linux-kernel - [RFC PATCH] Don't copy mark from encapsulated packet when routing VXLAN

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Date:   Mon, 30 Sep 2019 06:27:43 +0000
From:   Jethro Beekman <jethro@...tanix.com>
To:     "David S. Miller" <davem@...emloft.net>,
        Petr Machata <petrm@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Stefano Brivio <sbrivio@...hat.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Litao jiao <jiaolitao@...secom.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Jethro Beekman <jethro@...tanix.com>
Subject: [RFC PATCH] Don't copy mark from encapsulated packet when routing
 VXLAN

When using rule-based routing to send traffic via VXLAN, a routing
loop may occur. Say you have the following routing setup:

ip rule add from all fwmark 0x2/0x2 lookup 2
ip route add table 2 default via 10.244.2.0 dev vxlan1 onlink

The intention is to route packets with mark 2 through VXLAN, and
this works fine. However, the current vxlan code copies the mark
to the encapsulated packet. Immediately after egress on the VXLAN
interface, the encapsulated packet is routed, with no opportunity
to mangle the encapsulated packet. The mark is copied from the
inner packet to the outer packet, and the same routing rule and
table shown above will apply, resulting in ELOOP.

This patch simply doesn't copy the mark from the encapsulated packet.
I don't intend this code to land as is, but I want to start a
discussion on how to make separate routing of VXLAN inner and
encapsulated traffic easier.

Signed-off-by: Jethro Beekman <jethro@...tanix.com>
---
 drivers/net/vxlan.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 3d9bcc9..f9ed1b7 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c
@@ -2236,7 +2236,6 @@ static struct rtable *vxlan_get_route(struct vxlan_dev *vxlan, struct net_device
 	memset(&fl4, 0, sizeof(fl4));
 	fl4.flowi4_oif = oif;
 	fl4.flowi4_tos = RT_TOS(tos);
-	fl4.flowi4_mark = skb->mark;
 	fl4.flowi4_proto = IPPROTO_UDP;
 	fl4.daddr = daddr;
 	fl4.saddr = *saddr;
@@ -2294,7 +2293,6 @@ static struct dst_entry *vxlan6_get_route(struct vxlan_dev *vxlan,
 	fl6.daddr = *daddr;
 	fl6.saddr = *saddr;
 	fl6.flowlabel = ip6_make_flowinfo(RT_TOS(tos), label);
-	fl6.flowi6_mark = skb->mark;
 	fl6.flowi6_proto = IPPROTO_UDP;
 	fl6.fl6_dport = dport;
 	fl6.fl6_sport = sport;
-- 
2.7.4

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