From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 72E16C433DF for ; Mon, 24 Aug 2020 10:48:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 56D1F2071E for ; Mon, 24 Aug 2020 10:48:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727042AbgHXKr7 (ORCPT ); Mon, 24 Aug 2020 06:47:59 -0400 Received: from correo.us.es ([193.147.175.20]:51608 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725968AbgHXKr5 (ORCPT ); Mon, 24 Aug 2020 06:47:57 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 34796114807 for ; Mon, 24 Aug 2020 12:47:49 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 20B4DDA730 for ; Mon, 24 Aug 2020 12:47:49 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id 16050DA704; Mon, 24 Aug 2020 12:47:49 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id ED980DA730; Mon, 24 Aug 2020 12:47:46 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Mon, 24 Aug 2020 12:47:46 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from us.es (unknown [90.77.255.23]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) (Authenticated sender: 1984lsi) by entrada.int (Postfix) with ESMTPSA id D315942EE38E; Mon, 24 Aug 2020 12:47:46 +0200 (CEST) Date: Mon, 24 Aug 2020 12:47:46 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Florian Westphal Cc: Phil Sutter , netfilter-devel@vger.kernel.org Subject: Re: nfnetlink: Busy-loop in nfnetlink_rcv_msg() Message-ID: <20200824104746.GA22845@salvia> References: <20200821230615.GW23632@orbyte.nwl.cc> <20200822184621.GH15804@breakpoint.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200822184621.GH15804@breakpoint.cc> User-Agent: Mutt/1.10.1 (2018-07-13) X-Virus-Scanned: ClamAV using ClamSMTP Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Hi Florian, Sorry, I overlook your reply. On Sat, Aug 22, 2020 at 08:46:21PM +0200, Florian Westphal wrote: > Phil Sutter wrote: > > Starting firewalld with two active zones in an lxc container provokes a > > situation in which nfnetlink_rcv_msg() loops indefinitely, because > > nc->call_rcu() (nf_tables_getgen() in this case) returns -EAGAIN every > > time. > > > > I identified netlink_attachskb() as the originator for the above error > > code. The conditional leading to it looks like this: > > > > | if ((atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf || > > | test_bit(NETLINK_S_CONGESTED, &nlk->state))) { > > | [...] > > | if (!*timeo) { > > > > *timeo is zero, so this seems to be a non-blocking socket. Both > > NETLINK_S_CONGESTED bit is set and sk->sk_rmem_alloc exceeds > > sk->sk_rcvbuf. > > > > From user space side, firewalld seems to simply call sendto() and the > > call never returns. > > > > How to solve that? I tried to find other code which does the same, but I > > haven't found one that does any looping. Should nfnetlink_rcv_msg() > > maybe just return -EAGAIN to the caller if it comes from call_rcu > > backend? > > Yes, I think thats the most straightforward solution. > > We can of course also intercept -EAGAIN in nf_tables_api.c and translate > it to -ENOBUFS like in nft_get_set_elem(). > > But I think a generic solution it better. The call_rcu backends should > not result in changes to nf_tables internal state so they do not load > modules and therefore don't need a restart. Handling this from the core would be better, so people don't have to remember to use the nfnetlink_unicast() that I'm proposing. Looking at the tree, call_rcu is not enough to assume this: there are several nfnetlink subsystems calling netlink_unicast() that translate EAGAIN to ENOBUFS, from .call and .call_rcu. The way to identify this would be to decorate callbacks to know what are specifically GET commands. So either do this or just extend my patch to use nfnetlink_send() everywhere to remove all existing translations from EAGAIN to ENOBUFS.