From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Thu, 8 Feb 2018 13:53:52 -0800
Subject: netfilter: ipt_CLUSTERIP: fix a refcount bug in
 clusterip_config_find_get()
Patch-mainline: v4.16-rc3
Git-commit: db93a3632b0f8773a3899e04a3a3e0aa7a26eb46
References: bsc#1076830

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>
Acked-by: Michal Kubecek <mkubecek@suse.cz>

---
 net/ipv4/netfilter/ipt_CLUSTERIP.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index 45a80260ed8b..e4275e9f7b11 100644
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -154,8 +154,12 @@ clusterip_config_find_get(struct net *net, __be32 clusterip, int entry)
 #endif
 		if (unlikely(!refcount_inc_not_zero(&c->refcount)))
 			c = NULL;
-		else if (entry)
-			refcount_inc(&c->entries);
+		else if (entry) {
+			if (unlikely(!refcount_inc_not_zero(&c->entries))) {
+				clusterip_config_put(c);
+				c = NULL;
+			}
+		}
 	}
 	rcu_read_unlock_bh();
 
-- 
2.16.2