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From:   Ben Hutchings <ben@decadent.org.uk>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
CC:     akpm@linux-foundation.org, "Cong Wang" <xiyou.wangcong@gmail.com>,
        "Pablo Neira Ayuso" <pablo@netfilter.org>,
        "Florian Westphal" <fw@strlen.de>,
        "Eric Dumazet" <eric.dumazet@gmail.com>
Date:   Thu, 07 Jun 2018 15:05:21 +0100
Message-ID: <lsq.1528380321.493310480@decadent.org.uk>
Subject: [PATCH 3.16 235/410] netfilter: ipt_CLUSTERIP: fix a refcount bug
 in clusterip_config_find_get()
In-Reply-To: <lsq.1528380320.647747352@decadent.org.uk>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Cong Wang <xiyou.wangcong@gmail.com>

commit db93a3632b0f8773a3899e04a3a3e0aa7a26eb46 upstream.

In clusterip_config_find_get() we hold RCU read lock so it could
run concurrently with clusterip_config_entry_put(), as a result,
the refcnt could go back to 1 from 0, which leads to a double
list_del()... Just replace refcount_inc() with
refcount_inc_not_zero(), as for c->refcount.

Fixes: d73f33b16883 ("netfilter: CLUSTERIP: RCU conversion")
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Florian Westphal <fw@strlen.de>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
[bwh: Backported to 3.16: s/refcount/atomic/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
 net/ipv4/netfilter/ipt_CLUSTERIP.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -147,8 +147,12 @@ clusterip_config_find_get(struct net *ne
 	if (c) {
 		if (unlikely(!atomic_inc_not_zero(&c->refcount)))
 			c = NULL;
-		else if (entry)
-			atomic_inc(&c->entries);
+		else if (entry) {
+			if (unlikely(!atomic_inc_not_zero(&c->entries))) {
+				clusterip_config_put(c);
+				c = NULL;
+			}
+		}
 	}
 	rcu_read_unlock_bh();