linux-kernel - RE: [PATCH] usb: gadget: f_fs: report error if excess data received

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Date:	Thu, 12 May 2016 09:51:49 +0000
From:	"Du, Changbin" <changbin.du@...el.com>
To:	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Al Viro <viro@...iv.linux.org.uk>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"mina86@...a86.com" <mina86@...a86.com>,
	"rui.silva@...aro.org" <rui.silva@...aro.org>,
	"k.opasiak@...sung.com" <k.opasiak@...sung.com>,
	"lars@...afoo.de" <lars@...afoo.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb: gadget: f_fs: report error if excess data received

Hi,
> 
> we need a min() here. Better version below:
No need. copy_to_iter will do it for us.

Best Regards,
Du, Changbin

> 
> diff --git a/drivers/usb/gadget/function/f_fs.c
> b/drivers/usb/gadget/function/f_fs.c
> index 73515d54e1cc..6c49b152f46e 100644
> --- a/drivers/usb/gadget/function/f_fs.c
> +++ b/drivers/usb/gadget/function/f_fs.c
> @@ -156,6 +156,8 @@ struct ffs_io_data {
>  	struct usb_request *req;
> 
>  	struct ffs_data *ffs;
> +
> +	ssize_t expected_len;
>  };
> 
>  struct ffs_desc_helper {
> @@ -730,8 +732,10 @@ static ssize_t ffs_epfile_io(struct file *file, struct
> ffs_io_data *io_data)
>  		 * Controller may require buffer size to be aligned to
>  		 * maxpacketsize of an out endpoint.
>  		 */
> -		if (io_data->read)
> +		if (io_data->read) {
> +			io_data->expected_len = data_len;
>  			data_len = usb_ep_align_maybe(gadget, ep->ep,
> data_len);
> +		}
>  		spin_unlock_irq(&epfile->ffs->eps_lock);
> 
>  		data = kmalloc(data_len, GFP_KERNEL);
> @@ -811,7 +815,15 @@ static ssize_t ffs_epfile_io(struct file *file, struct
> ffs_io_data *io_data)
>  		 */
>  		ret = interrupted ? -EINTR : ep->status;
>  		if (io_data->read && ret > 0) {
> -			ret = copy_to_iter(data, ret, &io_data->data);
> +			ssize_t bytes;
> +
> +			if (ret > io_data->expected_len)
> +				pr_debug("FFS: size mismatch: %zd for %zd",
> +						ret, io_data->expected_len);
> +
> +			bytes = min(ret, io_data->expected_len);
> +
> +			ret = copy_to_iter(data, bytes, &io_data->data);
>  			if (!ret)
>  				ret = -EFAULT;
>  		}
> 
> 
> --
> balbi