lib: objagg: 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 objagg_stats {
	...
        struct objagg_obj_stats_info stats_info[];
};

size = sizeof(*objagg_stats) + sizeof(objagg_stats->stats_info[0]) * count;
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, stats_info, count), GFP_KERNEL);

Notice that, in this case, variable alloc_size 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>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/objagg.c

@@ -605,12 +605,10 @@ const struct objagg_stats *objagg_stats_get(struct objagg *objagg)
 {
 	struct objagg_stats *objagg_stats;
 	struct objagg_obj *objagg_obj;
-	size_t alloc_size;
 	int i;
 
-	alloc_size = sizeof(*objagg_stats) +
-		     sizeof(objagg_stats->stats_info[0]) * objagg->obj_count;
-	objagg_stats = kzalloc(alloc_size, GFP_KERNEL);
+	objagg_stats = kzalloc(struct_size(objagg_stats, stats_info,
+					   objagg->obj_count), GFP_KERNEL);
 	if (!objagg_stats)
 		return ERR_PTR(-ENOMEM);