netfilter: ipt_CLUSTERIP: fix a refcount bug in clusterip_config_find_get()

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 3.2: s/refcount/atomic/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
index db6785c..cb21acc 100644 (file)
--- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
+++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
@@ -135,8 +135,12 @@ clusterip_config_find_get(__be32 clusterip, int entry)
        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();