netdev - [PATCH net 1/2] net: sched: act_mirred: drop dst for the direction from egress to ingress

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Message-Id: <e6c13028614a219ddf2854a160125aa85bac7bf9.1636734751.git.lucien.xin@gmail.com>
Date:   Fri, 12 Nov 2021 11:33:11 -0500
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, davem@...emloft.net,
        kuba@...nel.org,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Subject: [PATCH net 1/2] net: sched: act_mirred: drop dst for the direction from egress to ingress

Without dropping dst, the packets sent from local mirred/redirected
to ingress will may still use the old dst. ip_rcv() will drop it as
the old dst is for output and its .input is dst_discard.

This patch is to fix by also dropping dst for those packets that are
mirred or redirected from egress to ingress in act_mirred.

Note that we don't drop it for the direction change from ingress to
egress, as on which there might be a user case attaching a metadata
dst by act_tunnel_key that would be used later.

Fixes: b57dc7c13ea9 ("net/sched: Introduce action ct")
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/sched/act_mirred.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/net/sched/act_mirred.c b/net/sched/act_mirred.c
index d64b0eeccbe4..efc963ab995a 100644
--- a/net/sched/act_mirred.c
+++ b/net/sched/act_mirred.c
@@ -19,6 +19,7 @@
 #include <linux/if_arp.h>
 #include <net/net_namespace.h>
 #include <net/netlink.h>
+#include <net/dst.h>
 #include <net/pkt_sched.h>
 #include <net/pkt_cls.h>
 #include <linux/tc_act/tc_mirred.h>
@@ -228,6 +229,7 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	bool want_ingress;
 	bool is_redirect;
 	bool expects_nh;
+	bool at_ingress;
 	int m_eaction;
 	int mac_len;
 	bool at_nh;
@@ -263,7 +265,8 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 	 * ingress - that covers the TC S/W datapath.
 	 */
 	is_redirect = tcf_mirred_is_act_redirect(m_eaction);
-	use_reinsert = skb_at_tc_ingress(skb) && is_redirect &&
+	at_ingress = skb_at_tc_ingress(skb);
+	use_reinsert = at_ingress && is_redirect &&
 		       tcf_mirred_can_reinsert(retval);
 	if (!use_reinsert) {
 		skb2 = skb_clone(skb, GFP_ATOMIC);
@@ -271,10 +274,12 @@ static int tcf_mirred_act(struct sk_buff *skb, const struct tc_action *a,
 			goto out;
 	}
 
+	want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
+
 	/* All mirred/redirected skbs should clear previous ct info */
 	nf_reset_ct(skb2);
-
-	want_ingress = tcf_mirred_act_wants_ingress(m_eaction);
+	if (want_ingress && !at_ingress) /* drop dst for egress -> ingress */
+		skb_dst_drop(skb2);
 
 	expects_nh = want_ingress || !m_mac_header_xmit;
 	at_nh = skb->data == skb_network_header(skb);
-- 
2.27.0