1 files changed, 128 insertions, 0 deletions
diff --git a/extensions/libxt_tcpmss.c b/extensions/libxt_tcpmss.c
new file mode 100644
index 0000000..b54a890
--- /dev/null
+++ b/extensions/libxt_tcpmss.c
@@ -0,0 +1,128 @@
+/* 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 <xtables.h>
+#include <linux/netfilter/xt_tcpmss.h>
+
+static void tcpmss_help(void)
+{
+	printf(
+"tcpmss match options:\n"
+"[!] --mss value[:value]	Match TCP MSS range.\n"
+"				(only valid for TCP SYN or SYN/ACK packets)\n");
+}
+
+static const struct option tcpmss_opts[] = {
+	{ "mss", 1, NULL, '1' },
+	{ .name = NULL }
+};
+
+static u_int16_t
+parse_tcp_mssvalue(const char *mssvalue)
+{
+	unsigned int mssvaluenum;
+
+	if (xtables_strtoui(mssvalue, NULL, &mssvaluenum, 0, UINT16_MAX))
+		return mssvaluenum;
+
+	xtables_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);
+}
+
+static int
+tcpmss_parse(int c, char **argv, int invert, unsigned int *flags,
+             const void *entry, struct xt_entry_match **match)
+{
+	struct xt_tcpmss_match_info *mssinfo =
+		(struct xt_tcpmss_match_info *)(*match)->data;
+
+	switch (c) {
+	case '1':
+		if (*flags)
+			xtables_error(PARAMETER_PROBLEM,
+				   "Only one `--mss' allowed");
+		xtables_check_inverse(optarg, &invert, &optind, 0, argv);
+		parse_tcp_mssvalues(optarg,
+				    &mssinfo->mss_min, &mssinfo->mss_max);
+		if (invert)
+			mssinfo->invert = 1;
+		*flags = 1;
+		break;
+	default:
+		return 0;
+	}
+	return 1;
+}
+
+static void tcpmss_check(unsigned int flags)
+{
+	if (!flags)
+		xtables_error(PARAMETER_PROBLEM,
+			   "tcpmss match: You must specify `--mss'");
+}
+
+static void
+tcpmss_print(const void *ip, const struct xt_entry_match *match, int numeric)
+{
+	const struct xt_tcpmss_match_info *info = (void *)match->data;
+
+	printf("tcpmss match %s", info->invert ? "!" : "");
+	if (info->mss_min == info->mss_max)
+		printf("%u ", info->mss_min);
+	else
+		printf("%u:%u ", info->mss_min, info->mss_max);
+}
+
+static void tcpmss_save(const void *ip, const struct xt_entry_match *match)
+{
+	const struct xt_tcpmss_match_info *info = (void *)match->data;
+
+	printf("%s--mss ", info->invert ? "! " : "");
+	if (info->mss_min == info->mss_max)
+		printf("%u ", info->mss_min);
+	else
+		printf("%u:%u ", info->mss_min, info->mss_max);
+}
+
+static struct xtables_match tcpmss_match = {
+	.family		= NFPROTO_UNSPEC,
+	.name		= "tcpmss",
+	.version	= XTABLES_VERSION,
+	.size		= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
+	.userspacesize	= XT_ALIGN(sizeof(struct xt_tcpmss_match_info)),
+	.help		= tcpmss_help,
+	.parse		= tcpmss_parse,
+	.final_check	= tcpmss_check,
+	.print		= tcpmss_print,
+	.save		= tcpmss_save,
+	.extra_opts	= tcpmss_opts,
+};
+
+void _init(void)
+{
+	xtables_register_match(&tcpmss_match);
+}