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

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