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

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Message-ID: <4FAA44D7.1040209@mev.co.uk>
Date:	Wed, 9 May 2012 11:20:07 +0100
From:	Ian Abbott <abbotti@....co.uk>
To:	H Hartley Sweeten <hartleys@...ionengravers.com>
CC:	Linux Kernel <linux-kernel@...r.kernel.org>,
	"devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
	"fmhess@...rs.sourceforge.net" <fmhess@...rs.sourceforge.net>,
	Ian Abbott <ian.abbott@....co.uk>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] staging: comedi: remove __user annotation inside of struct's

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.

-- 
-=( Ian Abbott @ MEV Ltd.    E-mail: <abbotti@....co.uk>        )=-
-=( Tel: +44 (0)161 477 1898   FAX: +44 (0)161 718 3587         )=-
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