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@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv6/ip6_gre.c b/net/ipv6/ip6_gre.c
index 4e636e60a360d5c22dc856c2c80d361127ba41b6..2be66e7b4a78ab05a51c836b09c6085e1c484c39 100644 (file)
--- 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;