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

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Date:	Wed, 9 May 2012 07:24:36 -0700
From:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:	Ian Abbott <abbotti@....co.uk>
Cc:	H Hartley Sweeten <hartleys@...ionengravers.com>,
	"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 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.

thanks,

greg k-h
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