extensions/libip6t_length.c

   1 /* Shared library add-on to ip6tables to add packet length matching support. */
   2
   3 #include <stdio.h>
   4 #include <netdb.h>
   5 #include <string.h>
   6 #include <stdlib.h>
   7 #include <getopt.h>
   8
   9 #include <ip6tables.h>
  10 #include <linux/netfilter_ipv6/ip6t_length.h>
  11
  12 /* Function which prints out usage message. */
  13 static void
  14 help(void)
  15 {
  16         printf(
  17 "length v%s options:\n"
  18 "[!] --length length[:length]    Match packet length against value or range\n"
  19 "                                of values (inclusive)\n",
  20 IPTABLES_VERSION);
  21
  22 }
  23
  24 static struct option opts[] = {
  25         { "length", 1, 0, '1' },
  26         {0}
  27 };
  28
  29 static u_int16_t
  30 parse_length(const char *s)
  31 {
  32
  33         int len;
  34
  35         if (string_to_number(s, 0, 0xFFFF, &len) == -1)
  36                 exit_error(PARAMETER_PROBLEM, "length invalid: `%s'\n", s);
  37         else
  38                 return (u_int16_t )len;
  39 }
  40
  41 /* If a single value is provided, min and max are both set to the value */
  42 static void
  43 parse_lengths(const char *s, struct ip6t_length_info *info)
  44 {
  45         char *buffer;
  46         char *cp;
  47
  48         buffer = strdup(s);
  49         if ((cp = strchr(buffer, ':')) == NULL)
  50                 info->min = info->max = parse_length(buffer);
  51         else {
  52                 *cp = '\0';
  53                 cp++;
  54
  55                 info->min = buffer[0] ? parse_length(buffer) : 0;
  56                 info->max = cp[0] ? parse_length(cp) : 0xFFFF;
  57         }
  58         free(buffer);
  59
  60         if (info->min > info->max)
  61                 exit_error(PARAMETER_PROBLEM,
  62                            "length min. range value `%u' greater than max. "
  63                            "range value `%u'", info->min, info->max);
  64
  65 }
  66
  67 /* Function which parses command options; returns true if it
  68    ate an option */
  69 static int
  70 parse(int c, char **argv, int invert, unsigned int *flags,
  71       const struct ip6t_entry *entry,
  72       unsigned int *nfcache,
  73       struct ip6t_entry_match **match)
  74 {
  75         struct ip6t_length_info *info = (struct ip6t_length_info *)(*match)->data;
  76
  77         switch (c) {
  78                 case '1':
  79                         if (*flags)
  80                                 exit_error(PARAMETER_PROBLEM,
  81                                            "length: `--length' may only be "
  82                                            "specified once");
  83                         check_inverse(optarg, &invert, &optind, 0);
  84                         parse_lengths(argv[optind-1], info);
  85                         if (invert)
  86                                 info->invert = 1;
  87                         *flags = 1;
  88                         break;
  89
  90                 default:
  91                         return 0;
  92         }
  93         return 1;
  94 }
  95
  96 /* Final check; must have specified --length. */
  97 static void
  98 final_check(unsigned int flags)
  99 {
 100         if (!flags)
 101                 exit_error(PARAMETER_PROBLEM,
 102                            "length: You must specify `--length'");
 103 }
 104
 105 /* Common match printing code. */
 106 static void
 107 print_length(struct ip6t_length_info *info)
 108 {
 109         if (info->invert)
 110                 printf("! ");
 111
 112         if (info->max == info->min)
 113                 printf("%u ", info->min);
 114         else
 115                 printf("%u:%u ", info->min, info->max);
 116 }
 117
 118 /* Prints out the matchinfo. */
 119 static void
 120 print(const struct ip6t_ip6 *ip,
 121       const struct ip6t_entry_match *match,
 122       int numeric)
 123 {
 124         printf("length ");
 125         print_length((struct ip6t_length_info *)match->data);
 126 }
 127
 128 /* Saves the union ip6t_matchinfo in parsable form to stdout. */
 129 static void
 130 save(const struct ip6t_ip6 *ip, const struct ip6t_entry_match *match)
 131 {
 132         printf("--length ");
 133         print_length((struct ip6t_length_info *)match->data);
 134 }
 135
 136 struct ip6tables_match length = {
 137         .name           = "length",
 138         .version        = IPTABLES_VERSION,
 139         .size           = IP6T_ALIGN(sizeof(struct ip6t_length_info)),
 140         .userspacesize  = IP6T_ALIGN(sizeof(struct ip6t_length_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_match6(&length);
 152 }