libxt_length.c revision 500f483fff529dcd88ec96b9d5054be6cd6363a0 
1/* Shared library add-on to iptables to add packet length matching support. */
2#include <stdio.h>
3#include <netdb.h>
4#include <string.h>
5#include <stdlib.h>
6#include <getopt.h>
7
8#include <xtables.h>
9#include <linux/netfilter/xt_length.h>
10
11/* Function which prints out usage message. */
12static void
13help(void)
14{
15	printf(
16"length v%s options:\n"
17"[!] --length length[:length]    Match packet length against value or range\n"
18"                                of values (inclusive)\n",
19IPTABLES_VERSION);
20
21}
22
23static const struct option opts[] = {
24	{ "length", 1, NULL, '1' },
25	{ }
26};
27
28static u_int16_t
29parse_length(const char *s)
30{
31	unsigned int len;
32
33	if (string_to_number(s, 0, 0xFFFF, &len) == -1)
34		exit_error(PARAMETER_PROBLEM, "length invalid: `%s'\n", s);
35	else
36		return (u_int16_t )len;
37}
38
39/* If a single value is provided, min and max are both set to the value */
40static void
41parse_lengths(const char *s, struct xt_length_info *info)
42{
43	char *buffer;
44	char *cp;
45
46	buffer = strdup(s);
47	if ((cp = strchr(buffer, ':')) == NULL)
48		info->min = info->max = parse_length(buffer);
49	else {
50		*cp = '\0';
51		cp++;
52
53		info->min = buffer[0] ? parse_length(buffer) : 0;
54		info->max = cp[0] ? parse_length(cp) : 0xFFFF;
55	}
56	free(buffer);
57
58	if (info->min > info->max)
59		exit_error(PARAMETER_PROBLEM,
60		           "length min. range value `%u' greater than max. "
61		           "range value `%u'", info->min, info->max);
62
63}
64
65/* Function which parses command options; returns true if it
66   ate an option */
67static int
68parse(int c, char **argv, int invert, unsigned int *flags,
69      const void *entry,
70      struct xt_entry_match **match)
71{
72	struct xt_length_info *info = (struct xt_length_info *)(*match)->data;
73
74	switch (c) {
75		case '1':
76			if (*flags)
77				exit_error(PARAMETER_PROBLEM,
78				           "length: `--length' may only be "
79				           "specified once");
80			check_inverse(optarg, &invert, &optind, 0);
81			parse_lengths(argv[optind-1], info);
82			if (invert)
83				info->invert = 1;
84			*flags = 1;
85			break;
86
87		default:
88			return 0;
89	}
90	return 1;
91}
92
93/* Final check; must have specified --length. */
94static void
95final_check(unsigned int flags)
96{
97	if (!flags)
98		exit_error(PARAMETER_PROBLEM,
99			   "length: You must specify `--length'");
100}
101
102/* Common match printing code. */
103static void
104print_length(struct xt_length_info *info)
105{
106	if (info->invert)
107		printf("! ");
108
109	if (info->max == info->min)
110		printf("%u ", info->min);
111	else
112		printf("%u:%u ", info->min, info->max);
113}
114
115/* Prints out the matchinfo. */
116static void
117print(const void *ip,
118      const struct xt_entry_match *match,
119      int numeric)
120{
121	printf("length ");
122	print_length((struct xt_length_info *)match->data);
123}
124
125/* Saves the union ipt_matchinfo in parsable form to stdout. */
126static void
127save(const void *ip, const struct xt_entry_match *match)
128{
129	printf("--length ");
130	print_length((struct xt_length_info *)match->data);
131}
132
133static struct xtables_match length = {
134	.family		= AF_INET,
135	.name		= "length",
136	.version	= IPTABLES_VERSION,
137	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
138	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
139	.help		= &help,
140	.parse		= &parse,
141	.final_check	= &final_check,
142	.print		= &print,
143	.save		= &save,
144	.extra_opts	= opts
145};
146
147static struct xtables_match length6 = {
148	.family		= AF_INET6,
149	.name		= "length",
150	.version	= IPTABLES_VERSION,
151	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
152	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
153	.help		= &help,
154	.parse		= &parse,
155	.final_check	= &final_check,
156	.print		= &print,
157	.save		= &save,
158	.extra_opts	= opts
159};
160
161void _init(void)
162{
163	xtables_register_match(&length);
164	xtables_register_match(&length6);
165}
166