Path: csiph.com!news.mixmin.net!aioe.org!bofh.it!news.nic.it!robomod From: Pablo Neira Ayuso Newsgroups: linux.kernel Subject: Re: userns, netns, and quick physical memory consumption by unprivileged user Date: Sat, 12 Mar 2016 12:50:01 +0100 Message-ID: References: X-Original-To: Florian Westphal X-Virus-Status: clean(F-Secure/fsigk_smtp/522/antivirus1-rhel7.int) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.23 (2014-03-12) Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 37 Organization: linux.* mail to news gateway X-Original-Cc: "Yuriy M. Kaminskiy" , netdev@vger.kernel.org, containers@lists.osdl.org, linux-kernel@vger.kernel.org, netfilter-devel@vger.kernel.org X-Original-Date: Sat, 12 Mar 2016 12:41:40 +0100 X-Original-Message-ID: <20160312114140.GA2023@salvia> X-Original-References: <20160311153406.GB6620@breakpoint.cc> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1356407 On Fri, Mar 11, 2016 at 04:34:06PM +0100, Florian Westphal wrote: > Yuriy M. Kaminskiy wrote: > > BTW, all those hash/conntrack/etc default sizes was calculated from > > physical memory size in assumption there will be only *one* instance of > > those tables. Obviously, introduction of network namespaces (and > > especially unprivileged user-ns) thrown this assumption in the window > > (and here comes that "falling back to vmalloc" message again; in pre-netns > > world, those tables were allocated *once* on early system startup, with > > typically plenty of free and unfragmented memory). > > No idea how to fix this expect by removing conntrack support in net > namespaces completely. > > I'd disallow all write accesses to skb->nfct (NAT, CONNMARK, > CONNSECMARK, ...) and then no longer clear skb->nfct when forwarding > packet from init_ns to container. > > Containers could then still test conntrack as seen from init namespace pov > in PREROUTING/FORWARD/INPUT (but not OUTPUT, obviously). > > [ OUTPUT *might* be doable as well by allowing NEW creation in output > but skipping nat and deferring the confirmation/commit of the new > entry to the table until skb leaves initns ] > > We could key conntrack entries to initns conntrack table > instead of adding one new table per netns, but seems like this only > replaces one problem with a new one (filling/blocking initns table from > another netns). We can add a global perns limit in terms of conntrack entries that can only be set via CAP_NET_ADMIN from the initns. Thus, we avoid the filling/blocking from another netns, or hide this knob to unpriviledged userns somehow. In the previous netfilter workshop I remember we agreed on going towards having a single conntrack table for netns, so I suggest we follow that direction.