netfilter: nft_flow_offload: don't offload when sequence numbers need adjustment

We can't deal with tcp sequence number rewrite in flow_offload.
While at it, simplify helper check, we only need to know if the extension
is present, we don't need the helper data.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nft_flow_offload.c

@@ -12,7 +12,6 @@
 #include <net/netfilter/nf_conntrack_core.h>
 #include <linux/netfilter/nf_conntrack_common.h>
 #include <net/netfilter/nf_flow_table.h>
-#include <net/netfilter/nf_conntrack_helper.h>
 
 struct nft_flow_offload {
 	struct nft_flowtable	*flowtable;
@@ -67,7 +66,6 @@ static void nft_flow_offload_eval(const struct nft_expr *expr,
 {
 	struct nft_flow_offload *priv = nft_expr_priv(expr);
 	struct nf_flowtable *flowtable = &priv->flowtable->data;
-	const struct nf_conn_help *help;
 	enum ip_conntrack_info ctinfo;
 	struct nf_flow_route route;
 	struct flow_offload *flow;
@@ -93,8 +91,8 @@ static void nft_flow_offload_eval(const struct nft_expr *expr,
 		goto out;
 	}
 
-	help = nfct_help(ct);
-	if (help)
+	if (nf_ct_ext_exist(ct, NF_CT_EXT_HELPER) ||
+	    ct->status & IPS_SEQ_ADJUST)
 		goto out;
 
 	if (!nf_ct_is_confirmed(ct))