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Date: Thu, 26 Jan 2017 22:49:10 +0200 (EET)
From: Julian Anastasov <ja@....bg>
To: David Windsor <dwindsor@...il.com>
cc: netdev@...r.kernel.org, kernel-hardening@...ts.openwall.com,
        netfilter-devel@...r.kernel.org, lvs-devel@...r.kernel.org,
        wensong@...ux-vs.org, horms@...ge.net.au, pablo@...filter.org,
        keescook@...omium.org, elena.reshetova@...el.com, ishkamiel@...il.com
Subject: Re: [PATCH v2 net] net: free ip_vs_dest structs when refcnt=0


	Hello,

On Mon, 23 Jan 2017, David Windsor wrote:

> Currently, the ip_vs_dest cache frees ip_vs_dest objects when their
> reference count becomes < 0.  Aside from not being semantically sound,
> this is problematic for the new type refcount_t, which will be introduced
> shortly in a separate patch. refcount_t is the new kernel type for
> holding reference counts, and provides overflow protection and a
> constrained interface relative to atomic_t (the type currently being
> used for kernel reference counts).
> 
> Per Julian Anastasov: "The problem is that dest_trash currently holds
> deleted dests (unlinked from RCU lists) with refcnt=0."  Changing
> dest_trash to hold dest with refcnt=1 will allow us to free ip_vs_dest
> structs when their refcnt=0, in ip_vs_dest_put_and_free().
> 
> Signed-off-by: David Windsor <dwindsor@...il.com>

	Thanks! I tested the first version and this one
just adds the needed changes in comments, so

Signed-off-by: Julian Anastasov <ja@....bg>

	Simon and Pablo, this is more appropriate for
ipvs-next/nf-next. Please apply!

> ---
>  include/net/ip_vs.h            | 2 +-
>  net/netfilter/ipvs/ip_vs_ctl.c | 8 +++-----
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/include/net/ip_vs.h b/include/net/ip_vs.h
> index cd6018a..a3e78ad 100644
> --- a/include/net/ip_vs.h
> +++ b/include/net/ip_vs.h
> @@ -1421,7 +1421,7 @@ static inline void ip_vs_dest_put(struct ip_vs_dest *dest)
>  
>  static inline void ip_vs_dest_put_and_free(struct ip_vs_dest *dest)
>  {
> -	if (atomic_dec_return(&dest->refcnt) < 0)
> +	if (atomic_dec_and_test(&dest->refcnt))
>  		kfree(dest);
>  }
>  
> diff --git a/net/netfilter/ipvs/ip_vs_ctl.c b/net/netfilter/ipvs/ip_vs_ctl.c
> index 55e0169..5fc4836 100644
> --- a/net/netfilter/ipvs/ip_vs_ctl.c
> +++ b/net/netfilter/ipvs/ip_vs_ctl.c
> @@ -711,7 +711,6 @@ ip_vs_trash_get_dest(struct ip_vs_service *svc, int dest_af,
>  		      dest->vport == svc->port))) {
>  			/* HIT */
>  			list_del(&dest->t_list);
> -			ip_vs_dest_hold(dest);
>  			goto out;
>  		}
>  	}
> @@ -741,7 +740,7 @@ static void ip_vs_dest_free(struct ip_vs_dest *dest)
>   *  When the ip_vs_control_clearup is activated by ipvs module exit,
>   *  the service tables must have been flushed and all the connections
>   *  are expired, and the refcnt of each destination in the trash must
> - *  be 0, so we simply release them here.
> + *  be 1, so we simply release them here.
>   */
>  static void ip_vs_trash_cleanup(struct netns_ipvs *ipvs)
>  {
> @@ -1080,11 +1079,10 @@ static void __ip_vs_del_dest(struct netns_ipvs *ipvs, struct ip_vs_dest *dest,
>  	if (list_empty(&ipvs->dest_trash) && !cleanup)
>  		mod_timer(&ipvs->dest_trash_timer,
>  			  jiffies + (IP_VS_DEST_TRASH_PERIOD >> 1));
> -	/* dest lives in trash without reference */
> +	/* dest lives in trash with reference */
>  	list_add(&dest->t_list, &ipvs->dest_trash);
>  	dest->idle_start = 0;
>  	spin_unlock_bh(&ipvs->dest_trash_lock);
> -	ip_vs_dest_put(dest);
>  }
>  
>  
> @@ -1160,7 +1158,7 @@ static void ip_vs_dest_trash_expire(unsigned long data)
>  
>  	spin_lock(&ipvs->dest_trash_lock);
>  	list_for_each_entry_safe(dest, next, &ipvs->dest_trash, t_list) {
> -		if (atomic_read(&dest->refcnt) > 0)
> +		if (atomic_read(&dest->refcnt) > 1)
>  			continue;
>  		if (dest->idle_start) {
>  			if (time_before(now, dest->idle_start +
> -- 
> 2.7.4

Regards

--
Julian Anastasov <ja@....bg>

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