avoid overflow in integer multiplication

This changeset basically replaces `ruby_xmalloc(x * y)` into
`ruby_xmalloc2(x, y)`.  Some convenient functions are also
provided for instance `rb_xmalloc_mul_add(x, y, z)` which allocates
x * y + z byes.

1 files changed, 1 insertions, 1 deletions

diff --git a/string.c b/string.c
index 3f0e69689c..77f360b8d2 100644
--- a/string.c
+++ b/string.c
@@ -2175,7 +2175,7 @@ rb_str_modify_expand(VALUE str, long expand)
     if (expand < 0) {
 	rb_raise(rb_eArgError, "negative expanding string size");
     }
-    if (expand > LONG_MAX - len) {
+    if (expand >= LONG_MAX - len) {
 	rb_raise(rb_eArgError, "string size too big");
     }