linux-kernel - Re: [PATCH v2 1/2] mm, kasan: improve double-free detection

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Date:	Mon, 9 May 2016 16:34:05 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Dmitry Vyukov <dvyukov@...gle.com>
CC:	"Luruo, Kuthonuzo" <kuthonuzo.luruo@....com>,
	"glider@...gle.com" <glider@...gle.com>,
	"cl@...ux.com" <cl@...ux.com>,
	"penberg@...nel.org" <penberg@...nel.org>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
	"iamjoonsoo.kim@....com" <iamjoonsoo.kim@....com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v2 1/2] mm, kasan: improve double-free detection



On 05/09/2016 04:20 PM, Dmitry Vyukov wrote:
> On Mon, May 9, 2016 at 3:01 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>>
>>
>> On 05/09/2016 02:35 PM, Luruo, Kuthonuzo wrote:
>>>
>>> This patch with atomic bit op is similar in spirit to v1 except that it increases metadata size.
>>>
>>
>> I don't think that this is a big deal. That will slightly increase size of objects <= (128 - 32) bytes.
>> And if someone think otherwise, we can completely remove 'alloc_size'
>> (we use it only to print size in report - not very useful).
> 
> 
> Where did 128 come from?
> We now should allocate only 32 bytes for 16-byte user object. If not,
> there is something to fix.
> 

I just said this wrong. I mean that the patch increases size of objects that have object_size <= (128 - 32).
For bigger objects, the new 'struct kasan_[alloc,free]_meta' still fits into optimal redzone.