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Date: Wed, 24 Jul 2019 15:09:10 +0200
From: Rasmus Villemoes <linux@...musvillemoes.dk>
To: Yann Droneaud <ydroneaud@...eya.com>,
David Laight <David.Laight@...LAB.COM>, Joe Perches <joe@...ches.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: Jonathan Corbet <corbet@....net>, Stephen Kitt <steve@....org>,
Kees Cook <keescook@...omium.org>, Nitin Gote <nitin.r.gote@...el.com>,
"jannh@...gle.com" <jannh@...gle.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms
On 24/07/2019 14.05, Yann Droneaud wrote:
> Hi,
>
> Beware that snprintf(), per C standard, is supposed to return the
> length of the formatted string, regarless of the size of the
> destination buffer.
>
> So encouraging developper to write something like code below because
> snprintf() in kernel behave in a non-standard way,
The kernel's snprintf() does not behave in a non-standard way, at least
not with respect to its return value. It doesn't support %n or floating
point, of course, and there are some quirks regarding precision (see
lib/test_printf.c for details).
There's the non-standard scnprintf() for getting the length of the
formatted string, which can safely be used in an append loop. Or one can
use the seq_buf API.
Rasmus
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