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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 C9CF9C4360C for ; Sun, 13 Oct 2019 18:32:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A4579206B7 for ; Sun, 13 Oct 2019 18:32:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728239AbfJMSc6 (ORCPT ); Sun, 13 Oct 2019 14:32:58 -0400 Received: from Chamillionaire.breakpoint.cc ([193.142.43.52]:34850 "EHLO Chamillionaire.breakpoint.cc" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727354AbfJMSc6 (ORCPT ); Sun, 13 Oct 2019 14:32:58 -0400 Received: from fw by Chamillionaire.breakpoint.cc with local (Exim 4.92) (envelope-from ) id 1iJifo-0007KM-B8; Sun, 13 Oct 2019 20:32:56 +0200 From: Florian Westphal To: Cc: Florian Westphal Subject: [PATCH nf-next] netfilter: ecache: document extension area access rules Date: Sun, 13 Oct 2019 20:19:45 +0200 Message-Id: <20191013181945.21578-1-fw@strlen.de> X-Mailer: git-send-email 2.21.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: netfilter-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netfilter-devel@vger.kernel.org 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 --- 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; -- 2.21.0