release/src/router/iptables/extensions/libipt_tcpmss.c

   1 /* Shared library add-on to iptables to add tcp MSS matching support. */
   2 #include <stdio.h>
   3 #include <netdb.h>
   4 #include <string.h>
   5 #include <stdlib.h>
   6 #include <getopt.h>
   7
   8 #include <iptables.h>
   9 #include <linux/netfilter_ipv4/ipt_tcpmss.h>
  10
  11 /* Function which prints out usage message. */
  12 static void
  13 help(void)
  14 {
  15         printf(
  16 "tcpmss match v%s options:\n"
  17 "[!] --mss value[:value]        Match TCP MSS range.\n"
  18 "                               (only valid for TCP SYN or SYN/ACK packets)\n",
  19 IPTABLES_VERSION);
  20 }
  21
  22 static struct option opts[] = {
  23         { "mss", 1, 0, '1' },
  24         {0}
  25 };
  26
  27 static u_int16_t
  28 parse_tcp_mssvalue(const char *mssvalue)
  29 {
  30         unsigned int mssvaluenum;
  31
  32         if (string_to_number(mssvalue, 0, 65535, &mssvaluenum) != -1)
  33                 return (u_int16_t)mssvaluenum;
  34
  35         exit_error(PARAMETER_PROBLEM,
  36                    "Invalid mss `%s' specified", mssvalue);
  37 }
  38
  39 static void
  40 parse_tcp_mssvalues(const char *mssvaluestring,
  41                     u_int16_t *mss_min, u_int16_t *mss_max)
  42 {
  43         char *buffer;
  44         char *cp;
  45
  46         buffer = strdup(mssvaluestring);
  47         if ((cp = strchr(buffer, ':')) == NULL)
  48                 *mss_min = *mss_max = parse_tcp_mssvalue(buffer);
  49         else {
  50                 *cp = '\0';
  51                 cp++;
  52
  53                 *mss_min = buffer[0] ? parse_tcp_mssvalue(buffer) : 0;
  54                 *mss_max = cp[0] ? parse_tcp_mssvalue(cp) : 0xFFFF;
  55         }
  56         free(buffer);
  57 }
  58
  59 /* Function which parses command options; returns true if it
  60    ate an option */
  61 static int
  62 parse(int c, char **argv, int invert, unsigned int *flags,
  63       const struct ipt_entry *entry,
  64       unsigned int *nfcache,
  65       struct ipt_entry_match **match)
  66 {
  67         struct ipt_tcpmss_match_info *mssinfo =
  68                 (struct ipt_tcpmss_match_info *)(*match)->data;
  69
  70         switch (c) {
  71         case '1':
  72                 if (*flags)
  73                         exit_error(PARAMETER_PROBLEM,
  74                                    "Only one `--mss' allowed");
  75                 check_inverse(optarg, &invert, &optind, 0);
  76                 parse_tcp_mssvalues(argv[optind-1],
  77                                     &mssinfo->mss_min, &mssinfo->mss_max);
  78                 if (invert)
  79                         mssinfo->invert = 1;
  80                 *flags = 1;
  81                 break;
  82         default:
  83                 return 0;
  84         }
  85         return 1;
  86 }
  87
  88 static void
  89 print_tcpmss(u_int16_t mss_min, u_int16_t mss_max, int invert, int numeric)
  90 {
  91         if (invert)
  92                 printf("! ");
  93
  94         if (mss_min == mss_max)
  95                 printf("%u ", mss_min);
  96         else
  97                 printf("%u:%u ", mss_min, mss_max);
  98 }
  99
 100 /* Final check; must have specified --mss. */
 101 static void
 102 final_check(unsigned int flags)
 103 {
 104         if (!flags)
 105                 exit_error(PARAMETER_PROBLEM,
 106                            "tcpmss match: You must specify `--mss'");
 107 }
 108
 109 /* Prints out the matchinfo. */
 110 static void
 111 print(const struct ipt_ip *ip,
 112       const struct ipt_entry_match *match,
 113       int numeric)
 114 {
 115         const struct ipt_tcpmss_match_info *mssinfo =
 116                 (const struct ipt_tcpmss_match_info *)match->data;
 117
 118         printf("tcpmss match ");
 119         print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
 120                      mssinfo->invert, numeric);
 121 }
 122
 123 /* Saves the union ipt_matchinfo in parsable form to stdout. */
 124 static void
 125 save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
 126 {
 127         const struct ipt_tcpmss_match_info *mssinfo =
 128                 (const struct ipt_tcpmss_match_info *)match->data;
 129
 130         printf("--mss ");
 131         print_tcpmss(mssinfo->mss_min, mssinfo->mss_max,
 132                      mssinfo->invert, 0);
 133 }
 134
 135 static struct iptables_match tcpmss = {
 136         .next           = NULL,
 137         .name           = "tcpmss",
 138         .version        = IPTABLES_VERSION,
 139         .size           = IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
 140         .userspacesize  = IPT_ALIGN(sizeof(struct ipt_tcpmss_match_info)),
 141         .help           = &help,
 142         .parse          = &parse,
 143         .final_check    = &final_check,
 144         .print          = &print,
 145         .save           = &save,
 146         .extra_opts     = opts
 147 };
 148
 149 void _init(void)
 150 {
 151         register_match(&tcpmss);
 152 }