libxt_tcpmss.c revision 661f112072bc13a1625c4eb5983695e122ea97da 
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
13help(void)
14{
15	printf(
16"tcpmss match v%s options:\n"
17"[!] --mss value[:value]	Match TCP MSS range.\n"
18"				(only valid for TCP SYN or SYN/ACK packets)\n",
19IPTABLES_VERSION);
20}
21
22static const struct option opts[] = {
23	{ "mss", 1, 0, '1' },
24	{0}
25};
26
27static u_int16_t
28parse_tcp_mssvalue(const char *mssvalue)
29{
30	unsigned int mssvaluenum;
31
32	if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
33		return (u_int16_t)mssvaluenum;
34
35	exit_error(PARAMETER_PROBLEM,
36		   "Invalid mss `%s' specified", mssvalue);
37}
38
39static void
40parse_tcp_mssvalues(const char *mssvaluestring,
41		    u_int16_t *mss_min, u_int16_t *mss_max)
42{
43	char *buffer;
44	char *cp;
45
46	buffer = strdup(mssvaluestring);
47	if ((cp = strchr(buffer, ':')) == NULL)
48		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
49	else {
50		*cp = '\0';
51		cp++;
52
53		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
54		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
55	}
56	free(buffer);
57}
58
59/* Function which parses command options; returns true if it
60   ate an option */
61static int
62parse(int c, char **argv, int invert, unsigned int *flags,
63      const void *entry,
64      unsigned int *nfcache,
65      struct xt_entry_match **match)
66{
67	struct xt_tcpmss_match_info *mssinfo =
68		(struct xt_tcpmss_match_info *)(*match)->data;
69
70	switch (c) {
71	case '1':
72		if (*flags)
73			exit_error(PARAMETER_PROBLEM,
74				   "Only one `--mss' allowed");
75		check_inverse(optarg, &invert, &optind, 0);
76		parse_tcp_mssvalues(argv[optind-1],
77				    &mssinfo->mss_min, &mssinfo->mss_max);
78		if (invert)
79			mssinfo->invert = 1;
80		*flags = 1;
81		break;
82	default:
83		return 0;
84	}
85	return 1;
86}
87
88static void
89print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
90{
91	if (invert)
92		printf("! ");
93
94	if (mss_min == mss_max)
95		printf("%u ", mss_min);
96	else
97		printf("%u:%u ", mss_min, mss_max);
98}
99
100/* Final check; must have specified --mss. */
101static void
102final_check(unsigned int flags)
103{
104	if (!flags)
105		exit_error(PARAMETER_PROBLEM,
106			   "tcpmss match: You must specify `--mss'");
107}
108
109/* Prints out the matchinfo. */
110static void
111print(const void *ip,
112      const struct xt_entry_match *match,
113      int numeric)
114{
115	const struct xt_tcpmss_match_info *mssinfo =
116		(const struct xt_tcpmss_match_info *)match->data;
117
118	printf("tcpmss match ");
119	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
120		     mssinfo->invert, numeric);
121}
122
123/* Saves the union ipt_matchinfo in parsable form to stdout. */
124static void
125save(const void *ip, const struct xt_entry_match *match)
126{
127	const struct xt_tcpmss_match_info *mssinfo =
128		(const struct xt_tcpmss_match_info *)match->data;
129
130	printf("--mss ");
131	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
132		     mssinfo->invert, 0);
133}
134
135static struct xtables_match tcpmss = {
136	.family		= AF_INET,
137	.name		= "tcpmss",
138	.version	= IPTABLES_VERSION,
139	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
140	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
141	.help		= &help,
142	.parse		= &parse,
143	.final_check	= &final_check,
144	.print		= &print,
145	.save		= &save,
146	.extra_opts	= opts
147};
148
149static struct xtables_match tcpmss6 = {
150	.family		= AF_INET6,
151	.name		= "tcpmss",
152	.version	= IPTABLES_VERSION,
153	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
154	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
155	.help		= &help,
156	.parse		= &parse,
157	.final_check	= &final_check,
158	.print		= &print,
159	.save		= &save,
160	.extra_opts	= opts
161};
162
163void _init(void)
164{
165	xtables_register_match(&tcpmss);
166	xtables_register_match(&tcpmss6);
167}
168