linux-kernel - Re: Fw: [PATCH] lib/kstrtox.c Stop parsing integer on overflow

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Message-ID: <CACVxJT9+9SqOqj91bVXHEugi8JL6G8oVqH-AKLnHW8ydENLQPQ@mail.gmail.com>
Date:	Fri, 20 Feb 2015 14:08:04 +0300
From:	Alexey Dobriyan <adobriyan@...il.com>
To:	Anshul Garg <aksgarg1989@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Fw: [PATCH] lib/kstrtox.c Stop parsing integer on overflow

On Thu, Feb 19, 2015 at 8:53 PM, Anshul Garg <aksgarg1989@...il.com> wrote:
> On Wed, Feb 18, 2015 at 1:14 PM, Alexey Dobriyan <adobriyan@...il.com> wrote:
>> On Tue, Feb 17, 2015 at 04:17:24PM -0800, Andrew Morton wrote:
>>> ?
>>>
>>> Begin forwarded message:
>>>
>>> Date: Mon, 16 Feb 2015 10:48:50 -0800
>>> From: Anshul Garg <aksgarg1989@...il.com>
>>> To: linux-kernel@...r.kernel.org
>>> Cc: aksgarg1989@...il.com, anshul.g@...sung.com, torvalds@...ux-foundation.org
>>> Subject: [PATCH] lib/kstrtox.c Stop parsing integer on overflow
>>>
>>>
>>> From: Anshul Garg <aksgarg1989@...il.com>
>>>
>>> While converting string representation to integer
>>> break the loop if overflow is detected.
>>>
>>> Signed-off-by: Anshul Garg <aksgarg1989@...il.com>
>>> ---
>>>  lib/kstrtox.c |    4 +++-
>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/lib/kstrtox.c b/lib/kstrtox.c
>>> index ec8da78..6f30209 100644
>>> --- a/lib/kstrtox.c
>>> +++ b/lib/kstrtox.c
>>> @@ -70,8 +70,10 @@ unsigned int _parse_integer(const char *s, unsigned int base, unsigned long long
>>>                * it in the max base we support (16)
>>>                */
>>>               if (unlikely(res & (~0ull << 60))) {
>>> -                     if (res > div_u64(ULLONG_MAX - val, base))
>>> +                     if (res > div_u64(ULLONG_MAX - val, base)) {
>>>                               overflow = 1;
>>> +                             break;
>>> +                     }
>>>               }
>>>               res = res * base + val;
>>>               rv++;
>>
>> The _notion_ of a patch is OK if you want EVERY simple_strtoull() call
>> to stop parsing past overflow right now. It SHOULD have done so from day 1,
>> but it doesn't do that.
>>
>> When I wrote kstrto*() code I deliberatedly didn't break this bug
>> because of the sheer number of call sites.
>>
>> If you are OK with changing bug-for-bug compatibility,
>> then patch simply need to delete overflow detection code.
>>
>>         Alexey
>
> I think this patch won't break any existing module using this function.
> because this function sets KSTRTOX_OVERFLOW as error status.
>
> which is checked by calling function to determine whether value is correct
> or not.
>
> If this flag is set we can simply discard the parsed value.

Which is my previous email is all about.

If you discard, every single simple_strto*() call will change its behaviour.
If you're OK with that, patch is incomplete.

  Alexey
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