cnetlink::get_neighbor() check pending notification for deleted neighs

When a route and its nexthop (neigh) get removed at the same time, we
may process the route removal before the neigh removal.

On route removal we try to unregister for nexthop notifications, and
remove any pending l3 interfaces.

Since cnetlink::get_neighbour() only asks the cache, it only returns
live neighs, but since the neigh was already removed from the cache,
it wont find any.

At the same time, since we did not process the neigh removal yet, we are
still registered for nh unreachable notifications, but since from the
perspective of the nl_l3::del_l3_route(), the nexthop is already
unreachable, so we fail to remove the unreachable notification.

Fix this by also going through the pending neigh deletions to find the
reference in case there is a neigh delete pending.

Fixes: dfe4485 ("add netlink functions")
Signed-off-by: Jonas Gorski <[email protected]>

src/netlink/cnetlink.cc

@@ -693,8 +693,39 @@ struct rtnl_neigh *cnetlink::get_neighbour(int ifindex,
                                            struct nl_addr *a) const {
   assert(ifindex);
   assert(a);
+
+  auto neigh = rtnl_neigh_get(caches[NL_NEIGH_CACHE], ifindex, a);
+
+  // check the garbage
+  if (neigh == nullptr) {
+    for (auto &obj : nl_objs) {
+      rtnl_neigh *n;
+
+      if (obj.get_action() != NL_ACT_DEL)
+        continue;
+
+      if (std::string("route/neigh")
+              .compare(nl_object_get_type(obj.get_old_obj())) != 0)
+        continue;
+
+      n = NEIGH_CAST(obj.get_old_obj());
+
+      if (rtnl_neigh_get_ifindex(n) != ifindex)
+        continue;
+
+      if (rtnl_neigh_get_family(n) != nl_addr_get_family(a))
+        continue;
+
+      if (nl_addr_cmp(rtnl_neigh_get_dst(n), a) == 0) {
+        nl_object_get(OBJ_CAST(n));
+        neigh = n;
+        break;
+      }
+    }
+  }
+
   // XXX TODO return unique_ptr
-  return rtnl_neigh_get(caches[NL_NEIGH_CACHE], ifindex, a);
+  return neigh;
 }
 
 bool cnetlink::is_bridge_interface(int ifindex) const {