netdev - Re: [Patch net] ipt_CLUSTERIP: fix a refcount bug in clusterip_config_find

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Date:   Thu, 8 Feb 2018 09:01:30 +0100
From:   Florian Westphal <fw@...len.de>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        pabeni@...hat.com, Eric Dumazet <eric.dumazet@...il.com>,
        Pablo Neira Ayuso <pablo@...filter.org>
Subject: Re: [Patch net] ipt_CLUSTERIP: fix a refcount bug in
 clusterip_config_find_get()

Cong Wang <xiyou.wangcong@...il.com> wrote:
> 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@...il.com>
> Cc: Pablo Neira Ayuso <pablo@...filter.org>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>
> ---
>  net/ipv4/netfilter/ipt_CLUSTERIP.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/ipt_CLUSTERIP.c b/net/ipv4/netfilter/ipt_CLUSTERIP.c
> index 1ff72b87a066..4537b1686c7c 100644
> --- a/net/ipv4/netfilter/ipt_CLUSTERIP.c
> +++ b/net/ipv4/netfilter/ipt_CLUSTERIP.c
> @@ -154,8 +154,10 @@ 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)))

this needs to call clusterip_config_put(c); too, else we leak one
reference.

Other than that this looks good.