libxt_tcpmss.c revision 181dead3f13befe02769ef479bcbb51801b7fc4e 
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 tcpmss_help(void)
13{
14	printf(
15"tcpmss match v%s options:\n"
16"[!] --mss value[:value]	Match TCP MSS range.\n"
17"				(only valid for TCP SYN or SYN/ACK packets)\n",
18IPTABLES_VERSION);
19}
20
21static const struct option tcpmss_opts[] = {
22	{ "mss", 1, NULL, '1' },
23	{ }
24};
25
26static u_int16_t
27parse_tcp_mssvalue(const char *mssvalue)
28{
29	unsigned int mssvaluenum;
30
31	if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
32		return (u_int16_t)mssvaluenum;
33
34	exit_error(PARAMETER_PROBLEM,
35		   "Invalid mss `%s' specified", mssvalue);
36}
37
38static void
39parse_tcp_mssvalues(const char *mssvaluestring,
40		    u_int16_t *mss_min, u_int16_t *mss_max)
41{
42	char *buffer;
43	char *cp;
44
45	buffer = strdup(mssvaluestring);
46	if ((cp = strchr(buffer, ':')) == NULL)
47		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
48	else {
49		*cp = '\0';
50		cp++;
51
52		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
53		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
54	}
55	free(buffer);
56}
57
58/* Function which parses command options; returns true if it
59   ate an option */
60static int
61tcpmss_parse(int c, char **argv, int invert, unsigned int *flags,
62             const void *entry, struct xt_entry_match **match)
63{
64	struct xt_tcpmss_match_info *mssinfo =
65		(struct xt_tcpmss_match_info *)(*match)->data;
66
67	switch (c) {
68	case '1':
69		if (*flags)
70			exit_error(PARAMETER_PROBLEM,
71				   "Only one `--mss' allowed");
72		check_inverse(optarg, &invert, &optind, 0);
73		parse_tcp_mssvalues(argv[optind-1],
74				    &mssinfo->mss_min, &mssinfo->mss_max);
75		if (invert)
76			mssinfo->invert = 1;
77		*flags = 1;
78		break;
79	default:
80		return 0;
81	}
82	return 1;
83}
84
85static void
86print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
87{
88	if (invert)
89		printf("! ");
90
91	if (mss_min == mss_max)
92		printf("%u ", mss_min);
93	else
94		printf("%u:%u ", mss_min, mss_max);
95}
96
97/* Final check; must have specified --mss. */
98static void tcpmss_check(unsigned int flags)
99{
100	if (!flags)
101		exit_error(PARAMETER_PROBLEM,
102			   "tcpmss match: You must specify `--mss'");
103}
104
105/* Prints out the matchinfo. */
106static void
107tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
108{
109	const struct xt_tcpmss_match_info *mssinfo =
110		(const struct xt_tcpmss_match_info *)match->data;
111
112	printf("tcpmss match ");
113	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
114		     mssinfo->invert, numeric);
115}
116
117/* Saves the union ipt_matchinfo in parsable form to stdout. */
118static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
119{
120	const struct xt_tcpmss_match_info *mssinfo =
121		(const struct xt_tcpmss_match_info *)match->data;
122
123	printf("--mss ");
124	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
125		     mssinfo->invert, 0);
126}
127
128static struct xtables_match tcpmss_match = {
129	.family		= AF_INET,
130	.name		= "tcpmss",
131	.version	= IPTABLES_VERSION,
132	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
133	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
134	.help		= tcpmss_help,
135	.parse		= tcpmss_parse,
136	.final_check	= tcpmss_check,
137	.print		= tcpmss_print,
138	.save		= tcpmss_save,
139	.extra_opts	= tcpmss_opts,
140};
141
142static struct xtables_match tcpmss_match6 = {
143	.family		= AF_INET6,
144	.name		= "tcpmss",
145	.version	= IPTABLES_VERSION,
146	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
147	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
148	.help		= tcpmss_help,
149	.parse		= tcpmss_parse,
150	.final_check	= tcpmss_check,
151	.print		= tcpmss_print,
152	.save		= tcpmss_save,
153	.extra_opts	= tcpmss_opts,
154};
155
156void _init(void)
157{
158	xtables_register_match(&tcpmss_match);
159	xtables_register_match(&tcpmss_match6);
160}
161