Patch "ip6_tunnel: get the min mtu properly in ip6_tnl_xmit" has been added to the 4.9-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    ip6_tunnel: get the min mtu properly in ip6_tnl_xmit

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ip6_tunnel-get-the-min-mtu-properly-in-ip6_tnl_xmit.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Wed Feb 28 16:13:29 CET 2018
From: Xin Long <lucien.xin@gmail.com>
Date: Mon, 18 Dec 2017 14:26:21 +0800
Subject: ip6_tunnel: get the min mtu properly in ip6_tnl_xmit

From: Xin Long <lucien.xin@gmail.com>


[ Upstream commit c9fefa08190fc879fb2e681035d7774e0a8c5170 ]

Now it's using IPV6_MIN_MTU as the min mtu in ip6_tnl_xmit, but
IPV6_MIN_MTU actually only works when the inner packet is ipv6.

With IPV6_MIN_MTU for ipv4 packets, the new pmtu for inner dst
couldn't be set less than 1280. It would cause tx_err and the
packet to be dropped when the outer dst pmtu is close to 1280.

Jianlin found it by running ipv4 traffic with the topo:

  (client) gre6 <---> eth1 (route) eth2 <---> gre6 (server)

After changing eth2 mtu to 1300, the performance became very
low, or the connection was even broken. The issue also affects
ip4ip6 and ip6ip6 tunnels.

So if the inner packet is ipv4, 576 should be considered as the
min mtu.

Note that for ip4ip6 and ip6ip6 tunnels, the inner packet can
only be ipv4 or ipv6, but for gre6 tunnel, it may also be ARP.
This patch using 576 as the min mtu for non-ipv6 packet works
for all those cases.

Reported-by: Jianlin Shi <jishi@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv6/ip6_tunnel.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/net/ipv6/ip6_tunnel.c
+++ b/net/ipv6/ip6_tunnel.c
@@ -1127,8 +1127,13 @@ route_lookup:
 		max_headroom += 8;
 		mtu -= 8;
 	}
-	if (mtu < IPV6_MIN_MTU)
-		mtu = IPV6_MIN_MTU;
+	if (skb->protocol == htons(ETH_P_IPV6)) {
+		if (mtu < IPV6_MIN_MTU)
+			mtu = IPV6_MIN_MTU;
+	} else if (mtu < 576) {
+		mtu = 576;
+	}
+
 	if (skb_dst(skb) && !t->parms.collect_md)
 		skb_dst(skb)->ops->update_pmtu(skb_dst(skb), NULL, skb, mtu);
 	if (skb->len - t->tun_hlen - eth_hlen > mtu && !skb_is_gso(skb)) {


Patches currently in stable-queue which might be from lucien.xin@gmail.com are

queue-4.9/ip6_tunnel-get-the-min-mtu-properly-in-ip6_tnl_xmit.patch