libxt_tcpmss.c revision c5e85736c207f211d82d2878a5781f512327dfce 
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
11static void tcpmss_help(void)
12{
13	printf(
14"tcpmss match options:\n"
15"[!] --mss value[:value]	Match TCP MSS range.\n"
16"				(only valid for TCP SYN or SYN/ACK packets)\n");
17}
18
19static const struct option tcpmss_opts[] = {
20	{ "mss", 1, NULL, '1' },
21	{ .name = NULL }
22};
23
24static u_int16_t
25parse_tcp_mssvalue(const char *mssvalue)
26{
27	unsigned int mssvaluenum;
28
29	if (xtables_strtoui(mssvalue, NULL, &mssvaluenum, 0, UINT16_MAX))
30		return mssvaluenum;
31
32	xtables_error(PARAMETER_PROBLEM,
33		   "Invalid mss `%s' specified", mssvalue);
34}
35
36static void
37parse_tcp_mssvalues(const char *mssvaluestring,
38		    u_int16_t *mss_min, u_int16_t *mss_max)
39{
40	char *buffer;
41	char *cp;
42
43	buffer = strdup(mssvaluestring);
44	if ((cp = strchr(buffer, ':')) == NULL)
45		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
46	else {
47		*cp = '\0';
48		cp++;
49
50		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
51		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
52	}
53	free(buffer);
54}
55
56static int
57tcpmss_parse(int c, char **argv, int invert, unsigned int *flags,
58             const void *entry, struct xt_entry_match **match)
59{
60	struct xt_tcpmss_match_info *mssinfo =
61		(struct xt_tcpmss_match_info *)(*match)->data;
62
63	switch (c) {
64	case '1':
65		if (*flags)
66			xtables_error(PARAMETER_PROBLEM,
67				   "Only one `--mss' allowed");
68		xtables_check_inverse(optarg, &invert, &optind, 0);
69		parse_tcp_mssvalues(argv[optind-1],
70				    &mssinfo->mss_min, &mssinfo->mss_max);
71		if (invert)
72			mssinfo->invert = 1;
73		*flags = 1;
74		break;
75	default:
76		return 0;
77	}
78	return 1;
79}
80
81static void tcpmss_check(unsigned int flags)
82{
83	if (!flags)
84		xtables_error(PARAMETER_PROBLEM,
85			   "tcpmss match: You must specify `--mss'");
86}
87
88static void
89tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
90{
91	const struct xt_tcpmss_match_info *info = (void *)match->data;
92
93	printf("tcpmss match %s", info->invert ? "!" : "");
94	if (info->mss_min == info->mss_max)
95		printf("%u ", info->mss_min);
96	else
97		printf("%u:%u ", info->mss_min, info->mss_max);
98}
99
100static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
101{
102	const struct xt_tcpmss_match_info *info = (void *)match->data;
103
104	printf("%s--mss ", info->invert ? "! " : "");
105	if (info->mss_min == info->mss_max)
106		printf("%u ", info->mss_min);
107	else
108		printf("%u:%u ", info->mss_min, info->mss_max);
109}
110
111static struct xtables_match tcpmss_match = {
112	.family		= NFPROTO_UNSPEC,
113	.name		= "tcpmss",
114	.version	= XTABLES_VERSION,
115	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
116	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
117	.help		= tcpmss_help,
118	.parse		= tcpmss_parse,
119	.final_check	= tcpmss_check,
120	.print		= tcpmss_print,
121	.save		= tcpmss_save,
122	.extra_opts	= tcpmss_opts,
123};
124
125void _init(void)
126{
127	xtables_register_match(&tcpmss_match);
128}
129