[IPV6] MIP6: Loadable module support for MIPv6.

This patch makes MIPv6 loadable module named "mip6".

Here is a modprobe.conf(5) example to load it automatically
when user application uses XFRM state for MIPv6:

alias xfrm-type-10-43 mip6
alias xfrm-type-10-60 mip6

Some MIPv6 feature is not included by this modular, however,
it should not be affected to other features like either IPsec
or IPv6 with and without the patch.
We may discuss XFRM, MH (RAW socket) and ancillary data/sockopt
separately for future work.

Loadable features:
* MH receiving check (to send ICMP error back)
* RO header parsing and building (i.e. RH2 and HAO in DSTOPTS)
* XFRM policy/state database handling for RO

These are NOT covered as loadable:
* Home Address flags and its rule on source address selection
* XFRM sub policy (depends on its own kernel option)
* XFRM functions to receive RO as IPv6 extension header
* MH sending/receiving through raw socket if user application
  opens it (since raw socket allows to do so)
* RH2 sending as ancillary data
* RH2 operation with setsockopt(2)

Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 31 insertions, 3 deletions

diff --git a/net/ipv6/raw.c b/net/ipv6/raw.c
index a22c9c93d931..aac6aeb8de8c 100644
--- a/net/ipv6/raw.c
+++ b/net/ipv6/raw.c
@@ -49,7 +49,7 @@
 #include <net/udp.h>
 #include <net/inet_common.h>
 #include <net/tcp_states.h>
-#ifdef CONFIG_IPV6_MIP6
+#if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)
 #include <net/mip6.h>
 #endif
 
@@ -137,6 +137,28 @@ static __inline__ int icmpv6_filter(struct sock *sk, struct sk_buff *skb)
         return 0;
 }
 
+#if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)
+static int (*mh_filter)(struct sock *sock, struct sk_buff *skb);
+
+int rawv6_mh_filter_register(int (*filter)(struct sock *sock,
+                                           struct sk_buff *skb))
+{
+        rcu_assign_pointer(mh_filter, filter);
+        return 0;
+}
+EXPORT_SYMBOL(rawv6_mh_filter_register);
+
+int rawv6_mh_filter_unregister(int (*filter)(struct sock *sock,
+                                             struct sk_buff *skb))
+{
+        rcu_assign_pointer(mh_filter, NULL);
+        synchronize_rcu();
+        return 0;
+}
+EXPORT_SYMBOL(rawv6_mh_filter_unregister);
+
+#endif
+
 /*
  *      demultiplex raw sockets.
  *      (should consider queueing the skb in the sock receive_queue
@@ -178,16 +200,22 @@ int ipv6_raw_deliver(struct sk_buff *skb, int nexthdr)
                 case IPPROTO_ICMPV6:
                         filtered = icmpv6_filter(sk, skb);
                         break;
-#ifdef CONFIG_IPV6_MIP6
+
+#if defined(CONFIG_IPV6_MIP6) || defined(CONFIG_IPV6_MIP6_MODULE)
                 case IPPROTO_MH:
+                {
                         /* XXX: To validate MH only once for each packet,
                          * this is placed here. It should be after checking
                          * xfrm policy, however it doesn't. The checking xfrm
                          * policy is placed in rawv6_rcv() because it is
                          * required for each socket.
                          */
-                        filtered = mip6_mh_filter(sk, skb);
+                        int (*filter)(struct sock *sock, struct sk_buff *skb);
+
+                        filter = rcu_dereference(mh_filter);
+                        filtered = filter ? filter(sk, skb) : 0;
                         break;
+                }
 #endif
                 default:
                         filtered = 0;