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

[Joe Perches <joe@perches.com>]

On Thu, 2019-02-07 at 18:28 -0600, Gustavo A. R. Silva wrote:
> 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.
[]
> diff --git a/net/bluetooth/a2mp.c b/net/bluetooth/a2mp.c
[]
> @@ -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.