netfilter: nf_flow_table: do not flow offload deleted conntrack entries

Conntrack entries can be deleted by the masquerade module. In that case,
flow offload should be deleted too, but GC and data-path of flow offload
do not check for conntrack status bits, hence flow offload entries will
be removed only by the timeout.

Update garbage collector and data-path to check for ct->status. If
IPS_DYING_BIT is set, garbage collector removes flow offload entries and
data-path routine ignores them.
Signed-off-by: Taehee Yoo <ap420073@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_flow_table_core.c

@@ -243,6 +243,7 @@ flow_offload_lookup(struct nf_flowtable *flow_table,
 {
 	struct flow_offload_tuple_rhash *tuplehash;
 	struct flow_offload *flow;
+	struct flow_offload_entry *e;
 	int dir;
 
 	tuplehash = rhashtable_lookup(&flow_table->rhashtable, tuple,
@@ -255,6 +256,10 @@ flow_offload_lookup(struct nf_flowtable *flow_table,
 	if (flow->flags & (FLOW_OFFLOAD_DYING | FLOW_OFFLOAD_TEARDOWN))
 		return NULL;
 
+	e = container_of(flow, struct flow_offload_entry, flow);
+	if (unlikely(nf_ct_is_dying(e->ct)))
+		return NULL;
+
 	return tuplehash;
 }
 EXPORT_SYMBOL_GPL(flow_offload_lookup);
@@ -301,8 +306,10 @@ static inline bool nf_flow_has_expired(const struct flow_offload *flow)
 static void nf_flow_offload_gc_step(struct flow_offload *flow, void *data)
 {
 	struct nf_flowtable *flow_table = data;
+	struct flow_offload_entry *e;
 
-	if (nf_flow_has_expired(flow) ||
+	e = container_of(flow, struct flow_offload_entry, flow);
+	if (nf_flow_has_expired(flow) || nf_ct_is_dying(e->ct) ||
 	    (flow->flags & (FLOW_OFFLOAD_DYING | FLOW_OFFLOAD_TEARDOWN)))
 		flow_offload_del(flow_table, flow);
 }