libxt_TCPMSS.c revision 1829ed482efbc8b390cc760d012b3a4450494e1a 
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			xtables_error(PARAMETER_PROBLEM,
57			           "TCPMSS target: Only one option may be specified");
58		if (!xtables_strtoui(optarg, NULL, &mssval,
59		    0, UINT16_MAX - hdrsize))
60			xtables_error(PARAMETER_PROBLEM, "Bad TCPMSS value \"%s\"", optarg);
61
62		mssinfo->mss = mssval;
63		*flags = 1;
64		break;
65
66	case '2':
67		if (*flags)
68			xtables_error(PARAMETER_PROBLEM,
69			           "TCPMSS target: Only one option may be specified");
70		mssinfo->mss = XT_TCPMSS_CLAMP_PMTU;
71		*flags = 1;
72		break;
73
74	default:
75		return 0;
76	}
77
78	return 1;
79}
80
81static int TCPMSS_parse(int c, char **argv, int invert, unsigned int *flags,
82                        const void *entry, struct xt_entry_target **target)
83{
84	return __TCPMSS_parse(c, argv, invert, flags, entry, target, 40);
85}
86
87static int TCPMSS_parse6(int c, char **argv, int invert, unsigned int *flags,
88                         const void *entry, struct xt_entry_target **target)
89{
90	return __TCPMSS_parse(c, argv, invert, flags, entry, target, 60);
91}
92
93static void TCPMSS_check(unsigned int flags)
94{
95	if (!flags)
96		xtables_error(PARAMETER_PROBLEM,
97		           "TCPMSS target: At least one parameter is required");
98}
99
100static void TCPMSS_print(const void *ip, const struct xt_entry_target *target,
101                         int numeric)
102{
103	const struct xt_tcpmss_info *mssinfo =
104		(const struct xt_tcpmss_info *)target->data;
105	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
106		printf("TCPMSS clamp to PMTU ");
107	else
108		printf("TCPMSS set %u ", mssinfo->mss);
109}
110
111static void TCPMSS_save(const void *ip, const struct xt_entry_target *target)
112{
113	const struct xt_tcpmss_info *mssinfo =
114		(const struct xt_tcpmss_info *)target->data;
115
116	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
117		printf("--clamp-mss-to-pmtu ");
118	else
119		printf("--set-mss %u ", mssinfo->mss);
120}
121
122static struct xtables_target tcpmss_target = {
123	.family		= NFPROTO_IPV4,
124	.name		= "TCPMSS",
125	.version	= XTABLES_VERSION,
126	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
127	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
128	.help		= TCPMSS_help,
129	.parse		= TCPMSS_parse,
130	.final_check	= TCPMSS_check,
131	.print		= TCPMSS_print,
132	.save		= TCPMSS_save,
133	.extra_opts	= TCPMSS_opts,
134};
135
136static struct xtables_target tcpmss_target6 = {
137	.family		= NFPROTO_IPV6,
138	.name		= "TCPMSS",
139	.version	= XTABLES_VERSION,
140	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
141	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_info)),
142	.help		= TCPMSS_help6,
143	.parse		= TCPMSS_parse6,
144	.final_check	= TCPMSS_check,
145	.print		= TCPMSS_print,
146	.save		= TCPMSS_save,
147	.extra_opts	= TCPMSS_opts,
148};
149
150void _init(void)
151{
152	xtables_register_target(&tcpmss_target);
153	xtables_register_target(&tcpmss_target6);
154}
155