libipt_MASQUERADE.c revision 03d99486d8283552705b58dc55b6085dffc38792 
1/* Shared library add-on to iptables to add masquerade support. */
2#include <stdio.h>
3#include <netdb.h>
4#include <string.h>
5#include <stdlib.h>
6#include <getopt.h>
7#include <iptables.h>
8#include <linux/netfilter_ipv4/ip_tables.h>
9#include <linux/netfilter/nf_nat.h>
10
11static void MASQUERADE_help(void)
12{
13	printf(
14"MASQUERADE target options:\n"
15" --to-ports <port>[-<port>]\n"
16"				Port (range) to map to.\n"
17" --random\n"
18"				Randomize source port.\n");
19}
20
21static const struct option MASQUERADE_opts[] = {
22	{ "to-ports", 1, NULL, '1' },
23	{ "random", 0, NULL, '2' },
24	{ .name = NULL }
25};
26
27static void MASQUERADE_init(struct xt_entry_target *t)
28{
29	struct ip_nat_multi_range *mr = (struct ip_nat_multi_range *)t->data;
30
31	/* Actually, it's 0, but it's ignored at the moment. */
32	mr->rangesize = 1;
33
34}
35
36/* Parses ports */
37static void
38parse_ports(const char *arg, struct ip_nat_multi_range *mr)
39{
40	const char *dash;
41	int port;
42
43	mr->range[0].flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
44
45	port = atoi(arg);
46	if (port <= 0 || port > 65535)
47		exit_error(PARAMETER_PROBLEM, "Port `%s' not valid\n", arg);
48
49	dash = strchr(arg, '-');
50	if (!dash) {
51		mr->range[0].min.tcp.port
52			= mr->range[0].max.tcp.port
53			= htons(port);
54	} else {
55		int maxport;
56
57		maxport = atoi(dash + 1);
58		if (maxport == 0 || maxport > 65535)
59			exit_error(PARAMETER_PROBLEM,
60				   "Port `%s' not valid\n", dash+1);
61		if (maxport < port)
62			/* People are stupid.  Present reader excepted. */
63			exit_error(PARAMETER_PROBLEM,
64				   "Port range `%s' funky\n", arg);
65		mr->range[0].min.tcp.port = htons(port);
66		mr->range[0].max.tcp.port = htons(maxport);
67	}
68}
69
70static int MASQUERADE_parse(int c, char **argv, int invert, unsigned int *flags,
71                            const void *e, struct xt_entry_target **target)
72{
73	const struct ipt_entry *entry = e;
74	int portok;
75	struct ip_nat_multi_range *mr
76		= (struct ip_nat_multi_range *)(*target)->data;
77
78	if (entry->ip.proto == IPPROTO_TCP
79	    || entry->ip.proto == IPPROTO_UDP
80	    || entry->ip.proto == IPPROTO_SCTP
81	    || entry->ip.proto == IPPROTO_DCCP
82	    || entry->ip.proto == IPPROTO_ICMP)
83		portok = 1;
84	else
85		portok = 0;
86
87	switch (c) {
88	case '1':
89		if (!portok)
90			exit_error(PARAMETER_PROBLEM,
91				   "Need TCP, UDP, SCTP or DCCP with port specification");
92
93		if (check_inverse(optarg, &invert, NULL, 0))
94			exit_error(PARAMETER_PROBLEM,
95				   "Unexpected `!' after --to-ports");
96
97		parse_ports(optarg, mr);
98		return 1;
99
100	case '2':
101		mr->range[0].flags |=  IP_NAT_RANGE_PROTO_RANDOM;
102		return 1;
103
104	default:
105		return 0;
106	}
107}
108
109static void
110MASQUERADE_print(const void *ip, const struct xt_entry_target *target,
111                 int numeric)
112{
113	struct ip_nat_multi_range *mr
114		= (struct ip_nat_multi_range *)target->data;
115	struct ip_nat_range *r = &mr->range[0];
116
117	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
118		printf("masq ports: ");
119		printf("%hu", ntohs(r->min.tcp.port));
120		if (r->max.tcp.port != r->min.tcp.port)
121			printf("-%hu", ntohs(r->max.tcp.port));
122		printf(" ");
123	}
124
125	if (r->flags & IP_NAT_RANGE_PROTO_RANDOM)
126		printf("random ");
127}
128
129static void
130MASQUERADE_save(const void *ip, const struct xt_entry_target *target)
131{
132	struct ip_nat_multi_range *mr
133		= (struct ip_nat_multi_range *)target->data;
134	struct ip_nat_range *r = &mr->range[0];
135
136	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
137		printf("--to-ports %hu", ntohs(r->min.tcp.port));
138		if (r->max.tcp.port != r->min.tcp.port)
139			printf("-%hu", ntohs(r->max.tcp.port));
140		printf(" ");
141	}
142
143	if (r->flags & IP_NAT_RANGE_PROTO_RANDOM)
144		printf("--random ");
145}
146
147static struct xtables_target masquerade_tg_reg = {
148	.name		= "MASQUERADE",
149	.version	= XTABLES_VERSION,
150	.family		= NFPROTO_IPV4,
151	.size		= XT_ALIGN(sizeof(struct ip_nat_multi_range)),
152	.userspacesize	= XT_ALIGN(sizeof(struct ip_nat_multi_range)),
153	.help		= MASQUERADE_help,
154	.init		= MASQUERADE_init,
155	.parse		= MASQUERADE_parse,
156	.print		= MASQUERADE_print,
157	.save		= MASQUERADE_save,
158	.extra_opts	= MASQUERADE_opts,
159};
160
161void _init(void)
162{
163	xtables_register_target(&masquerade_tg_reg);
164}
165