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Date:   Wed,  9 Sep 2020 11:42:13 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     netfilter-devel@...r.kernel.org
Cc:     davem@...emloft.net, netdev@...r.kernel.org
Subject: [PATCH 07/13] netfilter: conntrack: remove unneeded nf_ct_put

From: Florian Westphal <fw@...len.de>

We can delay refcount increment until we reassign the existing entry to
the current skb.

A 0 refcount can't happen while the nf_conn object is still in the
hash table and parallel mutations are impossible because we hold the
bucket lock.

Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Pablo Neira Ayuso <pablo@...filter.org>
---
 net/netfilter/nf_conntrack_core.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index 93e77ca0efad..234b7cab37c3 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -908,6 +908,7 @@ static void __nf_conntrack_insert_prepare(struct nf_conn *ct)
 		tstamp->start = ktime_get_real_ns();
 }
 
+/* caller must hold locks to prevent concurrent changes */
 static int __nf_ct_resolve_clash(struct sk_buff *skb,
 				 struct nf_conntrack_tuple_hash *h)
 {
@@ -921,13 +922,12 @@ static int __nf_ct_resolve_clash(struct sk_buff *skb,
 	if (nf_ct_is_dying(ct))
 		return NF_DROP;
 
-	if (!atomic_inc_not_zero(&ct->ct_general.use))
-		return NF_DROP;
-
 	if (((ct->status & IPS_NAT_DONE_MASK) == 0) ||
 	    nf_ct_match(ct, loser_ct)) {
 		struct net *net = nf_ct_net(ct);
 
+		nf_conntrack_get(&ct->ct_general);
+
 		nf_ct_acct_merge(ct, ctinfo, loser_ct);
 		nf_ct_add_to_dying_list(loser_ct);
 		nf_conntrack_put(&loser_ct->ct_general);
@@ -937,7 +937,6 @@ static int __nf_ct_resolve_clash(struct sk_buff *skb,
 		return NF_ACCEPT;
 	}
 
-	nf_ct_put(ct);
 	return NF_DROP;
 }
 
-- 
2.20.1

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