net: gre: provide multicast mappings for ipv4 and ipv6

My commit 6d55cb91a0020ac0 (gre: fix hard header destination
address checking) broke multicast.

The reason is that ip_gre used to get ipgre_header() calls with
zero destination if we have NOARP or multicast destination. Instead
the actual target was decided at ipgre_tunnel_xmit() time based on
per-protocol dissection.

Instead of allowing the "abuse" of ->header() calls with invalid
destination, this creates multicast mappings for ip_gre. This also
fixes "ip neigh show nud noarp" to display the proper multicast
mappings used by the gre device.

Reported-by: Doug Kehn <rdkehn@yahoo.com>
Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Acked-by: Doug Kehn <rdkehn@yahoo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 24 insertions, 0 deletions

diff --git a/include/net/if_inet6.h b/include/net/if_inet6.h
index 04977eefb0ee..fccc2180c61b 100644
--- a/include/net/if_inet6.h
+++ b/include/net/if_inet6.h
@@ -286,5 +286,21 @@ static inline void ipv6_ib_mc_map(const struct in6_addr *addr,
         buf[9]  = broadcast[9];
         memcpy(buf + 10, addr->s6_addr + 6, 10);
 }
+
+static inline int ipv6_ipgre_mc_map(const struct in6_addr *addr,
+                                    const unsigned char *broadcast, char *buf)
+{
+        if ((broadcast[0] | broadcast[1] | broadcast[2] | broadcast[3]) != 0) {
+                memcpy(buf, broadcast, 4);
+        } else {
+                /* v4mapped? */
+                if ((addr->s6_addr32[0] | addr->s6_addr32[1] |
+                     (addr->s6_addr32[2] ^ htonl(0x0000ffff))) != 0)
+                        return -EINVAL;
+                memcpy(buf, &addr->s6_addr32[3], 4);
+        }
+        return 0;
+}
+
 #endif
 #endif
diff --git a/include/net/ip.h b/include/net/ip.h
index a4f631108c54..7c416583b710 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -339,6 +339,14 @@ static inline void ip_ib_mc_map(__be32 naddr, const unsigned char *broadcast, ch
         buf[16] = addr & 0x0f;
 }
 
+static inline void ip_ipgre_mc_map(__be32 naddr, const unsigned char *broadcast, char *buf)
+{
+        if ((broadcast[0] | broadcast[1] | broadcast[2] | broadcast[3]) != 0)
+                memcpy(buf, broadcast, 4);
+        else
+                memcpy(buf, &naddr, sizeof(naddr));
+}
+
 #if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
 #include <linux/ipv6.h>
 #endif