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Commit 53c81e95 authored by Alexey Kodanev's avatar Alexey Kodanev Committed by David S. Miller
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ip6_vti: adjust vti mtu according to mtu of lower device 



LTP/udp6_ipsec_vti tests fail when sending large UDP datagrams over
ip6_vti that require fragmentation and the underlying device has an
MTU smaller than 1500 plus some extra space for headers. This happens
because ip6_vti, by default, sets MTU to ETH_DATA_LEN and not updating
it depending on a destination address or link parameter. Further
attempts to send UDP packets may succeed because pmtu gets updated on
ICMPV6_PKT_TOOBIG in vti6_err().

In case the lower device has larger MTU size, e.g. 9000, ip6_vti works
but not using the possible maximum size, output packets have 1500 limit.

The above cases require manual MTU setup after ip6_vti creation. However
ip_vti already updates MTU based on lower device with ip_tunnel_bind_dev().

Here is the example when the lower device MTU is set to 9000:

  # ip a sh ltp_ns_veth2
      ltp_ns_veth2@if7: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9000 ...
        inet 10.0.0.2/24 scope global ltp_ns_veth2
        inet6 fd00::2/64 scope global

  # ip li add vti6 type vti6 local fd00::2 remote fd00::1
  # ip li show vti6
      vti6@NONE: <POINTOPOINT,NOARP> mtu 1500 ...
        link/tunnel6 fd00::2 peer fd00::1

After the patch:
  # ip li add vti6 type vti6 local fd00::2 remote fd00::1
  # ip li show vti6
      vti6@NONE: <POINTOPOINT,NOARP> mtu 8832 ...
        link/tunnel6 fd00::2 peer fd00::1

Reported-by: default avatarPetr Vorel <pvorel@suse.cz>
Signed-off-by: default avatarAlexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f39a5c01

net/ipv6/ip6_vti.c

+20 −0
Original line number Diff line number Diff line
@@ -626,6 +626,7 @@ static void vti6_link_config(struct ip6_tnl *t) 
{

	struct net_device *dev = t->dev;

	struct __ip6_tnl_parm *p = &t->parms;

	struct net_device *tdev = NULL;



	memcpy(dev->dev_addr, &p->laddr, sizeof(struct in6_addr));

	memcpy(dev->broadcast, &p->raddr, sizeof(struct in6_addr));
@@ -638,6 +639,25 @@ static void vti6_link_config(struct ip6_tnl *t) 
		dev->flags |= IFF_POINTOPOINT;

	else

		dev->flags &= ~IFF_POINTOPOINT;



	if (p->flags & IP6_TNL_F_CAP_XMIT) {

		int strict = (ipv6_addr_type(&p->raddr) &

			      (IPV6_ADDR_MULTICAST | IPV6_ADDR_LINKLOCAL));

		struct rt6_info *rt = rt6_lookup(t->net,

						 &p->raddr, &p->laddr,

						 p->link, strict);



		if (rt)

			tdev = rt->dst.dev;

		ip6_rt_put(rt);

	}



	if (!tdev && p->link)

		tdev = __dev_get_by_index(t->net, p->link);



	if (tdev)

		dev->mtu = max_t(int, tdev->mtu - dev->hard_header_len,

				 IPV6_MIN_MTU);

}



/**