Commit 610b15c5 authored by Kees Cook's avatar Kees Cook
Browse files

overflow.h: Add allocation size calculation helpers 



In preparation for replacing unchecked overflows for memory allocations,
this creates helpers for the 3 most common calculations:

array_size(a, b): 2-dimensional array
array3_size(a, b, c): 3-dimensional array
struct_size(ptr, member, n): struct followed by n-many trailing members

Each of these return SIZE_MAX on overflow instead of wrapping around.

(Additionally renames a variable named "array_size" to avoid future
collision.)

Co-developed-by: default avatarMatthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 8fee81aa

drivers/md/dm-table.c

+5 −5
Original line number Diff line number Diff line
@@ -548,14 +548,14 @@ static int adjoin(struct dm_table *table, struct dm_target *ti) 
 * On the other hand, dm-switch needs to process bulk data using messages and

 * excessive use of GFP_NOIO could cause trouble.

 */

static char **realloc_argv(unsigned *array_size, char **old_argv)

static char **realloc_argv(unsigned *size, char **old_argv)

{

	char **argv;

	unsigned new_size;

	gfp_t gfp;



	if (*array_size) {

		new_size = *array_size * 2;

	if (*size) {

		new_size = *size * 2;

		gfp = GFP_KERNEL;

	} else {

		new_size = 8;
@@ -563,8 +563,8 @@ static char **realloc_argv(unsigned *array_size, char **old_argv) 
	}

	argv = kmalloc(new_size * sizeof(*argv), gfp);

	if (argv) {

		memcpy(argv, old_argv, *array_size * sizeof(*argv));

		*array_size = new_size;

		memcpy(argv, old_argv, *size * sizeof(*argv));

		*size = new_size;

	}



	kfree(old_argv);

include/linux/overflow.h

+73 −0
Original line number Diff line number Diff line
@@ -202,4 +202,77 @@ 


#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */



/**

 * array_size() - Calculate size of 2-dimensional array.

 *

 * @a: dimension one

 * @b: dimension two

 *

 * Calculates size of 2-dimensional array: @a * @b.

 *

 * Returns: number of bytes needed to represent the array or SIZE_MAX on

 * overflow.

 */

static inline __must_check size_t array_size(size_t a, size_t b)

{

	size_t bytes;



	if (check_mul_overflow(a, b, &bytes))

		return SIZE_MAX;



	return bytes;

}



/**

 * array3_size() - Calculate size of 3-dimensional array.

 *

 * @a: dimension one

 * @b: dimension two

 * @c: dimension three

 *

 * Calculates size of 3-dimensional array: @a * @b * @c.

 *

 * Returns: number of bytes needed to represent the array or SIZE_MAX on

 * overflow.

 */

static inline __must_check size_t array3_size(size_t a, size_t b, size_t c)

{

	size_t bytes;



	if (check_mul_overflow(a, b, &bytes))

		return SIZE_MAX;

	if (check_mul_overflow(bytes, c, &bytes))

		return SIZE_MAX;



	return bytes;

}



static inline __must_check size_t __ab_c_size(size_t n, size_t size, size_t c)

{

	size_t bytes;



	if (check_mul_overflow(n, size, &bytes))

		return SIZE_MAX;

	if (check_add_overflow(bytes, c, &bytes))

		return SIZE_MAX;



	return bytes;

}



/**

 * struct_size() - Calculate size of structure with trailing array.

 * @p: Pointer to the structure.

 * @member: Name of the array member.

 * @n: Number of elements in the array.

 *

 * Calculates size of memory needed for structure @p followed by an

 * array of @n @member elements.

 *

 * Return: number of bytes needed or SIZE_MAX on overflow.

 */

#define struct_size(p, member, n)					\

	__ab_c_size(n,							\

		    sizeof(*(p)->member) + __must_be_array((p)->member),\

		    sizeof(*(p)))



#endif /* __LINUX_OVERFLOW_H */

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