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

   1 /*
   2    Shared library add-on to iptables to add match support for random match.
   3
   4    This file is distributed under the terms of the GNU General Public
   5    License (GPL). Copies of the GPL can be obtained from:
   6    ftp://prep.ai.mit.edu/pub/gnu/GPL
   7
   8    2001-10-14 Fabrice MARIE <fabrice@netfilter.org> : initial development.
   9 */
  10
  11 #include <stdio.h>
  12 #include <netdb.h>
  13 #include <string.h>
  14 #include <stdlib.h>
  15 #include <syslog.h>
  16 #include <getopt.h>
  17 #include <iptables.h>
  18 #include <linux/netfilter_ipv4/ip_tables.h>
  19 #include <linux/netfilter_ipv4/ipt_random.h>
  20
  21 /**
  22  * The kernel random routing returns numbers between 0 and 255.
  23  * To ease the task of the user in choosing the probability
  24  * of matching, we want him to be able to use percentages.
  25  * Therefore we have to accept numbers in percentage here,
  26  * turn them into number between 0 and 255 for the kernel module,
  27  * and turn them back to percentages when we print/save
  28  * the rule.
  29  */
  30
  31
  32 /* Function which prints out usage message. */
  33 static void
  34 help(void)
  35 {
  36         printf(
  37 "random v%s options:\n"
  38 "  [--average      percent ]    The probability in percentage of the match\n"
  39 "                               If ommited, a probability of 50%% percent is set.\n"
  40 "                               Percentage must be within : 1 <= percent <= 99.\n\n",
  41 IPTABLES_VERSION);
  42 }
  43
  44 static struct option opts[] = {
  45         { "average", 1, 0, '1' },
  46         { 0 }
  47 };
  48
  49 /* Initialize the target. */
  50 static void
  51 init(struct ipt_entry_match *m, unsigned int *nfcache)
  52 {
  53         struct ipt_rand_info *randinfo = (struct ipt_rand_info *)(m)->data;
  54
  55         /* We assign the average to be 50 which is our default value */
  56         /* 50 * 2.55 = 128 */
  57         randinfo->average = 128;
  58 }
  59
  60 #define IPT_RAND_OPT_AVERAGE    0x01
  61
  62 /* Function which parses command options; returns true if it
  63    ate an option */
  64 static int
  65 parse(int c, char **argv, int invert, unsigned int *flags,
  66       const struct ipt_entry *entry,
  67       unsigned int *nfcache,
  68       struct ipt_entry_match **match)
  69 {
  70         struct ipt_rand_info *randinfo = (struct ipt_rand_info *)(*match)->data;
  71         unsigned int num;
  72
  73         switch (c) {
  74         case '1':
  75                 /* check for common mistakes... */
  76                 if (invert)
  77                         exit_error(PARAMETER_PROBLEM,
  78                                    "Can't specify ! --average");
  79                 if (*flags & IPT_RAND_OPT_AVERAGE)
  80                         exit_error(PARAMETER_PROBLEM,
  81                                    "Can't specify --average twice");
  82
  83                 /* Remember, this function will interpret a leading 0 to be
  84                    Octal, a leading 0x to be hexdecimal... */
  85                 if (string_to_number(optarg, 1, 99, &num) == -1 || num < 1)
  86                         exit_error(PARAMETER_PROBLEM,
  87                                    "bad --average `%s', must be between 1 and 99", optarg);
  88
  89                 /* assign the values */
  90                 randinfo->average = (int)(num * 2.55);
  91                 *flags |= IPT_RAND_OPT_AVERAGE;
  92                 break;
  93         default:
  94                 return 0;
  95         }
  96         return 1;
  97 }
  98
  99 /* Final check; nothing. */
 100 static void final_check(unsigned int flags)
 101 {
 102 }
 103
 104 /* Prints out the targinfo. */
 105 static void
 106 print(const struct ipt_ip *ip,
 107       const struct ipt_entry_match *match,
 108       int numeric)
 109 {
 110         const struct ipt_rand_info *randinfo
 111                 = (const struct ipt_rand_info *)match->data;
 112         div_t result = div((randinfo->average*100), 255);
 113         if (result.rem > 127)  /* round up... */
 114                 ++result.quot;
 115
 116         printf(" random %u%% ", result.quot);
 117 }
 118
 119 /* Saves the union ipt_targinfo in parsable form to stdout. */
 120 static void
 121 save(const struct ipt_ip *ip, const struct ipt_entry_match *match)
 122 {
 123         const struct ipt_rand_info *randinfo
 124                 = (const struct ipt_rand_info *)match->data;
 125         div_t result = div((randinfo->average *100), 255);
 126         if (result.rem > 127)  /* round up... */
 127                 ++result.quot;
 128
 129         printf("--average %u ", result.quot);
 130 }
 131
 132 struct iptables_match rand_match = {
 133         .next           = NULL,
 134         .name           = "random",
 135         .version        = IPTABLES_VERSION,
 136         .size           = IPT_ALIGN(sizeof(struct ipt_rand_info)),
 137         .userspacesize  = IPT_ALIGN(sizeof(struct ipt_rand_info)),
 138         .help           = &help,
 139         .init           = &init,
 140         .parse          = &parse,
 141         .final_check    = &final_check,
 142         .print          = &print,
 143         .save           = &save,
 144         .extra_opts     = opts
 145 };
 146
 147 void _init(void)
 148 {
 149         register_match(&rand_match);
 150 }