Re: [PATCH] usb: use memdup_user()

From: Oliver Neukum <oliver@neukum.org>
To: Greg KH <greg@kroah.com>
Cc: Pekka Enberg <penberg@cs.helsinki.fi>,
	David Brownell <david-b@pacbell.net>,
	Li Hong <lihong.hi@gmail.com>,
	linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] usb: use memdup_user()
Date: Tue, 5 May 2009 10:50:52 +0200	[thread overview]
Message-ID: <200905051050.52768.oliver@neukum.org> (raw)
In-Reply-To: <20090504145348.GA10545@kroah.com>

Am Montag, 4. Mai 2009 16:53:48 schrieb Greg KH:
> > On Mon, May 4, 2009 at 10:02 AM, David Brownell <david-b@pacbell.net> 
wrote:
> > > Unless it's incorrect to use that, I have to say that it
> > > makes more sense to use that utility than recreate it by
> > > open-coding...
> >
> > Yup, and I don't really see how anyone can avoid "thinking about a new
> > primitive" anyway. We have it in the kernel now and surely it will
> > appear under drivers/usb/ sooner or later...
>
> Well, how about passing the GPF flags down to memdup_user() so that we
> can use it in the usb subsystem, and Oliver's complaint will be resolve?

It would always be GFP_KERNEL. Unless you can use GFP_KERNEL you must
not use copy_to/from_user. It would not make sense for all other users of that
API. I don't think that the API as such is bad, just that USB needs extra care
with memory allocations (and user memory access)

We are limited to GFP_NOIO during pre/post_reset and suspend/resume
and while we hold any locks these methods take. This is not simple and
people need to be reminded.

	Regards
		Oliver