From: Roy Marples <roy@marples.name>
Date: Fri, 30 Aug 2019 10:06:20 +0000 (+0100)
Subject: inet6: Stop reacting to kernel neighbour messages about a router
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2c340935edbe3a6e9b1ff50ff7f9f23414986180;p=thirdparty%2Fdhcpcd.git

inet6: Stop reacting to kernel neighbour messages about a router

It's unreliable and very corner case.
See the comment for the ipv6nd_neighbour() function.
---

diff --git a/src/if-bsd.c b/src/if-bsd.c
index ed5041d5..47219e1a 100644
--- a/src/if-bsd.c
+++ b/src/if-bsd.c
@@ -1083,20 +1083,17 @@ if_rtm(struct dhcpcd_ctx *ctx, const struct rt_msghdr *rtm)
 	 * BSD announces host routes.
 	 * As such, we should be notified of reachability by its
 	 * existance with a hardware address.
-	 * Ensure we don't call this for an incomplete state.
+	 * Ensure we don't call this for a newly incomplete state.
 	 */
 	if (rt.rt_dest.sa_family == AF_INET6 &&
 	    rt.rt_flags & RTF_HOST &&
 	    !(rtm->rtm_type == RTM_ADD && !(rt.rt_dflags & RTDF_GATELINK)))
 	{
-		int flags = 0;
+		bool reachable;
 
-		if (rt.rt_dflags & RTDF_GATELINK)
-			flags |= IPV6ND_ROUTER;
-		if (rtm->rtm_type != RTM_DELETE)
-			flags |= IPV6ND_REACHABLE;
-
-		ipv6nd_neighbour(ctx, &rt.rt_ss_dest.sin6.sin6_addr, flags);
+		reachable = rtm->rtm_type != RTM_DELETE &&
+		    rt.rt_dflags & RTDF_GATELINK;
+		ipv6nd_neighbour(ctx, &rt.rt_ss_dest.sin6.sin6_addr, reachable);
 	}
 #endif
 
diff --git a/src/if-linux.c b/src/if-linux.c
index 1b7e6164..287b7f1b 100644
--- a/src/if-linux.c
+++ b/src/if-linux.c
@@ -680,8 +680,6 @@ link_neigh(struct dhcpcd_ctx *ctx, __unused struct interface *ifp,
 	struct ndmsg *r;
 	struct rtattr *rta;
 	size_t len;
-	struct in6_addr addr6;
-	int flags;
 
 	if (nlm->nlmsg_type != RTM_NEWNEIGH && nlm->nlmsg_type != RTM_DELNEIGH)
 		return 0;
@@ -692,14 +690,13 @@ link_neigh(struct dhcpcd_ctx *ctx, __unused struct interface *ifp,
 	rta = (struct rtattr *)RTM_RTA(r);
 	len = RTM_PAYLOAD(nlm);
         if (r->ndm_family == AF_INET6) {
-		flags = 0;
-		if (r->ndm_flags & NTF_ROUTER)
-			flags |= IPV6ND_ROUTER;
-		if (nlm->nlmsg_type == RTM_NEWNEIGH &&
+		bool reachable;
+		struct in6_addr addr6;
+
+		reachable = (nlm->nlmsg_type == RTM_NEWNEIGH &&
 		    r->ndm_state &
 		    (NUD_REACHABLE | NUD_STALE | NUD_DELAY | NUD_PROBE |
 		     NUD_PERMANENT))
-		        flags |= IPV6ND_REACHABLE;
 		memset(&addr6, 0, sizeof(addr6));
 		while (RTA_OK(rta, len)) {
 			switch (rta->rta_type) {
@@ -710,7 +707,7 @@ link_neigh(struct dhcpcd_ctx *ctx, __unused struct interface *ifp,
 			}
 			rta = RTA_NEXT(rta, len);
 		}
-		ipv6nd_neighbour(ctx, &addr6, flags);
+		ipv6nd_neighbour(ctx, &addr6, reachable);
 	}
 
 	return 0;
diff --git a/src/if-sun.c b/src/if-sun.c
index 0db7371c..2e776cc5 100644
--- a/src/if-sun.c
+++ b/src/if-sun.c
@@ -812,8 +812,7 @@ if_rtm(struct dhcpcd_ctx *ctx, const struct rt_msghdr *rtm)
 			else
 				sdl.sdl_alen = 0;
 			ipv6nd_neighbour(ctx, &dst6,
-			    rtm->rtm_type != RTM_DELETE && sdl.sdl_alen ?
-			    IPV6ND_REACHABLE : 0);
+			    rtm->rtm_type != RTM_DELETE && sdl.sdl_alen);
 		}
 		break;
 	}
diff --git a/src/ipv6nd.c b/src/ipv6nd.c
index cb9e1086..35401b75 100644
--- a/src/ipv6nd.c
+++ b/src/ipv6nd.c
@@ -554,8 +554,21 @@ ipv6nd_startexpire(struct interface *ifp)
 	    ipv6nd_expire, ifp);
 }
 
+/*
+ * Neighbour reachability.
+ *
+ * RFC 4681 6.2.5 says when a node is no longer a router it MUST
+ * send a RA with a zero lifetime.
+ * All OS's I know of set the NA router flag if they are a router
+ * or not and disregard that they are actively advertising or
+ * shutting down. If the interface is disabled, it cant't send a NA at all.
+ *
+ * As such we CANNOT rely on the NA Router flag and MUST use
+ * unreachability or receive a RA with a lifetime of zero to remove
+ * the node as a default router.
+ */
 void
-ipv6nd_neighbour(struct dhcpcd_ctx *ctx, struct in6_addr *addr, int flags)
+ipv6nd_neighbour(struct dhcpcd_ctx *ctx, struct in6_addr *addr, bool reachable)
 {
 	struct ra *rap, *rapr;
 
@@ -570,11 +583,7 @@ ipv6nd_neighbour(struct dhcpcd_ctx *ctx, struct in6_addr *addr, int flags)
 	if (rap == NULL || rap->expired)
 		return;
 
-	if (!(flags & IPV6ND_ROUTER) && rap->lifetime != 0) {
-		loginfox("%s: %s is no longer a router",
-		    rap->iface->name, rap->sfrom);
-		rap->lifetime = 0;
-	} else if (flags & IPV6ND_REACHABLE) {
+	if (reachable) {
 		if (rap->isreachable)
 			return;
 		loginfox("%s: %s is reachable again",
diff --git a/src/ipv6nd.h b/src/ipv6nd.h
index b169b8be..16c4dc79 100644
--- a/src/ipv6nd.h
+++ b/src/ipv6nd.h
@@ -91,9 +91,6 @@ struct rs_state {
 #define	RETRANS_TIMER			1000	/* milliseconds */
 #define	DELAY_FIRST_PROBE_TIME		5	/* seconds */
 
-#define	IPV6ND_REACHABLE		(1 << 0)
-#define	IPV6ND_ROUTER			(1 << 1)
-
 void ipv6nd_printoptions(const struct dhcpcd_ctx *,
     const struct dhcp_opt *, size_t);
 void ipv6nd_startrs(struct interface *);
@@ -112,7 +109,7 @@ int ipv6nd_dadcompleted(const struct interface *);
 void ipv6nd_advertise(struct ipv6_addr *);
 void ipv6nd_startexpire(struct interface *);
 void ipv6nd_drop(struct interface *);
-void ipv6nd_neighbour(struct dhcpcd_ctx *, struct in6_addr *, int);
+void ipv6nd_neighbour(struct dhcpcd_ctx *, struct in6_addr *, bool);
 #endif /* INET6 */
 
 #endif /* IPV6ND_H */