netfilter: nf_flow_table: add support for sending flows back to the slow path

Since conntrack hasn't seen any packets from the offloaded flow in a
while, and the timeout for offloaded flows is set to an extremely long
value, we need to fix up the state before we can send a flow back to the
slow path.

For TCP, reset td_maxwin in both directions, which makes it resync its
state on the next packets.

Use the regular timeout for TCP and UDP established connections.

This allows the slow path to take over again once the offload state has
been torn down
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_flow_table_core.c

@@ -100,6 +100,43 @@ flow_offload_alloc(struct nf_conn *ct, struct nf_flow_route *route)
 }
 EXPORT_SYMBOL_GPL(flow_offload_alloc);
 
+static void flow_offload_fixup_tcp(struct ip_ct_tcp *tcp)
+{
+	tcp->state = TCP_CONNTRACK_ESTABLISHED;
+	tcp->seen[0].td_maxwin = 0;
+	tcp->seen[1].td_maxwin = 0;
+}
+
+static void flow_offload_fixup_ct_state(struct nf_conn *ct)
+{
+	const struct nf_conntrack_l4proto *l4proto;
+	struct net *net = nf_ct_net(ct);
+	unsigned int *timeouts;
+	unsigned int timeout;
+	int l4num;
+
+	l4num = nf_ct_protonum(ct);
+	if (l4num == IPPROTO_TCP)
+		flow_offload_fixup_tcp(&ct->proto.tcp);
+
+	l4proto = __nf_ct_l4proto_find(nf_ct_l3num(ct), l4num);
+	if (!l4proto)
+		return;
+
+	timeouts = l4proto->get_timeouts(net);
+	if (!timeouts)
+		return;
+
+	if (l4num == IPPROTO_TCP)
+		timeout = timeouts[TCP_CONNTRACK_ESTABLISHED];
+	else if (l4num == IPPROTO_UDP)
+		timeout = timeouts[UDP_CT_REPLIED];
+	else
+		return;
+
+	ct->timeout = nfct_time_stamp + timeout;
+}
+
 void flow_offload_free(struct flow_offload *flow)
 {
 	struct flow_offload_entry *e;
@@ -107,7 +144,8 @@ void flow_offload_free(struct flow_offload *flow)
 	dst_release(flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].tuple.dst_cache);
 	dst_release(flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].tuple.dst_cache);
 	e = container_of(flow, struct flow_offload_entry, flow);
-	nf_ct_delete(e->ct, 0, 0);
+	if (flow->flags & FLOW_OFFLOAD_DYING)
+		nf_ct_delete(e->ct, 0, 0);
 	nf_ct_put(e->ct);
 	kfree_rcu(e, rcu_head);
 }
@@ -164,6 +202,8 @@ EXPORT_SYMBOL_GPL(flow_offload_add);
 static void flow_offload_del(struct nf_flowtable *flow_table,
 			     struct flow_offload *flow)
 {
+	struct flow_offload_entry *e;
+
 	rhashtable_remove_fast(&flow_table->rhashtable,
 			       &flow->tuplehash[FLOW_OFFLOAD_DIR_ORIGINAL].node,
 			       nf_flow_offload_rhash_params);
@@ -171,12 +211,20 @@ static void flow_offload_del(struct nf_flowtable *flow_table,
 			       &flow->tuplehash[FLOW_OFFLOAD_DIR_REPLY].node,
 			       nf_flow_offload_rhash_params);
 
+	e = container_of(flow, struct flow_offload_entry, flow);
+	clear_bit(IPS_OFFLOAD_BIT, &e->ct->status);
+
 	flow_offload_free(flow);
 }
 
 void flow_offload_teardown(struct flow_offload *flow)
 {
+	struct flow_offload_entry *e;
+
 	flow->flags |= FLOW_OFFLOAD_TEARDOWN;
+
+	e = container_of(flow, struct flow_offload_entry, flow);
+	flow_offload_fixup_ct_state(e->ct);
 }
 EXPORT_SYMBOL_GPL(flow_offload_teardown);