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

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Message-ID: <CA+HOOsiXxJQMj8cJx-tmxO=Ee48f6SWJ18JX0ndfXEZS-MjueA@mail.gmail.com>
Date:	Thu, 19 Feb 2015 23:23:42 +0530
From:	Anshul Garg <aksgarg1989@...il.com>
To:	Alexey Dobriyan <adobriyan@...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 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.
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