flow_offload: 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[];
};

instance = kzalloc(sizeof(struct foo) + count * sizeof(struct boo), 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);

This code was detected with the help of Coccinelle.

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

index 5ce7d47a960e..3d93e51b83e0 100644
@@ -7,8 +7,7 @@ struct flow_rule *flow_rule_alloc(unsigned int num_actions)
 {
 	struct flow_rule *rule;
 
-	rule = kzalloc(sizeof(struct flow_rule) +
-		       sizeof(struct flow_action_entry) * num_actions,
+	rule = kzalloc(struct_size(rule, action.entries, num_actions),
 		       GFP_KERNEL);
 	if (!rule)
 		return NULL;

2.21.0

From: "Gustavo A. R. Silva" <[email protected]>
Date: Thu, 23 May 2019 17:56:53 -0500

Applied.