net: netfilter: add bpf_ct_set_nat_info kfunc helper

Introduce bpf_ct_set_nat_info kfunc helper in order to set source and
destination nat addresses/ports in a new allocated ct entry not inserted
in the connection tracking table yet.

Signed-off-by: Lorenzo Bianconi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

net/netfilter/nf_conntrack_bpf.c

···
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_bpf.h>
 #include <net/netfilter/nf_conntrack_core.h>
+#include <net/netfilter/nf_nat.h>
 
 /* bpf_ct_opts - Options for CT lookup helpers
  *
···
 
 	memset(&ct->proto, 0, sizeof(ct->proto));
 	__nf_ct_set_timeout(ct, timeout * HZ);
-	ct->status |= IPS_CONFIRMED;
 
 out:
 	if (opts->netns_id >= 0)
···
 	struct nf_conn *nfct = (struct nf_conn *)nfct_i;
 	int err;
 
+	nfct->status |= IPS_CONFIRMED;
 	err = nf_conntrack_hash_check_insert(nfct);
 	if (err < 0) {
 		nf_conntrack_free(nfct);
···
 	return nf_ct_change_status_common(nfct, status);
 }
 
+/* bpf_ct_set_nat_info - Set source or destination nat address
+ *
+ * Set source or destination nat address of the newly allocated
+ * nf_conn before insertion. This must be invoked for referenced
+ * PTR_TO_BTF_ID to nf_conn___init.
+ *
+ * Parameters:
+ * @nfct	- Pointer to referenced nf_conn object, obtained using
+ *		  bpf_xdp_ct_alloc or bpf_skb_ct_alloc.
+ * @addr	- Nat source/destination address
+ * @port	- Nat source/destination port. Non-positive values are
+ *		  interpreted as select a random port.
+ * @manip	- NF_NAT_MANIP_SRC or NF_NAT_MANIP_DST
+ */
+int bpf_ct_set_nat_info(struct nf_conn___init *nfct,
+			union nf_inet_addr *addr, int port,
+			enum nf_nat_manip_type manip)
+{
+#if ((IS_MODULE(CONFIG_NF_NAT) && IS_MODULE(CONFIG_NF_CONNTRACK)) || \
+     IS_BUILTIN(CONFIG_NF_NAT))
+	struct nf_conn *ct = (struct nf_conn *)nfct;
+	u16 proto = nf_ct_l3num(ct);
+	struct nf_nat_range2 range;
+
+	if (proto != NFPROTO_IPV4 && proto != NFPROTO_IPV6)
+		return -EINVAL;
+
+	memset(&range, 0, sizeof(struct nf_nat_range2));
+	range.flags = NF_NAT_RANGE_MAP_IPS;
+	range.min_addr = *addr;
+	range.max_addr = range.min_addr;
+	if (port > 0) {
+		range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
+		range.min_proto.all = cpu_to_be16(port);
+		range.max_proto.all = range.min_proto.all;
+	}
+
+	return nf_nat_setup_info(ct, &range, manip) == NF_DROP ? -ENOMEM : 0;
+#else
+	return -EOPNOTSUPP;
+#endif
+}
+
 __diag_pop()
 
 BTF_SET8_START(nf_ct_kfunc_set)
···
 BTF_ID_FLAGS(func, bpf_ct_change_timeout, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_ct_set_status, KF_TRUSTED_ARGS)
 BTF_ID_FLAGS(func, bpf_ct_change_status, KF_TRUSTED_ARGS)
+BTF_ID_FLAGS(func, bpf_ct_set_nat_info, KF_TRUSTED_ARGS)
 BTF_SET8_END(nf_ct_kfunc_set)
 
 static const struct btf_kfunc_id_set nf_conntrack_kfunc_set = {