From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lord Glauber Costa of Sealand Subject: Re: [PATCH review 3/6] userns: Recommend use of memory control groups. Date: Mon, 28 Jan 2013 11:50:00 +0400 Message-ID: <51062DA8.1060804@parallels.com> References: <87ehh8it9s.fsf@xmission.com> <87txq4hedl.fsf@xmission.com> <51062AB5.9060203@parallels.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <51062AB5.9060203-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> 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: "Eric W. Biederman" Cc: linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux Containers , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.vger.kernel.org On 01/28/2013 11:37 AM, Lord Glauber Costa of Sealand wrote: > 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..." ? > > I just saw in a later patch of yours that your concern here seems not limited to backed ram by tmpfs, but with things like the internal structures for userns , to avoid patterns in the form: 'for (;;) unshare(...)' Humm, it does seem sensible. The kernel memory controller aims to prevent exactly things like that. But they all exist already before userns: there are destructive patterns like that with sockets, dentries, processes, and pretty much every other resource in the kernel. So Although the recommendation per-se makes sense, I am wondering if it is worth it to mention anything in the user_ns config?