From: Kees Cook keescook@chromium.org
commit 9b80e4c4ddaca3501177ed41e49d0928ba2122a8 upstream
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: Rasmus Villemoes linux@rasmusvillemoes.dk Link: https://lore.kernel.org/lkml/202008151007.EF679DF@keescook/ Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Florian Fainelli florian.fainelli@broadcom.com --- include/linux/overflow.h | 39 ++++++++++++++++++++++++--------------- 1 file changed, 24 insertions(+), 15 deletions(-)
diff --git a/include/linux/overflow.h b/include/linux/overflow.h index 63e7c77ba942..35af574d006f 100644 --- a/include/linux/overflow.h +++ b/include/linux/overflow.h @@ -44,6 +44,16 @@ #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 @@ -53,32 +63,32 @@ * 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
@@ -191,21 +201,20 @@ })
-#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 */
@@ -228,7 +237,7 @@ * '*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; \ @@ -238,7 +247,7 @@ *_d = (_a_full << _to_shift); \ (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \ (*_d >> _to_shift) != _a); \ -}) +}))
/** * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX