TCP MSS matching support (untested).

2 files changed, 162 insertions, 0 deletions

diff --git a/extensions/.TCPMSS-test b/extensions/.TCPMSS-test
index ff0294ce..d6ea82f8 100755
--- a/extensions/.TCPMSS-test
+++ b/extensions/.TCPMSS-test
@@ -1,2 +1,3 @@
 #! /bin/sh
 [ -f $KERNEL_DIR/include/linux/netfilter_ipv4/ipt_TCPMSS.h ] && echo TCPMSS
+[ -f $KERNEL_DIR/include/linux/netfilter_ipv4/ipt_tcpmss.h ] && echo tcpmss
diff --git a/extensions/libipt_tcpmss.c b/extensions/libipt_tcpmss.c
new file mode 100644
index 00000000..35e6b5f9
--- /dev/null
+++ b/extensions/libipt_tcpmss.c
@@ -0,0 +1,161 @@
+/* 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)
+{
+	int mssvaluenum;
+
+	if ((mssvaluenum = string_to_number(mssvalue, 0, 65535)) != -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");
+		if (check_inverse(optarg, &invert))
+			optind++;
+		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(mss_info->mss_min, mss_info->mss_max,
+		     mss_info->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(mss_info->mss_min, mss_info->mss_max,
+		     mss_info->invert, 0);
+}
+
+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);
+}