arp/ndp: respond with true MAC address of LAN local remote hosts

When we receive an ARP request or NDP neigbour solicitation over
the tap interface for a host on the local network segment attached
to the template interface, we respond with that host's real MAC
address, if available.

Signed-off-by: Jon Maloy <jmaloy@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

3 files changed, 10 insertions, 3 deletions

diff --git a/arp.c b/arp.c
index ad088b1..b4a686f 100644
--- a/arp.c
+++ b/arp.c
@@ -69,6 +69,7 @@ static bool ignore_arp(const struct ctx *c,
  */
 int arp(const struct ctx *c, struct iov_tail *data)
 {
+	union inany_addr tgt;
 	struct {
 		struct ethhdr eh;
 		struct arphdr ah;
@@ -102,8 +103,11 @@ int arp(const struct ctx *c, struct iov_tail *data)
 	resp.ah.ar_hln = ah->ar_hln;
 	resp.ah.ar_pln = ah->ar_pln;
 
-	/* ARP message */
-	memcpy(resp.am.sha,		c->our_tap_mac,	sizeof(resp.am.sha));
+	/* MAC address to return in ARP message */
+	inany_from_af(&tgt, AF_INET, am->tip);
+	fwd_neigh_mac_get(c, &tgt, resp.am.sha);
+
+	/* Rest of ARP message */
 	memcpy(resp.am.sip,		am->tip,	sizeof(resp.am.sip));
 	memcpy(resp.am.tha,		am->sha,	sizeof(resp.am.tha));
 	memcpy(resp.am.tip,		am->sip,	sizeof(resp.am.tip));
diff --git a/inany.c b/inany.c
index 65a39f9..7680439 100644
--- a/inany.c
+++ b/inany.c
@@ -16,6 +16,7 @@
 #include "ip.h"
 #include "siphash.h"
 #include "inany.h"
+#include "fwd.h"
 
 const union inany_addr inany_loopback4 = INANY_INIT4(IN4ADDR_LOOPBACK_INIT);
 const union inany_addr inany_any4 = INANY_INIT4(IN4ADDR_ANY_INIT);
diff --git a/ndp.c b/ndp.c
index 588b48f..7e2ae2a 100644
--- a/ndp.c
+++ b/ndp.c
@@ -196,6 +196,7 @@ static void ndp_send(const struct ctx *c, const struct in6_addr *dst,
 static void ndp_na(const struct ctx *c, const struct in6_addr *dst,
 	    const struct in6_addr *addr)
 {
+	union inany_addr tgt;
 	struct ndp_na na = {
 		.ih = {
 			.icmp6_type		= NA,
@@ -213,7 +214,8 @@ static void ndp_na(const struct ctx *c, const struct in6_addr *dst,
 		}
 	};
 
-	memcpy(na.target_l2_addr.mac, c->our_tap_mac, ETH_ALEN);
+	inany_from_af(&tgt, AF_INET6, addr);
+	fwd_neigh_mac_get(c, &tgt, na.target_l2_addr.mac);
 
 	ndp_send(c, dst, &na, sizeof(na));
 }