zebra: Notice when our neighbor entry is removed and fight back

Notice when someone deletes a neighbor entry we've put in for
rfc-5549 gets deleted by some evil evil person.  When this happens
notice and push it back in, immediately.

Ticket: CM-18612
Signed-off-by: Donald Sharp <sharpd@cumulusnetworks.com>

3 files changed, 57 insertions, 22 deletions

diff --git a/zebra/interface.c b/zebra/interface.c
index 4f761a5e9..6f59a2d39 100644
--- a/zebra/interface.c
+++ b/zebra/interface.c
@@ -825,6 +825,7 @@ void if_nbr_ipv6ll_to_ipv4ll_neigh_update(struct interface *ifp,
 					  struct in6_addr *address, int add)
 {
 	struct zebra_vrf *zvrf = vrf_info_lookup(ifp->vrf_id);
+	struct zebra_if *zif = ifp->info;
 	char buf[16] = "169.254.0.1";
 	struct in_addr ipv4_ll;
 	char mac[6];
@@ -845,6 +846,16 @@ void if_nbr_ipv6ll_to_ipv4ll_neigh_update(struct interface *ifp,
 
 	/* Add arp record */
 	kernel_neigh_update(add, ifp->ifindex, ipv4_ll.s_addr, mac, 6, ns_id);
+
+	/*
+	 * We need to note whether or not we originated a v6
+	 * neighbor entry for this interface.  So that when
+	 * someone unwisely accidently deletes this entry
+	 * we can shove it back in.
+	 */
+	zif->v6_2_v4_ll_neigh_entry = !!add;
+	memcpy(&zif->v6_2_v4_ll_addr6, address, sizeof(*address));
+
 	zvrf->neigh_updates++;
 }
 
diff --git a/zebra/interface.h b/zebra/interface.h
index fba3201c5..9634bfdb3 100644
--- a/zebra/interface.h
+++ b/zebra/interface.h
@@ -272,6 +272,13 @@ struct zebra_if {
 	struct interface *link;
 
 	struct thread *speed_update;
+
+	/*
+	 * Does this interface have a v6 to v4 ll neighbor entry
+	 * for bgp unnumbered?
+	 */
+	bool v6_2_v4_ll_neigh_entry;
+	struct in6_addr v6_2_v4_ll_addr6;
 };
 
 DECLARE_HOOK(zebra_if_extra_info, (struct vty * vty, struct interface *ifp),
diff --git a/zebra/rt_netlink.c b/zebra/rt_netlink.c
index 3053c56d1..d1edea804 100644
--- a/zebra/rt_netlink.c
+++ b/zebra/rt_netlink.c
@@ -2112,21 +2112,53 @@ static int netlink_ipneigh_change(struct sockaddr_nl *snl, struct nlmsghdr *h,
 
 	ndm = NLMSG_DATA(h);
 
-	/* We only process neigh notifications if EVPN is enabled */
-	if (!is_evpn_enabled())
-		return 0;
-
 	/* The interface should exist. */
 	ifp = if_lookup_by_index_per_ns(zebra_ns_lookup(ns_id),
 					ndm->ndm_ifindex);
 	if (!ifp || !ifp->info)
 		return 0;
 
-	/* Drop "permanent" entries. */
-	if (ndm->ndm_state & NUD_PERMANENT)
+	zif = (struct zebra_if *)ifp->info;
+
+	/* Parse attributes and extract fields of interest. */
+	memset(tb, 0, sizeof tb);
+	netlink_parse_rtattr(tb, NDA_MAX, NDA_RTA(ndm), len);
+
+	if (!tb[NDA_DST]) {
+		zlog_warn("%s family %s IF %s(%u) - no DST",
+			  nl_msg_type_to_str(h->nlmsg_type),
+			  nl_family_to_str(ndm->ndm_family), ifp->name,
+			  ndm->ndm_ifindex);
 		return 0;
+	}
+
+	memset(&ip, 0, sizeof(struct ipaddr));
+	ip.ipa_type = (ndm->ndm_family == AF_INET) ? IPADDR_V4 : IPADDR_V6;
+	memcpy(&ip.ip.addr, RTA_DATA(tb[NDA_DST]), RTA_PAYLOAD(tb[NDA_DST]));
+
+	/* Drop some "permanent" entries. */
+	if (ndm->ndm_state & NUD_PERMANENT) {
+		char buf[16] = "169.254.0.1";
+		struct in_addr ipv4_ll;
+
+		if (ndm->ndm_family != AF_INET)
+			return 0;
+
+		if (!zif->v6_2_v4_ll_neigh_entry)
+			return 0;
+
+		if (h->nlmsg_type != RTM_DELNEIGH)
+			return 0;
+
+		inet_pton(AF_INET, buf, &ipv4_ll);
+		if (ipv4_ll.s_addr != ip.ip._v4_addr.s_addr)
+			return 0;
+
+		if_nbr_ipv6ll_to_ipv4ll_neigh_update(
+			ifp, &zif->v6_2_v4_ll_addr6, true);
+		return 0;
+	}
 
-	zif = (struct zebra_if *)ifp->info;
 	/* The neighbor is present on an SVI. From this, we locate the
 	 * underlying
 	 * bridge because we're only interested in neighbors on a VxLAN bridge.
@@ -2148,22 +2180,7 @@ static int netlink_ipneigh_change(struct sockaddr_nl *snl, struct nlmsghdr *h,
 	else
 		return 0;
 
-	/* Parse attributes and extract fields of interest. */
-	memset(tb, 0, sizeof tb);
-	netlink_parse_rtattr(tb, NDA_MAX, NDA_RTA(ndm), len);
-
-	if (!tb[NDA_DST]) {
-		zlog_warn("%s family %s IF %s(%u) - no DST",
-			  nl_msg_type_to_str(h->nlmsg_type),
-			  nl_family_to_str(ndm->ndm_family), ifp->name,
-			  ndm->ndm_ifindex);
-		return 0;
-	}
 	memset(&mac, 0, sizeof(struct ethaddr));
-	memset(&ip, 0, sizeof(struct ipaddr));
-	ip.ipa_type = (ndm->ndm_family == AF_INET) ? IPADDR_V4 : IPADDR_V6;
-	memcpy(&ip.ip.addr, RTA_DATA(tb[NDA_DST]), RTA_PAYLOAD(tb[NDA_DST]));
-
 	if (h->nlmsg_type == RTM_NEWNEIGH) {
 		if (tb[NDA_LLADDR]) {
 			if (RTA_PAYLOAD(tb[NDA_LLADDR]) != ETH_ALEN) {