[PATCH 3.16 235/410] netfilter: ipt_CLUSTERIP: fix a refcount bug in clusterip_config_find_get()

[Ben Hutchings]

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

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

From: Cong Wang <xiyou.wangcong@xxxxxxxxx>

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@xxxxxxxxx>
Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
Cc: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Reviewed-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[bwh: Backported to 3.16: s/refcount/atomic/]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 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();