linux-kernel - Re: [PATCH][next] Bluetooth: a2mp: Use struct

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Date:   Thu, 07 Feb 2019 20:00:42 -0800
From:   Joe Perches <joe@...ches.com>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] Bluetooth: a2mp: Use struct_size() helper

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.