netdev - [PATCH net] net: sched: act_mirred: drop skb's dst

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Date:   Sat, 12 Oct 2019 15:16:20 +0800
From:   Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>,
        "David S . Miller" <davem@...emloft.net>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH net] net: sched: act_mirred: drop skb's dst_entry in ingress redirection

In act_mirred's ingress redirection, if the skb's dst_entry is valid
when call function netif_receive_skb, the fllowing l3 stack process
(ip_rcv_finish_core) will check dst_entry and skip the routing
decision. Using the old dst_entry is unexpected and may discard the
skb in some case. For example dst->dst_input points to dst_discard.

This patch drops the skb's dst_entry before calling netif_receive_skb
so that the skb can be made routing decision like a normal ingress
skb.

Signed-off-by: Zhiyuan Hou <zhiyuan2048@...ux.alibaba.com>
---
 net/sched/act_mirred.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index 9ce073a05414..6108a64c0cd5 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -18,6 +18,7 @@
 #include <linux/gfp.h>
 #include <linux/if_arp.h>
 #include <net/net_namespace.h>
+#include <net/dst.h>
 #include <net/netlink.h>
 #include <net/pkt_sched.h>
 #include <net/pkt_cls.h>
@@ -298,8 +299,10 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 
 	if (!want_ingress)
 		err = dev_queue_xmit(skb2);
-	else
+	else {
+		skb_dst_drop(skb2);
 		err = netif_receive_skb(skb2);
+	}
 
 	if (err) {
 out:
-- 
2.21.0