ipv6: Consider RTF_CACHE when searching the fib6 tree

It is a prep work for the later bug-fix patch which will stop /128 route
from disappearing after pmtu update.

The later bug-fix patch will allow a /128 route and its RTF_CACHE clone
both exist at the same fib6_node.  To do this, we need to prepare the
existing fib6 tree search to expect RTF_CACHE for /128 route.

Note that the fn->leaf is sorted by rt6i_metric.  Hence,
RTF_CACHE (if there is any) is always at the front.  This property
leads to the following:

1. When doing ip6_route_del(), it should honor the RTF_CACHE flag which
   the caller is used to ask for deleting clone or non-clone.
   The rtm_to_fib6_config() should also check the RTM_F_CLONED and
   then set RTF_CACHE accordingly so that:
   - 'ip -6 r del...' will make ip6_route_del() to delete a route
     and all its clones. Note that its clones is flushed by fib6_del()
   - 'ip -6 r flush table cache' will make ip6_route_del() to
      only delete clone(s).

2. Exclude RTF_CACHE from addrconf_get_prefix_route() which
   should not configure on a cloned route.

3. No change is need for rt6_device_match() since it currently could
   return a RTF_CACHE clone route, so the later bug-fix patch will not
   affect it.

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Reviewed-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -2121,6 +2121,8 @@ static struct rt6_info *addrconf_get_prefix_route(const struct in6_addr *pfx,
 	fn = fib6_locate(&table->tb6_root, pfx, plen, NULL, 0);
 	if (!fn)
 		goto out;
+
+	noflags |= RTF_CACHE;
 	for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
 		if (rt->dst.dev->ifindex != dev->ifindex)
 			continue;

net/ipv6/route.c

@@ -1785,6 +1785,9 @@ static int ip6_route_del(struct fib6_config *cfg)
 
 	if (fn) {
 		for (rt = fn->leaf; rt; rt = rt->dst.rt6_next) {
+			if ((rt->rt6i_flags & RTF_CACHE) &&
+			    !(cfg->fc_flags & RTF_CACHE))
+				continue;
 			if (cfg->fc_ifindex &&
 			    (!rt->dst.dev ||
 			     rt->dst.dev->ifindex != cfg->fc_ifindex))
@@ -2433,6 +2436,9 @@ static int rtm_to_fib6_config(struct sk_buff *skb, struct nlmsghdr *nlh,
 	if (rtm->rtm_type == RTN_LOCAL)
 		cfg->fc_flags |= RTF_LOCAL;
 
+	if (rtm->rtm_flags & RTM_F_CLONED)
+		cfg->fc_flags |= RTF_CACHE;
+
 	cfg->fc_nlinfo.portid = NETLINK_CB(skb).portid;
 	cfg->fc_nlinfo.nlh = nlh;
 	cfg->fc_nlinfo.nl_net = sock_net(skb->sk);