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>

1 files changed, 8 insertions, 0 deletions

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