summaryrefslogtreecommitdiffstats
path: root/extensions/libipt_tcpmss.c
blob: 87353bfe07149909782f4328324e56570f6fc3fe (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
/* Shared library add-on to iptables to add tcp MSS matching support. */
#include <stdio.h>
#include <netdb.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>

#include <iptables.h>
#include <linux/netfilter_ipv4/ipt_tcpmss.h>

/* Function which prints out usage message. */
static void
help(void)
{
	printf(
"tcpmss match v%s options:\n"
"[!] --mss value[:value]	Match TCP MSS range.\n"
"				(only valid for TCP SYN or SYN/ACK packets)\n",
NETFILTER_VERSION);
}

static struct option opts[] = {
	{ "mss", 1, 0, '1' },
	{0}
};

/* Initialize the match. */
static void
init(struct ipt_entry_match *m, unsigned int *nfcache)
{
	*nfcache |= NFC_IP_PROTO_UNKNOWN;
}

static u_int16_t
parse_tcp_mssvalue(const char *mssvalue)
{
	unsigned int mssvaluenum;

	if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
		return (u_int16_t)mssvaluenum;

	exit_error(PARAMETER_PROBLEM,
		   "Invalid mss `%s' specified", mssvalue);
}

static void
parse_tcp_mssvalues(const char *mssvaluestring,
		    u_int16_t *mss_min, u_int16_t *mss_max)
{
	char *buffer;
	char *cp;

	buffer = strdup(mssvaluestring);
	if ((cp = strchr(buffer, ':')) == NULL)
		*mss_min = *mss_max = parse_tcp_mssvalue(buffer);
	else {
		*cp = '\0';
		cp++;

		*mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
		*mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
	}
	free(buffer);
}

/* Function which parses command options; returns true if it
   ate an option */
static int
parse(int c, char **argv, int invert, unsigned int *flags,
      const struct ipt_entry *entry,
      unsigned int *nfcache,
      struct ipt_entry_match **match)
{
	struct ipt_tcpmss_match_info *mssinfo =
		(struct ipt_tcpmss_match_info *)(*match)->data;

	switch (c) {
	case '1':
		if (*flags)
			exit_error(PARAMETER_PROBLEM,
				   "Only one `--mss' allowed");
		check_inverse(optarg, &invert, &optind, 0);
		parse_tcp_mssvalues(argv[optind-1],
				    &mssinfo->mss_min, &mssinfo->mss_max);
		if (invert)
			mssinfo->invert = 1;
		*flags = 1;
		break;
	default:
		return 0;
	}
	return 1;
}

static void
print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
{
	if (invert)
		printf("! ");

	if (mss_min == mss_max)
		printf("%u", mss_min);
	else
		printf("%u:%u", mss_min, mss_max);
}

/* Final check; must have specified --mss. */
static void
final_check(unsigned int flags)
{
	if (!flags)
		exit_error(PARAMETER_PROBLEM,
			   "tcpmss match: You must specify `--mss'");
}

/* Prints out the matchinfo. */
static void
print(const struct ipt_ip *ip,
      const struct ipt_entry_match *match,
      int numeric)
{
	const struct ipt_tcpmss_match_info *mssinfo =
		(const struct ipt_tcpmss_match_info *)match->data;

	printf("tcpmss match ");
	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
		     mssinfo->invert, numeric);
}

/* Saves the union ipt_matchinfo in parsable form to stdout. */
static void
save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
{
	const struct ipt_tcpmss_match_info *mssinfo =
		(const struct ipt_tcpmss_match_info *)match->data;

	printf("--mss ");
	print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
		     mssinfo->invert, 0);
}

static
struct iptables_match tcpmss
= { NULL,
    "tcpmss",
    NETFILTER_VERSION,
    IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
    IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
    &help,
    &init,
    &parse,
    &final_check,
    &print,
    &save,
    opts
};

void _init(void)
{
	register_match(&tcpmss);
}