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

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Date:	Mon, 09 Mar 2009 11:30:18 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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

Andrew Morton wrote:
> 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?
> 

Yes, either buggy or should use GFP_KERNEL.

All are in -mm only, except the first one:

drivers/isdn/i4l/isdn_common.c:
	struct sk_buff *skb = alloc_skb(hl + len, GFP_ATOMIC);
	...
	if (copy_from_user(skb_put(skb, len), buf, len)) {


net/irda/af_irda.c:
	ias_opt = kmalloc(sizeof(struct irda_ias_set), GFP_ATOMIC);
	...
	if (copy_from_user(ias_opt, optval, optlen)) {


fs/btrfs/ioctl.c:
	vol_args = kmalloc(sizeof(*vol_args), GFP_NOFS);
	...
	if (copy_from_user(vol_args, arg, sizeof(*vol_args))) {


fs/ocfs2/dlm/dlmfs.c:
	lvb_buf = kmalloc(writelen, GFP_NOFS);
	...
	bytes_left = copy_from_user(lvb_buf, buf, writelen);


net/sunrpc/auth_gss/auth_gss.c:
	buf = kmalloc(mlen, GFP_NOFS);
	...
	if (copy_from_user(buf, src, mlen))
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