netfilter: nft_set_rbtree: allow loose matching of closing element in interval

Allow to find closest matching for the right side of an interval (end
flag set on) so we allow lookups in inner ranges, eg. 10-20 in 5-25.

Fixes: ba0e4d9917b4 ("netfilter: nf_tables: get set elements via netlink")
Reported-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_set_rbtree.c

@@ -135,9 +135,12 @@ static bool __nft_rbtree_get(const struct net *net, const struct nft_set *set,
 		d = memcmp(this, key, set->klen);
 		if (d < 0) {
 			parent = rcu_dereference_raw(parent->rb_left);
-			interval = rbe;
+			if (!(flags & NFT_SET_ELEM_INTERVAL_END))
+				interval = rbe;
 		} else if (d > 0) {
 			parent = rcu_dereference_raw(parent->rb_right);
+			if (flags & NFT_SET_ELEM_INTERVAL_END)
+				interval = rbe;
 		} else {
 			if (!nft_set_elem_active(&rbe->ext, genmask))
 				parent = rcu_dereference_raw(parent->rb_left);
@@ -154,7 +157,10 @@ static bool __nft_rbtree_get(const struct net *net, const struct nft_set *set,
 
 	if (set->flags & NFT_SET_INTERVAL && interval != NULL &&
 	    nft_set_elem_active(&interval->ext, genmask) &&
-	    !nft_rbtree_interval_end(interval)) {
+	    ((!nft_rbtree_interval_end(interval) &&
+	      !(flags & NFT_SET_ELEM_INTERVAL_END)) ||
+	     (nft_rbtree_interval_end(interval) &&
+	      (flags & NFT_SET_ELEM_INTERVAL_END)))) {
 		*elem = interval;
 		return true;
 	}