ipvs: Use struct_size() helper

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = alloc(size, GFP_KERNEL)

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

size = struct_size(instance, entry, count);

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/ipvs/ip_vs_ctl.c

@@ -2722,8 +2722,7 @@ do_ip_vs_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
 		int size;
 
 		get = (struct ip_vs_get_services *)arg;
-		size = sizeof(*get) +
-			sizeof(struct ip_vs_service_entry) * get->num_services;
+		size = struct_size(get, entrytable, get->num_services);
 		if (*len != size) {
 			pr_err("length: %u != %u\n", *len, size);
 			ret = -EINVAL;
@@ -2764,8 +2763,7 @@ do_ip_vs_get_ctl(struct sock *sk, int cmd, void __user *user, int *len)
 		int size;
 
 		get = (struct ip_vs_get_dests *)arg;
-		size = sizeof(*get) +
-			sizeof(struct ip_vs_dest_entry) * get->num_dests;
+		size = struct_size(get, entrytable, get->num_dests);
 		if (*len != size) {
 			pr_err("length: %u != %u\n", *len, size);
 			ret = -EINVAL;