libxt_TCPMSS.c revision 03d99486d8283552705b58dc55b6085dffc38792 
1/* Shared library add-on to iptables to add TCPMSS target support.
2 *
3 * Copyright (c) 2000 Marc Boucher
4*/
5#include <stdio.h>
6#include <string.h>
7#include <stdlib.h>
8#include <getopt.h>
9
10#include <xtables.h>
11#include <linux/netfilter/x_tables.h>
12#include <linux/netfilter/xt_TCPMSS.h>
13
14struct mssinfo {
15	struct xt_entry_target t;
16	struct xt_tcpmss_info mss;
17};
18
19static void __TCPMSS_help(int hdrsize)
20{
21	printf(
22"TCPMSS target mutually-exclusive options:\n"
23"  --set-mss value               explicitly set MSS option to specified value\n"
24"  --clamp-mss-to-pmtu           automatically clamp MSS value to (path_MTU - %d)\n",
25hdrsize);
26}
27
28static void TCPMSS_help(void)
29{
30	__TCPMSS_help(40);
31}
32
33static void TCPMSS_help6(void)
34{
35	__TCPMSS_help(60);
36}
37
38static const struct option TCPMSS_opts[] = {
39	{ "set-mss", 1, NULL, '1' },
40	{ "clamp-mss-to-pmtu", 0, NULL, '2' },
41	{ .name = NULL }
42};
43
44static int __TCPMSS_parse(int c, char **argv, int invert, unsigned int *flags,
45                          const void *entry, struct xt_entry_target **target,
46                          int hdrsize)
47{
48	struct xt_tcpmss_info *mssinfo
49		= (struct xt_tcpmss_info *)(*target)->data;
50
51	switch (c) {
52		unsigned int mssval;
53
54	case '1':
55		if (*flags)
56			exit_error(PARAMETER_PROBLEM,
57			           "TCPMSS target: Only one option may be specified");
58		if (string_to_number(optarg, 0, 65535 - hdrsize, &mssval) == -1)
59			exit_error(PARAMETER_PROBLEM, "Bad TCPMSS value `%s'", optarg);
60
61		mssinfo->mss = mssval;
62		*flags = 1;
63		break;
64
65	case '2':
66		if (*flags)
67			exit_error(PARAMETER_PROBLEM,
68			           "TCPMSS target: Only one option may be specified");
69		mssinfo->mss = XT_TCPMSS_CLAMP_PMTU;
70		*flags = 1;
71		break;
72
73	default:
74		return 0;
75	}
76
77	return 1;
78}
79
80static int TCPMSS_parse(int c, char **argv, int invert, unsigned int *flags,
81                        const void *entry, struct xt_entry_target **target)
82{
83	return __TCPMSS_parse(c, argv, invert, flags, entry, target, 40);
84}
85
86static int TCPMSS_parse6(int c, char **argv, int invert, unsigned int *flags,
87                         const void *entry, struct xt_entry_target **target)
88{
89	return __TCPMSS_parse(c, argv, invert, flags, entry, target, 60);
90}
91
92static void TCPMSS_check(unsigned int flags)
93{
94	if (!flags)
95		exit_error(PARAMETER_PROBLEM,
96		           "TCPMSS target: At least one parameter is required");
97}
98
99static void TCPMSS_print(const void *ip, const struct xt_entry_target *target,
100                         int numeric)
101{
102	const struct xt_tcpmss_info *mssinfo =
103		(const struct xt_tcpmss_info *)target->data;
104	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
105		printf("TCPMSS clamp to PMTU ");
106	else
107		printf("TCPMSS set %u ", mssinfo->mss);
108}
109
110static void TCPMSS_save(const void *ip, const struct xt_entry_target *target)
111{
112	const struct xt_tcpmss_info *mssinfo =
113		(const struct xt_tcpmss_info *)target->data;
114
115	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
116		printf("--clamp-mss-to-pmtu ");
117	else
118		printf("--set-mss %u ", mssinfo->mss);
119}
120
121static struct xtables_target tcpmss_target = {
122	.family		= NFPROTO_IPV4,
123	.name		= "TCPMSS",
124	.version	= XTABLES_VERSION,
125	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
126	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
127	.help		= TCPMSS_help,
128	.parse		= TCPMSS_parse,
129	.final_check	= TCPMSS_check,
130	.print		= TCPMSS_print,
131	.save		= TCPMSS_save,
132	.extra_opts	= TCPMSS_opts,
133};
134
135static struct xtables_target tcpmss_target6 = {
136	.family		= NFPROTO_IPV6,
137	.name		= "TCPMSS",
138	.version	= XTABLES_VERSION,
139	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
140	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
141	.help		= TCPMSS_help6,
142	.parse		= TCPMSS_parse6,
143	.final_check	= TCPMSS_check,
144	.print		= TCPMSS_print,
145	.save		= TCPMSS_save,
146	.extra_opts	= TCPMSS_opts,
147};
148
149void _init(void)
150{
151	xtables_register_target(&tcpmss_target);
152	xtables_register_target(&tcpmss_target6);
153}
154