libxt_length.c revision ddac6c5bc636003d664d25c08ea3fe176565096c 
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
11static void length_help(void)
12{
13	printf(
14"length match options:\n"
15"[!] --length length[:length]    Match packet length against value or range\n"
16"                                of values (inclusive)\n");
17}
18
19static const struct option length_opts[] = {
20	{ "length", 1, NULL, '1' },
21	{ .name = NULL }
22};
23
24static u_int16_t
25parse_length(const char *s)
26{
27	unsigned int len;
28
29	if (string_to_number(s, 0, 0xFFFF, &len) == -1)
30		exit_error(PARAMETER_PROBLEM, "length invalid: `%s'\n", s);
31	else
32		return (u_int16_t )len;
33}
34
35/* If a single value is provided, min and max are both set to the value */
36static void
37parse_lengths(const char *s, struct xt_length_info *info)
38{
39	char *buffer;
40	char *cp;
41
42	buffer = strdup(s);
43	if ((cp = strchr(buffer, ':')) == NULL)
44		info->min = info->max = parse_length(buffer);
45	else {
46		*cp = '\0';
47		cp++;
48
49		info->min = buffer[0] ? parse_length(buffer) : 0;
50		info->max = cp[0] ? parse_length(cp) : 0xFFFF;
51	}
52	free(buffer);
53
54	if (info->min > info->max)
55		exit_error(PARAMETER_PROBLEM,
56		           "length min. range value `%u' greater than max. "
57		           "range value `%u'", info->min, info->max);
58
59}
60
61static int
62length_parse(int c, char **argv, int invert, unsigned int *flags,
63             const void *entry, struct xt_entry_match **match)
64{
65	struct xt_length_info *info = (struct xt_length_info *)(*match)->data;
66
67	switch (c) {
68		case '1':
69			if (*flags)
70				exit_error(PARAMETER_PROBLEM,
71				           "length: `--length' may only be "
72				           "specified once");
73			check_inverse(optarg, &invert, &optind, 0);
74			parse_lengths(argv[optind-1], info);
75			if (invert)
76				info->invert = 1;
77			*flags = 1;
78			break;
79
80		default:
81			return 0;
82	}
83	return 1;
84}
85
86static void length_check(unsigned int flags)
87{
88	if (!flags)
89		exit_error(PARAMETER_PROBLEM,
90			   "length: You must specify `--length'");
91}
92
93static void
94print_length(struct xt_length_info *info)
95{
96	if (info->invert)
97		printf("! ");
98
99	if (info->max == info->min)
100		printf("%u ", info->min);
101	else
102		printf("%u:%u ", info->min, info->max);
103}
104
105static void
106length_print(const void *ip, const struct xt_entry_match *match, int numeric)
107{
108	printf("length ");
109	print_length((struct xt_length_info *)match->data);
110}
111
112static void length_save(const void *ip, const struct xt_entry_match *match)
113{
114	printf("--length ");
115	print_length((struct xt_length_info *)match->data);
116}
117
118static struct xtables_match length_match = {
119	.family		= AF_UNSPEC,
120	.name		= "length",
121	.version	= XTABLES_VERSION,
122	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
123	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
124	.help		= length_help,
125	.parse		= length_parse,
126	.final_check	= length_check,
127	.print		= length_print,
128	.save		= length_save,
129	.extra_opts	= length_opts,
130};
131
132void _init(void)
133{
134	xtables_register_match(&length_match);
135}
136