From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3988CC43613 for ; Thu, 20 Jun 2019 10:24:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1B878206BA for ; Thu, 20 Jun 2019 10:24:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730669AbfFTKYR (ORCPT ); Thu, 20 Jun 2019 06:24:17 -0400 Received: from mga03.intel.com ([134.134.136.65]:55912 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726081AbfFTKYR (ORCPT ); Thu, 20 Jun 2019 06:24:17 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 20 Jun 2019 03:24:16 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.63,396,1557212400"; d="scan'208";a="358487338" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.145]) by fmsmga005.fm.intel.com with ESMTP; 20 Jun 2019 03:24:12 -0700 Received: from andy by smile with local (Exim 4.92) (envelope-from ) id 1hduEk-0007HN-VY; Thu, 20 Jun 2019 13:24:10 +0300 Date: Thu, 20 Jun 2019 13:24:10 +0300 From: Andy Shevchenko To: Jeff Layton Cc: linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org, idryomov@gmail.com, zyan@redhat.com, sage@redhat.com, agruenba@redhat.com, joe@perches.com, pmladek@suse.com, rostedt@goodmis.org, geert+renesas@glider.be Subject: Re: [PATCH v2 0/3] ceph: don't NULL terminate virtual xattr values Message-ID: <20190620102410.GT9224@smile.fi.intel.com> References: <20190619164528.31958-1-jlayton@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190619164528.31958-1-jlayton@kernel.org> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 19, 2019 at 12:45:25PM -0400, Jeff Layton wrote: > v2: drop bogus EXPORT_SYMBOL of static function > > The only real difference between this set and the one I sent originally > is the removal of a spurious EXPORT_SYMBOL in the snprintf patch. > > I'm mostly sending this with a wider cc list in an effort to get a > review from the maintainers of the printf code. Basically ceph needs a > snprintf variant that does not NULL terminate in order to handle its > virtual xattrs. > > Joe Perches had expressed some concerns about stack usage in vsnprintf > with this, but I'm not sure I really understand the basis of that > concern. If it is problematic, then I could use suggestions as to how > best to fix that up. It might be problematic, since vsnprintf() can be called recursively. > ----------------------------8<----------------------------- > > kcephfs has several "virtual" xattrs that return strings that are > currently populated using snprintf(), which always NULL terminates the > string. > > This leads to the string being truncated when we use a buffer length > acquired by calling getxattr with a 0 size first. The last character > of the string ends up being clobbered by the termination. So, then don't use snprintf() for this, simple memcpy() designed for that kind of things. > The convention with xattrs is to not store the termination with string > data, given that we have the length. This is how setfattr/getfattr > operate. Fine. > This patch makes ceph's virtual xattrs not include NULL termination > when formatting their values. In order to handle this, a new > snprintf_noterm function is added, and ceph is changed over to use > this to populate the xattr value buffer. In terms of vsnprintf(), and actually compiler point of view, it's not a string anymore, it's a text-based data. Personally, I don't see an advantage of a deep intrusion into vsnprintf(). The wrapper can be made to achieve this w/o touching the generic code. Thus, you can quickly and cleanly fix the issue, while discussing this with wider audience. > Finally, we fix ceph to > return -ERANGE properly when the string didn't fit in the buffer. > > Jeff Layton (3): > lib/vsprintf: add snprintf_noterm > ceph: don't NULL terminate virtual xattr strings > ceph: return -ERANGE if virtual xattr value didn't fit in buffer > > fs/ceph/xattr.c | 49 +++++++------- > include/linux/kernel.h | 2 + > lib/vsprintf.c | 144 ++++++++++++++++++++++++++++------------- > 3 files changed, 129 insertions(+), 66 deletions(-) > > -- > 2.21.0 > -- With Best Regards, Andy Shevchenko