extensions/libxt_TCPOPTSTRIP.c

   1 /*
   2  * Shared library add-on to iptables to add TCPOPTSTRIP target support.
   3  * Copyright (c) 2007 Sven Schnelle <svens@bitebene.org>
   4  * Copyright © CC Computer Consultants GmbH, 2007
   5  * Jan Engelhardt <jengelh@computergmbh.de>
   6  */
   7 #include <getopt.h>
   8 #include <stdbool.h>
   9 #include <stdio.h>
  10 #include <string.h>
  11 #include <stdlib.h>
  12 #include <xtables.h>
  13 #include <netinet/tcp.h>
  14 #include <linux/netfilter/x_tables.h>
  15 #include <linux/netfilter/xt_TCPOPTSTRIP.h>
  16 #ifndef TCPOPT_MD5SIG
  17 #       define TCPOPT_MD5SIG 19
  18 #endif
  19
  20 enum {
  21         FLAG_STRIP = 1 << 0,
  22 };
  23
  24 struct tcp_optionmap {
  25         const char *name, *desc;
  26         const unsigned int option;
  27 };
  28
  29 static const struct option tcpoptstrip_tg_opts[] = {
  30         {.name = "strip-options", .has_arg = true, .val = 's'},
  31         { .name = NULL }
  32 };
  33
  34 static const struct tcp_optionmap tcp_optionmap[] = {
  35         {"wscale",         "Window scale",         TCPOPT_WINDOW},
  36         {"mss",            "Maximum Segment Size", TCPOPT_MAXSEG},
  37         {"sack-permitted", "SACK permitted",       TCPOPT_SACK_PERMITTED},
  38         {"sack",           "Selective ACK",        TCPOPT_SACK},
  39         {"timestamp",      "Timestamp",            TCPOPT_TIMESTAMP},
  40         {"md5",            "MD5 signature",        TCPOPT_MD5SIG},
  41         { .name = NULL }
  42 };
  43
  44 static void tcpoptstrip_tg_help(void)
  45 {
  46         const struct tcp_optionmap *w;
  47
  48         printf(
  49 "TCPOPTSTRIP target options:\n"
  50 "  --strip-options value     strip specified TCP options denoted by value\n"
  51 "                            (separated by comma) from TCP header\n"
  52 "  Instead of the numeric value, you can also use the following names:\n"
  53         );
  54
  55         for (w = tcp_optionmap; w->name != NULL; ++w)
  56                 printf("    %-14s    strip \"%s\" option\n", w->name, w->desc);
  57 }
  58
  59 static void tcpoptstrip_tg_init(struct xt_entry_target *t)
  60 {
  61         struct xt_tcpoptstrip_target_info *info = (void *)t->data;
  62
  63         /* strictly necessary? play safe for now. */
  64         memset(info->strip_bmap, 0, sizeof(info->strip_bmap));
  65 }
  66
  67 static void parse_list(struct xt_tcpoptstrip_target_info *info, char *arg)
  68 {
  69         unsigned int option;
  70         char *p;
  71         int i;
  72
  73         while (true) {
  74                 p = strchr(arg, ',');
  75                 if (p != NULL)
  76                         *p = '\0';
  77
  78                 option = 0;
  79                 for (i = 0; tcp_optionmap[i].name != NULL; ++i)
  80                         if (strcmp(tcp_optionmap[i].name, arg) == 0) {
  81                                 option = tcp_optionmap[i].option;
  82                                 break;
  83                         }
  84
  85                 if (option == 0 &&
  86                     !xtables_strtoui(arg, NULL, &option, 0, UINT8_MAX))
  87                         xtables_error(PARAMETER_PROBLEM,
  88                                    "Bad TCP option value \"%s\"", arg);
  89
  90                 if (option < 2)
  91                         xtables_error(PARAMETER_PROBLEM,
  92                                    "Option value may not be 0 or 1");
  93
  94                 if (tcpoptstrip_test_bit(info->strip_bmap, option))
  95                         xtables_error(PARAMETER_PROBLEM,
  96                                    "Option \"%s\" already specified", arg);
  97
  98                 tcpoptstrip_set_bit(info->strip_bmap, option);
  99                 if (p == NULL)
 100                         break;
 101                 arg = p + 1;
 102         }
 103 }
 104
 105 static int tcpoptstrip_tg_parse(int c, char **argv, int invert,
 106                                 unsigned int *flags, const void *entry,
 107                                 struct xt_entry_target **target)
 108 {
 109         struct xt_tcpoptstrip_target_info *info = (void *)(*target)->data;
 110
 111         switch (c) {
 112         case 's':
 113                 if (*flags & FLAG_STRIP)
 114                         xtables_error(PARAMETER_PROBLEM,
 115                                    "You can specify --strip-options only once");
 116                 parse_list(info, optarg);
 117                 *flags |= FLAG_STRIP;
 118                 return true;
 119         }
 120
 121         return false;
 122 }
 123
 124 static void tcpoptstrip_tg_check(unsigned int flags)
 125 {
 126         if (flags == 0)
 127                 xtables_error(PARAMETER_PROBLEM,
 128                            "TCPOPTSTRIP: --strip-options parameter required");
 129 }
 130
 131 static void
 132 tcpoptstrip_print_list(const struct xt_tcpoptstrip_target_info *info,
 133                        bool numeric)
 134 {
 135         unsigned int i, j;
 136         const char *name;
 137         bool first = true;
 138
 139         for (i = 0; i < 256; ++i) {
 140                 if (!tcpoptstrip_test_bit(info->strip_bmap, i))
 141                         continue;
 142                 if (!first)
 143                         printf(",");
 144
 145                 first = false;
 146                 name  = NULL;
 147                 if (!numeric)
 148                         for (j = 0; tcp_optionmap[j].name != NULL; ++j)
 149                                 if (tcp_optionmap[j].option == i)
 150                                         name = tcp_optionmap[j].name;
 151
 152                 if (name != NULL)
 153                         printf("%s", name);
 154                 else
 155                         printf("%u", i);
 156         }
 157 }
 158
 159 static void
 160 tcpoptstrip_tg_print(const void *ip, const struct xt_entry_target *target,
 161                      int numeric)
 162 {
 163         const struct xt_tcpoptstrip_target_info *info =
 164                 (const void *)target->data;
 165
 166         printf("TCPOPTSTRIP options ");
 167         tcpoptstrip_print_list(info, numeric);
 168 }
 169
 170 static void
 171 tcpoptstrip_tg_save(const void *ip, const struct xt_entry_target *target)
 172 {
 173         const struct xt_tcpoptstrip_target_info *info =
 174                 (const void *)target->data;
 175
 176         printf("--strip-options ");
 177         tcpoptstrip_print_list(info, true);
 178 }
 179
 180 static struct xtables_target tcpoptstrip_tg_reg = {
 181         .version       = XTABLES_VERSION,
 182         .name          = "TCPOPTSTRIP",
 183         .family        = NFPROTO_UNSPEC,
 184         .size          = XT_ALIGN(sizeof(struct xt_tcpoptstrip_target_info)),
 185         .userspacesize = XT_ALIGN(sizeof(struct xt_tcpoptstrip_target_info)),
 186         .help          = tcpoptstrip_tg_help,
 187         .init          = tcpoptstrip_tg_init,
 188         .parse         = tcpoptstrip_tg_parse,
 189         .final_check   = tcpoptstrip_tg_check,
 190         .print         = tcpoptstrip_tg_print,
 191         .save          = tcpoptstrip_tg_save,
 192         .extra_opts    = tcpoptstrip_tg_opts,
 193 };
 194
 195 void _init(void)
 196 {
 197         xtables_register_target(&tcpoptstrip_tg_reg);
 198 }