netfilter: nft_masq: add range specified flag setting

With nf_tables it is not possible to use port range for masquerading. Masquerade statement has option "to [:port-port]" which give no effect to translation behavior. But it must change source port of packet to one from ":port-port" range.

My network:

	+-----------------------------+
	|   ROUTER                    |
	|                             |
	|                   Masquerade|
	| 10.0.0.1            1.1.1.1 |
	| +------+           +------+ |
	| | eth1 |           | eth2 | |
	+-+--^---+-----------+---^--+-+
	     |                   |
	     |                   |
	+----v------+     +------v----+
	|           |     |           |
	| 10.0.0.2  |     |  1.1.1.2  |
	|           |     |           |
	|PC1        |     |PC2        |
	+-----------+     +-----------+

For testing i used rule like this:

rule ip nat POSTROUTING oifname eth2 masquerade to :666

Run netcat for 1.1.1.2 667(UDP) and get dump from PC2:

	15:22:25.591567 a8:f9:4b:aa:08:44 > a8:f9:4b:ac:e7:8f, ethertype IPv4 (0x0800), length 60: 1.1.1.1.34466 > 1.1.1.2.667: UDP, length 1

Address translation works fine, but source port are not belongs to specified range.

I see in similar source code (i.e. nft_redir.c, nft_nat.c) that there is setting NF_NAT_RANGE_PROTO_SPECIFIED flag. After adding this, repeat test for kernel with this patch, and get dump:

	16:16:22.324710 a8:f9:4b:aa:08:44 > a8:f9:4b:ac:e7:8f, ethertype IPv4 (0x0800), length 60: 1.1.1.1.666 > 1.1.1.2.667: UDP, length 1

Now it is works fine.

---
 net/netfilter/nft_masq.c | 2 ++
 1 file changed, 2 insertions(+)

index bc9fd98c5d6d..448376e59074 100644
@@ -113,6 +113,7 @@ static void nft_masq_ipv4_eval(const struct nft_expr *expr,
 			&regs->data[priv->sreg_proto_min]);
 		range.max_proto.all = (__force __be16)nft_reg_load16(
 			&regs->data[priv->sreg_proto_max]);
+		range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 	}
 	regs->verdict.code = nf_nat_masquerade_ipv4(pkt->skb, nft_hook(pkt),
 						    &range, nft_out(pkt));

@@ -159,6 +160,7 @@ static void nft_masq_ipv6_eval(const struct nft_expr *expr,
 			&regs->data[priv->sreg_proto_min]);
 		range.max_proto.all = (__force __be16)nft_reg_load16(
 			&regs->data[priv->sreg_proto_max]);
+		range.flags |= NF_NAT_RANGE_PROTO_SPECIFIED;
 	}
 	regs->verdict.code = nf_nat_masquerade_ipv6(pkt->skb, &range,
 						    nft_out(pkt));

2.21.0