ipv6: Don't remove permanent routes with exceptions from tb6_gc_hlist.

The cited commit mechanically put fib6_remove_gc_list()
just after every fib6_clean_expires() call.

When a temporary route is promoted to a permanent route,
there may already be exception routes tied to it.

If fib6_remove_gc_list() removes the route from tb6_gc_hlist,
such exception routes will no longer be aged.

Let's replace fib6_remove_gc_list() with a new helper
fib6_may_remove_gc_list() and use fib6_age_exceptions() there.

Note that net->ipv6 is only compiled when CONFIG_IPV6 is
enabled, so fib6_{add,remove,may_remove}_gc_list() are guarded.

Fixes: 5eb902b8e719 ("net/ipv6: Remove expired routes with a separated list of routes.")
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://patch.msgid.link/20260320072317.2561779-3-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 26 insertions, 7 deletions

diff --git a/include/net/ip6_fib.h b/include/net/ip6_fib.h
index 88b0dd4d8e09..9f8b6814a96a 100644
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -507,12 +507,14 @@ void fib6_rt_update(struct net *net, struct fib6_info *rt,
 void inet6_rt_notify(int event, struct fib6_info *rt, struct nl_info *info,
 		     unsigned int flags);
 
+void fib6_age_exceptions(struct fib6_info *rt, struct fib6_gc_args *gc_args,
+			 unsigned long now);
 void fib6_run_gc(unsigned long expires, struct net *net, bool force);
-
 void fib6_gc_cleanup(void);
 
 int fib6_init(void);
 
+#if IS_ENABLED(CONFIG_IPV6)
 /* Add the route to the gc list if it is not already there
  *
  * The callers should hold f6i->fib6_table->tb6_lock.
@@ -545,6 +547,23 @@ static inline void fib6_remove_gc_list(struct fib6_info *f6i)
 		hlist_del_init(&f6i->gc_link);
 }
 
+static inline void fib6_may_remove_gc_list(struct net *net,
+					   struct fib6_info *f6i)
+{
+	struct fib6_gc_args gc_args;
+
+	if (hlist_unhashed(&f6i->gc_link))
+		return;
+
+	gc_args.timeout = READ_ONCE(net->ipv6.sysctl.ip6_rt_gc_interval);
+	gc_args.more = 0;
+
+	rcu_read_lock();
+	fib6_age_exceptions(f6i, &gc_args, jiffies);
+	rcu_read_unlock();
+}
+#endif
+
 struct ipv6_route_iter {
 	struct seq_net_private p;
 	struct fib6_walker w;
diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index 0e55f139e05d..f4e23b543585 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c
@@ -2862,7 +2862,7 @@ void addrconf_prefix_rcv(struct net_device *dev, u8 *opt, int len, bool sllao)
 					fib6_add_gc_list(rt);
 				} else {
 					fib6_clean_expires(rt);
-					fib6_remove_gc_list(rt);
+					fib6_may_remove_gc_list(net, rt);
 				}
 
 				spin_unlock_bh(&table->tb6_lock);
@@ -4840,7 +4840,7 @@ static int modify_prefix_route(struct net *net, struct inet6_ifaddr *ifp,
 
 		if (!(flags & RTF_EXPIRES)) {
 			fib6_clean_expires(f6i);
-			fib6_remove_gc_list(f6i);
+			fib6_may_remove_gc_list(net, f6i);
 		} else {
 			fib6_set_expires(f6i, expires);
 			fib6_add_gc_list(f6i);
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index fadfca49d6b1..dd26657b6a4a 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -1133,7 +1133,7 @@ static int fib6_add_rt2node(struct fib6_node *fn, struct fib6_info *rt,
 					return -EEXIST;
 				if (!(rt->fib6_flags & RTF_EXPIRES)) {
 					fib6_clean_expires(iter);
-					fib6_remove_gc_list(iter);
+					fib6_may_remove_gc_list(info->nl_net, iter);
 				} else {
 					fib6_set_expires(iter, rt->expires);
 					fib6_add_gc_list(iter);
@@ -2348,8 +2348,8 @@ static void fib6_flush_trees(struct net *net)
 /*
  *	Garbage collection
  */
-static void fib6_age_exceptions(struct fib6_info *rt, struct fib6_gc_args *gc_args,
-				unsigned long now)
+void fib6_age_exceptions(struct fib6_info *rt, struct fib6_gc_args *gc_args,
+			 unsigned long now)
 {
 	bool may_expire = rt->fib6_flags & RTF_EXPIRES && rt->expires;
 	int old_more = gc_args->more;
diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index 08cd86f49bf9..cb521700cee7 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -1033,7 +1033,7 @@ int rt6_route_rcv(struct net_device *dev, u8 *opt, int len,
 
 		if (!addrconf_finite_timeout(lifetime)) {
 			fib6_clean_expires(rt);
-			fib6_remove_gc_list(rt);
+			fib6_may_remove_gc_list(net, rt);
 		} else {
 			fib6_set_expires(rt, jiffies + HZ * lifetime);
 			fib6_add_gc_list(rt);