From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id BCFAA8E005B for ; Mon, 31 Dec 2018 05:12:03 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id l45so29258260edb.1 for ; Mon, 31 Dec 2018 02:12:03 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id z6-v6si275337ejx.166.2018.12.31.02.12.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 31 Dec 2018 02:12:01 -0800 (PST) Date: Mon, 31 Dec 2018 11:11:58 +0100 From: Michal Hocko Subject: Re: [PATCH] netfilter: account ebt_table_info to kmemcg Message-ID: <20181231101158.GC22445@dhcp22.suse.cz> References: <20181229015524.222741-1-shakeelb@google.com> <20181229073325.GZ16738@dhcp22.suse.cz> <20181229095215.nbcijqacw5b6aho7@breakpoint.cc> <20181229100615.GB16738@dhcp22.suse.cz> <20181230074513.GA22445@dhcp22.suse.cz> <20181230080028.GB22445@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Shakeel Butt 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 On Sun 30-12-18 19:59:53, Shakeel Butt wrote: > On Sun, Dec 30, 2018 at 12:00 AM Michal Hocko wrote: > > > > On Sun 30-12-18 08:45:13, Michal Hocko wrote: > > > 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. > > > > Forgot to mention. Since b8c8a338f75e ("Revert "vmalloc: back off when > > the current task is killed"") there is no way to bail out from the > > vmalloc allocation loop so if the request is really large then the memcg > > oom will not help. Is that a problem here? > > > > Yes, I think it will be an issue here. > > > Maybe it is time to revisit fatal_signal_pending check. > > Yes, we will need something to handle the memcg OOM. I will think more > on that front or if you have any ideas, please do propose. I can see three options here: - do not force charge on memcg oom or introduce a limited charge overflow (reserves basically). - revert the revert and reintroduce the fatal_signal_pending check into vmalloc - be more specific and check tsk_is_oom_victim in vmalloc and fail -- Michal Hocko SUSE Labs