linux-kernel - Re: [PATCH] zram: Prevent use of unmapped buffer

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Date:	Thu, 29 Nov 2012 11:08:18 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Nitin Gupta <ngupta@...are.org>
Cc:	Greg KH <greg@...ah.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Sam Hansen <solid.se7en@...il.com>, Tomas M <tomas@...x.org>,
	Mihail Kasadjikov <hamer.mk@...il.com>,
	Linux Driver Project <devel@...uxdriverproject.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] zram: Prevent use of unmapped buffer

On Thu, Nov 29, 2012 at 10:45 AM, Nitin Gupta <ngupta@...are.org> wrote:
> On 11/28/2012 05:33 PM, Minchan Kim wrote:
>>
>> On Wed, Nov 28, 2012 at 02:15:05PM +0900, Minchan Kim wrote:
>>>
>>> Hi Nitin,
>>>
>>> On Mon, Nov 26, 2012 at 11:26:07PM -0800, Nitin Gupta wrote:
>>>>
>>>> The commit c8f2f0db1 ("zram: Fix handling of incompressible pages")
>>>> introduced a bug which caused a kunmap()'ed buffer to be used in case
>>>
>>> I got confused by the descripton. :(
>>> The descripton is not right.
>>> The problem is to access freed memory, not accessing to kunmaped buffer.
>>>
>>> partial I/O write.
>>>
>>> 1. uncmem = kmalloc
>>> 2. zram_decompress_page(uncmem)
>>> 3. memcpy(uncmem, user_mem)
>>> 4. lzo1x_1_compress(uncmem)
>>> 5. kfree(uncmem)
>>> 6. src = uncmem
>>> 7. memcpy(cmem, src, clen) <----- HIT
>>>
>>>> of partial writes where the data was found to be incompressible.
>>>>
>> I got it. You shouldn't mention partial write for proper description
>> because it was usecase for swap-over-zram so it can't make partial write.
>> Without partial write mention, your description is right but the problem
>> I mentioned above is another problem for partial write so we need a
>> another
>> patch. I will cook.
>
>
> I will include explanation of both the cases: use of unmapped buffer
> and freed buffer, when I resend these patches.
>

As you know, I am going to solve lockdep problem and disksize setting problem.
Apparently, it conflict with your diet series.
So I would like to order our patches following as.

1. bug fix patch of unmapped/freed buffer - Nitin
2. diet patch based on 1 - Nitin
3. disksize setting and lockdep problem - Minchan

I will wait your two patchsets.
If you have some trouble to hold the time to make the patch, please tell me.
I will send 1 and 3 ahead so you can send 2 based on it.

-- 
Kind regards,
Minchan Kim
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