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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 04/10] sscanf: fix overflow
Date: Wed, 06 May 2015 09:49:35 +0200	[thread overview]
Message-ID: <878ud2rvqo.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <CACVxJT9yTO8-wRJ4Y_w=DguCiniyu_dP1BXg+KE1ME+PrabgrA@mail.gmail.com> (Alexey Dobriyan's message of "Tue, 5 May 2015 14:10:36 +0300")

On Tue, May 05 2015, Alexey Dobriyan <adobriyan@gmail.com> wrote:

> On Tue, May 5, 2015 at 12:51 PM, Rasmus Villemoes
> <linux@rasmusvillemoes.dk> wrote:
>> On Sat, May 02 2015, Alexey Dobriyan <adobriyan@gmail.com> wrote:
>>
>>> Fun fact:
>>>
>>>       uint8_t val;
>>>       sscanf("256", "%hhu", &val);
>>>
>>> will return 1 (as it should), and make val=0 (as it should not).
>>>
>>
>> What do you base these "should" and "should not" on? Both C99 and POSIX
>> say that the behaviour is undefined - the kernel can obviously define
>> its own semantics for scanf, but what do you think they should be?
>
> POSIX can say whatever it wants,

That was sort of the point, POSIX doesn't say anything, which is why I
asked what you think the semantics should be.

> it's about common sense.
>
> sscanf(), both kernel and libc, in this situation returns 0 when "0"
> character is nowhere to be found in the string!  It should either
> return 25

Really? Do you consider it common sense that sscanf("256 123", "%hhu%d", &x,
&y) can end up returning 2, putting 25 in x and 6 in y?

> or do not return anything

I agree that _that_ would be the sane thing to do, but again, I'm
confused why you then said the first example should return 1.

Rasmus

  reply	other threads:[~2015-05-06  7:49 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-02  0:47 [PATCH 01/10] Add parse_integer() (replacement for simple_strto*()) Alexey Dobriyan
2015-05-02  0:48 ` [PATCH 02/10] parse_integer: rewrite kstrto*() Alexey Dobriyan
2015-05-02  0:50 ` [PATCH 03/10] parse_integer: convert sscanf() Alexey Dobriyan
2015-05-02  1:10   ` [PATCH CORRECT " Alexey Dobriyan
2015-05-02  0:51 ` [PATCH 04/10] sscanf: fix overflow Alexey Dobriyan
2015-05-05  9:51   ` Rasmus Villemoes
2015-05-05 11:10     ` Alexey Dobriyan
2015-05-06  7:49       ` Rasmus Villemoes [this message]
2015-05-02  0:53 ` [PATCH 05/10] parse_integer: convert lib/ Alexey Dobriyan
2015-05-04 14:10   ` Rasmus Villemoes
2015-05-04 14:57     ` Alexey Dobriyan
2015-05-02  0:55 ` [PATCH 06/10] parse_integer: convert mm/ Alexey Dobriyan
2015-05-04 14:33   ` Rasmus Villemoes
2015-05-04 15:09     ` Alexey Dobriyan
2015-05-02  0:56 ` [PATCH 07/10] parse_integer: convert misc fs/ code Alexey Dobriyan
2015-05-02  0:59 ` [PATCH 08/10] fs/cachefiles/: convert to parse_integer() Alexey Dobriyan
2015-05-02  1:01 ` [PATCH 09/10] ocfs2: convert to parse_integer()/kstrto*() Alexey Dobriyan
2015-05-02  1:03 ` [PATCH 10/10] ext2, ext3, ext4: " Alexey Dobriyan
2015-05-04 13:24 ` [PATCH 01/10] Add parse_integer() (replacement for simple_strto*()) Rasmus Villemoes
2015-05-04 14:32   ` Alexey Dobriyan
2015-05-04 16:44     ` Rasmus Villemoes
2015-05-04 19:54       ` Alexey Dobriyan
2015-05-04 21:48         ` Rasmus Villemoes

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