Re: [PATCH][next] Bluetooth: a2mp: Use struct_size() helper

On 2/7/19 10:00 PM, Joe Perches wrote:

On Thu, 2019-02-07 at 18:28 -0600, Gustavo A. R. Silva wrote:

quoted

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[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = alloc(size, GFP_KERNEL)

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

size = struct_size(instance, entry, count);
instance = alloc(size, GFP_KERNEL)

This code was detected with the help of Coccinelle.

[]

quoted

diff --git a/net/bluetooth/a2mp.c b/net/bluetooth/a2mp.c

[]

quoted

@@ -174,7 +174,7 @@ static int a2mp_discover_req(struct amp_mgr *mgr, struct sk_buff *skb,
 			num_ctrl++;
 	}
 
-	len = num_ctrl * sizeof(struct a2mp_cl) + sizeof(*rsp);
+	len = struct_size(rsp, cl, num_ctrl);
 	rsp = kmalloc(len, GFP_ATOMIC);
 	if (!rsp) {
 		read_unlock(&hci_dev_list_lock);

At least a weakness in this code is len is u16
and struct_size is size_t so there's a size
truncation possible.

That's true.  I didn't change the type to size_t because of the call
to le16_to_cpu():

u16 len = le16_to_cpu(hdr->len);

I've been changing the type of the variable in other cases.

--
Gustavo