summaryrefslogtreecommitdiffstats
path: root/extensions/libipt_tcpmss.c
diff options
context:
space:
mode:
Diffstat (limited to 'extensions/libipt_tcpmss.c')
-rw-r--r--extensions/libipt_tcpmss.c161
1 files changed, 161 insertions, 0 deletions
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);
+}