Merge branch 'ipv6-multipath-routing-fixes'

Ido Schimmel says:

====================
ipv6: Multipath routing fixes

This patchset contains two fixes for IPv6 multipath routing. See the
commit messages for more details.
====================

Link: https://patch.msgid.link/20250402114224.293392-1-idosch@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv6/route.c

@@ -412,12 +412,37 @@ static bool rt6_check_expired(const struct rt6_info *rt)
 	return false;
 }
 
+static struct fib6_info *
+rt6_multipath_first_sibling_rcu(const struct fib6_info *rt)
+{
+	struct fib6_info *iter;
+	struct fib6_node *fn;
+
+	fn = rcu_dereference(rt->fib6_node);
+	if (!fn)
+		goto out;
+	iter = rcu_dereference(fn->leaf);
+	if (!iter)
+		goto out;
+
+	while (iter) {
+		if (iter->fib6_metric == rt->fib6_metric &&
+		    rt6_qualify_for_ecmp(iter))
+			return iter;
+		iter = rcu_dereference(iter->fib6_next);
+	}
+
+out:
+	return NULL;
+}
+
 void fib6_select_path(const struct net *net, struct fib6_result *res,
 		      struct flowi6 *fl6, int oif, bool have_oif_match,
 		      const struct sk_buff *skb, int strict)
 {
-	struct fib6_info *match = res->f6i;
+	struct fib6_info *first, *match = res->f6i;
 	struct fib6_info *sibling;
+	int hash;
 
 	if (!match->nh && (!match->fib6_nsiblings || have_oif_match))
 		goto out;
@@ -440,16 +465,25 @@ void fib6_select_path(const struct net *net, struct fib6_result *res,
 		return;
 	}
 
-	if (fl6->mp_hash <= atomic_read(&match->fib6_nh->fib_nh_upper_bound))
+	first = rt6_multipath_first_sibling_rcu(match);
+	if (!first)
 		goto out;
 
-	list_for_each_entry_rcu(sibling, &match->fib6_siblings,
+	hash = fl6->mp_hash;
+	if (hash <= atomic_read(&first->fib6_nh->fib_nh_upper_bound) &&
+	    rt6_score_route(first->fib6_nh, first->fib6_flags, oif,
+			    strict) >= 0) {
+		match = first;
+		goto out;
+	}
+
+	list_for_each_entry_rcu(sibling, &first->fib6_siblings,
 				fib6_siblings) {
 		const struct fib6_nh *nh = sibling->fib6_nh;
 		int nh_upper_bound;
 
 		nh_upper_bound = atomic_read(&nh->fib_nh_upper_bound);
-		if (fl6->mp_hash > nh_upper_bound)
+		if (hash > nh_upper_bound)
 			continue;
 		if (rt6_score_route(nh, sibling->fib6_flags, oif, strict) < 0)
 			break;