From owner-freebsd-arch@freebsd.org  Wed May 25 21:14:11 2016
Return-Path: <owner-freebsd-arch@freebsd.org>
Delivered-To: freebsd-arch@mailman.ysv.freebsd.org
Received: from mx1.freebsd.org (mx1.freebsd.org
 [IPv6:2001:1900:2254:206a::19:1])
 by mailman.ysv.freebsd.org (Postfix) with ESMTP id 9DE18B4AC7D
 for <freebsd-arch@mailman.ysv.freebsd.org>;
 Wed, 25 May 2016 21:14:11 +0000 (UTC)
 (envelope-from truckman@FreeBSD.org)
Received: from gw.catspoiler.org (unknown [IPv6:2602:304:b010:ef20::f2])
 (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
 (Client CN "gw.catspoiler.org", Issuer "gw.catspoiler.org" (not verified))
 by mx1.freebsd.org (Postfix) with ESMTPS id 8073818B5
 for <freebsd-arch@freebsd.org>; Wed, 25 May 2016 21:14:11 +0000 (UTC)
 (envelope-from truckman@FreeBSD.org)
Received: from FreeBSD.org (mousie.catspoiler.org [192.168.101.2])
 by gw.catspoiler.org (8.15.2/8.15.2) with ESMTP id u4PLE1NA007337;
 Wed, 25 May 2016 14:14:07 -0700 (PDT)
 (envelope-from truckman@FreeBSD.org)
Message-Id: <201605252114.u4PLE1NA007337@gw.catspoiler.org>
Date: Wed, 25 May 2016 14:14:01 -0700 (PDT)
From: Don Lewis <truckman@FreeBSD.org>
Subject: Re: is ut_user[] in struct utmpx NUL terminated?
To: ed@nuxi.nl
cc: freebsd-arch@freebsd.org
In-Reply-To: <CABh_MKn20ABaQ=N2s44jscsDUZ6n2s8nWX5DdYa4jGNfUqAf=g@mail.gmail.com>
MIME-Version: 1.0
Content-Type: TEXT/plain; charset=us-ascii
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.22
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <https://lists.freebsd.org/mailman/options/freebsd-arch>,
 <mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch/>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <https://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
 <mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Wed, 25 May 2016 21:14:11 -0000

On 16 May, Ed Schouten wrote:
> Hi Don,
> 
> 2016-05-16 1:07 GMT+02:00 Don Lewis <truckman@freebsd.org>:
>> There is a lot of code that expects ut_user[] to be NUL terminated.
> 
> Our implementation of utmpx should be pretty friendly to use:
> 
> - You can call pututxline() with strings that are not null terminated.
> - The getutx*() functions return entries in which all strings are null
> terminated.

The latter doesn't appear to be true.  If I stuff a non-NUL terminated
32 character user name into ut_user and then call pututxline(), it calls
utx_to_futx(), which uses the UTOF_STRING() macro, which in turn uses
snprintf() to copy the data to the corresponding field in a struct futx
before saving the latter.  Going in the other direction, getutxent()
calls futx_to_utx(), which uses the FTOU_STRING() macro, which in turn
uses strncpy() to copy the data back out.  If the original name was 32
characters, then the ut_user value in the returned struct utmpx will not
be NUL terminated.