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

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Message-ID: <CAAeHK+w087z_pEWN=ZBDZN=XqqQMFZ9eevX44LERFV-d=G3F8g@mail.gmail.com>
Date:   Mon, 6 Mar 2017 18:05:28 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.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 Mon, Mar 6, 2017 at 5:12 PM, Andrey Ryabinin <aryabinin@...tuozzo.com> wrote:
> 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 about

Object at ffff880068388540 belongs to cache kmalloc-128 of size 128
Accessed address is 123 bytes inside of [ffff880068388540, ffff8800683885c0)

?

>
>
>> What do you think?
>>
>
> Not better.