Subject: Re: Re: [PATCH] ipvs: fix race between ip_vs_conn_new() andip_vs_del_dest()

From: <[email-masked]>
Date: Wed, 25 Jul 2018 10:46:37 +0800 (CST)

Thanks for your reviewing, I have sent patch-v2, please check it.

> 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 <[email-masked]>
> > Reviewed-by: Jiang Biao <[email-masked]>
> > ---
> > 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