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

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Message-id: <5739F6C0.1000202@samsung.com>
Date:	Mon, 16 May 2016 18:35:12 +0200
From:	Krzysztof Opasiak <k.opasiak@...sung.com>
To:	Michal Nazarewicz <mina86@...a86.com>,
	"Du, Changbin" <changbin.du@...el.com>,
	Felipe Balbi <felipe.balbi@...ux.intel.com>,
	Alan Stern <stern@...land.harvard.edu>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"rui.silva@...aro.org" <rui.silva@...aro.org>,
	"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 Michal,

On 05/16/2016 06:05 PM, Michal Nazarewicz wrote:
> So I’ve been looking at AIO handling in f_fs and either I’m stupid or
> the code is broken.  Here’s part of ffs_user_copy_worker:
> 
> 	int ret = io_data->req->status ? io_data->req->status :
> 					 io_data->req->actual;
> 	if (io_data->read && ret > 0) {
> 		use_mm(io_data->mm);
> 		ret = copy_to_iter(io_data->buf, ret, &io_data->data);
> 		if (iov_iter_count(&io_data->data))
> 			ret = -EFAULT;
> 		unuse_mm(io_data->mm);
> 	}
> 
> First of all, shouldn’t the copy_to_iter invocation be:
> 
> 		if (copy_to_iter(io_data->buf, ret, &io_data->data))
>                 	ret = -EFAULT;
> 
> Second of all, if the request reads fewer bytes than user requested,
> iov_iter_count(…) will be non-zero (namely it will be the difference
> between user’s buffer size and data read).  This should not result in
> EFAULT though.
> 
> So, am I going crazy? Or does this need to be fixed as well?
> 

I think it has been already fixed:

http://permalink.gmane.org/gmane.linux.usb.general/139316

Cheers,
-- 
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics