netdev - [net-next PATCH 2/5] ip6gretap: Fix MTU to allow for Ethernet header

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Date:	Thu, 14 Apr 2016 15:33:45 -0400
From:	Alexander Duyck <aduyck@...antis.com>
To:	jesse@...nel.org, netdev@...r.kernel.org, davem@...emloft.net,
	alexander.duyck@...il.com, tom@...bertland.com
Subject: [net-next PATCH 2/5] ip6gretap: Fix MTU to allow for Ethernet header

When we were creating an ip6gretap interface the MTU was about 6 bytes
short of what was needed.  It turns out we were not taking the Ethernet
header into account and as a result we were eating into the 8 bytes
reserved for the encap limit.

Signed-off-by: Alexander Duyck <aduyck@...antis.com>
---
 net/ipv6/ip6_gre.c |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 4e636e60a360..2be66e7b4a78 100644
--- a/net/ipv6/ip6_gre.c
+++ b/net/ipv6/ip6_gre.c
@@ -987,6 +987,8 @@ static void ip6gre_tnl_link_config(struct ip6_tnl *t, int set_mtu)
 				dev->mtu = rt->dst.dev->mtu - addend;
 				if (!(t->parms.flags & IP6_TNL_F_IGN_ENCAP_LIMIT))
 					dev->mtu -= 8;
+				if (dev->type == ARPHRD_ETHER)
+					dev->mtu -= ETH_HLEN;
 
 				if (dev->mtu < IPV6_MIN_MTU)
 					dev->mtu = IPV6_MIN_MTU;