libipt_MASQUERADE.c revision bf97128c7262f17a02fec41cdae75b472ba77f88 
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 <xtables.h>
8#include <limits.h> /* INT_MAX in ip_tables.h */
9#include <linux/netfilter_ipv4/ip_tables.h>
10#include <net/netfilter/nf_nat.h>
11
12static void MASQUERADE_help(void)
13{
14	printf(
15"MASQUERADE target options:\n"
16" --to-ports <port>[-<port>]\n"
17"				Port (range) to map to.\n"
18" --random\n"
19"				Randomize source port.\n");
20}
21
22static const struct option MASQUERADE_opts[] = {
23	{ "to-ports", 1, NULL, '1' },
24	{ "random", 0, NULL, '2' },
25	{ .name = NULL }
26};
27
28static void MASQUERADE_init(struct xt_entry_target *t)
29{
30	struct nf_nat_multi_range *mr = (struct nf_nat_multi_range *)t->data;
31
32	/* Actually, it's 0, but it's ignored at the moment. */
33	mr->rangesize = 1;
34
35}
36
37/* Parses ports */
38static void
39parse_ports(const char *arg, struct nf_nat_multi_range *mr)
40{
41	const char *dash;
42	int port;
43
44	mr->range[0].flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
45
46	port = atoi(arg);
47	if (port <= 0 || port > 65535)
48		xtables_error(PARAMETER_PROBLEM, "Port \"%s\" not valid\n", arg);
49
50	dash = strchr(arg, '-');
51	if (!dash) {
52		mr->range[0].min.tcp.port
53			= mr->range[0].max.tcp.port
54			= htons(port);
55	} else {
56		int maxport;
57
58		maxport = atoi(dash + 1);
59		if (maxport == 0 || maxport > 65535)
60			xtables_error(PARAMETER_PROBLEM,
61				   "Port `%s' not valid\n", dash+1);
62		if (maxport < port)
63			/* People are stupid.  Present reader excepted. */
64			xtables_error(PARAMETER_PROBLEM,
65				   "Port range `%s' funky\n", arg);
66		mr->range[0].min.tcp.port = htons(port);
67		mr->range[0].max.tcp.port = htons(maxport);
68	}
69}
70
71static int MASQUERADE_parse(int c, char **argv, int invert, unsigned int *flags,
72                            const void *e, struct xt_entry_target **target)
73{
74	const struct ipt_entry *entry = e;
75	int portok;
76	struct nf_nat_multi_range *mr
77		= (struct nf_nat_multi_range *)(*target)->data;
78
79	if (entry->ip.proto == IPPROTO_TCP
80	    || entry->ip.proto == IPPROTO_UDP
81	    || entry->ip.proto == IPPROTO_SCTP
82	    || entry->ip.proto == IPPROTO_DCCP
83	    || entry->ip.proto == IPPROTO_ICMP)
84		portok = 1;
85	else
86		portok = 0;
87
88	switch (c) {
89	case '1':
90		if (!portok)
91			xtables_error(PARAMETER_PROBLEM,
92				   "Need TCP, UDP, SCTP or DCCP with port specification");
93
94		if (xtables_check_inverse(optarg, &invert, NULL, 0, argv))
95			xtables_error(PARAMETER_PROBLEM,
96				   "Unexpected `!' after --to-ports");
97
98		parse_ports(optarg, mr);
99		return 1;
100
101	case '2':
102		mr->range[0].flags |=  IP_NAT_RANGE_PROTO_RANDOM;
103		return 1;
104
105	default:
106		return 0;
107	}
108}
109
110static void
111MASQUERADE_print(const void *ip, const struct xt_entry_target *target,
112                 int numeric)
113{
114	const struct nf_nat_multi_range *mr = (const void *)target->data;
115	const struct nf_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	const struct nf_nat_multi_range *mr = (const void *)target->data;
133	const struct nf_nat_range *r = &mr->range[0];
134
135	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
136		printf("--to-ports %hu", ntohs(r->min.tcp.port));
137		if (r->max.tcp.port != r->min.tcp.port)
138			printf("-%hu", ntohs(r->max.tcp.port));
139		printf(" ");
140	}
141
142	if (r->flags & IP_NAT_RANGE_PROTO_RANDOM)
143		printf("--random ");
144}
145
146static struct xtables_target masquerade_tg_reg = {
147	.name		= "MASQUERADE",
148	.version	= XTABLES_VERSION,
149	.family		= NFPROTO_IPV4,
150	.size		= XT_ALIGN(sizeof(struct nf_nat_multi_range)),
151	.userspacesize	= XT_ALIGN(sizeof(struct nf_nat_multi_range)),
152	.help		= MASQUERADE_help,
153	.init		= MASQUERADE_init,
154	.parse		= MASQUERADE_parse,
155	.print		= MASQUERADE_print,
156	.save		= MASQUERADE_save,
157	.extra_opts	= MASQUERADE_opts,
158};
159
160void _init(void)
161{
162	xtables_register_target(&masquerade_tg_reg);
163}
164