cfg80211: 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/reg.c

@@ -427,14 +427,10 @@ static const struct ieee80211_regdomain *
 reg_copy_regd(const struct ieee80211_regdomain *src_regd)
 {
 	struct ieee80211_regdomain *regd;
-	int size_of_regd;
 	unsigned int i;
 
-	size_of_regd =
-		sizeof(struct ieee80211_regdomain) +
-		src_regd->n_reg_rules * sizeof(struct ieee80211_reg_rule);
-
-	regd = kzalloc(size_of_regd, GFP_KERNEL);
+	regd = kzalloc(struct_size(regd, reg_rules, src_regd->n_reg_rules),
+		       GFP_KERNEL);
 	if (!regd)
 		return ERR_PTR(-ENOMEM);
 
@@ -948,12 +944,10 @@ static int regdb_query_country(const struct fwdb_header *db,
 	unsigned int ptr = be16_to_cpu(country->coll_ptr) << 2;
 	struct fwdb_collection *coll = (void *)((u8 *)db + ptr);
 	struct ieee80211_regdomain *regdom;
-	unsigned int size_of_regd, i;
-
-	size_of_regd = sizeof(struct ieee80211_regdomain) +
-		coll->n_rules * sizeof(struct ieee80211_reg_rule);
+	unsigned int i;
 
-	regdom = kzalloc(size_of_regd, GFP_KERNEL);
+	regdom = kzalloc(struct_size(regdom, reg_rules, coll->n_rules),
+			 GFP_KERNEL);
 	if (!regdom)
 		return -ENOMEM;
 
@@ -1450,7 +1444,7 @@ static struct ieee80211_regdomain *
 regdom_intersect(const struct ieee80211_regdomain *rd1,
 		 const struct ieee80211_regdomain *rd2)
 {
-	int r, size_of_regd;
+	int r;
 	unsigned int x, y;
 	unsigned int num_rules = 0;
 	const struct ieee80211_reg_rule *rule1, *rule2;
@@ -1481,10 +1475,7 @@ regdom_intersect(const struct ieee80211_regdomain *rd1,
 	if (!num_rules)
 		return NULL;
 
-	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 NULL;