From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754031Ab3A1IGK (ORCPT ); Mon, 28 Jan 2013 03:06:10 -0500 Received: from out02.mta.xmission.com ([166.70.13.232]:40812 "EHLO out02.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753659Ab3A1IGH (ORCPT ); Mon, 28 Jan 2013 03:06:07 -0500 From: ebiederm@xmission.com (Eric W. Biederman) To: Lord Glauber Costa of Sealand Cc: Linux Containers , , References: <87ehh8it9s.fsf@xmission.com> <87txq4hedl.fsf@xmission.com> <51062AB5.9060203@parallels.com> Date: Mon, 28 Jan 2013 00:05:57 -0800 In-Reply-To: <51062AB5.9060203@parallels.com> (Lord Glauber Costa of Sealand's message of "Mon, 28 Jan 2013 11:37:25 +0400") Message-ID: <874ni1vije.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-AID: U2FsdGVkX1/Wvwooo7ZUq1pRG+GEXlvOm+SocbOm1FQ= X-SA-Exim-Connect-IP: 98.207.153.68 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 0.1 XMSubLong Long Subject * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0003] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa01 1397; Body=1 Fuz1=1 Fuz2=1] * 0.5 XM_Body_Dirty_Words Contains a dirty word * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa01 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;Lord Glauber Costa of Sealand X-Spam-Relay-Country: Subject: Re: [PATCH review 3/6] userns: Recommend use of memory control groups. X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Wed, 14 Nov 2012 14:26:46 -0700) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Lord Glauber Costa of Sealand writes: > On 01/26/2013 06:22 AM, Eric W. Biederman wrote: >> >> In the help text describing user namespaces recommend use of memory >> control groups. In many cases memory control groups are the only >> mechanism there is to limit how much memory a user who can create >> user namespaces can use. >> >> Signed-off-by: "Eric W. Biederman" >> --- >> Documentation/namespaces/resource-control.txt | 10 ++++++++++ >> init/Kconfig | 7 +++++++ >> 2 files changed, 17 insertions(+), 0 deletions(-) >> create mode 100644 Documentation/namespaces/resource-control.txt >> >> diff --git a/Documentation/namespaces/resource-control.txt b/Documentation/namespaces/resource-control.txt >> new file mode 100644 >> index 0000000..3d8178a >> --- /dev/null >> +++ b/Documentation/namespaces/resource-control.txt >> @@ -0,0 +1,10 @@ >> +There are a lot of kinds of objects in the kernel that don't have >> +individual limits or that have limits that are ineffective when a set >> +of processes is allowed to switch user ids. With user namespaces >> +enabled in a kernel for people who don't trust their users or their >> +users programs to play nice this problems becomes more acute. >> + >> +Therefore it is recommended that memory control groups be enabled in >> +kernels that enable user namespaces, and it is further recommended >> +that userspace configure memory control groups to limit how much >> +memory users they don't trust to play nice can use. >> diff --git a/init/Kconfig b/init/Kconfig >> index 7d30240..c8c58bd 100644 >> --- a/init/Kconfig >> +++ b/init/Kconfig >> @@ -1035,6 +1035,13 @@ config USER_NS >> help >> This allows containers, i.e. vservers, to use user namespaces >> to provide different user info for different servers. >> + >> + When user namespaces are enabled in the kernel it is >> + recommended that the MEMCG and MEMCG_KMEM options also be >> + enabled and that user-space use the memory control groups to >> + limit the amount of memory a memory unprivileged users can >> + use. >> + >> If unsure, say N. > > Since this becomes an official recommendation that people will likely > follow, are we really that much concerned about the types of abuses the > MEMCG_KMEM will prevent? Those are mostly metadata-based abuses users > could do in their own local disks without mounting anything extra (and > things that look like that) > > Unless there is a specific concern here, shouldn't we say "... that the > MEMCG (and possibly MEMCG_KMEM) options..." ? There are quite a few specific concerns. The easiest to spot is unshare(CLONE_NEWUSER), and the other namespaces. Then there are network devices. Then there is I don't know what else. Most distro's don't seem to care at all about limiting a users memory so in that sense it is not a concern. On the other hand for everyone who wants to limit a user's memory the only way that is going to happen in a reasonable amount of implementation time is with memory control groups, and slabs and kmalloc are most definitely part of the memory needs to be limited. Eric