linux-kernel - Re: [PATCH -v2] memdup

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Message-Id: <20090308200033.f5282b5b.akpm@linux-foundation.org>
Date:	Sun, 8 Mar 2009 20:00:33 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Arjan van de Ven <arjan@...radead.org>, adobriyan@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -v2] memdup_user(): introduce

On Mon, 09 Mar 2009 10:22:08 +0800 Li Zefan <lizf@...fujitsu.com> wrote:

> >>> +EXPORT_SYMBOL(memdup_user);
> > 
> > Hi,
> > 
> > I like the general idea of this a lot; it will make things much less
> > error prone (and we can add some sanity checks on "len" to catch the
> > standard security holes around copy_from_user usage). I'd even also
> > want a memdup_array() like thing in the style of calloc().
> > 
> > However, I have two questions/suggestions for improvement:
> > 
> > I would like to question the use of the gfp argument here;
> > copy_from_user sleeps, so you can't use GFP_ATOMIC anyway.
> > You can't use GFP_NOFS etc, because the pagefault path will happily do
> > things that are equivalent, if not identical, to GFP_KERNEL.
> > 
> > So the only value you can pass in correctly, as far as I can see, is
> > GFP_KERNEL. Am I wrong?
> > 
> 
> Right! I just dug and found a few kmalloc(GFP_ATOMIC/GFP_NOFS)+copy_from_user(),
> so we have one more reason to use this memdup_user().

gack, those callsites are probably buggy.  Where are they?
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