nl80211: Use struct_size() in kzalloc()

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 = kzalloc(size, GFP_KERNEL)

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

instance = kzalloc(struct_size(instance, entry, count), GFP_KERNEL)

Notice that, in this case, variable size_of_regd is not necessary,
hence it is removed.

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -3876,8 +3876,7 @@ static struct cfg80211_acl_data *parse_acl_data(struct wiphy *wiphy,
 	if (n_entries > wiphy->max_acl_mac_addrs)
 		return ERR_PTR(-ENOTSUPP);
 
-	acl = kzalloc(sizeof(*acl) + (sizeof(struct mac_address) * n_entries),
-		      GFP_KERNEL);
+	acl = kzalloc(struct_size(acl, mac_addrs, n_entries), GFP_KERNEL);
 	if (!acl)
 		return ERR_PTR(-ENOMEM);
 
@@ -6916,7 +6915,7 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
 	struct nlattr *nl_reg_rule;
 	char *alpha2;
 	int rem_reg_rules, r;
-	u32 num_rules = 0, rule_idx = 0, size_of_regd;
+	u32 num_rules = 0, rule_idx = 0;
 	enum nl80211_dfs_regions dfs_region = NL80211_DFS_UNSET;
 	struct ieee80211_regdomain *rd;
 
@@ -6941,10 +6940,7 @@ static int nl80211_set_reg(struct sk_buff *skb, struct genl_info *info)
 	if (!reg_is_valid_request(alpha2))
 		return -EINVAL;
 
-	size_of_regd = sizeof(struct ieee80211_regdomain) +
-		       num_rules * sizeof(struct ieee80211_reg_rule);
-
-	rd = kzalloc(size_of_regd, GFP_KERNEL);
+	rd = kzalloc(struct_size(rd, reg_rules, num_rules), GFP_KERNEL);
 	if (!rd)
 		return -ENOMEM;