TCP MSS matching support (untested).

diff --git a/extensions/.TCPMSS-test b/extensions/.TCPMSS-test
index ff0294ce5a44449b164d334d1bdbeba7b67a5e96..d6ea82f8717dd4a7db6b1b6ba432e0e0b3e099ed 100755 (executable)
--- 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 (file)
index 0000000..35e6b5f
--- /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);
+}