1 files changed, 133 insertions, 0 deletions
diff --git a/extensions/libxt_length.c b/extensions/libxt_length.c
new file mode 100644
index 0000000..96e8b6c
--- /dev/null
+++ b/extensions/libxt_length.c
@@ -0,0 +1,133 @@
+/* Shared library add-on to iptables to add packet length matching support. */
+#include <stdio.h>
+#include <netdb.h>
+#include <string.h>
+#include <stdlib.h>
+#include <getopt.h>
+
+#include <xtables.h>
+#include <linux/netfilter/xt_length.h>
+
+static void length_help(void)
+{
+	printf(
+"length match options:\n"
+"[!] --length length[:length]    Match packet length against value or range\n"
+"                                of values (inclusive)\n");
+}
+  
+static const struct option length_opts[] = {
+	{ "length", 1, NULL, '1' },
+	{ .name = NULL }
+};
+
+static u_int16_t
+parse_length(const char *s)
+{
+	unsigned int len;
+	
+	if (!xtables_strtoui(s, NULL, &len, 0, UINT32_MAX))
+		xtables_error(PARAMETER_PROBLEM, "length invalid: \"%s\"\n", s);
+	else
+		return len;
+}
+
+/* If a single value is provided, min and max are both set to the value */
+static void
+parse_lengths(const char *s, struct xt_length_info *info)
+{
+	char *buffer;
+	char *cp;
+
+	buffer = strdup(s);
+	if ((cp = strchr(buffer, ':')) == NULL)
+		info->min = info->max = parse_length(buffer);
+	else {
+		*cp = '\0';
+		cp++;
+
+		info->min = buffer[0] ? parse_length(buffer) : 0;
+		info->max = cp[0] ? parse_length(cp) : 0xFFFF;
+	}
+	free(buffer);
+	
+	if (info->min > info->max)
+		xtables_error(PARAMETER_PROBLEM,
+		           "length min. range value `%u' greater than max. "
+		           "range value `%u'", info->min, info->max);
+	
+}
+
+static int
+length_parse(int c, char **argv, int invert, unsigned int *flags,
+             const void *entry, struct xt_entry_match **match)
+{
+	struct xt_length_info *info = (struct xt_length_info *)(*match)->data;
+
+	switch (c) {
+		case '1':
+			if (*flags)
+				xtables_error(PARAMETER_PROBLEM,
+				           "length: `--length' may only be "
+				           "specified once");
+			xtables_check_inverse(optarg, &invert, &optind, 0, argv);
+			parse_lengths(optarg, info);
+			if (invert)
+				info->invert = 1;
+			*flags = 1;
+			break;
+			
+		default:
+			return 0;
+	}
+	return 1;
+}
+
+static void length_check(unsigned int flags)
+{
+	if (!flags)
+		xtables_error(PARAMETER_PROBLEM,
+			   "length: You must specify `--length'");
+}
+
+static void
+length_print(const void *ip, const struct xt_entry_match *match, int numeric)
+{
+	const struct xt_length_info *info = (void *)match->data;
+
+	printf("length %s", info->invert ? "!" : "");
+	if (info->min == info->max)
+		printf("%u ", info->min);
+	else
+		printf("%u:%u ", info->min, info->max);
+}
+
+static void length_save(const void *ip, const struct xt_entry_match *match)
+{
+	const struct xt_length_info *info = (void *)match->data;
+
+	printf("%s--length ", info->invert ? "! " : "");
+	if (info->min == info->max)
+		printf("%u ", info->min);
+	else
+		printf("%u:%u ", info->min, info->max);
+}
+
+static struct xtables_match length_match = {
+	.family		= NFPROTO_UNSPEC,
+	.name		= "length",
+	.version	= XTABLES_VERSION,
+	.size		= XT_ALIGN(sizeof(struct xt_length_info)),
+	.userspacesize	= XT_ALIGN(sizeof(struct xt_length_info)),
+	.help		= length_help,
+	.parse		= length_parse,
+	.final_check	= length_check,
+	.print		= length_print,
+	.save		= length_save,
+	.extra_opts	= length_opts,
+};
+
+void _init(void)
+{
+	xtables_register_match(&length_match);
+}