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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id AF1F6CDB465 for ; Thu, 19 Oct 2023 13:04:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345629AbjJSNEm (ORCPT ); Thu, 19 Oct 2023 09:04:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55012 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345770AbjJSNEi (ORCPT ); Thu, 19 Oct 2023 09:04:38 -0400 Received: from ganesha.gnumonks.org (ganesha.gnumonks.org [IPv6:2001:780:45:1d:225:90ff:fe52:c662]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 18043187 for ; Thu, 19 Oct 2023 06:04:36 -0700 (PDT) Received: from [78.30.34.192] (port=40402 helo=gnumonks.org) by ganesha.gnumonks.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1qtShT-0036T6-8W; Thu, 19 Oct 2023 15:04:34 +0200 Date: Thu, 19 Oct 2023 15:04:30 +0200 From: Pablo Neira Ayuso To: Phil Sutter , Florian Westphal , netfilter-devel@vger.kernel.org Subject: Re: [nf-next PATCH v3 3/3] netfilter: nf_tables: Add locking for NFT_MSG_GETRULE_RESET requests Message-ID: References: <20231019113347.8753-1-phil@nwl.cc> <20231019113347.8753-4-phil@nwl.cc> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org On Thu, Oct 19, 2023 at 02:33:50PM +0200, Phil Sutter wrote: > On Thu, Oct 19, 2023 at 01:38:04PM +0200, Pablo Neira Ayuso wrote: > > On Thu, Oct 19, 2023 at 01:33:47PM +0200, Phil Sutter wrote: > > > Rule reset is not concurrency-safe per-se, so multiple CPUs may reset > > > the same rule at the same time. At least counter and quota expressions > > > will suffer from value underruns in this case. > > > > > > Prevent this by introducing dedicated locking callbacks for nfnetlink > > > and the asynchronous dump handling to serialize access. > > > > > > Signed-off-by: Phil Sutter > > > --- > > > Changes since v2: > > > - Keep local variable 'nft_net' in nf_tables_getrule_reset() > > > - No need for local variable 'family' in same function (used only once > > > after all the churn) > > > --- > > > net/netfilter/nf_tables_api.c | 74 ++++++++++++++++++++++++++++------- > > > 1 file changed, 60 insertions(+), 14 deletions(-) > > > > > > diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c > > > index 584d3b204372..fbb688c9903c 100644 > > > --- a/net/netfilter/nf_tables_api.c > > > +++ b/net/netfilter/nf_tables_api.c > > [...] > > > +static int nf_tables_dumpreset_rules(struct sk_buff *skb, > > > + struct netlink_callback *cb) > > > +{ > > > + struct nftables_pernet *nft_net = nft_pernet(sock_net(skb->sk)); > > > + int ret; > > > + > > > + mutex_lock(&nft_net->commit_mutex); > > > + ret = nf_tables_dump_rules(skb, cb); > > > + mutex_unlock(&nft_net->commit_mutex); > > > > NACK. > > > > This just mitigates the problem we are discussing, when there is an > > interference with an ongoing transaction. > > This fixes for user space's ability to underrun counters and quotas > because expressions' dump callbacks are not concurrency safe in reset > mode. > > What you're concerned with is a different issue. I'd suggest you add comment to this code, feel free to add better wording: /* Mutex is held is to prevent that two concurrent dump-and-reset calls * do not underrun counters and quotas. The commit_mutex is used for the * lack a better lock, this is not transaction path. */ mutex_lock(&nft_net->commit_mutex); ret = nf_tables_dump_rules(skb, cb); mutex_unlock(&nft_net->commit_mutex);