linux-kernel - Re: [PATCH 1/2] string: Add stracpy and stracpy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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