advertise removed prefix delegation in RIO with lifetime 0

RFC 4191 section 4 states:
   ... When ceasing to be an advertising
   interface and sending Router Advertisements with a Router Lifetime of
   zero, the Router Advertisement SHOULD also set the Route Lifetime to
   zero in all Route Information Options.

Since RIOs reflect the prefix delegations owned by the router, it is
reasonable to assume that invalid RIOs should be sent along invalid PIOs
required by RFC 7084 L-13.

This extends the functionality introduced in commit 83e14f4 where
removed addresses were advertised as invalid PIO in 3 consecutive RAs.

Other related improvements introduced here:
   - further precaution has been taken in netlink.c to prevent possible
    overlapping between current list of interface IPv6 addresses and the
    list of invalid addresses
   - IPv6 route parsing was moved to netlink.c and was splitted in 2
     functions; this allows dprefix caching in iface->addr6 list,
     necessary for generating invalid RIOs after prefix get deleted
   - all prefixes are advertised as invalid on odhcpd shutdown

Signed-off-by: Alin Nastac <alin.nastac@gmail.com>

Author: alinnastac

src/netlink.c

@@ -26,6 +26,7 @@
 #include <netlink/attr.h>
 
 #include <arpa/inet.h>
+#include <net/route.h>
 #include <libubox/list.h>
 
 #include "odhcpd.h"
@@ -54,8 +55,15 @@ static struct event_socket rtnl_event = {
 	.sock_bufsize = 133120,
 };
 
-int netlink_init(void)
+static FILE *fp_ipv6_route = NULL;
+
+int netlink_init(bool ipv6)
 {
+	if (ipv6 && !(fp_ipv6_route = fopen("/proc/net/ipv6_route", "r"))) {
+		syslog(LOG_ERR, "fopen(/proc/net/ipv6_route): %m");
+		goto err;
+	}
+
 	rtnl_socket = create_socket(NETLINK_ROUTE);
 	if (!rtnl_socket) {
 		syslog(LOG_ERR, "Unable to open nl socket: %m");
@@ -100,9 +108,67 @@ int netlink_init(void)
 		rtnl_event.ev.uloop.fd = -1;
 	}
 
+	if (fp_ipv6_route) {
+		fclose(fp_ipv6_route);
+		fp_ipv6_route = NULL;
+	}
+
 	return -1;
 }
 
+/* Detect whether a default IPv6 route exists */
+bool netlink_default_ipv6_route_exists()
+{
+	bool found_default = false;
+	char line[512], ifname[16];
+
+	if (!fp_ipv6_route)
+		return false;
+	rewind(fp_ipv6_route);
+
+	while (fgets(line, sizeof(line), fp_ipv6_route)) {
+		if (sscanf(line, "00000000000000000000000000000000 00 "
+					"%*s %*s %*s %*s %*s %*s %*s %15s", ifname) &&
+				strcmp(ifname, "lo")) {
+			found_default = true;
+			break;
+		}
+	}
+
+	return found_default;
+}
+
+/* Find the source prefixes of all IPv6 addresses */
+static void find_addr6_dprefix(struct odhcpd_ipaddr *n, ssize_t len)
+{
+	struct odhcpd_ipaddr p = { .addr.in6 = IN6ADDR_ANY_INIT, .prefix = 0,
+					.dprefix = 0, .preferred = 0, .valid = 0};
+	char line[512];
+	uint32_t rflags;
+
+	if (!fp_ipv6_route || len <= 0)
+		return;
+	rewind(fp_ipv6_route);
+
+	while (fgets(line, sizeof(line), fp_ipv6_route)) {
+		if (sscanf(line, "%8" SCNx32 "%8" SCNx32 "%*8" SCNx32 "%*8" SCNx32 " %hhx %*s "
+				"%*s 00000000000000000000000000000000 %*s %*s %*s %" SCNx32 " lo",
+				&p.addr.in6.s6_addr32[0], &p.addr.in6.s6_addr32[1], &p.prefix, &rflags) &&
+				p.prefix > 0 && (rflags & RTF_NONEXTHOP) && (rflags & RTF_REJECT)) {
+			// Find source prefixes by scanning through unreachable-routes
+			p.addr.in6.s6_addr32[0] = htonl(p.addr.in6.s6_addr32[0]);
+			p.addr.in6.s6_addr32[1] = htonl(p.addr.in6.s6_addr32[1]);
+
+			for (ssize_t i = 0; i < len; ++i) {
+				if (n[i].prefix <= 64 && n[i].prefix >= p.prefix &&
+						!odhcpd_bmemcmp(&p.addr.in6, &n[i].addr.in6, p.prefix)) {
+					n[i].dprefix = p.prefix;
+					break;
+				}
+			}
+		}
+	}
+}
 
 int netlink_add_netevent_handler(struct netevent_handler *handler)
 {
@@ -212,6 +278,20 @@ static void refresh_iface_addr6(int ifindex)
 			}
 
 			if (change) {
+				/*
+				 * Remove invalid prefixes that were added back to the interface.
+				 */
+				for (ssize_t i = 0; i < len; ++i) {
+					size_t j = 0;
+					while (j < iface->invalid_addr6_len) {
+						if (addr[i].prefix <= iface->invalid_addr6[j].prefix &&
+						    odhcpd_bmemcmp(&addr[i].addr.in6, &iface->invalid_addr6[j].addr.in6, iface->invalid_addr6[j].prefix) == 0)
+							odhcpd_del_intf_invalid_addr6(iface, j);
+						else
+							++j;
+					}
+				}
+
 				/*
 				 * Keep track on removed prefixes, so we could advertise them as invalid
 				 * for at least a couple of times.
@@ -756,6 +836,9 @@ ssize_t netlink_get_interface_addrs(int ifindex, bool v6, struct odhcpd_ipaddr *
 			addr[i].valid += now;
 	}
 
+	if (v6)
+		find_addr6_dprefix(addr, ctxt.ret);
+
 free:
 	nlmsg_free(msg);
 out:

src/odhcpd.c

@@ -77,6 +77,7 @@ int main(int argc, char **argv)
 {
 	openlog("odhcpd", LOG_PERROR | LOG_PID, LOG_DAEMON);
 	int opt;
+	bool ipv6 = ipv6_enabled();
 
 	while ((opt = getopt(argc, argv, "hl:")) != -1) {
 		switch (opt) {
@@ -109,10 +110,10 @@ int main(int argc, char **argv)
 	signal(SIGINT, sighandler);
 	signal(SIGTERM, sighandler);
 
-	if (netlink_init())
+	if (netlink_init(ipv6))
 		return 4;
 
-	if (ipv6_enabled()) {
+	if (ipv6) {
 		if (router_init())
 			return 4;
 

src/odhcpd.h

@@ -399,6 +399,26 @@ inline static struct dhcp_assignment *alloc_assignment(size_t extra_len)
 	return a;
 }
 
+inline static void odhcpd_del_intf_invalid_addr6(struct interface *iface, size_t idx)
+{
+	if (idx + 1 < iface->invalid_addr6_len)
+		memmove(&iface->invalid_addr6[idx], &iface->invalid_addr6[idx + 1],
+				sizeof(*iface->invalid_addr6) * (iface->invalid_addr6_len - idx - 1));
+
+	iface->invalid_addr6_len--;
+
+	if (iface->invalid_addr6_len) {
+		struct odhcpd_ipaddr *new_invalid_addr6 = realloc(iface->invalid_addr6,
+				sizeof(*iface->invalid_addr6) * iface->invalid_addr6_len);
+
+		if (new_invalid_addr6)
+			iface->invalid_addr6 = new_invalid_addr6;
+	} else {
+		free(iface->invalid_addr6);
+		iface->invalid_addr6 = NULL;
+	}
+}
+
 // Exported main functions
 int odhcpd_register(struct odhcpd_event *event);
 int odhcpd_deregister(struct odhcpd_event *event);
@@ -452,6 +472,7 @@ void dhcpv6_ia_enum_addrs(struct interface *iface, struct dhcp_assignment *c, ti
 				dhcpv6_binding_cb_handler_t func, void *arg);
 void dhcpv6_ia_write_statefile(void);
 
+bool netlink_default_ipv6_route_exists();
 int netlink_add_netevent_handler(struct netevent_handler *hdlr);
 ssize_t netlink_get_interface_addrs(const int ifindex, bool v6,
 		struct odhcpd_ipaddr **addrs);
@@ -468,7 +489,7 @@ void netlink_dump_neigh_table(const bool proxy);
 void netlink_dump_addr_table(const bool v6);
 
 // Exported module initializers
-int netlink_init(void);
+int netlink_init(bool ipv6);
 int router_init(void);
 int dhcpv6_init(void);
 int ndp_init(void);