libipt_SNAT.c revision ddac6c5bc636003d664d25c08ea3fe176565096c 
1/* Shared library add-on to iptables to add source-NAT 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#define IPT_SNAT_OPT_SOURCE 0x01
12#define IPT_SNAT_OPT_RANDOM 0x02
13
14/* Source NAT data consists of a multi-range, indicating where to map
15   to. */
16struct ipt_natinfo
17{
18	struct xt_entry_target t;
19	struct ip_nat_multi_range mr;
20};
21
22static void SNAT_help(void)
23{
24	printf(
25"SNAT target options:\n"
26" --to-source <ipaddr>[-<ipaddr>][:port-port]\n"
27"				Address to map source to.\n"
28"[--random]\n");
29}
30
31static const struct option SNAT_opts[] = {
32	{ "to-source", 1, NULL, '1' },
33	{ "random", 0, NULL, '2' },
34	{ .name = NULL }
35};
36
37static struct ipt_natinfo *
38append_range(struct ipt_natinfo *info, const struct ip_nat_range *range)
39{
40	unsigned int size;
41
42	/* One rangesize already in struct ipt_natinfo */
43	size = XT_ALIGN(sizeof(*info) + info->mr.rangesize * sizeof(*range));
44
45	info = realloc(info, size);
46	if (!info)
47		exit_error(OTHER_PROBLEM, "Out of memory\n");
48
49	info->t.u.target_size = size;
50	info->mr.range[info->mr.rangesize] = *range;
51	info->mr.rangesize++;
52
53	return info;
54}
55
56/* Ranges expected in network order. */
57static struct xt_entry_target *
58parse_to(char *arg, int portok, struct ipt_natinfo *info)
59{
60	struct ip_nat_range range;
61	char *colon, *dash, *error;
62	const struct in_addr *ip;
63
64	memset(&range, 0, sizeof(range));
65	colon = strchr(arg, ':');
66
67	if (colon) {
68		int port;
69
70		if (!portok)
71			exit_error(PARAMETER_PROBLEM,
72				   "Need TCP or UDP with port specification");
73
74		range.flags |= IP_NAT_RANGE_PROTO_SPECIFIED;
75
76		port = atoi(colon+1);
77		if (port <= 0 || port > 65535)
78			exit_error(PARAMETER_PROBLEM,
79				   "Port `%s' not valid\n", colon+1);
80
81		error = strchr(colon+1, ':');
82		if (error)
83			exit_error(PARAMETER_PROBLEM,
84				   "Invalid port:port syntax - use dash\n");
85
86		dash = strchr(colon, '-');
87		if (!dash) {
88			range.min.tcp.port
89				= range.max.tcp.port
90				= htons(port);
91		} else {
92			int maxport;
93
94			maxport = atoi(dash + 1);
95			if (maxport <= 0 || maxport > 65535)
96				exit_error(PARAMETER_PROBLEM,
97					   "Port `%s' not valid\n", dash+1);
98			if (maxport < port)
99				/* People are stupid. */
100				exit_error(PARAMETER_PROBLEM,
101					   "Port range `%s' funky\n", colon+1);
102			range.min.tcp.port = htons(port);
103			range.max.tcp.port = htons(maxport);
104		}
105		/* Starts with a colon? No IP info...*/
106		if (colon == arg)
107			return &(append_range(info, &range)->t);
108		*colon = '\0';
109	}
110
111	range.flags |= IP_NAT_RANGE_MAP_IPS;
112	dash = strchr(arg, '-');
113	if (colon && dash && dash > colon)
114		dash = NULL;
115
116	if (dash)
117		*dash = '\0';
118
119	ip = numeric_to_ipaddr(arg);
120	if (!ip)
121		exit_error(PARAMETER_PROBLEM, "Bad IP address `%s'\n",
122			   arg);
123	range.min_ip = ip->s_addr;
124	if (dash) {
125		ip = numeric_to_ipaddr(dash+1);
126		if (!ip)
127			exit_error(PARAMETER_PROBLEM, "Bad IP address `%s'\n",
128				   dash+1);
129		range.max_ip = ip->s_addr;
130	} else
131		range.max_ip = range.min_ip;
132
133	return &(append_range(info, &range)->t);
134}
135
136static int SNAT_parse(int c, char **argv, int invert, unsigned int *flags,
137                      const void *e, struct xt_entry_target **target)
138{
139	const struct ipt_entry *entry = e;
140	struct ipt_natinfo *info = (void *)*target;
141	int portok;
142
143	if (entry->ip.proto == IPPROTO_TCP
144	    || entry->ip.proto == IPPROTO_UDP
145	    || entry->ip.proto == IPPROTO_ICMP)
146		portok = 1;
147	else
148		portok = 0;
149
150	switch (c) {
151	case '1':
152		if (check_inverse(optarg, &invert, NULL, 0))
153			exit_error(PARAMETER_PROBLEM,
154				   "Unexpected `!' after --to-source");
155
156		if (*flags & IPT_SNAT_OPT_SOURCE) {
157			if (!kernel_version)
158				get_kernel_version();
159			if (kernel_version > LINUX_VERSION(2, 6, 10))
160				exit_error(PARAMETER_PROBLEM,
161					   "Multiple --to-source not supported");
162		}
163		*target = parse_to(optarg, portok, info);
164		/* WTF do we need this for?? */
165		if (*flags & IPT_SNAT_OPT_RANDOM)
166			info->mr.range[0].flags |= IP_NAT_RANGE_PROTO_RANDOM;
167		*flags |= IPT_SNAT_OPT_SOURCE;
168		return 1;
169
170	case '2':
171		if (*flags & IPT_SNAT_OPT_SOURCE) {
172			info->mr.range[0].flags |= IP_NAT_RANGE_PROTO_RANDOM;
173			*flags |= IPT_SNAT_OPT_RANDOM;
174		} else
175			*flags |= IPT_SNAT_OPT_RANDOM;
176		return 1;
177
178	default:
179		return 0;
180	}
181}
182
183static void SNAT_check(unsigned int flags)
184{
185	if (!(flags & IPT_SNAT_OPT_SOURCE))
186		exit_error(PARAMETER_PROBLEM,
187			   "You must specify --to-source");
188}
189
190static void print_range(const struct ip_nat_range *r)
191{
192	if (r->flags & IP_NAT_RANGE_MAP_IPS) {
193		struct in_addr a;
194
195		a.s_addr = r->min_ip;
196		printf("%s", ipaddr_to_numeric(&a));
197		if (r->max_ip != r->min_ip) {
198			a.s_addr = r->max_ip;
199			printf("-%s", ipaddr_to_numeric(&a));
200		}
201	}
202	if (r->flags & IP_NAT_RANGE_PROTO_SPECIFIED) {
203		printf(":");
204		printf("%hu", ntohs(r->min.tcp.port));
205		if (r->max.tcp.port != r->min.tcp.port)
206			printf("-%hu", ntohs(r->max.tcp.port));
207	}
208}
209
210static void SNAT_print(const void *ip, const struct xt_entry_target *target,
211                       int numeric)
212{
213	struct ipt_natinfo *info = (void *)target;
214	unsigned int i = 0;
215
216	printf("to:");
217	for (i = 0; i < info->mr.rangesize; i++) {
218		print_range(&info->mr.range[i]);
219		printf(" ");
220		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
221			printf("random ");
222	}
223}
224
225static void SNAT_save(const void *ip, const struct xt_entry_target *target)
226{
227	struct ipt_natinfo *info = (void *)target;
228	unsigned int i = 0;
229
230	for (i = 0; i < info->mr.rangesize; i++) {
231		printf("--to-source ");
232		print_range(&info->mr.range[i]);
233		printf(" ");
234		if (info->mr.range[i].flags & IP_NAT_RANGE_PROTO_RANDOM)
235			printf("--random ");
236	}
237}
238
239static struct xtables_target snat_tg_reg = {
240	.name		= "SNAT",
241	.version	= XTABLES_VERSION,
242	.family		= PF_INET,
243	.size		= XT_ALIGN(sizeof(struct ip_nat_multi_range)),
244	.userspacesize	= XT_ALIGN(sizeof(struct ip_nat_multi_range)),
245	.help		= SNAT_help,
246	.parse		= SNAT_parse,
247	.final_check	= SNAT_check,
248	.print		= SNAT_print,
249	.save		= SNAT_save,
250	.extra_opts	= SNAT_opts,
251};
252
253void _init(void)
254{
255	xtables_register_target(&snat_tg_reg);
256}
257