netdev - Adding support for VRF traffic passed by mangle table

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Message-ID: <1491188266363.26046@alliedtelesis.co.nz>
Date:   Mon, 3 Apr 2017 02:57:46 +0000
From:   Jack Ma <Jack.Ma@...iedtelesis.co.nz>
To:     "dsa@...ulusnetworks.com" <dsa@...ulusnetworks.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Adding support for VRF traffic passed by mangle table

Hi David,

I formatted a patch to support vrf flow passed by iptables(mangle table). And previously, we lost the flow.oif which would result in a routing look-up failure. This patch wraps vrf response flow with the correct master interface by using the skb->dev, which was set to the real ingress device.
Without this patch, VRF traffic permitted by firewall rules that changes nf_mark would be dropped while doing fib_lookup.
Kernel documentations suggested two way of fixing this:

 
        <
        [2] Iptables on ingress supports PREROUTING with skb->dev set to the real
            ingress device and both INPUT and PREROUTING rules with skb->dev set to
            the VRF device. For egress POSTROUTING and OUTPUT rules can be written
            using either the VRF device or real egress device.
        >


Could you please look at this patch and give me some feedback?
Thanks for your time and considerations.

Regards,
Jack




diff --git a/net/ipv4/netfilter.c b/net/ipv4/netfilter.c
index c0cc6aa..07168d4 100644
--- a/net/ipv4/netfilter.c
+++ b/net/ipv4/netfilter.c
@@ -46,6 +46,14 @@ int ip_route_me_harder(struct net *net, struct sk_buff *skb, unsigned int addr_t
                fl4.flowi4_oif = l3mdev_master_ifindex(dev);
        fl4.flowi4_mark = skb->mark;
        fl4.flowi4_flags = flags;
+
+       /* Since we have already known this is vrf flow passed by
+        * mangle table, we wrap the oif with the master interface.
+        */
+       if (fl4.flowi4_oif == 0 && fl4.daddr && skb->dev &&
+           netif_index_is_l3_master(net, skb->dev->ifindex))
+               fl4.flowi4_oif = skb->dev->ifindex;
+
        rt = ip_route_output_key(net, &fl4);
        if (IS_ERR(rt))
                return PTR_ERR(rt);
View attachment "VRF_support.patch" of type "text/x-patch" (64 bytes)