* [2.25 COMMITTED] Add check_mul_overflow_size_t
@ 2018-01-01 0:00 Florian Weimer
0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2018-01-01 0:00 UTC (permalink / raw)
To: libc-stable
Backported from commit 2e0bbbfbf95fc9e22692e93658a6fbdd2d4554da.
2018-01-04 Florian Weimer <fweimer@redhat.com>
* malloc/malloc-internal.h (check_mul_overflow_size_t): New.
diff --git a/malloc/malloc-internal.h b/malloc/malloc-internal.h
index de6103d7e1..dbd801a58e 100644
--- a/malloc/malloc-internal.h
+++ b/malloc/malloc-internal.h
@@ -81,5 +81,24 @@ void __malloc_fork_unlock_parent (void) internal_function attribute_hidden;
/* Called in the child process after a fork. */
void __malloc_fork_unlock_child (void) internal_function attribute_hidden;
+/* Set *RESULT to LEFT * RIGHT. Return true if the multiplication
+ overflowed. */
+static inline bool
+check_mul_overflow_size_t (size_t left, size_t right, size_t *result)
+{
+#if __GNUC__ >= 5
+ return __builtin_mul_overflow (left, right, result);
+#else
+ /* size_t is unsigned so the behavior on overflow is defined. */
+ *result = left * right;
+ size_t half_size_t = ((size_t) 1) << (8 * sizeof (size_t) / 2);
+ if (__glibc_unlikely ((left | right) >= half_size_t))
+ {
+ if (__glibc_unlikely (right != 0 && *result / right != left))
+ return true;
+ }
+ return false;
+#endif
+}
#endif /* _MALLOC_INTERNAL_H */
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