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

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Date:   Mon, 6 Mar 2017 18:16:47 +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 6:05 PM, Andrey Konovalov <andreyknvl@...gle.com> wrote:
> 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)
>
> ?

Another alternative:

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

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