linux-kernel - Re: [PATCH] kasan: report only the first error

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Message-ID: <CAAeHK+zAt=iim4SoU5U8cD8i_yYoC_HGVKSvBGBgEO15KdZEPg@mail.gmail.com>
Date:   Wed, 22 Mar 2017 18:07:32 +0100
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mark Rutland <mark.rutland@....com>,
        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] kasan: report only the first error

On Wed, Mar 22, 2017 at 5:54 PM, Andrey Ryabinin
<aryabinin@...tuozzo.com> wrote:
> On 03/22/2017 07:34 PM, Andrey Konovalov wrote:
>> On Wed, Mar 22, 2017 at 5:06 PM, Andrey Ryabinin
>> <aryabinin@...tuozzo.com> wrote:
>>> Disable kasan after the first report. There are several reasons for this:
>>>  * Single bug quite often has multiple invalid memory accesses causing
>>>     storm in the dmesg.
>>>  * Write OOB access might corrupt metadata so the next report will print
>>>     bogus alloc/free stacktraces.
>>>  * Reports after the first easily could be not bugs by itself but just side
>>>     effects of the first one.
>>>
>>> Given that multiple reports only do harm, it makes sense to disable
>>> kasan after the first one. Except for the tests in lib/test_kasan.c
>>> as we obviously want to see all reports from test.
>>
>> Hi Andrey,
>>
>> Could you make it configurable via CONFIG_KASAN_SOMETHING (which can
>> default to showing only the first report)?
>
> I'd rather make this boot time configurable, but wouldn't want to without
> a good reason.

That would work for me.

>
>
>> I sometimes use KASAN to see what bad accesses a particular bug
>> causes, and seeing all of them (even knowing that they may be
>> corrupt/induced) helps a lot.
>
> I'm wondering why you need to see all reports?

To get a better picture of what are the consequences of a bug. For
example whether it leads to some bad or controllable memory
corruption. Sometimes it's easier to let KASAN track the memory
accesses then do that manually.

>
>>
>> Thanks!
>>