Commit 9b80e4c4 authored by Kees Cook's avatar Kees Cook
Browse files

overflow: Add __must_check attribute to check_*() helpers 



Since the destination variable of the check_*_overflow() helpers will
contain a wrapped value on failure, it would be best to make sure callers
really did check the return result of the helper. Adjust the macros to use
a bool-wrapping static inline that is marked with __must_check. This means
the macros can continue to have their type-agnostic behavior while gaining
the function attribute (that cannot be applied directly to macros).

Suggested-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Link: https://lore.kernel.org/lkml/202008151007.EF679DF@keescook/


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
parent 9123e3a7

include/linux/overflow.h

+24 −15
Original line number Diff line number Diff line
@@ -43,6 +43,16 @@ 
#define is_non_negative(a) ((a) > 0 || (a) == 0)

#define is_negative(a) (!(is_non_negative(a)))



/*

 * Allows for effectively applying __must_check to a macro so we can have

 * both the type-agnostic benefits of the macros while also being able to

 * enforce that the return value is, in fact, checked.

 */

static inline bool __must_check __must_check_overflow(bool overflow)

{

	return unlikely(overflow);

}



#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW

/*

 * For simplicity and code hygiene, the fallback code below insists on
@@ -52,32 +62,32 @@ 
 * alias for __builtin_add_overflow, but add type checks similar to

 * below.

 */

#define check_add_overflow(a, b, d) ({		\

#define check_add_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_add_overflow(__a, __b, __d);	\

})

}))



#define check_sub_overflow(a, b, d) ({		\

#define check_sub_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_sub_overflow(__a, __b, __d);	\

})

}))



#define check_mul_overflow(a, b, d) ({		\

#define check_mul_overflow(a, b, d) __must_check_overflow(({	\

	typeof(a) __a = (a);			\

	typeof(b) __b = (b);			\

	typeof(d) __d = (d);			\

	(void) (&__a == &__b);			\

	(void) (&__a == __d);			\

	__builtin_mul_overflow(__a, __b, __d);	\

})

}))



#else
@@ -190,21 +200,20 @@ 
})





#define check_add_overflow(a, b, d)					\

#define check_add_overflow(a, b, d)	__must_check_overflow(		\

	__builtin_choose_expr(is_signed_type(typeof(a)),		\

			__signed_add_overflow(a, b, d),			\

			__unsigned_add_overflow(a, b, d))

			__unsigned_add_overflow(a, b, d)))



#define check_sub_overflow(a, b, d)					\

#define check_sub_overflow(a, b, d)	__must_check_overflow(		\

	__builtin_choose_expr(is_signed_type(typeof(a)),		\

			__signed_sub_overflow(a, b, d),			\

			__unsigned_sub_overflow(a, b, d))

			__unsigned_sub_overflow(a, b, d)))



#define check_mul_overflow(a, b, d)					\

#define check_mul_overflow(a, b, d)	__must_check_overflow(		\

	__builtin_choose_expr(is_signed_type(typeof(a)),		\

			__signed_mul_overflow(a, b, d),			\

			__unsigned_mul_overflow(a, b, d))



			__unsigned_mul_overflow(a, b, d)))



#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
@@ -227,7 +236,7 @@ 
 * '*d' will hold the results of the attempted shift, but is not

 * considered "safe for use" if false is returned.

 */

#define check_shl_overflow(a, s, d) ({					\

#define check_shl_overflow(a, s, d) __must_check_overflow(({		\

	typeof(a) _a = a;						\

	typeof(s) _s = s;						\

	typeof(d) _d = d;						\
@@ -237,7 +246,7 @@ 
	*_d = (_a_full << _to_shift);					\

	(_to_shift != _s || is_negative(*_d) || is_negative(_a) ||	\

	(*_d >> _to_shift) != _a);					\

})

}))



/**

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

CRA Git | Maintained and supported by SUSTech CRA and CCSE