libxt_tcpmss.c revision ea146a982e26c42f9954f140276f8deeb2edbe98 
1/* Shared library add-on to iptables to add tcp MSS 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_tcpmss.h>
10
11/* Function which prints out usage message. */
12static void
13help(void)
14{
15	printf(
16"tcpmss match v%s options:\n"
17"[!] --mss value[:value]	Match TCP MSS range.\n"
18"				(only valid for TCP SYN or SYN/ACK packets)\n",
19IPTABLES_VERSION);
20}
21
22static const struct option opts[] = {
23	{ "mss", 1, 0, '1' },
24	{0}
25};
26
27static u_int16_t
28parse_tcp_mssvalue(const char *mssvalue)
29{
30	unsigned int mssvaluenum;
31
32	if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
33		return (u_int16_t)mssvaluenum;
34
35	exit_error(PARAMETER_PROBLEM,
36		   "Invalid mss `%s' specified", mssvalue);
37}
38
39static void
40parse_tcp_mssvalues(const char *mssvaluestring,
41		    u_int16_t *mss_min, u_int16_t *mss_max)
42{
43	char *buffer;
44	char *cp;
45
46	buffer = strdup(mssvaluestring);
47	if ((cp = strchr(buffer, ':')) == NULL)
48		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
49	else {
50		*cp = '\0';
51		cp++;
52
53		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
54		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
55	}
56	free(buffer);
57}
58
59/* Function which parses command options; returns true if it
60   ate an option */
61static int
62parse(int c, char **argv, int invert, unsigned int *flags,
63      const void *entry,
64      struct xt_entry_match **match)
65{
66	struct xt_tcpmss_match_info *mssinfo =
67		(struct xt_tcpmss_match_info *)(*match)->data;
68
69	switch (c) {
70	case '1':
71		if (*flags)
72			exit_error(PARAMETER_PROBLEM,
73				   "Only one `--mss' allowed");
74		check_inverse(optarg, &invert, &optind, 0);
75		parse_tcp_mssvalues(argv[optind-1],
76				    &mssinfo->mss_min, &mssinfo->mss_max);
77		if (invert)
78			mssinfo->invert = 1;
79		*flags = 1;
80		break;
81	default:
82		return 0;
83	}
84	return 1;
85}
86
87static void
88print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
89{
90	if (invert)
91		printf("! ");
92
93	if (mss_min == mss_max)
94		printf("%u ", mss_min);
95	else
96		printf("%u:%u ", mss_min, mss_max);
97}
98
99/* Final check; must have specified --mss. */
100static void
101final_check(unsigned int flags)
102{
103	if (!flags)
104		exit_error(PARAMETER_PROBLEM,
105			   "tcpmss match: You must specify `--mss'");
106}
107
108/* Prints out the matchinfo. */
109static void
110print(const void *ip,
111      const struct xt_entry_match *match,
112      int numeric)
113{
114	const struct xt_tcpmss_match_info *mssinfo =
115		(const struct xt_tcpmss_match_info *)match->data;
116
117	printf("tcpmss match ");
118	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
119		     mssinfo->invert, numeric);
120}
121
122/* Saves the union ipt_matchinfo in parsable form to stdout. */
123static void
124save(const void *ip, const struct xt_entry_match *match)
125{
126	const struct xt_tcpmss_match_info *mssinfo =
127		(const struct xt_tcpmss_match_info *)match->data;
128
129	printf("--mss ");
130	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
131		     mssinfo->invert, 0);
132}
133
134static struct xtables_match tcpmss = {
135	.family		= AF_INET,
136	.name		= "tcpmss",
137	.version	= IPTABLES_VERSION,
138	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
139	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_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 tcpmss6 = {
149	.family		= AF_INET6,
150	.name		= "tcpmss",
151	.version	= IPTABLES_VERSION,
152	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
153	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_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(&tcpmss);
165	xtables_register_match(&tcpmss6);
166}
167