libxt_length.c revision 661f112072bc13a1625c4eb5983695e122ea97da 
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, 0, '1' },
25	{0}
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      unsigned int *nfcache,
71      struct xt_entry_match **match)
72{
73	struct xt_length_info *info = (struct xt_length_info *)(*match)->data;
74
75	switch (c) {
76		case '1':
77			if (*flags)
78				exit_error(PARAMETER_PROBLEM,
79				           "length: `--length' may only be "
80				           "specified once");
81			check_inverse(optarg, &invert, &optind, 0);
82			parse_lengths(argv[optind-1], info);
83			if (invert)
84				info->invert = 1;
85			*flags = 1;
86			break;
87
88		default:
89			return 0;
90	}
91	return 1;
92}
93
94/* Final check; must have specified --length. */
95static void
96final_check(unsigned int flags)
97{
98	if (!flags)
99		exit_error(PARAMETER_PROBLEM,
100			   "length: You must specify `--length'");
101}
102
103/* Common match printing code. */
104static void
105print_length(struct xt_length_info *info)
106{
107	if (info->invert)
108		printf("! ");
109
110	if (info->max == info->min)
111		printf("%u ", info->min);
112	else
113		printf("%u:%u ", info->min, info->max);
114}
115
116/* Prints out the matchinfo. */
117static void
118print(const void *ip,
119      const struct xt_entry_match *match,
120      int numeric)
121{
122	printf("length ");
123	print_length((struct xt_length_info *)match->data);
124}
125
126/* Saves the union ipt_matchinfo in parsable form to stdout. */
127static void
128save(const void *ip, const struct xt_entry_match *match)
129{
130	printf("--length ");
131	print_length((struct xt_length_info *)match->data);
132}
133
134static struct xtables_match length = {
135	.family		= AF_INET,
136	.name		= "length",
137	.version	= IPTABLES_VERSION,
138	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
139	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
140	.help		= &help,
141	.parse		= &parse,
142	.final_check	= &final_check,
143	.print		= &print,
144	.save		= &save,
145	.extra_opts	= opts
146};
147
148static struct xtables_match length6 = {
149	.family		= AF_INET6,
150	.name		= "length",
151	.version	= IPTABLES_VERSION,
152	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
153	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
154	.help		= &help,
155	.parse		= &parse,
156	.final_check	= &final_check,
157	.print		= &print,
158	.save		= &save,
159	.extra_opts	= opts
160};
161
162void _init(void)
163{
164	xtables_register_match(&length);
165	xtables_register_match(&length6);
166}
167