vrf: Use orig netdev to count Ip6InNoRoutes and a fresh route lookup when sending dest unreach [Linux 5.1]

vrf: Use orig netdev to count Ip6InNoRoutes and a fresh route lookup when sending dest unreach [Linux 5.1]

This Linux kernel change "vrf: Use orig netdev to count Ip6InNoRoutes and a fresh route lookup when sending dest unreach" is included in the Linux 5.1 release. This change is authored by Stephen Suryaputra <ssuryaextr [at] gmail.com> on Sat Apr 27 09:14:33 2019 -0400. The commit for this change in Linux stable tree is 1d3fd8a (patch).

vrf: Use orig netdev to count Ip6InNoRoutes and a fresh route lookup when sending dest unreach

When there is no route to an IPv6 dest addr, skb_dst(skb) points
to loopback dev in the case of that the IP6CB(skb)->iif is
enslaved to a vrf. This causes Ip6InNoRoutes to be incremented on the
loopback dev. This also causes the lookup to fail on icmpv6_send() and
the dest unreachable to not sent and Ip6OutNoRoutes gets incremented on
the loopback dev.

To reproduce:
* Gateway configuration:
        ip link add dev vrf_258 type vrf table 258
        ip link set dev enp0s9 master vrf_258
        ip addr add 66:1/64 dev enp0s9
        ip -6 route add unreachable default metric 8192 table 258
        sysctl -w net.ipv6.conf.all.forwarding=1
        sysctl -w net.ipv6.conf.enp0s9.forwarding=1
* Sender configuration:
        ip addr add 66::2/64 dev enp0s9
        ip -6 route add default via 66::1
and ping 67::1 for example from the sender.

Fix this by counting on the original netdev and reset the skb dst to
force a fresh lookup.

v2: Fix typo of destination address in the repro steps.
v3: Simplify the loopback check (per David Ahern) and use reverse
    Christmas tree format (per David Miller).

Signed-off-by: Stephen Suryaputra <ssuryaextr@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Tested-by: David Ahern <dsahern@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

There are 23 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 net/ipv6/route.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 7178e32..b4899f0 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -3668,23 +3668,34 @@ int ipv6_route_ioctl(struct net *net, unsigned int cmd, void __user *arg)

 static int ip6_pkt_drop(struct sk_buff *skb, u8 code, int ipstats_mib_noroutes)
 {
-   int type;
    struct dst_entry *dst = skb_dst(skb);
+   struct net *net = dev_net(dst->dev);
+   struct inet6_dev *idev;
+   int type;
+
+   if (netif_is_l3_master(skb->dev) &&
+       dst->dev == net->loopback_dev)
+       idev = __in6_dev_get_safely(dev_get_by_index_rcu(net, IP6CB(skb)->iif));
+   else
+       idev = ip6_dst_idev(dst);
+
    switch (ipstats_mib_noroutes) {
    case IPSTATS_MIB_INNOROUTES:
        type = ipv6_addr_type(&ipv6_hdr(skb)->daddr);
        if (type == IPV6_ADDR_ANY) {
-           IP6_INC_STATS(dev_net(dst->dev),
-                     __in6_dev_get_safely(skb->dev),
-                     IPSTATS_MIB_INADDRERRORS);
+           IP6_INC_STATS(net, idev, IPSTATS_MIB_INADDRERRORS);
            break;
        }
        /* FALLTHROUGH */
    case IPSTATS_MIB_OUTNOROUTES:
-       IP6_INC_STATS(dev_net(dst->dev), ip6_dst_idev(dst),
-                 ipstats_mib_noroutes);
+       IP6_INC_STATS(net, idev, ipstats_mib_noroutes);
        break;
    }
+
+   /* Start over by dropping the dst for l3mdev case */
+   if (netif_is_l3_master(skb->dev))
+       skb_dst_drop(skb);
+
    icmpv6_send(skb, ICMPV6_DEST_UNREACH, code, 0);
    kfree_skb(skb);
    return 0;

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