ip6_tunnel: Allow rcv/xmit even if remote address is a local address

Currently, ip6_tnl_xmit_ctl drops tunneled packets if the remote
address (outer v6 destination) is one of host's locally configured
addresses.
Same applies to ip6_tnl_rcv_ctl: it drops packets if the remote address
(outer v6 source) is a local address.

This prevents using ipxip6 (and ip6_gre) tunnels whose local/remote
endpoints are on same host; OTOH v4 tunnels (ipip or gre) allow such
configurations.

An example where this proves useful is a system where entities are
identified by their unique v6 addresses, and use tunnels to encapsulate
traffic between them. The limitation prevents placing several entities
on same host.

Introduce IP6_TNL_F_ALLOW_LOCAL_REMOTE which allows to bypass this
restriction.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/uapi/linux/ip6_tunnel.h b/include/uapi/linux/ip6_tunnel.h
index 425926c467d7..ffebbe365478 100644
--- a/include/uapi/linux/ip6_tunnel.h
+++ b/include/uapi/linux/ip6_tunnel.h
@@ -20,6 +20,8 @@
 #define IP6_TNL_F_RCV_DSCP_COPY 0x10
 /* copy fwmark from inner packet */
 #define IP6_TNL_F_USE_ORIG_FWMARK 0x20
+/* allow remote endpoint on the local node */
+#define IP6_TNL_F_ALLOW_LOCAL_REMOTE 0x40
 
 struct ip6_tnl_parm {
         char name[IFNAMSIZ];    /* name of tunnel device */