Re: [PATCH] ipvs: fix race between ip_vs_conn_new() and ip_vs_del_dest()

[Julian Anastasov]

	Hello,

On Tue, 24 Jul 2018, Tan Hu wrote:

> We came across infinite loop in ipvs when using ipvs in docker
> env.
> 
> When ipvs receives new packets and cannot find an ipvs connection,
> it will create a new connection, then if the dest is unavailable
> (i.e. IP_VS_DEST_F_AVAILABLE), the packet will be dropped sliently.
> 
> But if the dropped packet is the first packet of this connection,
> the connection control timer never has a chance to start and the
> ipvs connection cannot be released. This will lead to memory leak, or
> infinite loop in cleanup_net() when net namespace is released like
> this:
> 
>     ip_vs_conn_net_cleanup at ffffffffa0a9f31a [ip_vs]
>     __ip_vs_cleanup at ffffffffa0a9f60a [ip_vs]
>     ops_exit_list at ffffffff81567a49
>     cleanup_net at ffffffff81568b40
>     process_one_work at ffffffff810a851b
>     worker_thread at ffffffff810a9356
>     kthread at ffffffff810b0b6f
>     ret_from_fork at ffffffff81697a18
> 
> race condition:
>     CPU1                           CPU2
>     ip_vs_in()
>       ip_vs_conn_new()
>                                    ip_vs_del_dest()
>                                      __ip_vs_unlink_dest()
>                                        ~IP_VS_DEST_F_AVAILABLE
>       cp->dest && !IP_VS_DEST_F_AVAILABLE
>       __ip_vs_conn_put
>       ...
>       cleanup_net  ---> infinite looping
> 
> Fix this by checking whether the timer already started.

	Looks like an old bug...

> 
> Signed-off-by: Tan Hu <tan.hu@xxxxxxxxxx>
> Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> ---
>  net/netfilter/ipvs/ip_vs_core.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
> index 0679dd1..ca9e7cc 100644
> --- a/net/netfilter/ipvs/ip_vs_core.c
> +++ b/net/netfilter/ipvs/ip_vs_core.c
> @@ -1972,13 +1972,17 @@ static int ip_vs_in_icmp_v6(struct netns_ipvs *ipvs, struct sk_buff *skb,
>  	if (cp->dest && !(cp->dest->flags & IP_VS_DEST_F_AVAILABLE)) {
>  		/* the destination server is not available */

		Add: u32 flags = cp->flags;

>  
> +		/* when timer already started, silently drop the packet.*/
> +		if (timer_pending(&cp->timer))
> +			__ip_vs_conn_put(cp);
> +		else
> +			ip_vs_conn_put(cp);

	When ip_vs_conn_put is called for IP_VS_CONN_F_ONE_PACKET
it is possible to call ip_vs_conn_expire and to free cp with
ip_vs_conn_rcu_free immediately. What we can do is to avoid the
ip_vs_conn_expire_now call in such case by reading the flags
early (as above) and adding the needed check (as below).

> +
>  		if (sysctl_expire_nodest_conn(ipvs)) {

	Add !(flags & IP_VS_CONN_F_ONE_PACKET) check in above 'if'.

>  			/* try to expire the connection immediately */
>  			ip_vs_conn_expire_now(cp);
>  		}
> -		/* don't restart its timer, and silently
> -		   drop the packet. */
> -		__ip_vs_conn_put(cp);
> +
>  		return NF_DROP;
>  	}
>  

Regards

--
Julian Anastasov <ja@xxxxxx>