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.
