[PATCH v3] ipvs: fix race between ip_vs_conn_new() and ip_vs_del_dest()

From: Tan Hu
Date: Wed Jul 25 2018 - 03:13:30 EST

We came across infinite loop in ipvs when using ipvs in docker

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

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:
cleanup_net ---> infinite looping

Fix this by checking whether the timer already started.

Signed-off-by: Tan Hu <tan.hu@xxxxxxxxxx>
Reviewed-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
v2: fix use-after-free in CONN_ONE_PACKET case suggested by Julian Anastasov
v3: remove trailing whitespace for patch checking

net/netfilter/ipvs/ip_vs_core.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/ipvs/ip_vs_core.c b/net/netfilter/ipvs/ip_vs_core.c
index 0679dd1..a17104f 100644
--- a/net/netfilter/ipvs/ip_vs_core.c
+++ b/net/netfilter/ipvs/ip_vs_core.c
@@ -1972,13 +1972,20 @@ 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 */

- if (sysctl_expire_nodest_conn(ipvs)) {
+ __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);
+ if (sysctl_expire_nodest_conn(ipvs) &&
+ !(flags & IP_VS_CONN_F_ONE_PACKET)) {
/* try to expire the connection immediately */
- /* don't restart its timer, and silently
- drop the packet. */
- __ip_vs_conn_put(cp);
return NF_DROP;