Added Fabrice Marie's port of the length match
diff --git a/extensions/libipt_length.c b/extensions/libipt_length.c
new file mode 100644
index 0000000..7ea5084
--- /dev/null
+++ b/extensions/libipt_length.c
@@ -0,0 +1,162 @@
+/* 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 <iptables.h>
+#include <linux/netfilter_ipv4/ipt_length.h>
+
+/* Function which prints out usage message. */
+static void
+help(void)
+{
+ printf(
+"length v%s options:\n"
+"[!] --length length[:length] Match packet length against value or range\n"
+" of values (inclusive)\n",
+NETFILTER_VERSION);
+
+}
+
+static struct option opts[] = {
+ { "length", 1, 0, '1' },
+ {0}
+};
+
+/* Initialize the match. */
+static void
+init(struct ipt_entry_match *m, unsigned int *nfcache)
+{
+ *nfcache |= NFC_UNKNOWN;
+}
+
+static u_int16_t
+parse_length(const char *s)
+{
+ int len;
+
+ len = string_to_number(s, 0, 0xFFFF);
+
+ if (len == -1)
+ exit_error(PARAMETER_PROBLEM, "length invalid: `%s'\n", s);
+ else
+ return (u_int16_t )len;
+}
+
+/* If a single value is provided, min and max are both set to the value */
+static void
+parse_lengths(const char *s, struct ipt_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)
+ exit_error(PARAMETER_PROBLEM,
+ "length min. range value `%u' greater than max. "
+ "range value `%u'", info->min, info->max);
+
+}
+
+/* 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_length_info *info = (struct ipt_length_info *)(*match)->data;
+
+ switch (c) {
+ case '1':
+ if (*flags)
+ exit_error(PARAMETER_PROBLEM,
+ "length: `--length' may only be "
+ "specified once");
+ if (check_inverse(optarg, &invert))
+ optind++;
+ parse_lengths(argv[optind-1], info);
+ if (invert)
+ info->invert = 1;
+ *flags = 1;
+ break;
+
+ default:
+ return 0;
+ }
+ return 1;
+}
+
+/* Final check; must have specified --length. */
+static void
+final_check(unsigned int flags)
+{
+ if (!flags)
+ exit_error(PARAMETER_PROBLEM,
+ "length: You must specify `--length'");
+}
+
+/* Common match printing code. */
+static void
+print_length(struct ipt_length_info *info)
+{
+ if (info->invert)
+ fputc('!', stdout);
+
+ if (info->max == info->min)
+ printf("%u ", info->min);
+ else
+ printf("%u:%u ", info->min, info->max);
+}
+
+/* Prints out the matchinfo. */
+static void
+print(const struct ipt_ip *ip,
+ const struct ipt_entry_match *match,
+ int numeric)
+{
+ printf("length ");
+ print_length((struct ipt_length_info *)match->data);
+}
+
+/* Saves the union ipt_matchinfo in parsable form to stdout. */
+static void
+save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
+{
+ printf("--length ");
+ print_length((struct ipt_length_info *)match->data);
+}
+
+struct iptables_match length
+= { NULL,
+ "length",
+ NETFILTER_VERSION,
+ IPT_ALIGN(sizeof(struct ipt_length_info)),
+ IPT_ALIGN(sizeof(struct ipt_length_info)),
+ &help,
+ &init,
+ &parse,
+ &final_check,
+ &print,
+ &save,
+ opts
+};
+
+void _init(void)
+{
+ register_match(&length);
+}