linux-kernel - RE: [PATCH] staging: comedi: remove __user annotation inside of struct's

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Date:	Wed, 9 May 2012 10:52:34 -0500
From:	H Hartley Sweeten <hartleys@...ionengravers.com>
To:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	Ian Abbott <abbotti@....co.uk>
CC:	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"fmhess@...rs.sourceforge.net" <fmhess@...rs.sourceforge.net>,
	Ian Abbott <ian.abbott@....co.uk>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] staging: comedi: remove __user annotation inside of
 struct's

On Wednesday, May 09, 2012 7:25 AM, gregkh@...uxfoundation.org wrote:
> On Wed, May 09, 2012 at 11:20:07AM +0100, Ian Abbott wrote:
>> On 2012-05-09 00:55, H Hartley Sweeten wrote:
>>> On Tuesday, May 08, 2012 4:41 PM, H Hartley Sweeten wrote:
>>>>
>>>> The structs' comedi_insn, coomedi_insnlist, comedi_cmd,
>>>> comedi_chaninfo, and comedi_rangeinfo are all passed to
>>>> the kernel from user space using ioctl commands. They
>>>> are then copied to kernel space using copy_from_user()
>>>> before the data is passed to the drivers.
>>>>
>>>> The __user annotation should not be used with variables
>>>> inside the struct. This produces a lot of sparse warnings
>>>> like:
>>>>
>>>>warning: dereference of noderef expression
>>>>
>>>> Signed-off-by: H Hartley Sweeten<hsweeten@...ionengravers.com>
>>>> Cc: Ian Abbott<abbotti@....co.uk>
>>>> Cc: Mori Hess<fmhess@...rs.sourceforge.net>
>>>> Cc: Greg Kroah-Hartman<gregkh@...uxfoundation.org>
>>>>
>>>> ---
>>>>
>>>> Note: This patch exposes some new warnings about different
>>>> address space. These will be addressed.
>>>
>>> Please ignore this patch.
>>>
>>> It appears the annotations in the struct definitions are correct.
>> 
>> Personally, I think you were on the mark with the patch.  It's
>> better to avoid using __user in comedi.h so it can be used as-is in
>> user-space. All of the structures in comedi.h are used in user-space
>> (although Comedilib uses its own version of comedi.h without all the
>> typedef eliminations that have been done in "staging") and some of
>> them are also deep-copied into kernel-space objects of the same
>> type, where the pointers in the structs would no longer be
>> user-space pointers.
>
> When the kernel exports .h files, stuff like this should work
> "automatically", so there is no need to not put __user markings.
>
> So please, yes, continue to work to get this correct, it is very
> essencial to ensure we don't mess stuff up.

Greg,

Based on the discussion I assume this patch is ok then. Do you
want me to repost it?

I'll work on fixing the other issues with the user <-> kernel transitions.

Regards,
Hartley
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