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=-5.2 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 30B6CC433E1 for ; Sun, 23 Aug 2020 12:04:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1033220720 for ; Sun, 23 Aug 2020 12:04:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727056AbgHWMEl (ORCPT ); Sun, 23 Aug 2020 08:04:41 -0400 Received: from correo.us.es ([193.147.175.20]:44940 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726090AbgHWMEi (ORCPT ); Sun, 23 Aug 2020 08:04:38 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 06369DA705 for ; Sun, 23 Aug 2020 14:04:37 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id EA60BDA722 for ; Sun, 23 Aug 2020 14:04:36 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id E0082DA73F; Sun, 23 Aug 2020 14:04:36 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 74E9EDA722; Sun, 23 Aug 2020 14:04:34 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Sun, 23 Aug 2020 14:04:34 +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 589A342EE38F; Sun, 23 Aug 2020 14:04:34 +0200 (CEST) Date: Sun, 23 Aug 2020 14:04:34 +0200 X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: Phil Sutter , netfilter-devel@vger.kernel.org, Florian Westphal Subject: Re: nfnetlink: Busy-loop in nfnetlink_rcv_msg() Message-ID: <20200823120434.GA16617@salvia> References: <20200821230615.GW23632@orbyte.nwl.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200821230615.GW23632@orbyte.nwl.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 Phil, On Sat, Aug 22, 2020 at 01:06:15AM +0200, Phil Sutter wrote: > Hi, > > 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? It's a bug in the netlink frontend, which erroneously reports -EAGAIN to the nfnetlink when the socket buffer is full, see: https://patchwork.ozlabs.org/project/netfilter-devel/patch/20200823115536.16631-1-pablo@netfilter.org/ > This happening only in an lxc container may be due to some setsockopt() > calls not being allowed. In particular, setsockopt(SO_RCVBUFFORCE) > returns EPERM. SO_RCVBUFFORCE fails with EPERM if CAP_NET_ADMIN is not available. > The value of sk_rcvbuf is 425984, BTW. sk_rmem_alloc is 426240. In user > space, I see a call to setsockopt(SO_RCVBUF) with value 4194304. No idea > if this is related and how. Next problem is to track why socket buffer is getting full with GET_GENID. firewalld heavily uses NLM_F_ECHO, there I can see how it can easily reach the default socket buffer size, but with GET_GENID I'm not sure yet, probably the problem is elsewhere but it manifests in GET_GENID because it's the first thing that is done when sending a batch (maybe there are unread messages in the socket buffer, you might check /proc/net/netlink to see if the socket buffer keeps growing as firewalld moves on). Is this easy to reproduce? Or does this happens after some time of firewalld execution?