ICMPv6: Send router advertisement from own link-local address

I'm not quite sure how I ended up doing this, but for some strange
reason the code before this commit is sending the ICMPv6 Router
Advertisements from some weird non-standard source address.  This is
a violation of RFC4861 which clearly states that the source address
of router advertisements "MUST be the link-local address assigned to the
interface from which this message is sent."

Change-Id: Ib444af70fc8f0b433d371281601fd5a37b29039e

4 files changed, 25 insertions, 10 deletions

diff --git a/ggsn/ggsn.c b/ggsn/ggsn.c
index 46850a6..d521e57 100644
--- a/ggsn/ggsn.c
+++ b/ggsn/ggsn.c
@@ -202,6 +202,16 @@ int apn_start(struct apn_ctx *apn)
 				apn->tun.cfg.ipup_script);
 			tun_runscript(apn->tun.tun, apn->tun.cfg.ipup_script);
 		}
+
+		if (apn->cfg.apn_type_mask & (APN_TYPE_IPv6|APN_TYPE_IPv4v6)) {
+			if (tun_ipv6_linklocal_get(apn->tun.tun, &apn->v6_lladdr) < 0) {
+				LOGPAPN(LOGL_ERROR, apn, "Cannot obtain IPv6 link-local address of "
+					"interface: %s\n", strerror(errno));
+				apn_stop(apn, false);
+				return -1;
+			}
+		}
+
 		/* set back-pointer from TUN device to APN */
 		apn->tun.tun->priv = apn;
 		break;
@@ -573,6 +583,11 @@ static int encaps_tun(struct pdp_t *pdp, void *pack, unsigned len)
 {
 	struct iphdr *iph = (struct iphdr *)pack;
 	struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
+	struct tun_t *tun = (struct tun_t *)pdp->ipif;
+	struct apn_ctx *apn = tun->priv;
+
+	OSMO_ASSERT(tun);
+	OSMO_ASSERT(apn);
 
 	LOGPPDP(LOGL_DEBUG, pdp, "Packet received: forwarding to tun\n");
 
@@ -580,7 +595,7 @@ static int encaps_tun(struct pdp_t *pdp, void *pack, unsigned len)
 	case 6:
 		/* daddr: all-routers multicast addr */
 		if (IN6_ARE_ADDR_EQUAL(&ip6h->ip6_dst, &all_router_mcast_addr))
-			return handle_router_mcast(pdp->gsn, pdp, pack, len);
+			return handle_router_mcast(pdp->gsn, pdp, &apn->v6_lladdr, pack, len);
 		break;
 	case 4:
 		break;
diff --git a/ggsn/ggsn.h b/ggsn/ggsn.h
index 2dd963c..42f8e1c 100644
--- a/ggsn/ggsn.h
+++ b/ggsn/ggsn.h
@@ -78,6 +78,9 @@ struct apn_ctx {
 		struct osmo_fd fd;
 	} tun;
 
+	/* ipv6 link-local address */
+	struct in6_addr v6_lladdr;
+
 	struct apn_ctx_ip v4;
 	struct apn_ctx_ip v6;
 };
diff --git a/ggsn/icmpv6.c b/ggsn/icmpv6.c
index ac51bb1..11ced24 100644
--- a/ggsn/icmpv6.c
+++ b/ggsn/icmpv6.c
@@ -179,13 +179,9 @@ static bool icmpv6_validate_router_solicit(const uint8_t *pack, unsigned len)
 	return true;
 }
 
-/* RFC3307 link-local scope multicast address */
-static const struct in6_addr my_local_addr = {
-	.s6_addr = { 0x01,0x02,0,0,  0,0,0,0, 0,0,0,0,  0,0,0,0xff }
-};
-
 /* handle incoming packets to the all-routers multicast address */
-int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const uint8_t *pack, unsigned len)
+int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const struct in6_addr *own_ll_addr,
+			const uint8_t *pack, unsigned len)
 {
 	struct ippoolm_t *member = pdp->peer;
 	const struct ip6_hdr *ip6h = (struct ip6_hdr *)pack;
@@ -222,10 +218,10 @@ int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const uint8_t *pac
 				osmo_hexdump(pack, len));
 			return -1;
 		}
-		/* FIXME: Send router advertisement from GGSN link-local
+		/* Send router advertisement from GGSN link-local
 		 * address to MS link-local address, including prefix
 		 * allocated to this PDP context */
-		msg = icmpv6_construct_ra(&my_local_addr, &ip6h->ip6_src, &member->addr.v6);
+		msg = icmpv6_construct_ra(own_ll_addr, &ip6h->ip6_src, &member->addr.v6);
 		/* Send the constructed RA to the MS */
 		gtp_data_req(gsn, pdp, msgb_data(msg), msgb_length(msg));
 		msgb_free(msg);
diff --git a/ggsn/icmpv6.h b/ggsn/icmpv6.h
index ebff04e..b6eec63 100644
--- a/ggsn/icmpv6.h
+++ b/ggsn/icmpv6.h
@@ -3,4 +3,5 @@
 #include "../gtp/gtp.h"
 #include "../gtp/pdp.h"
 
-int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const uint8_t *pack, unsigned len);
+int handle_router_mcast(struct gsn_t *gsn, struct pdp_t *pdp, const struct in6_addr *own_ll_addr,
+			const uint8_t *pack, unsigned len);