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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 01/10] Add parse_integer() (replacement for simple_strto*())
Date: Mon, 04 May 2015 23:48:27 +0200	[thread overview]
Message-ID: <87383cui8k.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <20150504195435.GA21686@p183.telecom.by> (Alexey Dobriyan's message of "Mon, 4 May 2015 22:54:35 +0300")

On Mon, May 04 2015, Alexey Dobriyan <adobriyan@gmail.com> wrote:

>> There are lots of callers of memparse(), and I don't think any of them
>> are prepared to handle *endp ending up pointing before the passed-in
>> string (-EINVAL == -22, -ERANGE == -34). I can easily see how that could
>> lead to an infinite loop, maybe worse.
>
> Yeah, possible bug could become worse, I'll add error checking,
> but, seriously, you're defending this :^)
>
> 	case Opt_nr_inodes:
> ===>		/* memparse() will accept a K/M/G without a digit */
> ===>		if (!isdigit(*args[0].from))
> ===>			goto bad_val;
> 		pconfig->nr_inodes = memparse(args[0].from, &rest);
> 		break;
>

No, I'm not defending memparse(), simple_strto* or any of their
callers. I'm just trying to say that you can't change the semantics of
memparse() without considering all its callers.

I don't think there's any way to "add error checking" and preserve the
exact memparse() semantic - in other words, I don't think simple_strto*
can actually be implemented in terms of parse_integer. But that's not a
bad thing - we want to get rid of those.

> memparse() is misdesigned in the same sense strtoul() is misdesigned.
> Every "memparse(s, NULL)" user is a bug for example.

Yes, memparse is misdesigned, since it doesn't have a way to indicate
error. That leads me to: There's no point in adding error checking to
the integer parsing part without also checking the left shifts for
overflow.

I think the right approach is to rename memparse to legacy_memparse and
introduce a memparse with semantics that allow error checking. One could
start by introducing that under the name sane_memparse. But there are
probably lots of simple_strto*() uses that are easier to eliminate.

Rasmus

      reply	other threads:[~2015-05-04 21:48 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-02  0:47 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
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 [this message]

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