net: hns: Prefer struct_size over open coded arithmetic

As noted in the "Deprecated Interfaces, Language Features, Attributes,
and Conventions" documentation [1], size calculations (especially
multiplication) should not be performed in memory allocator (or similar)
function arguments due to the risk of them overflowing. This could lead
to values wrapping around and a smaller allocation being made than the
caller was expecting. Using those allocations could lead to linear
overflows of heap memory and other misbehaviors.

So, take the opportunity to refactor the hnae_handle structure to switch
the last member to flexible array, changing the code accordingly. Also,
fix the comment in the hnae_vf_cb structure to inform that the ae_handle
member must be the last member.

Then, use the struct_size() helper to do the arithmetic instead of the
argument "size + count * size" in the kzalloc() function.

This code was detected with the help of Coccinelle and audited and fixed
manually.

[1] https://www.kernel.org/doc/html/latest/process/deprecated.html#open-coded-arithmetic-in-allocator-arguments

Signed-off-by: Len Baker <len.baker@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/hisilicon/hns/hnae.h

@@ -558,7 +558,7 @@ struct hnae_handle {
 	enum hnae_media_type media_type;
 	struct list_head node;    /* list to hnae_ae_dev->handle_list */
 	struct hnae_buf_ops *bops; /* operation for the buffer */
-	struct hnae_queue **qs;  /* array base of all queues */
+	struct hnae_queue *qs[];  /* flexible array of all queues */
 };
 
 #define ring_to_dev(ring) ((ring)->q->dev->dev)

drivers/net/ethernet/hisilicon/hns/hns_ae_adapt.c

@@ -81,8 +81,8 @@ static struct hnae_handle *hns_ae_get_handle(struct hnae_ae_dev *dev,
 	vfnum_per_port = hns_ae_get_vf_num_per_port(dsaf_dev, port_id);
 	qnum_per_vf = hns_ae_get_q_num_per_vf(dsaf_dev, port_id);
 
-	vf_cb = kzalloc(sizeof(*vf_cb) +
-			qnum_per_vf * sizeof(struct hnae_queue *), GFP_KERNEL);
+	vf_cb = kzalloc(struct_size(vf_cb, ae_handle.qs, qnum_per_vf),
+			GFP_KERNEL);
 	if (unlikely(!vf_cb)) {
 		dev_err(dsaf_dev->dev, "malloc vf_cb fail!\n");
 		ae_handle = ERR_PTR(-ENOMEM);
@@ -108,7 +108,6 @@ static struct hnae_handle *hns_ae_get_handle(struct hnae_ae_dev *dev,
 		goto vf_id_err;
 	}
 
-	ae_handle->qs = (struct hnae_queue **)(&ae_handle->qs + 1);
 	for (i = 0; i < qnum_per_vf; i++) {
 		ae_handle->qs[i] = &ring_pair_cb->q;
 		ae_handle->qs[i]->rx_ring.q = ae_handle->qs[i];

drivers/net/ethernet/hisilicon/hns/hns_dsaf_main.h

@@ -210,7 +210,7 @@ struct hnae_vf_cb {
 	u8 port_index;
 	struct hns_mac_cb *mac_cb;
 	struct dsaf_device *dsaf_dev;
-	struct hnae_handle  ae_handle; /* must be the last number */
+	struct hnae_handle  ae_handle; /* must be the last member */
 };
 
 struct dsaf_int_xge_src {