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Subject: Re: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms
To:     Yann Droneaud <ydroneaud@opteya.com>,
        David Laight <David.Laight@ACULAB.COM>,
        Joe Perches <joe@perches.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
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Cc:     Jonathan Corbet <corbet@lwn.net>, Stephen Kitt <steve@sk2.org>,
        Kees Cook <keescook@chromium.org>,
        Nitin Gote <nitin.r.gote@intel.com>,
        "jannh@google.com" <jannh@google.com>,
        "kernel-hardening@lists.openwall.com" 
        <kernel-hardening@lists.openwall.com>,
        Andrew Morton <akpm@linux-foundation.org>
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From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <396d1eed-8edf-aa77-110b-c50ead3a5fd5@rasmusvillemoes.dk>
Date:   Wed, 24 Jul 2019 15:09:10 +0200
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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