bio-integrity: use struct_size() in kmalloc()

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;
    void *entry[];
};

instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);

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

instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);

This code was detected with the help of Coccinelle.

---
 block/bio-integrity.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 1b633a3526d4..ae8c68ecc0ca 100644
@@ -57,8 +57,8 @@ struct bio_integrity_payload *bio_integrity_alloc(struct bio *bio,
 	unsigned inline_vecs;
 
 	if (!bs || !mempool_initialized(&bs->bio_integrity_pool)) {
-		bip = kmalloc(sizeof(struct bio_integrity_payload) +
-			      sizeof(struct bio_vec) * nr_vecs, gfp_mask);
+		bip = kmalloc(struct_size(bip, bip_inline_vecs, nr_vecs),
+			      gfp_mask);
 		inline_vecs = nr_vecs;
 	} else {
 		bip = mempool_alloc(&bs->bio_integrity_pool, gfp_mask);

2.20.1