libipt_MASQUERADE.c revision 830132ac9c0d270bf9dcfe85c2464e3fe8c73fb9 
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
11/* Function which prints out usage message. */
12static void
13help(void)
14{
15	printf(
16"MASQUERADE v%s options:\n"
17" --to-ports <port>[-<port>]\n"
18"				Port (range) to map to.\n"
19" --random\n"
20"				Randomize source port.\n"
21"\n"
22,
23IPTABLES_VERSION);
24}
25
26static const struct option opts[] = {
27	{ "to-ports", 1, NULL, '1' },
28	{ "random", 0, NULL, '2' },
29	{ }
30};
31
32/* Initialize the target. */
33static void
34init(struct xt_entry_target *t)
35{
36	struct ip_nat_multi_range *mr = (struct ip_nat_multi_range *)t->data;
37
38	/* Actually, it's 0, but it's ignored at the moment. */
39	mr->rangesize = 1;
40
41}
42
43/* Parses ports */
44static void
45parse_ports(const char *arg, struct ip_nat_multi_range *mr)
46{
47	const char *dash;
48	int port;
49
50	mr->range[0].flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
51
52	port = atoi(arg);
53	if (port <= 0 || port > 65535)
54		exit_error(PARAMETER_PROBLEM, "Port `%s' not valid\n", arg);
55
56	dash = strchr(arg, '-');
57	if (!dash) {
58		mr->range[0].min.tcp.port
59			= mr->range[0].max.tcp.port
60			= htons(port);
61	} else {
62		int maxport;
63
64		maxport = atoi(dash + 1);
65		if (maxport == 0 || maxport > 65535)
66			exit_error(PARAMETER_PROBLEM,
67				   "Port `%s' not valid\n", dash+1);
68		if (maxport < port)
69			/* People are stupid.  Present reader excepted. */
70			exit_error(PARAMETER_PROBLEM,
71				   "Port range `%s' funky\n", arg);
72		mr->range[0].min.tcp.port = htons(port);
73		mr->range[0].max.tcp.port = htons(maxport);
74	}
75}
76
77/* Function which parses command options; returns true if it
78   ate an option */
79static int
80parse(int c, char **argv, int invert, unsigned int *flags,
81      const void *e,
82      struct xt_entry_target **target)
83{
84	const struct ipt_entry *entry = e;
85	int portok;
86	struct ip_nat_multi_range *mr
87		= (struct ip_nat_multi_range *)(*target)->data;
88
89	if (entry->ip.proto == IPPROTO_TCP
90	    || entry->ip.proto == IPPROTO_UDP
91	    || entry->ip.proto == IPPROTO_ICMP)
92		portok = 1;
93	else
94		portok = 0;
95
96	switch (c) {
97	case '1':
98		if (!portok)
99			exit_error(PARAMETER_PROBLEM,
100				   "Need TCP or UDP with port specification");
101
102		if (check_inverse(optarg, &invert, NULL, 0))
103			exit_error(PARAMETER_PROBLEM,
104				   "Unexpected `!' after --to-ports");
105
106		parse_ports(optarg, mr);
107		return 1;
108
109	case '2':
110		mr->range[0].flags |=  IP_NAT_RANGE_PROTO_RANDOM;
111		return 1;
112
113	default:
114		return 0;
115	}
116}
117
118/* Prints out the targinfo. */
119static void
120print(const void *ip,
121      const struct xt_entry_target *target,
122      int numeric)
123{
124	struct ip_nat_multi_range *mr
125		= (struct ip_nat_multi_range *)target->data;
126	struct ip_nat_range *r = &mr->range[0];
127
128	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
129		printf("masq ports: ");
130		printf("%hu", ntohs(r->min.tcp.port));
131		if (r->max.tcp.port != r->min.tcp.port)
132			printf("-%hu", ntohs(r->max.tcp.port));
133		printf(" ");
134	}
135
136	if (r->flags & IP_NAT_RANGE_PROTO_RANDOM)
137		printf("random ");
138}
139
140/* Saves the union ipt_targinfo in parsable form to stdout. */
141static void
142save(const void *ip, const struct xt_entry_target *target)
143{
144	struct ip_nat_multi_range *mr
145		= (struct ip_nat_multi_range *)target->data;
146	struct ip_nat_range *r = &mr->range[0];
147
148	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
149		printf("--to-ports %hu", ntohs(r->min.tcp.port));
150		if (r->max.tcp.port != r->min.tcp.port)
151			printf("-%hu", ntohs(r->max.tcp.port));
152		printf(" ");
153	}
154
155	if (r->flags & IP_NAT_RANGE_PROTO_RANDOM)
156		printf("--random ");
157}
158
159static struct iptables_target masq = {
160	.name		= "MASQUERADE",
161	.version	= IPTABLES_VERSION,
162	.size		= IPT_ALIGN(sizeof(struct ip_nat_multi_range)),
163	.userspacesize	= IPT_ALIGN(sizeof(struct ip_nat_multi_range)),
164	.help		= &help,
165	.init		= &init,
166	.parse		= &parse,
167	.print		= &print,
168	.save		= &save,
169	.extra_opts	= opts
170};
171
172void _init(void)
173{
174	register_target(&masq);
175}
176