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

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Message-ID: <1379346277.1934.9.camel@joe-AO722>
Date:	Mon, 16 Sep 2013 08:44:37 -0700
From:	Joe Perches <joe@...ches.com>
To:	Kees Cook <keescook@...omium.org>
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, 2013-09-16 at 08:25 -0700, Kees Cook wrote:
> 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.

I don't think adding an int and a size_t is a big deal.

I'm still hoping to hear from Al if expanding the struct
is OK and race-free.

> 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. :)

Shrug.  None of these are inline uses so the overall
code size doesn't change much.

I have patches that make seq_overflow public and replace
the current uses of the seq_printf/seq_puts/seq_putc
returns where appropriate.

Given that I was already touching a lot of the
seq_<foo> calls, I also have patches that convert all
the seq_printf(fmt) (no additional args) to seq_puts()
and all the seq_puts("[single char]") to seq_putc() as
separate patches.


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