Improve IPv6 NDP for non-local Thread Border routers (#2434)

* Add multiple routes support in NetworkManager

Support multiple routes to the same network learned via Router
Information Option. With this change, the kernel will have multiple
routing table entries to a given Thread network. The routes gateway
won't be updated with every new RIO any longer since every gateway
has its own entry.

* Enable IPv6 router reachability probing

Currently router reachability probing is disabled since HAOS enables
IPv6 forwarding and the necessary kernel options are not enabled. With
this change router reachability probing is enabled even though we are
a router on our own.

Note that Linux commit ea659e077528 ("[IPV6] ROUTE: Do not enable router
reachability probing in router mode.") by default disabled this
behavior. But since we are acting as a router as well as a host device,
we rather want this reachability probing.

See also: https://lore.kernel.org/netdev/b9182b02829b158d55acc53a0bcec1ed667b2668.1680000784.git.stefan@agner.ch/T/#u

buildroot-external/kernel/hassos.config

@@ -60,6 +60,8 @@ CONFIG_BT_HIDP=m
 CONFIG_BT_LEDS=y
 
 CONFIG_IPV6=y
+CONFIG_IPV6_ROUTER_PREF=y
+CONFIG_IPV6_REACHABILITY_PROBE=y
 CONFIG_IPV6_SIT=m
 
 CONFIG_IP_MROUTE=y

buildroot-external/patches/linux/0001-ipv6-add-option-to-explicitly-enable-reachability-te.patch

@@ -0,0 +1,56 @@
+From b9182b02829b158d55acc53a0bcec1ed667b2668 Mon Sep 17 00:00:00 2001
+Message-Id: <b9182b02829b158d55acc53a0bcec1ed667b2668.1680000784.git.stefan@agner.ch>
+From: Stefan Agner <stefan@agner.ch>
+Date: Tue, 28 Mar 2023 12:02:10 +0200
+Subject: [PATCH] ipv6: add option to explicitly enable reachability test
+
+Systems which act as host as well as router might prefer the host
+behavior. Currently the kernel does not allow to use IPv6 forwarding
+globally and at the same time use route reachability probing.
+
+Add a compile time flag to enable route reachability probe in any
+case.
+
+Signed-off-by: Stefan Agner <stefan@agner.ch>
+---
+ net/ipv6/Kconfig | 9 +++++++++
+ net/ipv6/route.c | 3 ++-
+ 2 files changed, 11 insertions(+), 1 deletion(-)
+
+diff --git a/net/ipv6/Kconfig b/net/ipv6/Kconfig
+index 658bfed1df8b..5147fd4c93ff 100644
+--- a/net/ipv6/Kconfig
++++ b/net/ipv6/Kconfig
+@@ -48,6 +48,15 @@ config IPV6_OPTIMISTIC_DAD
+ 
+ 	  If unsure, say N.
+ 
++config IPV6_REACHABILITY_PROBE
++	bool "IPv6: Always use reachability probing (RFC 4191)"
++	help
++	  By default reachability probing is disabled on router devices (when
++	  IPv6 forwarding is enabled). This option explicitly enables
++	  reachability probing always.
++
++	  If unsure, say N.
++
+ config INET6_AH
+ 	tristate "IPv6: AH transformation"
+ 	select XFRM_AH
+diff --git a/net/ipv6/route.c b/net/ipv6/route.c
+index 0fdb03df2287..5e1e1f02f400 100644
+--- a/net/ipv6/route.c
++++ b/net/ipv6/route.c
+@@ -2210,7 +2210,8 @@ struct rt6_info *ip6_pol_route(struct net *net, struct fib6_table *table,
+ 
+ 	strict |= flags & RT6_LOOKUP_F_IFACE;
+ 	strict |= flags & RT6_LOOKUP_F_IGNORE_LINKSTATE;
+-	if (net->ipv6.devconf_all->forwarding == 0)
++	if (net->ipv6.devconf_all->forwarding == 0 ||
++	    IS_ENABLED(IPV6_REACHABILITY_PROBE))
+ 		strict |= RT6_LOOKUP_F_REACHABLE;
+ 
+ 	rcu_read_lock();
+-- 
+2.40.0
+

buildroot-external/patches/network-manager/0001-ndisc-support-multiple-gateways-for-a-single-network.patch

@@ -0,0 +1,27 @@
+From a053500cf43a31ee82a6e0f3d644ea36f5c77ffb Mon Sep 17 00:00:00 2001
+Message-Id: <a053500cf43a31ee82a6e0f3d644ea36f5c77ffb.1679932288.git.stefan@agner.ch>
+From: Stefan Agner <stefan@agner.ch>
+Date: Mon, 27 Mar 2023 17:48:34 +0200
+Subject: [PATCH] ndisc: support multiple gateways for a single network
+
+---
+ src/core/ndisc/nm-ndisc.c | 3 ++-
+ 1 file changed, 2 insertions(+), 1 deletion(-)
+
+diff --git a/src/core/ndisc/nm-ndisc.c b/src/core/ndisc/nm-ndisc.c
+index 9a6038d406..67cdf5d99a 100644
+--- a/src/core/ndisc/nm-ndisc.c
++++ b/src/core/ndisc/nm-ndisc.c
+@@ -654,7 +654,8 @@ nm_ndisc_add_route(NMNDisc *ndisc, const NMNDiscRoute *new_item, gint64 now_msec
+         NMNDiscRoute *item = &g_array_index(rdata->routes, NMNDiscRoute, i);
+ 
+         if (IN6_ARE_ADDR_EQUAL(&item->network, &new_item->network)
+-            && item->plen == new_item->plen) {
++            && item->plen == new_item->plen
++            && IN6_ARE_ADDR_EQUAL(&item->gateway, &new_item->gateway)) {
+             if (new_item->expiry_msec <= now_msec) {
+                 g_array_remove_index(rdata->routes, i);
+                 return TRUE;
+-- 
+2.40.0
+