linux-kernel - Re: [PATCH] USB: core: urb: Use struct

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Date:   Tue, 8 Jan 2019 12:36:40 -0500 (EST)
From:   Alan Stern <stern@...land.harvard.edu>
To:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] USB: core: urb: Use struct_size() in kmalloc()

On Tue, 8 Jan 2019, 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;
>     void *entry[];
> };
> 
> instance = kmalloc(sizeof(struct foo) + sizeof(void *) * count, GFP_KERNEL);
> 
> Instead of leaving these open-coded and prone to type mistakes, we can
> now use the new struct_size() helper:
> 
> instance = kmalloc(struct_size(instance, entry, count), GFP_KERNEL);
> 
> This code was detected with the help of Coccinelle.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
> ---
>  drivers/usb/core/urb.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
> index f51750bcd152..0eab79f82ce4 100644
> --- a/drivers/usb/core/urb.c
> +++ b/drivers/usb/core/urb.c
> @@ -70,9 +70,8 @@ struct urb *usb_alloc_urb(int iso_packets, gfp_t mem_flags)
>  {
>  	struct urb *urb;
>  
> -	urb = kmalloc(sizeof(struct urb) +
> -		iso_packets * sizeof(struct usb_iso_packet_descriptor),
> -		mem_flags);
> +	urb = kmalloc(struct_size(urb, iso_frame_desc, iso_packets),
> +		      mem_flags);
>  	if (!urb)
>  		return NULL;
>  	usb_init_urb(urb);

Acked-by: Alan Stern <stern@...land.harvard.edu>