663,28 +671,28 @@ static int __init test_overflow_size_helpers(void)
flex_array_size, obj, data, var++);
err |= check_one_size_helper(5 * sizeof(*obj->data),
flex_array_size, obj, data, var++);
err |= check_one_size_helper(0, flex_array_size, obj, data, 0);
err |= check_one_size_helper(0, flex_array_size, obj, data, 0 + unconst);
err |= check_one_size_helper(sizeof(*obj->data),
flex_array_size, obj, data, 1);
flex_array_size, obj, data, 1 + unconst);
err |= check_one_size_helper(7 * sizeof(*obj->data),
flex_array_size, obj, data, 7);
flex_array_size, obj, data, 7 + unconst);
err |= check_one_size_helper(SIZE_MAX,
flex_array_size, obj, data, -1);
flex_array_size, obj, data, -1 + unconst);
err |= check_one_size_helper(SIZE_MAX,
flex_array_size, obj, data, SIZE_MAX - 4);
flex_array_size, obj, data, SIZE_MAX - 4 + unconst);
var = 4;
err |= check_one_size_helper(sizeof(*obj) + (4 * sizeof(*obj->data)),
struct_size, obj, data, var++);
err |= check_one_size_helper(sizeof(*obj) + (5 * sizeof(*obj->data)),
struct_size, obj, data, var++);
err |= check_one_size_helper(sizeof(*obj), struct_size, obj, data, 0);
err |= check_one_size_helper(sizeof(*obj), struct_size, obj, data, 0 + unconst);
err |= check_one_size_helper(sizeof(*obj) + sizeof(*obj->data),
struct_size, obj, data, 1);
struct_size, obj, data, 1 + unconst);
err |= check_one_size_helper(SIZE_MAX,
struct_size, obj, data, -3);
struct_size, obj, data, -3 + unconst);
err |= check_one_size_helper(SIZE_MAX,
struct_size, obj, data, SIZE_MAX - 3);
struct_size, obj, data, SIZE_MAX - 3 + unconst);
pr_info("%d overflow size helper tests finished\n", count);