LTP/udp6_ipsec_vti tests fail when sending large UDP datagrams
that require fragmentation and underlying device MTU <= 1500.
This happens because ip6_vti sets mtu to ETH_DATA_LEN and not
updating it depending on a destiantion address.
Futhure attempts to send UDP packets may succeed because pmtu
get updated on ICMPV6_PKT_TOOBIG in vti6_err().
Here is the example when output device MTU 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
Regarding ip_vti, it already tunes mtu with ip_tunnel_bind_dev():
# ip li add vti4 type vti local 10.0.0.2 remote 10.0.0.1
# ip li sh vti4
vti4@NONE: <POINTOPOINT,NOARP> mtu 8832 ...
link/ipip 10.0.0.2 peer 10.0.0.1
Reported-by: Petr Vorel <[email protected]>
Signed-off-by: Alexey Kodanev <[email protected]>
---
ip6_vti mtu offset is the same (168) as in ip_vti because ip_vti
offset includes two sizes of struct iphdr: in dev->hard_header_len
and in t_hlen in ip_tunnel_bind_dev(). I'm not sure if it's correct.
net/ipv6/ip6_vti.c | 18 ++++++++++++++++++
1 files changed, 18 insertions(+), 0 deletions(-)
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index dbb74f3..47e6464 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -638,6 +638,24 @@ 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)
+ return;
+
+ if (rt->dst.dev) {
+ dev->mtu = max(rt->dst.dev->mtu - dev->hard_header_len,
+ IPV6_MIN_MTU);
+ }
+ ip6_rt_put(rt);
+ }
}
/**
--
1.7.1
