netfilter: xt_hashlimit: use struct_size() helper

Make use of the struct_size() helper instead of an open-coded version in order to avoid any potential type mistakes, in particular in the context in which this code is being used.

So, replace code of the following form:

sizeof(struct xt_hashlimit_htable) + sizeof(struct hlist_head) * size

with:

struct_size(hinfo, hash, size)

This code was detected with the help of Coccinelle.

---
 net/netfilter/xt_hashlimit.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

index 8d86e39d6280..a30536b17ee1 100644
@@ -288,8 +288,7 @@ static int htable_create(struct net *net, struct hashlimit_cfg3 *cfg,
 			size = 16;
 	}
 	/* FIXME: don't use vmalloc() here or anywhere else -HW */
-	hinfo = vmalloc(sizeof(struct xt_hashlimit_htable) +
-	                sizeof(struct hlist_head) * size);
+	hinfo = vmalloc(struct_size(hinfo, hash, size));
 	if (hinfo == NULL)
 		return -ENOMEM;
 	*out_hinfo = hinfo;

2.21.0

Applied, thanks.