From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx107.postini.com [74.125.245.107]) by kanga.kvack.org (Postfix) with SMTP id 685006B0068 for ; Thu, 3 Jan 2013 01:26:53 -0500 (EST) Message-ID: <50E52316.6010602@redhat.com> Date: Thu, 03 Jan 2013 01:20:06 -0500 From: Rik van Riel MIME-Version: 1.0 Subject: Re: [PATCH 9/9] mm: introduce VM_POPULATE flag to better deal with racy userspace programs References: <1356050997-2688-1-git-send-email-walken@google.com> <1356050997-2688-10-git-send-email-walken@google.com> In-Reply-To: <1356050997-2688-10-git-send-email-walken@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michel Lespinasse Cc: Andy Lutomirski , Ingo Molnar , Al Viro , Hugh Dickins , Jorn_Engel , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 12/20/2012 07:49 PM, Michel Lespinasse wrote: > The vm_populate() code populates user mappings without constantly > holding the mmap_sem. This makes it susceptible to racy userspace > programs: the user mappings may change while vm_populate() is running, > and in this case vm_populate() may end up populating the new mapping > instead of the old one. > > In order to reduce the possibility of userspace getting surprised by > this behavior, this change introduces the VM_POPULATE vma flag which > gets set on vmas we want vm_populate() to work on. This way > vm_populate() may still end up populating the new mapping after such a > race, but only if the new mapping is also one that the user has > requested (using MAP_SHARED, MAP_LOCKED or mlock) to be populated. > > Signed-off-by: Michel Lespinasse Acked-by: Rik van Riel email@kvack.org