From mboxrd@z Thu Jan 1 00:00:00 1970 From: Joerg Marx Subject: Re: [PATCH] nf_conntrack_core.c: fix for dead connection after flushing conntrack cache Date: Mon, 10 May 2010 19:08:35 +0200 Message-ID: <4BE83D93.8080909@secunet.com> References: <4BE3D31F.6000607@secunet.com> <4BE73DE3.6080304@netfilter.org> <4BE824EA.6000303@trash.net> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4BE824EA.6000303@trash.net> Sender: netfilter-devel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Patrick McHardy Cc: Pablo Neira Ayuso , Netfilter Development Mailinglist , Mail List - Netfilter On 05/10/2010 05:23 PM, Patrick McHardy wrote: ... > > I think this should be fine since the race you describe only affects > unconfirmed conntracks, but it took me a while to realize that all > the other spots where the DYING bit is set are fine without holding > the conntrack lock. > > Could you please add a comment to the check in __nf_conntrack_confirm() > stating that the dying check is supposed to prevent races against > nf_ct_get_next_corpse()? The semantic of the DYING bit is unfortunately > a bit overloaded. > > Also, since the condition unconfirmed + dying in nf_conntrack_confirm() > is highly unlikely, I'd suggest to remove the dying check there and only > perform it in __nf_conntrack_confirm(). > I hope the comment is clearly pointing to the (solved) problem now. I also removed the obsolete check in nf_conntrack_confirm. diff --git a/include/net/netfilter/nf_conntrack_core.h b/include/net/netfilter/nf_conntrack_core.h index dffde8e..3d7524f 100644 --- a/include/net/netfilter/nf_conntrack_core.h +++ b/include/net/netfilter/nf_conntrack_core.h @@ -61,7 +61,7 @@ static inline int nf_conntrack_confirm(struct sk_buff *skb) int ret = NF_ACCEPT; if (ct && ct != &nf_conntrack_untracked) { - if (!nf_ct_is_confirmed(ct) && !nf_ct_is_dying(ct)) + if (!nf_ct_is_confirmed(ct)) ret = __nf_conntrack_confirm(skb); if (likely(ret == NF_ACCEPT)) nf_ct_deliver_cached_events(ct); diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 0c9bbe9..7ff9a40 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -422,6 +422,16 @@ __nf_conntrack_confirm(struct sk_buff *skb) spin_lock_bh(&nf_conntrack_lock); + /* We have to check the DYING flag inside the lock to prevent + a race against nf_ct_get_next_corpse() possibly called from + user context, else we insert an already 'dead' hash, blocking + further use of that particular connection -JM */ + + if (unlikely(nf_ct_is_dying(ct))) { + spin_unlock_bh(&nf_conntrack_lock); + return NF_ACCEPT; + } + /* See if there's one in the list already, including reverse: NAT could have grabbed it without realizing, since we're not in the hash. If there is, we lost race. */ --