From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) Subject: Re: [PATCH RESEND] userns: enable tmpfs support for user namespace Date: Thu, 17 Jan 2013 22:04:48 -0800 Message-ID: <87ip6vyqkf.fsf@xmission.com> References: <1358331945-4106-1-git-send-email-gaofeng@cn.fujitsu.com> <20130116143532.GA4035@sergelap> <50F74EC6.60004@cn.fujitsu.com> <20130117171451.GA31219@sergelap> <87fw1zbd03.fsf@xmission.com> <20130118042404.GA15079@sergelap> <87vcavys6k.fsf@xmission.com> <50F8DEBF.1020701@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50F8DEBF.1020701-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> (Glauber Costa's message of "Thu, 17 Jan 2013 21:33:51 -0800") List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Glauber Costa Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org List-Id: containers.vger.kernel.org Glauber Costa writes: > On 01/17/2013 09:29 PM, Eric W. Biederman wrote: >> Serge Hallyn writes: >> >>> Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org): >>>> Serge Hallyn writes: >>>> >>>>> I actually was waiting for Eric to do it, but I'll happily send it >>>>> to linux-fsdevel and lkml (in a bit). >>>> >>>> I might just. >>>> >>>> I will take a look at this in a week or so. I want to get through the >>>> core userspace bits first so I can just cross those off my list of >>>> things that need to be done. >>>> >>>> Eric >>> >>> Ok, I'll wait on sending it then - thanks. >> >> Next up is my patch to shadow-utils and then taking a good hard stare at >> what is left kernel side. >> >> One of the questions I need to answer is: Do cgroups actually work >> for what needs to be limited? Or does the the focus of cgroups on >> processes without other ownership in objects fundamentally limit what >> can be expressed with cgroups in a problematic way. In which case would >> some hierarchical limits based on user namespaces and rlimits be easier >> to implement and make more sense. >> >> I think the answer will be that cgroups are good enough but that >> question certainly needs looking at. >> >> Anyway. shadow-utils, minimal tmpfs, minimal devpts, and then the rest. >> > First easy question: > > cgroups are not necessarily configured. > > IIUC, the aim of this patch is to allow unprivileged mounts of tmpfs > relying on the fact that cgroups will stop memory abuse (correct me if I > am wrong). > > But what if the user is not using cgroups? The requirement for tmpfs to be safe is that there should be a control that root can use to prevent DOS attacks. If you don't choose to use what is available then shrug. Eric