add fortified implementations of fread/fwrite
A __size_mul_overflow utility is used to take advantage of the checked
overflow intrinsics in Clang and GCC (>= 5). The fallback for older
compilers is the optimized but less than ideal overflow checking pattern
used in OpenBSD.
Change-Id: Ibb0d4fd9b5acb67983e6a9f46844c2fd444f7e69
diff --git a/libc/include/sys/cdefs.h b/libc/include/sys/cdefs.h
index 7df8b60..8a11bc6 100644
--- a/libc/include/sys/cdefs.h
+++ b/libc/include/sys/cdefs.h
@@ -578,4 +578,19 @@
#define _BIONIC_NOT_BEFORE_21(x)
#endif /* __ANDROID_API__ >= 21 */
+#if __has_builtin(__builtin_umul_overflow) || __GNUC__ >= 5
+#if __LP64__
+#define __size_mul_overflow(a, b, result) __builtin_umull_overflow(a, b, result)
+#else
+#define __size_mul_overflow(a, b, result) __builtin_umul_overflow(a, b, result)
+#endif
+#else
+static __inline__ __always_inline int __size_mul_overflow(__SIZE_TYPE__ a, __SIZE_TYPE__ b,
+ __SIZE_TYPE__ *result) {
+ *result = a * b;
+ static const __SIZE_TYPE__ mul_no_overflow = 1UL << (sizeof(__SIZE_TYPE__) * 4);
+ return (a >= mul_no_overflow || b >= mul_no_overflow) && a > 0 && (__SIZE_TYPE__)-1 / a < b;
+}
+#endif
+
#endif /* !_SYS_CDEFS_H_ */