From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: [PATCH for-4.5] tools/pygrub: Fix TOCTOU race
 introduced by c/s 63dcc68
Date: Wed, 29 Oct 2014 20:43:04 +0100
Message-ID: <20141029194304.GA1606@aepfle.de>
References: <1414591781-19376-1-git-send-email-andrew.cooper3@citrix.com>
	<20141029160322.GA22428@aepfle.de> <54512D5B.1040003@citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Content-Disposition: inline
In-Reply-To: <54512D5B.1040003@citrix.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <Ian.Campbell@citrix.com>, Xen-devel <xen-devel@lists.xen.org>
List-Id: xen-devel@lists.xenproject.org

On Wed, Oct 29, Andrew Cooper wrote:

> The result is that I have positively proved that XenServer hit this race
> during automatic testing.  I agree that it shouldn't happen in reality
> for a system configured as expected, but that fact alone doesn't
> invalidate the fix itself.

I think it can happen even with upstream if two guests start at the same
time and both execute the code at the same time. Both will find the dir
does not exist yet and both will attempt to create the dir. I think one
of both will get an exception.

Olaf