linux-kernel - Re: [PATCH v2 6/9] kasan: improve slab object description

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Date:   Mon, 6 Mar 2017 19:12:41 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Andrey Konovalov <andreyknvl@...gle.com>
CC:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 6/9] kasan: improve slab object description

On 03/06/2017 04:45 PM, Andrey Konovalov wrote:
> On Fri, Mar 3, 2017 at 3:39 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>>
>>
>> On 03/03/2017 04:52 PM, Alexander Potapenko wrote:
>>> On Fri, Mar 3, 2017 at 2:31 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
>>>> On 03/02/2017 04:48 PM, Andrey Konovalov wrote:
>>>>> Changes slab object description from:
>>>>>
>>>>> Object at ffff880068388540, in cache kmalloc-128 size: 128
>>>>>
>>>>> to:
>>>>>
>>>>> The buggy address belongs to the object at ffff880068388540
>>>>>  which belongs to the cache kmalloc-128 of size 128
>>>>> The buggy address is located 123 bytes inside of
>>>>>  128-byte region [ffff880068388540, ffff8800683885c0)
>>>>>
>>>>> Makes it more explanatory and adds information about relative offset
>>>>> of the accessed address to the start of the object.
>>>>>
>>>>
>>>> I don't think that this is an improvement. You replaced one simple line with a huge
>>>> and hard to parse text without giving any new/useful information.
>>>> Except maybe offset, it useful sometimes, so wouldn't mind adding it to description.
>>> Agreed.
>>> How about:
>>> ===========
>>> Access 123 bytes inside of 128-byte region [ffff880068388540, ffff8800683885c0)
>>> Object at ffff880068388540 belongs to the cache kmalloc-128
>>> ===========
>>> ?
>>>
>>
>> I would just add the offset in the end:
>>         Object at ffff880068388540, in cache kmalloc-128 size: 128 accessed at offset y
> 
> Access can be inside or outside the object, so it's better to
> specifically say that.
> 

That what access offset and object's size tells us.


> I think we can do (basically what Alexander suggested):
> 
> Object at ffff880068388540 belongs to the cache kmalloc-128 of size 128
> Access 123 bytes inside of 128-byte region [ffff880068388540, ffff8800683885c0)

This is just wrong and therefore very confusing. The message says that we access 123 bytes,
while in fact we access x-bytes at offset 123. IOW 123 sounds like access size here not the offset.


> What do you think?
> 

Not better.