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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 D2AD8CA9EBC for ; Sat, 26 Oct 2019 11:47:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B3516206DD for ; Sat, 26 Oct 2019 11:47:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726527AbfJZLrw (ORCPT ); Sat, 26 Oct 2019 07:47:52 -0400 Received: from correo.us.es ([193.147.175.20]:46456 "EHLO mail.us.es" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726483AbfJZLrv (ORCPT ); Sat, 26 Oct 2019 07:47:51 -0400 Received: from antivirus1-rhel7.int (unknown [192.168.2.11]) by mail.us.es (Postfix) with ESMTP id 9F16B8C3C61 for ; Sat, 26 Oct 2019 13:47:47 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 8BCD5CA0F2 for ; Sat, 26 Oct 2019 13:47:47 +0200 (CEST) Received: by antivirus1-rhel7.int (Postfix, from userid 99) id 811AE21FF7; Sat, 26 Oct 2019 13:47:47 +0200 (CEST) Received: from antivirus1-rhel7.int (localhost [127.0.0.1]) by antivirus1-rhel7.int (Postfix) with ESMTP id 8EA2BB8005; Sat, 26 Oct 2019 13:47:45 +0200 (CEST) Received: from 192.168.1.97 (192.168.1.97) by antivirus1-rhel7.int (F-Secure/fsigk_smtp/550/antivirus1-rhel7.int); Sat, 26 Oct 2019 13:47:45 +0200 (CEST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/antivirus1-rhel7.int) Received: from salvia.here (sys.soleta.eu [212.170.55.40]) (Authenticated sender: pneira@us.es) by entrada.int (Postfix) with ESMTPA id 5E72342EE393; Sat, 26 Oct 2019 13:47:45 +0200 (CEST) X-SMTPAUTHUS: auth mail.us.es From: Pablo Neira Ayuso To: netfilter-devel@vger.kernel.org Cc: davem@davemloft.net, netdev@vger.kernel.org Subject: [PATCH 14/31] netfilter: ecache: document extension area access rules Date: Sat, 26 Oct 2019 13:47:16 +0200 Message-Id: <20191026114733.28111-15-pablo@netfilter.org> X-Mailer: git-send-email 2.11.0 In-Reply-To: <20191026114733.28111-1-pablo@netfilter.org> References: <20191026114733.28111-1-pablo@netfilter.org> 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 From: Florian Westphal Once ct->ext gets free'd via kfree() rather than kfree_rcu we can't access the extension area anymore without owning the conntrack. This is a special case: The worker is walking the pcpu dying list while holding dying list lock: Neither ct nor ct->ext can be free'd until after the walk has completed. Signed-off-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_ecache.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) diff --git a/net/netfilter/nf_conntrack_ecache.c b/net/netfilter/nf_conntrack_ecache.c index 6fba74b5aaf7..0d83c159671c 100644 --- a/net/netfilter/nf_conntrack_ecache.c +++ b/net/netfilter/nf_conntrack_ecache.c @@ -30,6 +30,7 @@ static DEFINE_MUTEX(nf_ct_ecache_mutex); #define ECACHE_RETRY_WAIT (HZ/10) +#define ECACHE_STACK_ALLOC (256 / sizeof(void *)) enum retry_state { STATE_CONGESTED, @@ -39,11 +40,11 @@ enum retry_state { static enum retry_state ecache_work_evict_list(struct ct_pcpu *pcpu) { - struct nf_conn *refs[16]; + struct nf_conn *refs[ECACHE_STACK_ALLOC]; + enum retry_state ret = STATE_DONE; struct nf_conntrack_tuple_hash *h; struct hlist_nulls_node *n; unsigned int evicted = 0; - enum retry_state ret = STATE_DONE; spin_lock(&pcpu->lock); @@ -54,10 +55,22 @@ static enum retry_state ecache_work_evict_list(struct ct_pcpu *pcpu) if (!nf_ct_is_confirmed(ct)) continue; + /* This ecache access is safe because the ct is on the + * pcpu dying list and we hold the spinlock -- the entry + * cannot be free'd until after the lock is released. + * + * This is true even if ct has a refcount of 0: the + * cpu that is about to free the entry must remove it + * from the dying list and needs the lock to do so. + */ e = nf_ct_ecache_find(ct); if (!e || e->state != NFCT_ECACHE_DESTROY_FAIL) continue; + /* ct is in NFCT_ECACHE_DESTROY_FAIL state, this means + * the worker owns this entry: the ct will remain valid + * until the worker puts its ct reference. + */ if (nf_conntrack_event(IPCT_DESTROY, ct)) { ret = STATE_CONGESTED; break; -- 2.11.0