netfilter: cttimeout: decouple unlink and free on netns destruction

Make it so netns pre_exit unlinks the objects from the pernet list, so
they cannot be found anymore.

netns core issues a synchronize_rcu() before calling the exit hooks so
any the time the exit hooks run unconfirmed nf_conn entries have been
free'd or they have been committed to the hashtable.

The exit hook still tags unconfirmed entries as dying, this can
now be removed in a followup change.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack_timeout.h

@@ -17,14 +17,6 @@ struct nf_ct_timeout {
 	char			data[];
 };
 
-struct ctnl_timeout {
-	struct list_head	head;
-	struct rcu_head		rcu_head;
-	refcount_t		refcnt;
-	char			name[CTNL_TIMEOUT_NAME_MAX];
-	struct nf_ct_timeout	timeout;
-};
-
 struct nf_conn_timeout {
 	struct nf_ct_timeout __rcu *timeout;
 };

net/netfilter/nfnetlink_cttimeout.c

@@ -33,8 +33,19 @@
 
 static unsigned int nfct_timeout_id __read_mostly;
 
+struct ctnl_timeout {
+	struct list_head	head;
+	struct rcu_head		rcu_head;
+	refcount_t		refcnt;
+	char			name[CTNL_TIMEOUT_NAME_MAX];
+	struct nf_ct_timeout	timeout;
+
+	struct list_head	free_head;
+};
+
 struct nfct_timeout_pernet {
 	struct list_head	nfct_timeout_list;
+	struct list_head	nfct_timeout_freelist;
 };
 
 MODULE_LICENSE("GPL");
@@ -574,10 +585,24 @@ static int __net_init cttimeout_net_init(struct net *net)
 	struct nfct_timeout_pernet *pernet = nfct_timeout_pernet(net);
 
 	INIT_LIST_HEAD(&pernet->nfct_timeout_list);
+	INIT_LIST_HEAD(&pernet->nfct_timeout_freelist);
 
 	return 0;
 }
 
+static void __net_exit cttimeout_net_pre_exit(struct net *net)
+{
+	struct nfct_timeout_pernet *pernet = nfct_timeout_pernet(net);
+	struct ctnl_timeout *cur, *tmp;
+
+	list_for_each_entry_safe(cur, tmp, &pernet->nfct_timeout_list, head) {
+		list_del_rcu(&cur->head);
+		list_add(&cur->free_head, &pernet->nfct_timeout_freelist);
+	}
+
+	/* core calls synchronize_rcu() after this */
+}
+
 static void __net_exit cttimeout_net_exit(struct net *net)
 {
 	struct nfct_timeout_pernet *pernet = nfct_timeout_pernet(net);
@@ -586,8 +611,8 @@ static void __net_exit cttimeout_net_exit(struct net *net)
 	nf_ct_unconfirmed_destroy(net);
 	nf_ct_untimeout(net, NULL);
 
-	list_for_each_entry_safe(cur, tmp, &pernet->nfct_timeout_list, head) {
-		list_del_rcu(&cur->head);
+	list_for_each_entry_safe(cur, tmp, &pernet->nfct_timeout_freelist, head) {
+		list_del(&cur->free_head);
 
 		if (refcount_dec_and_test(&cur->refcnt))
 			kfree_rcu(cur, rcu_head);
@@ -596,6 +621,7 @@ static void __net_exit cttimeout_net_exit(struct net *net)
 
 static struct pernet_operations cttimeout_ops = {
 	.init	= cttimeout_net_init,
+	.pre_exit = cttimeout_net_pre_exit,
 	.exit	= cttimeout_net_exit,
 	.id     = &nfct_timeout_id,
 	.size   = sizeof(struct nfct_timeout_pernet),