From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] netfilter: account ebt_table_info to kmemcg Date: Sun, 30 Dec 2018 08:45:13 +0100 Message-ID: <20181230074513.GA22445@dhcp22.suse.cz> References: <20181229015524.222741-1-shakeelb@google.com> <20181229073325.GZ16738@dhcp22.suse.cz> <20181229095215.nbcijqacw5b6aho7@breakpoint.cc> <20181229100615.GB16738@dhcp22.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Florian Westphal , Pablo Neira Ayuso , Jozsef Kadlecsik , Roopa Prabhu , Nikolay Aleksandrov , Andrew Morton , Linux MM , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, bridge@lists.linux-foundation.org, LKML , syzbot+7713f3aa67be76b1552c@syzkaller.appspotmail.com To: Shakeel Butt Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org On Sat 29-12-18 11:34:29, Shakeel Butt wrote: > On Sat, Dec 29, 2018 at 2:06 AM Michal Hocko wrote: > > > > On Sat 29-12-18 10:52:15, Florian Westphal wrote: > > > Michal Hocko wrote: > > > > On Fri 28-12-18 17:55:24, Shakeel Butt wrote: > > > > > The [ip,ip6,arp]_tables use x_tables_info internally and the underlying > > > > > memory is already accounted to kmemcg. Do the same for ebtables. The > > > > > syzbot, by using setsockopt(EBT_SO_SET_ENTRIES), was able to OOM the > > > > > whole system from a restricted memcg, a potential DoS. > > > > > > > > What is the lifetime of these objects? Are they bound to any process? > > > > > > No, they are not. > > > They are free'd only when userspace requests it or the netns is > > > destroyed. > > > > Then this is problematic, because the oom killer is not able to > > guarantee the hard limit and so the excessive memory consumption cannot > > be really contained. As a result the memcg will be basically useless > > until somebody tears down the charged objects by other means. The memcg > > oom killer will surely kill all the existing tasks in the cgroup and > > this could somehow reduce the problem. Maybe this is sufficient for > > some usecases but that should be properly analyzed and described in the > > changelog. > > > > Can you explain why you think the memcg hard limit will not be > enforced? From what I understand, the memcg oom-killer will kill the > allocating processes as you have mentioned. We do force charging for > very limited conditions but here the memcg oom-killer will take care > of I was talking about the force charge part. Depending on a specific allocation and its life time this can gradually get us over hard limit without any bound theoretically. > Anyways, the kernel is already charging the memory for > [ip,ip6,arp]_tables and this patch adds the charging for ebtables. > Without this patch, as Kirill has described and shown by syzbot, a low > priority memcg can force system OOM. I am not opposing the patch per-se. I would just like the changelog to be more descriptive about the life time and consequences. -- Michal Hocko SUSE Labs