linux-kernel - Re: [PATCH 1/2] remove all uses of printf's %n

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Message-ID: <CAGXu5jK7ALtFq74duH_ymoLnmoHKYmty+60HCG3YFyhghi2Scg@mail.gmail.com>
Date:	Mon, 16 Sep 2013 08:25:44 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	LKML <linux-kernel@...r.kernel.org>,
	George Spelvin <linux@...izon.com>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Jan Beulich <JBeulich@...e.com>,
	Motohiro KOSAKI <kosaki.motohiro@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] remove all uses of printf's %n

On Mon, Sep 16, 2013 at 8:09 AM, Joe Perches <joe@...ches.com> wrote:
> On Mon, 2013-09-16 at 07:59 -0700, Kees Cook wrote:
>> Perhaps instead of seq->count, there should be an access function?
>> seq_get_count(seq) or something?
>
> My thought was to add a seq_last_len()

That would mean growing the size of the seq_file structure and adding
instructions for all users. While I personally have no problem with
that, I worry others might. If we just use seq->count (or equivalent
function), then only those that want length will use it. I actually
think this uses fewer instructions than %n. Especially in the case
where seq_printf got replaced by seq_puts. :)

-Kees

-- 
Kees Cook
Chrome OS Security
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