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

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Date:	Mon, 09 Mar 2009 10:22:08 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>, adobriyan@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -v2] memdup_user(): introduce

>>> +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().

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