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 50DA0C4167D for ; Sat, 4 Nov 2023 10:36:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231903AbjKDKgK (ORCPT ); Sat, 4 Nov 2023 06:36:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40296 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229468AbjKDKgJ (ORCPT ); Sat, 4 Nov 2023 06:36:09 -0400 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [IPv6:2a0a:51c0:0:237:300::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12BCB191 for ; Sat, 4 Nov 2023 03:36:06 -0700 (PDT) Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1qzE0N-0002dd-9B; Sat, 04 Nov 2023 11:35:51 +0100 Date: Sat, 4 Nov 2023 11:35:51 +0100 From: Florian Westphal To: Jozsef Kadlecsik Cc: netfilter-devel@vger.kernel.org, Pablo Neira Ayuso , Linkui Xiao Subject: Re: [PATCH 1/1] netfilter: ipset: fix race condition between swap/destroy and kernel side add/del/test, v2 Message-ID: <20231104103551.GA9892@breakpoint.cc> References: <20231104100349.4184215-1-kadlec@netfilter.org> <20231104100349.4184215-2-kadlec@netfilter.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20231104100349.4184215-2-kadlec@netfilter.org> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org Jozsef Kadlecsik wrote: > Linkui Xiao reported that there's a race condition when ipset swap and destroy is > called, which can lead to crash in add/del/test element operations. Swap then > destroy are usual operations to replace a set with another one in a production > system. The issue can in some cases be reproduced with the script: Hi Jozsef, > iptables -A INPUT -m set --match-set hash_ip1 src -j ACCEPT > while [ 1 ] > do > # ... Ongoing traffic... > ipset create hash_ip2 hash:net family inet hashsize 1024 maxelem 1048576 > ipset add hash_ip2 172.20.0.0/16 > ipset swap hash_ip1 hash_ip2 > ipset destroy hash_ip2 > sleep 0.05 > done > > In the race case the possible order of the operations are > > CPU0 CPU1 > ip_set_test > ipset swap hash_ip1 hash_ip2 > ipset destroy hash_ip2 > hash_net_kadt > > Swap replaces hash_ip1 with hash_ip2 and then destroy removes hash_ip2 which > is the original hash_ip1. ip_set_test was called on hash_ip1 and because destroy > removed it, hash_net_kadt crashes. > > The fix is to protect both the list of the sets and the set pointers in an extended RCU > region and before exiting ip_set_swap(), wait to finish all started rcu_read_lock(). > The first version of the patch was written by Linkui Xiao . > > v2: synchronize_rcu() is moved into ip_set_swap() in order not to burden > ip_set_destroy() unnecessarily when all sets are destroyed. Hmm. Isn't it enough to only call synchronize_rcu() in ip_set_swap? All netfilter hooks run with rcu_read_lock() held, em_ipset.c wraps the entire ip_set_test() in rcu read lock/unlock pair. > @@ -704,13 +704,18 @@ ip_set_rcu_get(struct net *net, ip_set_id_t index) > struct ip_set_net *inst = ip_set_pernet(net); > > rcu_read_lock(); > - /* ip_set_list itself needs to be protected */ > + /* ip_set_list and the set pointer need to be protected */ > set = rcu_dereference(inst->ip_set_list)[index]; > - rcu_read_unlock(); > > return set; > } ... so I don't understand why ip_set_rcu_get() has to extend the locked section. AFAICS there are only two type of callers: 1. rcu read lock is already held (datapath) 2. ipset nfnl subsys mutex is held *probably* This could be changed in a separate patch to: - rcu_read_lock(); - /* ip_set_list itself needs to be protected */ - set = rcu_dereference(inst->ip_set_list)[index]; - rcu_read_unlock(); + /* ip_set_list and the set pointer need to be protected */ + return rcu_dereference_check(inst->ip_set_list, lockdep_nfnl_is_held(NFNL_SUBSYS_IPSET)[index]; This is an example, probably better to add a small "ip_set_dereference_nfnl" helper to hide the lockdep construct... Not saying the patch is wrong; rcu read locks nest and ipset locking is not simple so I might be missing something.