extensions/libxt_string.c

   1 /* Shared library add-on to iptables to add string matching support.
   2  *
   3  * Copyright (C) 2000 Emmanuel Roger  <winfield@freegates.be>
   4  *
   5  * 2005-08-05 Pablo Neira Ayuso <pablo@eurodev.net>
   6  *      - reimplemented to use new string matching iptables match
   7  *      - add functionality to match packets by using window offsets
   8  *      - add functionality to select the string matching algorithm
   9  *
  10  * ChangeLog
  11  *     29.12.2003: Michael Rash <mbr@cipherdyne.org>
  12  *             Fixed iptables save/restore for ascii strings
  13  *             that contain space chars, and hex strings that
  14  *             contain embedded NULL chars.  Updated to print
  15  *             strings in hex mode if any non-printable char
  16  *             is contained within the string.
  17  *
  18  *     27.01.2001: Gianni Tedesco <gianni@ecsc.co.uk>
  19  *             Changed --tos to --string in save(). Also
  20  *             updated to work with slightly modified
  21  *             ipt_string_info.
  22  */
  23 #define _GNU_SOURCE 1
  24 #include <stdio.h>
  25 #include <netdb.h>
  26 #include <string.h>
  27 #include <stdlib.h>
  28 #include <getopt.h>
  29 #include <ctype.h>
  30 #include <xtables.h>
  31 #include <stddef.h>
  32 #include <linux/netfilter/xt_string.h>
  33
  34 static void string_help(void)
  35 {
  36         printf(
  37 "string match options:\n"
  38 "--from                       Offset to start searching from\n"
  39 "--to                         Offset to stop searching\n"
  40 "--algo                       Algorithm\n"
  41 "--icase                      Ignore case (default: 0)\n"
  42 "[!] --string string          Match a string in a packet\n"
  43 "[!] --hex-string string      Match a hex string in a packet\n");
  44 }
  45
  46 static const struct option string_opts[] = {
  47         { "from", 1, NULL, '1' },
  48         { "to", 1, NULL, '2' },
  49         { "algo", 1, NULL, '3' },
  50         { "string", 1, NULL, '4' },
  51         { "hex-string", 1, NULL, '5' },
  52         { "icase", 0, NULL, '6' },
  53         { .name = NULL }
  54 };
  55
  56 static void string_init(struct xt_entry_match *m)
  57 {
  58         struct xt_string_info *i = (struct xt_string_info *) m->data;
  59
  60         if (i->to_offset == 0)
  61                 i->to_offset = UINT16_MAX;
  62 }
  63
  64 static void
  65 parse_string(const char *s, struct xt_string_info *info)
  66 {
  67         /* xt_string does not need \0 at the end of the pattern */
  68         if (strlen(s) <= XT_STRING_MAX_PATTERN_SIZE) {
  69                 strncpy(info->pattern, s, XT_STRING_MAX_PATTERN_SIZE);
  70                 info->patlen = strnlen(s, XT_STRING_MAX_PATTERN_SIZE);
  71                 return;
  72         }
  73         xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
  74 }
  75
  76 static void
  77 parse_algo(const char *s, struct xt_string_info *info)
  78 {
  79         /* xt_string needs \0 for algo name */
  80         if (strlen(s) < XT_STRING_MAX_ALGO_NAME_SIZE) {
  81                 strncpy(info->algo, s, XT_STRING_MAX_ALGO_NAME_SIZE);
  82                 return;
  83         }
  84         xtables_error(PARAMETER_PROBLEM, "ALGO too long \"%s\"", s);
  85 }
  86
  87 static void
  88 parse_hex_string(const char *s, struct xt_string_info *info)
  89 {
  90         int i=0, slen, sindex=0, schar;
  91         short hex_f = 0, literal_f = 0;
  92         char hextmp[3];
  93
  94         slen = strlen(s);
  95
  96         if (slen == 0) {
  97                 xtables_error(PARAMETER_PROBLEM,
  98                         "STRING must contain at least one char");
  99         }
 100
 101         while (i < slen) {
 102                 if (s[i] == '\\' && !hex_f) {
 103                         literal_f = 1;
 104                 } else if (s[i] == '\\') {
 105                         xtables_error(PARAMETER_PROBLEM,
 106                                 "Cannot include literals in hex data");
 107                 } else if (s[i] == '|') {
 108                         if (hex_f)
 109                                 hex_f = 0;
 110                         else {
 111                                 hex_f = 1;
 112                                 /* get past any initial whitespace just after the '|' */
 113                                 while (s[i+1] == ' ')
 114                                         i++;
 115                         }
 116                         if (i+1 >= slen)
 117                                 break;
 118                         else
 119                                 i++;  /* advance to the next character */
 120                 }
 121
 122                 if (literal_f) {
 123                         if (i+1 >= slen) {
 124                                 xtables_error(PARAMETER_PROBLEM,
 125                                         "Bad literal placement at end of string");
 126                         }
 127                         info->pattern[sindex] = s[i+1];
 128                         i += 2;  /* skip over literal char */
 129                         literal_f = 0;
 130                 } else if (hex_f) {
 131                         if (i+1 >= slen) {
 132                                 xtables_error(PARAMETER_PROBLEM,
 133                                         "Odd number of hex digits");
 134                         }
 135                         if (i+2 >= slen) {
 136                                 /* must end with a "|" */
 137                                 xtables_error(PARAMETER_PROBLEM, "Invalid hex block");
 138                         }
 139                         if (! isxdigit(s[i])) /* check for valid hex char */
 140                                 xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i]);
 141                         if (! isxdigit(s[i+1])) /* check for valid hex char */
 142                                 xtables_error(PARAMETER_PROBLEM, "Invalid hex char '%c'", s[i+1]);
 143                         hextmp[0] = s[i];
 144                         hextmp[1] = s[i+1];
 145                         hextmp[2] = '\0';
 146                         if (! sscanf(hextmp, "%x", &schar))
 147                                 xtables_error(PARAMETER_PROBLEM,
 148                                         "Invalid hex char `%c'", s[i]);
 149                         info->pattern[sindex] = (char) schar;
 150                         if (s[i+2] == ' ')
 151                                 i += 3;  /* spaces included in the hex block */
 152                         else
 153                                 i += 2;
 154                 } else {  /* the char is not part of hex data, so just copy */
 155                         info->pattern[sindex] = s[i];
 156                         i++;
 157                 }
 158                 if (sindex > XT_STRING_MAX_PATTERN_SIZE)
 159                         xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
 160                 sindex++;
 161         }
 162         info->patlen = sindex;
 163 }
 164
 165 #define STRING 0x1
 166 #define ALGO   0x2
 167 #define FROM   0x4
 168 #define TO     0x8
 169 #define ICASE  0x10
 170
 171 static int
 172 string_parse(int c, char **argv, int invert, unsigned int *flags,
 173              const void *entry, struct xt_entry_match **match)
 174 {
 175         struct xt_string_info *stringinfo =
 176             (struct xt_string_info *)(*match)->data;
 177         const int revision = (*match)->u.user.revision;
 178
 179         switch (c) {
 180         case '1':
 181                 if (*flags & FROM)
 182                         xtables_error(PARAMETER_PROBLEM,
 183                                    "Can't specify multiple --from");
 184                 stringinfo->from_offset = atoi(optarg);
 185                 *flags |= FROM;
 186                 break;
 187         case '2':
 188                 if (*flags & TO)
 189                         xtables_error(PARAMETER_PROBLEM,
 190                                    "Can't specify multiple --to");
 191                 stringinfo->to_offset = atoi(optarg);
 192                 *flags |= TO;
 193                 break;
 194         case '3':
 195                 if (*flags & ALGO)
 196                         xtables_error(PARAMETER_PROBLEM,
 197                                    "Can't specify multiple --algo");
 198                 parse_algo(optarg, stringinfo);
 199                 *flags |= ALGO;
 200                 break;
 201         case '4':
 202                 if (*flags & STRING)
 203                         xtables_error(PARAMETER_PROBLEM,
 204                                    "Can't specify multiple --string");
 205                 xtables_check_inverse(optarg, &invert, &optind, 0);
 206                 parse_string(argv[optind-1], stringinfo);
 207                 if (invert) {
 208                         if (revision == 0)
 209                                 stringinfo->u.v0.invert = 1;
 210                         else
 211                                 stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 212                 }
 213                 *flags |= STRING;
 214                 break;
 215
 216         case '5':
 217                 if (*flags & STRING)
 218                         xtables_error(PARAMETER_PROBLEM,
 219                                    "Can't specify multiple --hex-string");
 220
 221                 xtables_check_inverse(optarg, &invert, &optind, 0);
 222                 parse_hex_string(argv[optind-1], stringinfo);  /* sets length */
 223                 if (invert) {
 224                         if (revision == 0)
 225                                 stringinfo->u.v0.invert = 1;
 226                         else
 227                                 stringinfo->u.v1.flags |= XT_STRING_FLAG_INVERT;
 228                 }
 229                 *flags |= STRING;
 230                 break;
 231
 232         case '6':
 233                 if (revision == 0)
 234                         xtables_error(VERSION_PROBLEM,
 235                                    "Kernel doesn't support --icase");
 236
 237                 stringinfo->u.v1.flags |= XT_STRING_FLAG_IGNORECASE;
 238                 *flags |= ICASE;
 239                 break;
 240
 241         default:
 242                 return 0;
 243         }
 244         return 1;
 245 }
 246
 247 static void string_check(unsigned int flags)
 248 {
 249         if (!(flags & STRING))
 250                 xtables_error(PARAMETER_PROBLEM,
 251                            "STRING match: You must specify `--string' or "
 252                            "`--hex-string'");
 253         if (!(flags & ALGO))
 254                 xtables_error(PARAMETER_PROBLEM,
 255                            "STRING match: You must specify `--algo'");
 256 }
 257
 258 /* Test to see if the string contains non-printable chars or quotes */
 259 static unsigned short int
 260 is_hex_string(const char *str, const unsigned short int len)
 261 {
 262         unsigned int i;
 263         for (i=0; i < len; i++)
 264                 if (! isprint(str[i]))
 265                         return 1;  /* string contains at least one non-printable char */
 266         /* use hex output if the last char is a "\" */
 267         if ((unsigned char) str[len-1] == 0x5c)
 268                 return 1;
 269         return 0;
 270 }
 271
 272 /* Print string with "|" chars included as one would pass to --hex-string */
 273 static void
 274 print_hex_string(const char *str, const unsigned short int len)
 275 {
 276         unsigned int i;
 277         /* start hex block */
 278         printf("\"|");
 279         for (i=0; i < len; i++) {
 280                 /* see if we need to prepend a zero */
 281                 if ((unsigned char) str[i] <= 0x0F)
 282                         printf("0%x", (unsigned char) str[i]);
 283                 else
 284                         printf("%x", (unsigned char) str[i]);
 285         }
 286         /* close hex block */
 287         printf("|\" ");
 288 }
 289
 290 static void
 291 print_string(const char *str, const unsigned short int len)
 292 {
 293         unsigned int i;
 294         printf("\"");
 295         for (i=0; i < len; i++) {
 296                 if ((unsigned char) str[i] == 0x22)  /* escape any embedded quotes */
 297                         printf("%c", 0x5c);
 298                 printf("%c", (unsigned char) str[i]);
 299         }
 300         printf("\" ");  /* closing space and quote */
 301 }
 302
 303 static void
 304 string_print(const void *ip, const struct xt_entry_match *match, int numeric)
 305 {
 306         const struct xt_string_info *info =
 307             (const struct xt_string_info*) match->data;
 308         const int revision = match->u.user.revision;
 309         int invert = (revision == 0 ? info->u.v0.invert :
 310                                     info->u.v1.flags & XT_STRING_FLAG_INVERT);
 311
 312         if (is_hex_string(info->pattern, info->patlen)) {
 313                 printf("STRING match %s", invert ? "!" : "");
 314                 print_hex_string(info->pattern, info->patlen);
 315         } else {
 316                 printf("STRING match %s", invert ? "!" : "");
 317                 print_string(info->pattern, info->patlen);
 318         }
 319         printf("ALGO name %s ", info->algo);
 320         if (info->from_offset != 0)
 321                 printf("FROM %u ", info->from_offset);
 322         if (info->to_offset != 0)
 323                 printf("TO %u ", info->to_offset);
 324         if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
 325                 printf("ICASE ");
 326 }
 327
 328 static void string_save(const void *ip, const struct xt_entry_match *match)
 329 {
 330         const struct xt_string_info *info =
 331             (const struct xt_string_info*) match->data;
 332         const int revision = match->u.user.revision;
 333         int invert = (revision == 0 ? info->u.v0.invert :
 334                                     info->u.v1.flags & XT_STRING_FLAG_INVERT);
 335
 336         if (is_hex_string(info->pattern, info->patlen)) {
 337                 printf("%s--hex-string ", (invert) ? "! ": "");
 338                 print_hex_string(info->pattern, info->patlen);
 339         } else {
 340                 printf("%s--string ", (invert) ? "! ": "");
 341                 print_string(info->pattern, info->patlen);
 342         }
 343         printf("--algo %s ", info->algo);
 344         if (info->from_offset != 0)
 345                 printf("--from %u ", info->from_offset);
 346         if (info->to_offset != 0)
 347                 printf("--to %u ", info->to_offset);
 348         if (revision > 0 && info->u.v1.flags & XT_STRING_FLAG_IGNORECASE)
 349                 printf("--icase ");
 350 }
 351
 352
 353 static struct xtables_match string_match = {
 354     .name               = "string",
 355     .revision           = 0,
 356     .family             = AF_UNSPEC,
 357     .version            = XTABLES_VERSION,
 358     .size               = XT_ALIGN(sizeof(struct xt_string_info)),
 359     .userspacesize      = offsetof(struct xt_string_info, config),
 360     .help               = string_help,
 361     .init               = string_init,
 362     .parse              = string_parse,
 363     .final_check        = string_check,
 364     .print              = string_print,
 365     .save               = string_save,
 366     .extra_opts         = string_opts,
 367 };
 368
 369 static struct xtables_match string_match_v1 = {
 370     .name               = "string",
 371     .revision           = 1,
 372     .family             = AF_UNSPEC,
 373     .version            = XTABLES_VERSION,
 374     .size               = XT_ALIGN(sizeof(struct xt_string_info)),
 375     .userspacesize      = offsetof(struct xt_string_info, config),
 376     .help               = string_help,
 377     .init               = string_init,
 378     .parse              = string_parse,
 379     .final_check        = string_check,
 380     .print              = string_print,
 381     .save               = string_save,
 382     .extra_opts         = string_opts,
 383 };
 384
 385 void _init(void)
 386 {
 387         xtables_register_match(&string_match);
 388         xtables_register_match(&string_match_v1);
 389 }