RDMA/hfi1: Use struct_size() and flex_array_size() helpers

Make use of the struct_size() and flex_array_size() helpers instead of
open-coded versions, in order to avoid any potential type mistakes or
integer overflows that, in the worse scenario, could lead to heap
overflows.

Link: https://lore.kernel.org/r/20210927225333.GA192634@embeddedor
Link: https://github.com/KSPP/linux/issues/160Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/hfi1/user_exp_rcv.c

@@ -692,8 +692,7 @@ static int set_rcvarray_entry(struct hfi1_filedata *fd,
 	 * Allocate the node first so we can handle a potential
 	 * failure before we've programmed anything.
 	 */
-	node = kzalloc(sizeof(*node) + (sizeof(struct page *) * npages),
-		       GFP_KERNEL);
+	node = kzalloc(struct_size(node, pages, npages), GFP_KERNEL);
 	if (!node)
 		return -ENOMEM;
 
@@ -713,7 +712,7 @@ static int set_rcvarray_entry(struct hfi1_filedata *fd,
 	node->dma_addr = phys;
 	node->grp = grp;
 	node->freed = false;
-	memcpy(node->pages, pages, sizeof(struct page *) * npages);
+	memcpy(node->pages, pages, flex_array_size(node, pages, npages));
 
 	if (fd->use_mn) {
 		ret = mmu_interval_notifier_insert(