libxt_TCPMSS.c revision 1757ec846419c76da4e104f9675b40e05ac3eee6 
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 <xtables.h>
7#include <netinet/ip.h>
8#include <netinet/ip6.h>
9#include <linux/netfilter/xt_TCPMSS.h>
10
11enum {
12	O_SET_MSS = 0,
13	O_CLAMP_MSS,
14};
15
16struct mssinfo {
17	struct xt_entry_target t;
18	struct xt_tcpmss_info mss;
19};
20
21static void __TCPMSS_help(int hdrsize)
22{
23	printf(
24"TCPMSS target mutually-exclusive options:\n"
25"  --set-mss value               explicitly set MSS option to specified value\n"
26"  --clamp-mss-to-pmtu           automatically clamp MSS value to (path_MTU - %d)\n",
27hdrsize);
28}
29
30static void TCPMSS_help(void)
31{
32	__TCPMSS_help(sizeof(struct iphdr));
33}
34
35static void TCPMSS_help6(void)
36{
37	__TCPMSS_help(sizeof(struct ip6_hdr));
38}
39
40static const struct xt_option_entry TCPMSS4_opts[] = {
41	{.name = "set-mss", .id = O_SET_MSS, .type = XTTYPE_UINT16,
42	 .min = 0, .max = UINT16_MAX - sizeof(struct iphdr),
43	 .flags = XTOPT_PUT, XTOPT_POINTER(struct xt_tcpmss_info, mss)},
44	{.name = "clamp-mss-to-pmtu", .id = O_CLAMP_MSS, .type = XTTYPE_NONE},
45	XTOPT_TABLEEND,
46};
47
48static const struct xt_option_entry TCPMSS6_opts[] = {
49	{.name = "set-mss", .id = O_SET_MSS, .type = XTTYPE_UINT16,
50	 .min = 0, .max = UINT16_MAX - sizeof(struct ip6_hdr),
51	 .flags = XTOPT_PUT, XTOPT_POINTER(struct xt_tcpmss_info, mss)},
52	{.name = "clamp-mss-to-pmtu", .id = O_CLAMP_MSS, .type = XTTYPE_NONE},
53	XTOPT_TABLEEND,
54};
55
56static void TCPMSS_parse(struct xt_option_call *cb)
57{
58	struct xt_tcpmss_info *mssinfo = cb->data;
59
60	xtables_option_parse(cb);
61	if (cb->entry->id == O_CLAMP_MSS)
62		mssinfo->mss = XT_TCPMSS_CLAMP_PMTU;
63}
64
65static void TCPMSS_check(struct xt_fcheck_call *cb)
66{
67	if (cb->xflags == 0)
68		xtables_error(PARAMETER_PROBLEM,
69		           "TCPMSS target: At least one parameter is required");
70}
71
72static void TCPMSS_print(const void *ip, const struct xt_entry_target *target,
73                         int numeric)
74{
75	const struct xt_tcpmss_info *mssinfo =
76		(const struct xt_tcpmss_info *)target->data;
77	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
78		printf(" TCPMSS clamp to PMTU");
79	else
80		printf(" TCPMSS set %u", mssinfo->mss);
81}
82
83static void TCPMSS_save(const void *ip, const struct xt_entry_target *target)
84{
85	const struct xt_tcpmss_info *mssinfo =
86		(const struct xt_tcpmss_info *)target->data;
87
88	if(mssinfo->mss == XT_TCPMSS_CLAMP_PMTU)
89		printf(" --clamp-mss-to-pmtu");
90	else
91		printf(" --set-mss %u", mssinfo->mss);
92}
93
94static struct xtables_target tcpmss_tg_reg[] = {
95	{
96		.family        = NFPROTO_IPV4,
97		.name          = "TCPMSS",
98		.version       = XTABLES_VERSION,
99		.size          = XT_ALIGN(sizeof(struct xt_tcpmss_info)),
100		.userspacesize = XT_ALIGN(sizeof(struct xt_tcpmss_info)),
101		.help          = TCPMSS_help,
102		.print         = TCPMSS_print,
103		.save          = TCPMSS_save,
104		.x6_parse      = TCPMSS_parse,
105		.x6_fcheck     = TCPMSS_check,
106		.x6_options    = TCPMSS4_opts,
107	},
108	{
109		.family        = NFPROTO_IPV6,
110		.name          = "TCPMSS",
111		.version       = XTABLES_VERSION,
112		.size          = XT_ALIGN(sizeof(struct xt_tcpmss_info)),
113		.userspacesize = XT_ALIGN(sizeof(struct xt_tcpmss_info)),
114		.help          = TCPMSS_help6,
115		.print         = TCPMSS_print,
116		.save          = TCPMSS_save,
117		.x6_parse      = TCPMSS_parse,
118		.x6_fcheck     = TCPMSS_check,
119		.x6_options    = TCPMSS6_opts,
120	},
121};
122
123void _init(void)
124{
125	xtables_register_targets(tcpmss_tg_reg, ARRAY_SIZE(tcpmss_tg_reg));
126}
127