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

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@zte.com.cn>
> Reviewed-by: Jiang Biao <jiang.biao2@zte.com.cn>
> ---
> 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@ssi.bg>

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