From 71810d041524b4d296c0ba2b52f46165928110af Mon Sep 17 00:00:00 2001
From: David van Moolenbroek <david@minix3.org>
Date: Fri, 16 Dec 2016 21:26:32 +0000
Subject: [PATCH] ipv6: adjust MLD membership on address state changes

If MLD support is enabled, each locally assigned IPv6 address in the
appropriate state must be a member of the solicited-node multicast
group corresponding to that address.  Ensure that this is always the
case by (re-)deciding on the membership upon every address state
change.  By doing so, this patch enforces that user-initiated state
changes to addresses (e.g., deletion) never cause a desynchronization
with the corresponding solicited-node multicast group membership,
thereby making such user-initiated state changes simpler and safer.
---
 src/core/ipv6/nd6.c    | 47 ++++++++++++++++++++++++++++++------------
 src/core/netif.c       |  7 +++++++
 src/include/lwip/nd6.h |  3 +++
 3 files changed, 44 insertions(+), 13 deletions(-)

diff --git a/src/core/ipv6/nd6.c b/src/core/ipv6/nd6.c
index ca7d8e91..23cbf5f3 100644
--- a/src/core/ipv6/nd6.c
+++ b/src/core/ipv6/nd6.c
@@ -171,12 +171,6 @@ nd6_input(struct pbuf *p, struct netif *inp)
           /* We are using a duplicate address. */
           netif_ip6_addr_set_state(inp, i, IP6_ADDR_INVALID);
 
-#if LWIP_IPV6_MLD
-          /* Leave solicited node multicast group. */
-          ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(inp, i)->addr[3]);
-          mld6_leavegroup_netif(inp, &multicast_address);
-#endif /* LWIP_IPV6_MLD */
-
 #if LWIP_IPV6_AUTOCONFIG
           /* Check to see if this address was autoconfigured. */
           if (!ip6_addr_islinklocal(&target_address)) {
@@ -871,13 +865,6 @@ nd6_tmr(void)
           netif_ip6_addr_set_state(netif, i, IP6_ADDR_PREFERRED);
           /* @todo implement preferred and valid lifetimes. */
         } else if (netif->flags & NETIF_FLAG_UP) {
-#if LWIP_IPV6_MLD
-          if ((addr_state & IP6_ADDR_TENTATIVE_COUNT_MASK) == 0) {
-            /* Join solicited node multicast group. */
-            ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, i)->addr[3]);
-            mld6_joingroup_netif(netif, &multicast_address);
-          }
-#endif /* LWIP_IPV6_MLD */
           /* Send a NS for this address. */
           nd6_send_ns(netif, netif_ip6_addr(netif, i), ND6_SEND_FLAG_MULTICAST_DEST);
           /* tentative: set next state by increasing by one */
@@ -2074,4 +2061,38 @@ nd6_cleanup_netif(struct netif *netif)
   }
 }
 
+#if LWIP_IPV6_MLD
+/**
+ * The state of a local IPv6 address entry is about to change. If needed, join
+ * or leave the solicited-node multicast group for the address.
+ *
+ * @param netif The netif that owns the address.
+ * @param addr_idx The index of the address.
+ * @param new_state The new (IP6_ADDR_) state for the address.
+ */
+void
+nd6_adjust_mld_membership(struct netif *netif, s8_t addr_idx, u8_t new_state)
+{
+  u8_t old_state, old_member, new_member;
+
+  old_state = netif_ip6_addr_state(netif, addr_idx);
+
+  /* Determine whether we were, and should be, a member of the solicited-node
+   * multicast group for this address. For tentative addresses, the group is
+   * not joined until the address enters the TENTATIVE_1 (or VALID) state. */
+  old_member = (old_state != IP6_ADDR_INVALID && old_state != IP6_ADDR_TENTATIVE);
+  new_member = (new_state != IP6_ADDR_INVALID && new_state != IP6_ADDR_TENTATIVE);
+
+  if (old_member != new_member) {
+    ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, addr_idx)->addr[3]);
+
+    if (new_member) {
+      mld6_joingroup_netif(netif, &multicast_address);
+    } else {
+      mld6_leavegroup_netif(netif, &multicast_address);
+    }
+  }
+}
+#endif /* LWIP_IPV6_MLD */
+
 #endif /* LWIP_IPV6 */
diff --git a/src/core/netif.c b/src/core/netif.c
index 1d3de0ff..428b1484 100644
--- a/src/core/netif.c
+++ b/src/core/netif.c
@@ -1096,6 +1096,13 @@ netif_ip6_addr_set_state(struct netif* netif, s8_t addr_idx, u8_t state)
     u8_t new_valid = state & IP6_ADDR_VALID;
     LWIP_DEBUGF(NETIF_DEBUG | LWIP_DBG_STATE, ("netif_ip6_addr_set_state: netif address state being changed\n"));
 
+#if LWIP_IPV6_MLD
+    /* Reevaluate solicited-node multicast group membership. */
+    if (netif->flags & NETIF_FLAG_MLD6) {
+      nd6_adjust_mld_membership(netif, addr_idx, state);
+    }
+#endif /* LWIP_IPV6_MLD */
+
     if (old_valid && !new_valid) {
       /* address about to be removed by setting invalid */
 #if LWIP_TCP
diff --git a/src/include/lwip/nd6.h b/src/include/lwip/nd6.h
index 817dfb9e..8204fa4c 100644
--- a/src/include/lwip/nd6.h
+++ b/src/include/lwip/nd6.h
@@ -71,6 +71,9 @@ u16_t nd6_get_destination_mtu(const ip6_addr_t *ip6addr, struct netif *netif);
 void nd6_reachability_hint(const ip6_addr_t *ip6addr);
 #endif /* LWIP_ND6_TCP_REACHABILITY_HINTS */
 void nd6_cleanup_netif(struct netif *netif);
+#if LWIP_IPV6_MLD
+void nd6_adjust_mld_membership(struct netif *netif, s8_t addr_idx, u8_t new_state);
+#endif /* LWIP_IPV6_MLD */
 
 #ifdef __cplusplus
 }